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Do marsupials ever die in childbirth?

Do marsupials ever die in childbirth?


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Question: Do marsupials ever die in childbirth?

Obviously the notion of there being a linear ordering of "least advanced" to "most advanced" life forms isn't correct. Still, often marsupials are depicted as relic or archaic creatures with an inferior reproductive strategy, since besides possums they are restricted to Australia and New Guinea.

However, compared to some placental mammals, like the spotted hyena and humans, the marsupial method of always giving birth to very small young, who can finish developing outside of the mother's body, seems to be more sensible.

If there haven't been enough field observations of marsupials, then of course this is an unanswerable question, but I was wondering if anyone knew anything about papers or other materials which discuss the advantages of the marsupial reproductive strategy.


Reproduction – Life Cycle

What is a marsupial? A marsupial is an animal belonging to the order Marsupiala, infraclass Metatheria. Members include the kangaroo, koala, Tasmanian devil and the Virginia opossum. Marsupials give birth to fetal-like young following a brief gestation period. The young then nurse for an extended period of time. It is generally accepted that a marsupial is a non-placental mammal whose female carries her young in a pouch, or marsupium, which provides the developing young with the proper environment, warmth, possess a placenta, although the placenta is non-invasive and functions in nutrient and waste transfer for a very short period of time, about 3 days in the Virginia opossum.

Female opossum with young in pouch

With out a long-lasting and functional placenta, the young must be born early in their development after a short gestation period. Marsupial young are basically embryos at birth. Once born, the young must climb with a swimming motion up the fur on the female’s adbomen and latch onto a teat. Not all female marsupials possess a well-developed pouch, as found on the abdomen of the Virginia opossum. Some marsupials carry young in rudimentary pouches which are basically skin folds. Many other do not have a pouch at all. The pouchless young must firmly attach to the teats with their mouths and front paws.

The reproductive system of the opossum has fascinated many and has led to interesting folklore. It was once believed that the male opossum mated through the female opossum’s nose. She then sneezed the young through her nose and into the pouch. Of course, this is not true. There are several reasons why this belief was held. One reason is that opossums are so small at birth it is difficult to witness the event. Observers had seen the female with an empty pouch one day. The next day she was seen with her nose in the pouch making sneezing sounds. Later, upon examination of the pouch, tiny embryos were found. Actually, the female opossum was either cleaning the pouch prior to the birth or licking the area to soothe her swollen teats. Another reason for this belief is the shape of the male opossum’s penis. It is bifurcated, like a 2 pronged fork. It was believed that the shape of the penis was a perfect fit for the female opossum’s nose. This isn’t true either. The female has an internal, bifurcated reproductive tract as well.

Opossum sperm are interesting? Sperm heads align and pair inside the male reproductive tract during sperm maturation. The sperm are ejaculated as pairs and remain paired inside the female reproductive tract until just prior to fertilization at which time the paired sperm separate into single spermatozoa. Why this fascinating process occurs and why it occurs only in the American marsupials and not the Australian marsupials is not completely understood The pairing of spermatozoa may increase sperm motility in the female reproductive tract and/or may help protect the sperm acrosomes during passage n the female tract.

The breeding season for the Virginia opossum can begin as early as December and continue through October with most infants born between the months of February and June. A female opossum may have 1-3 litters per year. During the mating season, the male attracts the female by making clicking sounds with his mouth.

The female opossum is a spontaneous ovulator with an estrous cycle of about 28 days. She is in estrus a short period, about 36 hours. This is the time mating can occur. Sperm, which has become paired in the male opossum’s reproductive tract, will move through the lateral vaginal canals and become separate again in the female’s tract. If fertilization occurs, the fertilized eggs move from the oviducts to the uteri where they will gestate for a short period before being delivered through the medial vagina or central birth canal.

infant a few days old, next to dime for size comparison

11-13 days after mating over 20 infants may be born, although an average litter consists of 8-9 infants. The infants are so small at birth that 20 could fit into a teaspoon. Each of the hairless, embryonic-looking “pinkies” are no larger than the size of a bee or a dime and weigh approximately 0.13 grams. At birth, the infants must make a long and difficult journey from the birth canal into the pouch, latch onto a teat, and continue their development. The mother helps by licking the hair leading into the pouch, providing a moist path for the infants to follow.

The teat swells in the infant’s mouth helping it to remain attached for about 2 months and providing a source of nutrition. On average, there are only 13 teats in the pouch and not all may be functional. If more infants are born than the number of functional teats available, the excess infants will not survive. Also, if only one individual attaches, milk production by the mother probably will not occur.

This opossum is not pregnant. She is carrying 9 infants in her pouch

The young remain in the pouch for about 2 1/2 months and at around 55-70 days the eyes open. As they become too large to fit in the pouch, they climb onto the mother’s back and are carried as she searches for food. At this time the young are learning survival skills such as finding food sources and predator avoidance. If one of the young becomes separated from its mother it will make sneezing sounds to call her. She, in turn, will make clicking sounds.

The young are weaned at approximately 3 months of age and are on their own at 4 1/2 – 5 months when they are approximately 7-9 inches long from nose to rump, excluding the tail. In a few months they will reproduce and continue the fascinating life cycle of the Virginia opossum.

Breeding season brings on two major consequences. First, males extending their range to search for mates are more subject to injury or death by cars, dogs and other predators. Second, females laden with young cannot run as fast and have to forage earlier in the evening and later in the morning. They risk exposing themselves to increased predation and more encounters with people, pets and cars with possible injurious or fatal consequences. Many times the mother does not survive these encounters and the young, usually found still alive in the pouch, ultimately wind up in the hands of wildlife rehabilitators.

It is important to always check the pouch of a deceased female for live young. If found then seek immediate medical assistance.


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THE SCIENCE & PHILOSOPHY of FANTASY
Anthropomorphic Biology

INTRODUCTION
How can anthropomorphic creatures be? Some of it just doesn’t make sense to me, like how can their be both anthropomorphic animals, yet still feral ones? Also how would their biology work in reality if they did actually exist? How can insects not collapse if they were macro scaled? Well here I’m going to answer these questions with my knowledge of zoology.

Evolution & Natural Selection
Life evolved from one bacteria cell, and over many years later, we now have intelligent primates who could record their own history. How? Well evolution is a chance in a mutation that would hopefully benefit the survival of a species, rather than extinct it. These changes are caused by environmental changes, as well as quantum ones as well, through quantum tunneling that’s. Over time, species will adapt to their environment, better suiting it for its survival. Now the cruelest part of biology, natural selection. As if one species is risk in being endangered, their offspring may gain a mutation that will aid their survival in new rapid changing environment. Those who do not have that mutation will die off, and those who have it, will carry it on to their children.
Now how can furries actually evolve from ferals? Well in creation arguments, you will hear that if we evolved from monkeys, why are there still monkeys? First of all, that’s stupid, second of all, we evolved from neither from a monkey nor ape, but a common ancestor that splitted into two different species, which is why we have ape, and primate. So, if we go back to every animal alive today’s common ancestor, and somehow all of them coincidentally split into anthro & feral, and somehow come up with the same genetic makeup, while evolving in different environments, having the same exact changes during those periods, BUT. The only thing that changes is their body structure to a more primate stance, and nervous system to gain higher awarity & intellect… I have a hard time believing in that happened naturally, so I’m going to add some force, that shifted & splitted every common ancestor into anthro and feral, but the actual primates weren’t affected, because their cells did mutate into entirely different separate species.

Vocal Communication
If anthros can talk, why can’t my dog? Well why can we speak in complex languages? Our vocal cords gives us the ability to vibrate air into many sounds & shapes, but our tongues, lips, and noses, does the talking. Yes, noses, because if you ever closed your nostrils, you will hear your voice a bit blocked. By using our muscles to make many forms in our tunnel mouths, at which sound travels through to escape and vibrate the air. That’s why animals can’t form complex languages like us, but what if they could? Well they would have flatter faces, and larger lips, but I don’t like that, it looks unattractive, in my opinion of course. So instead, let's give them more flexible mouths, tongues, and able to control the pitch and strength at which air exits their lungs. That should do it. Also, you know how snakes or other reptiles with forked tongues have that lisssssp every time the make pronounce an s sound. That’s not of their forked tongues, snakes and other animals hiss, because they have no vocal cords to makes different noises. The tongue is used to taste the chemicals in the air, to find prey, and avoid predators. reptiles use something in the roof of their mouths called a jacobson’s organ, it’s how they can taste scent. Even if that lisp was true, then how could they pronounce “Th” without hissing?

Scalp Hair
Sometimes when I see an anthropomorphic creature with hair on their scalp, it looks like they just slapped on a wig, plus how can reptiles & birds have hairs? so how can anthros actually have hair? If you shave an anthro’s scalp, what would you expect to be underneath? Their original fur? Nope, a plain bald scalp, as their hair &, fur is rooted into their skin. How would reptiles, birds, and amphibians have scalp hair? They don’t have hair, but their skin evolved to look, and feel like hair. Reptiles are finger nail skinned, made of keratin. Birds have their plumage as their hair, flight for pointy and outstanding, and down for fluffy & curly. Amphibians have like this jelly fluid hair, really jiggly and slimy, and quite transparent, might be the same for a fish. Though one particular species is at risk with having hair, and that would be cetaceans, Or whales, but why? Whales can only breathe through their blowholes, because their nostrils are on top of their head, if you have hair blocking that, then they’ll suffocate. That’s why I have fantasized the Cretacean Root Ring, or CRR. basically it’s a ring of hair rooted on the edge of the blowhole, so no whales can suffocate on their own hair, but what about nose hairs? Sure, they can have those too, but I rather not.

Breasts
Every female anthropomorphic creature I see has breasts, or boobs. It makes some sense with mammals, but how could birds? Reptiles, and other classes can have these jiggly boogalas? Well here’s the thing, they don’t, they’re just squishy lumps that mimic breasts, without containing the mammary glands to feed their young, just some loose tissue to attract mates. Which does make a lick of sense since we do draw them like that, but we’re human, so are the anthros, as they’re anthropomorphization of us. Since these bubbly pairs attract mates, and can reproduce more, then that means that species can carry on those sexy over the shoulder boulder holders to the next generation.

Reproduction
Lets say you’re a young pup, and you hear about the news that you’re going to have a baby brother, being “created” by your mother fox, and your father snow jaguar. Then your parents return from the hospital, and you see that your baby brother is an egg, and you know from first grade that dogs don’t lay eggs… Wtf? Welcome to interspecies breeding, I’m still trying to figure out how this could work. Why can’t this work? Well the DNA in Meiosis, the beginning of cell division for a fertilized egg, is like a zipper as I’ve been told. If it can’t fit in the correct proteins, than it simply won’t divide into new life, and instead die off, as well with the sperm. I made a chart a while back explaining this but it still wouldn’t make sense. How can one species, trying to birth another species, have the same development cycle? Why do different species even have different development cycles? Well reproduction isn’t easy, and requires a lot of energy, but it’s crucial to future generations. First, Fish had to lay, and fertilize their eggs separately. Then, amphibians could fertilize internally, also known as insemination, but their eggs are too fragile, and could only survive in water. Later, reptiles & birds could keep their eggs in a liquid environment on land, while also contained in a rock hard sheild, difficult for predators to penetrate through. Finally, mammals were the ones to develop their young internally inside the female, which increases chances of survival by keeping the fetus sterile from any outside harmful bacteria, and if the mother, or baby is sick, they can transfer nutrients to heal each other. Now what if we replaced every anthro species with a mammal reproduction cycle, well that means we have to replace their reproductive organs as well, which just doesn’t work, and makes it less attractive. What if we just separate it, and say that only this anthropomorphic class, and can give birth to that one, nope, there are still anthro parents who give birth to other classes. Okay, I guess I’m going to have to use the chart then.

That there’s chances for a baby to be born from that species. And that every anthropomorphic species has omini reproductive organs, either to lay jelly eggs, hard shell eggs, or give birth live, but if two separate species were developing inside the womb, then it could increase the chance of infant mortality.

Bird Wings
What do you imagine an anthro bird wing to be like? On back of the shoulders like an angel? Maybe their wings are just arms, or how about they have claws emerging from their elbows? I think it’s the third one, because it’s more biologically accurate, as prehistoric, and some birds to this day, had claws & spurs on their wings, which should give them the ability to grab, and manipulate tools. Also, their muscles connecting from their shoulders to arms are much more stretched, and able to flap much more quickly, stretching & contracting up & down. It also requires a lot of energy to flap those suckers.

Arthropods
Imagine giant walking talking insects, and if you looked through an electron microscope, they’re terrifying, so now macro scale them, and give them some adorable faces, and intelligence, and you have an anthropomorphized arthropod. However, physics says that they will collapse from their own body weight, as their yellow blood will spill out of the exoskeleton, killing it all together, why? Well insects are just hollow cavities filled with blood & organs, but they’re so miniscule that the weight is non existent to the insect. Larger classes of animals, mostly with vertebrae, have closed circulatory systems, meaning that their supply of blood circulates through their bodies in tubes, delivering the nutrients, and retrieving the pollutants in tiny branching rings of capillaries, to each organ. Now in insects, and tinier invertebrate, their circulatory systems are open, as their yellow blood doesn’t always travel in tubes, known as hemolymph, as ours is hemoglobin. Instead, the organs just float inside the cavity, while the heart pumps the blood in, as a long tube, and the lung is the belly, or abdomen, exchanging the air for oxygen, and expelling carbon dioxide. Size also determines on how fast a heart will beat, as it takes more energy to pump more fluid around the body, and if the heart is pumping too quickly, then it’ll exhaust itself, or if it’s pumping too slowly, then the organs won’t have enough time to receive and exchange. Tiny animals with smaller hearts, have super quick heart beats, because it takes less energy to pump mini hearts. So if you somehow use a macro ray, to grow an insect to the size of you, [Somehow giving it more mass to evenly distribute its weight], and its exoskeleton can hold all that sloshing liquid, it still would die from it having an open circulatory system, that blood can’t evenly flow, and still have enough time get oxygen to the brain, it just wouldn’t work, and a brain that size is too fragile. Anthropomorphic macro arthropods both need an endoskeleton, and exoskeleton, as well as a closed circulatory system.
Insects have many eyes, called compound eyes, as they see the world in a mosaic structure, not a duplicate one, as in every eye is the same picture. Light passes through the lens, hitting their retinas, which brings the information to their mind that they’re seeing. Now in reality compound eyes look horrendous, but the colors are magnificent, but I want to give the illusion of pupils. So I thought, how about that the lens can be maneuvered by iris muscles around the many compound eyes, as each tilt of the colorful lens, reveals even more colors, and on direct focus would reveal the whole color, polarization. When a sleep, the lenses can turn completely sideways, blocking all light, giving the illusion of a shut off television screen. The tilting of the lenses can also give the illusion for eyelids, anger, sorrow, joy, insanity, fear, and so on.

Hermaphrodites
A hermaphrodite, or a herm, is a fictional gender [Like Tumblr ], that both contain male & female reproductive organs. It should make sense that it should exist from an evolutionary argument, that two combined sexes are better than one, that sexual selection doesn’t have to exist, just reproduce with yourself, to make more and pass on your genes to the next generation. Before I explain why this can’t work, let me explain the difference between sexual reproduction, and asexual reproduction. Sexual reproduction occurs when two opposite genders with XX & XY sex cells, fertilize, and exchange genetic information to reproduce more life, as this requires reproductive organs. In Asexual reproduction, the organism has no sexual reproductive organs, as they reproduce by budding, and can even control when to bud, like if food becomes scarce, it will retract the bud, and when food is plentiful, it continues the budding. Now why this can’t work. First, the hormone mixing of estrogen, & testosterone. Transgenders who go through hormone treatment go through many psychological issues, like depression, and mood swings, that could lead to suicide. Maybe it’s natural for a herm? No, the main reason a hermaphrodite, with both a penis & vagina, is because of accidental inbreeding with self. Inbreeding can lead to many genetic problems for future off spring, as having too many, or too little chromosomes, and fatal diseases such as weakened organs, deformed bodies, and intellectual disabilities. That would mean that the future generation has a low chance of survival, herms can only be created artificially, not naturally. I would expect more realism from a hermaphrodite purebred pug, rather than a herm wolf.

Pure Breeds
If interspecies breeding wasn’t confusing enough, then how can you explain pure breeds? The reason we have purebred dogs is that because created them, as they’re artificially selected, not naturally. In the wild, animals can compete, and mate with whoever they want of their own species. In captivity, or domestication, people decide which animal mates who, selecting specific breeds to combine them into one new breed. However, most purebreds are more vulnerable to fatal diseases, than mutts. Mutts are healthy dogs, where their genetics are distributed to make the code for a happy healthy puppy. Some pure breeds are forced to mate with their own parents & siblings, which is the definition of incest, pugs are more inbred than any other breed on the planet. For pure breeds to exist, you would think that once anthro dogs gained intelligence, they were able to choose their mates, however, those who looked deformed and unhealthy are not likely able to mate. So the only way I can imagine this, is that there was a canine oppression century, where they were forced to mate, or rape to whoever their captive tells them to. That’s the only possible way I can find this remotely possible.

Consumption
Every species has a specific diet to chew. Herbivores eat vegetation, carnivores eat other animals, omnivores eat both vegetation, and animals. Why isn’t every animal an omnivore? Well first of all, their teeth evolved to eat only specific materials, herbivores have smooth flat teeth to chew the tough cell walls of plant cells, carnivores teeth are sharp, and razor like, to tear through its thick meat, and cracking bones. Omnivores both have flat & sharp teeth, to consume both plants, and other animals. So every anthropomorphic animal should at have omnivore teeth, or liquify it in a blender. Can they eat raw food? No, because humans can’t eat raw food without becoming ill, so we began to cook our food in fire, to add more flavor, and kill harmful bacteria that would harm our immune systems.

Clothes
Why would anthro’s wear clothes if they have fur, or skin already adapted to their environment? Well humans began to wear clothes, because it was much more comfortable, and increased our chances of survival, which passed on to our future offspring. So we lost our fur, not all of it, but most. I think anthro’s with fur would wear clothes because their hairs are much more shorter, compared to their animal ancestors. I also think that certain classes of animals should wear specific kind of clothes. Like amphibians with their slimy skin should wear like swimming clothes, to absorb the mucus, and poison.

Speciesism
I don’t think that’s a real world. In history, we have learned that the more diversity there’s, the more people are going to hate on eachother. I prefer to call it Classism, as in mammals, reptiles, birds, etc. Classism is like racism, not hate, but poor judgement, and the idea that every class is a like. In racism, the only thing that’s diverse is pigments in skin. Or the amount of melanin your skin cells contain, the more melanin, the darker the skin is. We have race because humans began to migrate to different climates around the world, which their skin adapted to decrease the chance of skin cancer from the sun’s invisible UV rays. Race is only one factor, but animal class is many, which would definitely give rise to more political & ideological groups.

Poisonous & Venomous Rights
Should poisonous & venomous animals have rights? They’re walking chemical weapons, with fangs ready to inject venom, or skins that secrete poisons? Are they allowed to be free to travel, to vote, to live? I think venomous animals are okay, because they have the choice to kill, and their venom glands can be removed surgically, but poisonous creatures, can’t. Like an anthro dart frog, how can they interact with other people without accidentally killing them, should they be locked up until a universal antidote has been cured for all classes, or remove a gene that prevents future poisonous anthros?

Demographics, Economics, Innovation
Throughout the years of free enterprise, known as capitalism, have been taking lot of risks to invent the technologies we use today, certain companies target specific demographics to sell their products, demographics are pretty limited, but what if we expanded, and increased the use of products, meaning that it would require more progress and efficiency. Do you think that anthros will have developed more advanced technology, and be more advanced than our modern world. Or would the overproduction of products of inflation would fall it into communism? Well for capitalism, there’s a equilibrium between supply & demand, Demand is the customer, the supply is the product. If supply increases, then customer’s pay less, if the supply goes down, then they pay more. I’m no expert in economics, so I’ll leave this open for the experts to answer.

Hygiene & Cosmetics
Have you ever been to a zoo, well I have and it wreaks. I love animals, but only from a distance, that’s why I’m a cat person [Actually I’m a marsupial person, or fox person, depending how I’m feeling], because they don’t stink. So would anthros smell like their feral counterparts? That depends, first, where does the smell come from, and second, who says it stinks. The person who finds the odors either natural, or disgusting, depends on their personality, and senses of scent & taste. So not all animal odors smell the same to that individual. So now where the scent is coming from? Microscopic bacteria that live inside, and outside the animal. Most of these bacteria can be harmful to us, so when we smell these odors, our bodies are telling us, if you consume this, you may die. However, today in developed countries, we have better access to clean water, and medicine, [though antibiotics will mutate viruses into superbugs]. So we don’t have to worry of getting a virus. Would anthro’s smell like ferals, if they don’t bathe, and live in developing countries, than yeah. If anthros followed basic hygiene, sprayed deodorant, perfumes, and colognes, than you would receive yourself a sexy clean anthropomorphic skunk. Also having a nice warm bath with your furry partner won’t be as romantic as you expect. It’s more ugly really. What about combining, or grooming your fur, is there a barber shop that takes care of that?

Homologous Classifications
Homologous means relating to in body, and structure, and this is an important aspect in evolution, so in the evolution of humans, anthros, and ferals. When, and what’s the line that separates these two that makes it entirely different species? Well what makes a species, a species if the species can breed with each other, and produce fertile offspring, then it belongs to the same species, if that species can’t breed with that species, then it doesn’t belong to the species, this is known as reproductive isolation. At first I wanted that anthros can breed both with humans & ferals, because that’s attractive for some reason, and humans are obviously isolated from ferals. The only issue with that, is that hereditary says that their genes will be mixing into that pool, giving births that aren’t natural to that species, like can you imagine a whale giving birth to an infant human? So they must be isolated. So there’s a certain boundary that separates these three species, or classes. What if humans, or anthros are allergic to each other? Well I think they would spend more time with each other, not in harmony, but in contact, and more likely to evolve a immunity over pesky allergies.

Doctor or Vet?
For a larger demographic, and variety in species, that also means we need a variety in medical science too. So would an anthro go to a vet, or a physician? Their anatomy is human structure, but their organs are mostly entirely different from a human. Their psychology may be the same, but they do still have instincts that helped them survive in the past. There lifespan has also increased, due to evolution, and invention of medicine. Or do we need an entirely new job for anthros? One that both understands human anatomy, psychology, but also understanding zoology, and pet biology? What would we call this new job, well what were to origin words for vet, and doctor. Well what I can gather is that vet came from horse racing, and doctor is a teacher, or a professional in medical science, of restoring health to a patient. So I guess that this new job, and field of medicine will likely have an equine name to it, so an Equinesition? Also, what would going to the this anthro doctor be like? Well I think it goes like this.

Fill out the forum, that identifies your class, species, gender, and your basic biology, and since we have a huge variety of anthropomorphic species, like billions on the globe, I think you’re going to be there for a long time, so get comfortable.

2. After you fill out what felt like an eternity of that ridiculous forum, you hand it to the secretary at the front.

3. You wait for your doctor to call you in, what shouldn’t be too long, hopefully, at least you don’t have universal healthcare, that waiting time would be months!

4. The Equinesition will call your name, and lead you into the room. Now what will he do? Will he/she perform a combination of veterinary and anatomical measurements , or will the Equinesition perform a entirely new form of medical practice?


13 Facts About Opossums

Opossums, which include the roughly 100 species in the order Didelphimorphia, are some of the most misunderstood animals in the Americas. They’re often thought of as dimwitted, dirty creatures whose most impressive trick is acting like roadkill. The truth is just the opposite: Opossums are smarter, cleaner, and more beneficial to humans than many of their woodland neighbors. Read on for more opossum facts.

1. OPOSSUMS AND POSSUMS AREN’T THE SAME ANIMAL.

In North America, opossum and possum describe the same thing, but in Australia the word possum refers to a completely different animal. Among the most well known of their respective types are the Virginia opossum and the brushtail possum. Both are small to medium sized, omnivorous marsupials, but the similarities end there. The possum looks like a cute cross between a squirrel and a chinchilla and it belongs to a different order than the North American mammal that shares (most of) its name. Despite the potential for confusion, possum is accepted as the shortened version of opossum in this part of the world (and if you see the word possum in this list, you can assume it’s referring to the animal from the Americas).

2. THEY’RE THE ONLY MARSUPIALS FOUND NORTH OF MEXICO.

Marsupials—mammals that carry and nurse their young in pouches—are absent from much of the world, and in Canada and the United States opossums are the sole representatives of the group. Like other marsupials, mother possums give birth to tiny, underdeveloped offspring (called joeys) that immediately crawl into a pouch where they live and nurse during their first months of life. Only once they’ve grown big and strong enough do they venture out, transitioning between their mother’s back and the warmth of the pouch until they mature into adults.

3. THEY CAN’T CHOOSE WHEN THEY PLAY DEAD.

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Perhaps the most famous characteristic of the opossum is its tendency to play dead in front of predators. When the animal experiences intense fear in the face of danger, it seizes up and flops to the ground where it can remain for hours staring blankly ahead and sticking out its tongue. It’s an impressive defensive mechanism, but its effectiveness can’t be chalked up to the possum’s acting skills. Possums have no control over when they play dead or for how long they do it: The comatose-like state is an involuntary reaction triggered by stress.

4. AN OFFENSIVE ODOR SELLS THE PERFORMANCE.

A picture of a possum playing dead doesn’t really do it justice. To get the full experience, you need to be standing over to it to smell the putrid odor it emits when pretending to be a corpse. The smelly substance it secretes from its anus is just one more reason for foxes and bobcats to look for their dinner elsewhere.

5. THEY SLOW THE SPREAD OF LYME DISEASE.

Even if possums aren’t the cutest creatures in the forest, they should be a welcome addition to your backyard. Unlike other mammals that carry ticks, and therefore spread Lyme Disease, possums gobble up 90 percent of the ticks that attach to them. According to the National Wildlife Federation, a single possum consumes 5000 of the parasites per tick season. That means the more possums that are in your area, the fewer ticks you’ll encounter.

6. THEIR MEMORIES ARE SURPRISINGLY SHARP.

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Opossums have impressive memories—at least when it comes to food. Researchers found that possums are better at remembering which runway led to a tasty treat than rats, cats, dogs, and pigs. They can also recall the smell of toxic substances up to a year after trying them.

7. THEY’RE IMMUNE TO MOST SNAKE VENOM.

While most animals look at a snake and see danger, a possum sees its next meal. The animals are immune to the venom of nearly every type of snake found in their native range, the one exception being the coral snake. Possums take advantage of this adaptation by chowing down on snakes on a regular basis.

Researchers have been trying to harvest possums’ antivenom powers for decades. A few years ago, a team of scientists made progress on this front when they recreated a peptide found in possums and and found that mice given the peptide and rattlesnake venom were successfully protected from the venom’s harmful effects.

8. THEY ALMOST NEVER GET RABIES.

While possums aren’t totally immune to rabies (a few cases have been documented), finding a specimen with the disease is extremely unlikely. Marsupials like possums have a lower body temperature than the placental mammals that dominate North America—in other words, their bodies don’t provide a suitable environment for the virus.

9. THEIR TAIL ACTS AS A FIFTH APPENDAGE.

iStock

Opossums are one of a handful of animals with prehensile tails. These appendages are sometimes used as an extra arm: They can carry grass and leaves for building nests or grip the sides of trees to provide extra stability while climbing. Baby possums can even use their tails to hang from branches upside down as they’re often depicted doing in cartoons. But it’s a myth that possums sleep this way: Their tails are only strong enough to hold them for a short amount of time.

10. THEY’RE CONSTANTLY SELF-GROOMING.

Thanks to their whole acting-and-smelling-like-a-corpse routine, opossums aren’t known as the most sanitary animals in nature. But they take cleanliness seriously: The Washington Department of Fish and Wildlife writes that possums, like housecats, use their tongue and paws to groom themselves frequently and thoroughly. Possums largely lack sweat glands, and this behavior is believed to help them cool down. It also has the added effect of rendering them odorless (when they’re not secreting stinky predator-repellant, that is).

11. THEIR EYES AREN’T TOTALLY BLACK.

iStock

One of the opossum’s most recognizable features is its pair of opaque eyes. Opossum eyes do have whites and irises, but because their pupils are so large, their eyes appear completely black from a distance. The exaggerated pupil dilation is thought to help the nocturnal animals see after the sun goes down.

12. THEY’RE SOCIAL CREATURES.

It was long assumed that opossums like to keep to themselves, but a study published in the journal Biology Letters suggests they have a social side. Researchers at the Federal University of Pernambuco in Recife, Brazil observed some possums in captivity sharing dens even if they weren’t mates. In one case, 13 white-eared opossums of various age groups were cohabiting the same space. The scientists suspect that male and female possums living in the wild may even build nests together as a way to trigger the female’s reproductive hormones.

13. THEIR REPRODUCTIVE SYSTEMS ARE COMPLICATED.

The way it gives birth and raises its young isn’t the only thing that’s interesting about the opossum's reproductive life. Females have two vaginal tracts and two uteri, and males in turn have a forked or bifurcated penis. This is fairly typical for marsupials, but when European colonizers first landed in North America centuries ago, they didn’t know what to make of the confusing genitalia. One explanation they came up with was that male opossums impregnated females through the nose.


Do marsupials wash their pouch? April 8, 2009 8:20 AM Subscribe

I saw this related but slightly stupider question and it didn't help much. Do they get all sandy and dusty inside? Should I imagine them like a mouth with natural saliva processes washing it out, or do the animals actually go wade out into a river or turn themselves upside-down regularly?

I'm not from Australia and I've never seen marsupials in the wild.

Best answer: Here's how it works among kangaroos, at least (Paraphrased from Kangaroos: Biology of the Largest Marsupials):

The pouch secretes a waxy compound that dries into a dark scale when the pouch has been unoccupied. About 1-2 days before birth the female holds the pouch open with her forepaws and licks the scale away. The cleaning is most extensive 1-2 hours before birth occurs.

While the pouch is occupied, the San Diego Zoo says that the mother cleans the pouch out, but it doesn't specify whether this is done by licking or washing:

"Do the joeys eliminate (pee and poop) in the pouch? Yes, indeed! When they are very small they don't produce much, and when they get bigger, some is absorbed through the pouch lining. It can get kind of smelly, though, so the mothers clean out their pouches from time to time."
posted by jedicus at 8:39 AM on April 8, 2009 [2 favorites]

Response by poster: So I guess they can lick out whatever dust accumulates? Or is the waxy compound actually performing a digestive sort of function?

elendil71: it looks like herd, mob and troop are all acceptable.
posted by creasy boy at 8:48 AM on April 8, 2009

Best answer: Here's an interesting journal article on how joeys survive in the "microbially enriched environment" of the pouch during developement.

In some marsupials (diprotodonts) "pouch cleaning, via licking, immediately prior to the birth of the young has been reported and is presumed to reduce bacterial flora." Others seem to rely solely on secretions from the mother's epithelial cells. The joey's get immunoglobins from their mother's milk and from her egg's yolk sac prior before they're born, but often die if the microbial count doesn't decrease before they enter the pouch.

Pretty fascinating (and more than a little gross).
posted by Thoughtcrime at 8:49 AM on April 8, 2009

Best answer: Or is the waxy compound actually performing a digestive sort of function?

Think of it like the wax in your ears. It traps gunk, is sloughed off through natural processes and moving around (aka "epithelial migration"), or you can rub it out manually, and your ear just keeps making more (which also helps the natural "migration" process). If you're a kangaroo, you can lick it out.
posted by Cool Papa Bell at 9:28 AM on April 8, 2009


The real reasons why childbirth is so painful and dangerous

Giving birth can be a long and painful process. It can also be deadly. The World Health Organization estimates that about 830 women die every day because of complications during pregnancy and childbirth &ndash and that statistic is actually a 44% reduction on the 1990 level.

"The figures are just horrifying," says Jonathan Wells, who studies childhood nutrition at University College London in the UK. "It's extremely rare for mammalian mothers to pay such a high price for offspring production."

So why exactly is childbirth so risky for humans? And is there anything we can do to further reduce those death rates?

Scientists first began thinking about the problem of human childbirth in the middle of the 20th Century. They soon came up with an idea that seemed to explain what was going on. The trouble began, they said, with the earliest members of our evolutionary lineage &ndash the hominins.

From an early date in our prehistory, hominin babies may have had to twist and turn to pass through the birth canal

The oldest hominin fossils so far found date back about seven million years. They belong to animals that shared very few of our features, except perhaps one: some researchers think that, even at this early stage, hominins were walking upright on two legs.

To walk on two legs efficiently, the hominin skeleton had to be pushed and pulled into a new configuration, and that affected the pelvis.

In most primates the birth canal in the pelvis is relatively straight. In hominins, it soon began to look very different. Hips became relatively narrow and the birth canal became distorted &ndash a cylinder that varied in size and shape along its length.

So from an early date in our prehistory, hominin babies may have had to twist and turn to pass through the birth canal. This would have made birth a far more difficult task than it had been previously.

Then things got even worse.

About two million years ago, our hominin ancestors began to change again. They lost their more ape-like features such as a relatively short body, long arms and small brain. Instead they began to gain more human-like ones, like taller bodies, shorter arms and bigger brains.

That last trait in particular was bad news for female hominins.

I was going to find evidence that supported the obstetric dilemma, but very soon everything came crashing down

Big-brained adults start out life as big-brained babies, so evolution came into conflict with itself. On the one hand, female hominins had to maintain a narrow pelvis with a constricted birth canal in order to walk efficiently on two legs. But at the same time the foetuses they carried were evolving to have larger heads, which were a tighter and tighter fit through those narrow pelvises.

Childbirth became a distressingly painful and potentially lethal business, and it remains so to this day.

In 1960, an anthropologist called Sherwood Washburn gave this idea a name: the obstetrical dilemma. It is now often called the "obstetric dilemma". Scientists thought it explained the problem of human childbirth perfectly. Many still think it does.

But some, including Wells, are no longer happy with this standard explanation. In the last five years, Wells and several other researchers have begun to push against the classic story of the obstetric dilemma.

They think Washburn's idea is too simplistic, and that all sorts of other factors also contribute to the problem of childbirth.

Holly Dunsworth of the University of Rhode Island, Kingston, was drawn to the obstetric dilemma while she was still a grad student. "I thought it was so exciting, I was going to find evidence that supported the obstetric dilemma," she says. "But very soon everything came crashing down."

We have bigger babies and longer pregnancies than you would expect

The problem was with the predictions Washburn made. "When Washburn wrote his article, he was actually saying that the obstetric dilemma was solved by giving birth to babies at a relatively early stage in their development," says Wells.

Go back to that moment two million years ago when human brains began to grow larger. Washburn suggested that humans found a solution of sorts: shortening the length of the human pregnancy. Human babies were forced out into the world earlier than they really should be, so that they were still relatively small, with diminutive, underdeveloped brains.

Washburn's explanation seems logical. Anyone who has held a newborn can appreciate how underdeveloped and vulnerable they are. The standard view is that other primates hold onto their pregnancies for longer and give birth to babies that are more developmentally advanced.

But, says Dunsworth, it is simply not true.

"We have bigger babies and longer pregnancies than you would expect," she says.

Women give birth to babies with larger brains than we would expect

In an absolute sense human pregnancies are long. They typically last 38-40 weeks, whereas a chimpanzee pregnancy is 32 weeks long, and gorillas and orang-utans give birth after about 37 weeks.

As Dunsworth and her colleagues explained in a 2012 paper, this remains true even if we adjust the pregnancy durations to take into account differences in body mass. Human pregnancies last 37 days longer than they should do for an ape our size.

The same thing applies for brain size. Women give birth to babies with larger brains than we would expect of a primate with the average woman's body mass. This means that a key prediction of Washburn's obstetric dilemma is incorrect.

There are other problems with Washburn's idea too.

A central assumption of the obstetric dilemma is that the size and shape of the human pelvis &ndash and the female pelvis in particular &ndash is highly constrained by our habit of walking upright on two legs. After all, if evolution could have "solved" the problem of human childbirth by simply making women's hips a little wider and the birth canal a little larger, it surely would have done so by now.

The birth canal is extraordinarily variable in size and shape

In 2015, Anna Warrener at Harvard University in Cambridge, Massachusetts, and her colleagues questioned this assumption.

The researchers collected metabolic data from male and female volunteers who were walking and running in the lab. Volunteers with wider hips were no more inefficient at walking and running than their narrow-hipped peers. From purely energetic considerations, at least, there does not seem to be anything stopping humans evolving wider hips that would make childbirth easier.

"The basic premise of the obstetric dilemma &ndash that having a small or narrow pelvis is best for biomechanical efficiency &ndash is likely not correct," says Helen Kurki of the University of Victoria in British Columbia, Canada.

Kurki was not involved with Warrener's study, but her own research has identified yet more problems for the traditional obstetric dilemma hypothesis.

If the female pelvis really is tightly governed by two opposing forces &ndash the need to be narrow for walking and the need to be wide for giving birth &ndash the shape of the birth canal should vary little between women. It should be "stabilised" by natural selection.

Pregnant women sometimes joke that their developing foetus feels like an energy-sapping parasite

But after analysing hundreds of human skeletons, Kurki reported in 2015 that the birth canal is extraordinarily variable in size and shape. It varies even more than the size and shape of human arms, a trait that is known to vary between individuals.

"I think my findings do support shifting attitudes to the obstetric dilemma," says Kurki.

Washburn's tidy narrative does not seem quite as satisfying as it once did. There has to be something else going on.

Dunsworth thinks she has identified one important missing piece in the puzzle: energy.

"We max out toward the end of pregnancy," says Dunsworth, herself a mother. "Those last weeks and months of pregnancy are tiring. They are pushing right against the possible sustainable metabolic rates in humans. It has to end at some point."

Evolution could, in principle, make the pelvis larger &ndash but it has not had to

Pregnant women sometimes joke that their developing foetus feels like an energy-sapping parasite. In a sense it really is, and its energy demands grow with every passing day.

In particular, human brains have an almost insatiable appetite for energy. Growing a second, tiny brain inside the womb can push a pregnant woman close to the edge, metabolically speaking.

Dunsworth calls this idea the energetics of gestation and growth (EGG) hypothesis. It suggests the timing of childbirth is governed by the difficulties of continuing to nourish a developing foetus beyond 39 weeks &ndash not by the difficulties of squeezing the baby out through the birth canal.

Dunsworth thinks people obsess too much about the tight fit between a baby's head and its mother's birth canal. It might seem too much of a coincidence that the two are so closely size-matched, but she says the pelvis has simply evolved to be the size it needs to be. Evolution could, in principle, make the pelvis larger &ndash but it has not had to.

For most of human evolution, childbirth might have been quite a lot easier

By and large, Kurki shares this view. "The obstetric canal is big enough, the majority of the time, for the foetus to pass through," she says.

This is true. But even so, take another look at the maternal mortality figures: 830 deaths every day. Even among women who do not lose their lives during childbirth, some studies say the process leads to life-changing but non-lethal injuries in as many as 40% of cases. The price women pay for childbirth seems extraordinarily high.

Wells agrees. "It's impossible to imagine the problem has been this bad over the long term."

Perhaps it has not. In 2012, Wells and his colleagues took a look at the prehistory of childbirth, and came to a surprising conclusion. For most of human evolution, childbirth might have been quite a lot easier.

The prehistory of childbirth is a difficult subject to study. The hominin pelvis is rarely preserved in the fossil record, and newborn skulls are even thinner on the ground. But from the meagre evidence available it seems that some earlier species of human, including Homo erectus and even some Neanderthals, had a relatively easy time of it when it came to giving birth.

A shift to farming may have led to developmental changes that made childbirth far more difficult

In fact, Wells and his colleagues suspect childbirth might even have been a relatively minor problem in our species &ndash at least to begin with. There are very few newborn baby skeletons among the human remains from early hunter-gatherer groups, which might hint that death rates among newborns were relatively low.

If there was a rise in newborn death rates at the dawn of farming, there were almost certainly several factors involved.

For instance, early farmers began living in relatively dense settlements, so transmissible disease probably became a far greater problem. Newborns are often particularly vulnerable when an infection is going around a community.

But Wells and his colleagues suspect a shift to farming also led to developmental changes that made childbirth far more difficult. A rise in infant mortality at the dawn of farming might be due in part to a raised risk of death during childbirth.

Human childbirth suddenly became more difficult about 10,000 years ago

There is one striking feature archaeologists have noticed when comparing the skeletons of early farmers with their hunter-gatherer ancestors. The farmers were noticeably shorter in stature, probably because their carbohydrate-rich diet was not particularly nutritious compared to the protein-rich hunter-gatherer diet.

This is a telling observation for those who study childbirth, says Wells, because there is evidence of a link between a woman's height and the size and shape of her pelvis. In general, the shorter a woman, the narrower her hips. In other words, the shift to farming almost certainly made childbirth a little bit more challenging.

On top of that, the carbohydrate-rich diets that became more common with farming can cause a developing foetus to grow larger and fatter. That makes the baby harder to deliver.

Combine these two factors and human childbirth &ndash which might have been relatively easy for millions of years &ndash suddenly became more difficult about 10,000 years ago.

Something rather like this "farming revolution effect" replays whenever human diets become poorly nutritious &ndash particularly if those diets also contain a lot of carbohydrates and sugars, which encourage foetal growth.

"We can make a simple prediction that the nutritional status of mothers should be associated with a local prevalence of maternal mortality and difficulties with giving birth," says Wells. The statistics clearly follow such a pattern, suggesting that improving nutrition might be a fairly easy way to reduce maternal mortality.

Pregnant women have adapted to nourish their foetus for as long as they can

Both Dunsworth and Kurki think that Wells has identified something significant in his work &ndash something that perhaps would only be evident to a researcher with the right background in nutrition and development.

"I'm so lucky that Jonathan is describing these complex issues from his perspective of human health," says Dunsworth. "At the same time I'm approaching the problem from my perspective of human evolution."

So we now have a new explanation for the difficulties of human childbirth. Pregnant women have adapted to nourish their foetus for as long as they can before it grows too large to feed internally. The female pelvis has adapted to be just the right size to allow this maximally-nourished foetus to travel through safely. And dietary changes in the last few thousand years have upset this fine balance, making childbirth risky &ndash particularly for mothers who have a poor diet.

However, Dunsworth says that is probably not the end of the story.

Washburn's ideas made good intuitive sense for decades, until Dunsworth, Wells, Kurki and others began to pick them apart. "What if the EGG perspective is too good to be true?" asks Dunsworth. "We have to keep searching and keep collecting evidence."

This is exactly what other researchers are doing.

For instance, in 2015 Barbara Fischer of the Konrad Lorenz Institute for Evolution and Cognition Research in Klosterneuburg, Austria and Philipp Mitteroecker of the University of Vienna, Austria took another look at the female pelvis.

A woman's pelvis takes on a shape more conducive to childbirth in her late teens &ndash when she reaches peak fertility

It seemed to them that Dunsworth's EGG hypothesis &ndash compelling though it is &ndash could actually be seen as complementary to Washburn's ideas, rather than disproving them entirely. Dunsworth agrees: she thinks many factors are involved in the evolution of modern childbirth.

Fischer and Mitteroecker investigated whether there is any correlation between female head size and pelvis size. Head size is heritable, at least to some extent, so women would benefit during childbirth if those with larger heads also naturally had a wider pelvis.

The researchers' analysis of 99 skeletons suggested such a link does indeed exist. They concluded that a woman's head size and her pelvic dimensions must somehow be linked at the genetic level.

"This does not mean that the [problem of childbirth] has been resolved," says Fischer. But the problem would be even worse if there was no link between head size and pelvis width.

And there is another complication: women's bodies change as they get older.

A May 2016 study led by Marcia Ponce de León and Christoph Zollikofer at the University of Zurich, Switzerland examined pelvic data from 275 people &ndash male and female &ndash of all ages. The researchers concluded that the pelvis changes dimensions during the course of a woman's lifetime.

Many babies are now born by Caesarean section

Their data suggested that a woman's pelvis takes on a shape more conducive to childbirth in her late teens &ndash when she reaches peak fertility. It then stays that way until around her 40th birthday, when it then gradually changes shape to become less suitable for childbirth, ready for the menopause.

The scientists suggest these changes make childbirth a little easier than it otherwise would be. They call this idea the "developmental obstetric dilemma" (DOD).

"The DOD hypothesis provides a developmental explanation for the variation in pelvic obstetric dimensions," says Ponce de León.

If all these evolutionary pressures are acting on childbirth, is the process still changing and evolving even now?

In December 2016, Fischer and Mitteroecker made headlines with a theoretical paper that addressed this question.

Earlier studies had suggested that larger babies have a better chance of survival and that size at birth is at least somewhat heritable. Together, these factors might lead the average human foetus to push up against the size limit imposed by the female pelvis, even though it can be fatal to push too far.

We all either did or didn't arrive in the world through a pelvis

But many babies are now born by Caesarean section, an operation in which the baby is taken out of the mother's abdomen without ever entering the birth canal. Fischer and Mitteroecker suggested that, in societies where C-sections have become more common, foetuses can now grow "too large" and still have a reasonable chance of survival.

In theory, as a consequence the number of women giving birth to babies that are too big to fit through their pelvis might have risen by 10 or 20% in just a few decades, at least in some parts of the world. Or, to put it in cruder terms, people in these societies might be evolving to have larger babies.

For now this is only an idea and there is no hard evidence that it is really happening. But it is an intriguing thought.

"We all either did or didn't arrive in the world through a pelvis," says Wells. "If we did, that pelvis mattered. And if we didn't, that in itself is interesting."

Ever since live birth evolved, babies have been constrained to some degree by the size of the birth canal. But maybe, for some babies at least, that is no longer true.

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'Virgin Birth' By Shark Confirmed: Second Case Ever

Scientists have confirmed the second-ever case of a &ldquovirgin birth&rdquo in a shark, indicating once again that female sharks can reproduce without mating and raising the possibility that many female sharks have this incredible capacity.

Lead author Dr. Demian Chapman, shark scientist with the Institute for Ocean Conservation Science at Stony Brook University, Beth Firchau, Curator of Fishes for the Virginia Aquarium & Marine Science Center, and Dr. Mahmood Shivji, Director of the Guy Harvey Research Institute and Professor at Nova Southeastern University in Florida, have proven through DNA testing that the offspring of a female blacktip shark named &ldquoTidbit&rdquo contained no genetic material from a father. Tidbit had lived at the Virginia Aquarium in the Norfolk Canyon Aquarium for eight years since shortly after her birth in the wild.

In May 2007, Chapman and Shivji were part of a team that made the groundbreaking scientific discovery confirming -&ndash for the first time ever -- a virgin birth in a female shark. That shark was a hammerhead residing at an Omaha, Nebraska zoo and had not been in contact with male sharks for at least three years. That study was published in the journal Biology Letters and captured global media and scientific attention. The DNA-fingerprinting techniques used to prove both cases of virgin birth (scientifically known as &ldquoparthenogenesis&rdquo) are identical to those used in human paternity testing.

&ldquoIt is now clear that parthenogenesis occurs in sharks other than just hammerheads,&rdquo Chapman said. &ldquoThe first case was no fluke. It is quite possible that this is something female sharks of many species can do on occasion.&rdquo

Sharks&rsquo ability to reproduce alone should not be viewed as an adequate replacement for normal sexual reproduction, Chapman cautioned. For one, the blacktip and hammerhead sharks that reproduced without mating both only produced one pup, rather than an entire litter. Shark litters can contain anywhere from a few to more than a hundred shark pups, depending upon the species. &ldquoThe revelation that female sharks can reproduce alone shouldn&rsquot stop us from worrying about driving shark populations to very low levels through overfishing,&rdquo said Chapman. &ldquoIt is very unlikely that a small number of female survivors could build their numbers up very quickly by undergoing virgin birth.&rdquo

Tidbit was an Atlantic blacktip shark whom Virginia Aquarium biologists believe had only just reached sexual maturity.

&ldquoWe have never observed her in reproductive behavior or showing typical signs of having been bred,&rdquo said Firchau. Scientists did not even know that Tidbit was pregnant until after she unfortunately died and an autopsy (called a necropsy for animals) was performed. &ldquoSadness turned to surprise during the necropsy when we found that she was pregnant,&rdquo Firchau said. &ldquoThere were no male blacktips in the tank for the past eight years!&rdquo

The phenomenon of &ldquovirgin birth&rdquo occurs when a baby is conceived without male sperm having first fertilized the female&rsquos eggs, and has been proven in some bony fish, amphibians, reptiles, and birds. In the type of parthenogenesis seen in these sharks, known as automictic parthenogenesis, the newly forming pup acquires one set of chromosomes when the mother's chromosomes split during egg development. But instead of uniting with similarly split chromosomes from sperm, as occurs in sexual reproduction, the mother&rsquos set is paired with a copy of itself. This results in offspring of reduced genetic diversity who may be at a disadvantage for surviving in the wild.

&ldquoThe finding of parthenogenesis in blacktip sharks, which are close relatives of some of the larger predatory sharks in the ocean including the tiger, bull and dusky sharks, raises intriguing questions about how frequently parthenogenesis may occur in the wild in this group of heavily fished sharks,&rdquo said Shivji. &ldquoIt is possible that parthenogenesis could become more common in these sharks if population densities become so low that females have trouble finding mates.&rdquo Populations of all of these sharks have declined in the past twenty years due to overexploitation, mainly to supply the shark fin markets.

There have been nearly a dozen reports of suspected virgin births in sharks in recent years, but scientists largely assumed these cases were the result of long-term sperm storage by females after mating with males. Virgin birth is now the more probable explanation, and DNA testing is underway to confirm it in additional sharks. Chapman is currently analyzing the DNA of yet another shark species with Dr. Kevin Feldheim of the Field Museum in Chicago.

Story Source:

Materials provided by Stony Brook University. Note: Content may be edited for style and length.


Marsupial

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marsupial, any of more than 250 species belonging to the infraclass Metatheria (sometimes called Marsupialia), a mammalian group characterized by premature birth and continued development of the newborn while attached to the nipples on the mother’s lower belly. The pouch—or marsupium, from which the group takes its name—is a flap of skin covering the nipples. Although prominent in many species, it is not a universal feature. In some species the nipples are fully exposed or are bounded by mere remnants of a pouch. The young remain firmly attached to the milk-giving teats for a period corresponding roughly to the latter part of development of the fetus in the womb of a placental mammal (eutherian).

The largest and most-varied assortment of marsupials—some 200 species—is found in Australia, New Guinea, and neighbouring islands, where they make up most of the native mammals found there. In addition to larger species such as kangaroos, wallabies, wombats, and the koala (Phascolarctos cinereus), there are numerous smaller forms, many of which are carnivorous, with the Tasmanian devil (Sarcophilus harrisii) being the largest of this group (family Dasyuridae). About 70 species live in the Americas, mainly in South and Central America, but one, the Virginia opossum (Didelphis virginiana), ranges through the United States into Canada. The largest living marsupial is the red kangaroo (Macropus rufus), males of which can grow to about 2 metres (6.6 feet) in height, 3 metres (10 feet) from muzzle to tail tip, and a weight of up to 90 kg (about 200 pounds). The smallest are the planigales (see marsupial mouse), especially the long-tailed planigale ( Planigale ingrami), measuring barely 12 cm (4.7 inches) in total length. Most marsupials range from the size of a squirrel to that of a medium-size dog.

The structural and behavioral parallels with placental mammals are sometimes quite striking. Such resemblances are examples of convergent evolution—a tendency for organisms to adapt in similar ways to similar habitats. Thus, there are marsupials that look remarkably like moles, shrews, squirrels, mice, dogs, and hyenas. Others are the ecological counterparts, less in structure than in habits, of cats, small bears, and rabbits. Even the larger grazing marsupials (such as kangaroos), which resemble no placental mammals, can be thought of as filling the same ecological role (niche) as the deer and antelope found elsewhere.

The niches that marsupials fill are closely associated with structure. The burrowing species, such as the marsupial moles (Notoryctes typhlops and N. caurinus) and the wombats, have powerful foreclaws with which they can tunnel into the ground for food and shelter. Terrestrial forms, such as kangaroos and wallabies, possess well-developed hind limbs that serve both as formidable weapons and as catapults by which they can bound over the plains. The gliders have a membrane along either flank, attached to the forelegs and hind legs, that enables these arboreal animals to glide down from a high perch. A few marsupials—such as tree kangaroos, koalas, and some cuscuses—spend most of their lives in trees. The water opossum, or yapok (Chironectes minimus), of Central and South America is semiaquatic.

The diets of marsupials are as varied as the niches they occupy. Many dasyurids live chiefly on insects and other small animals. Dunnarts (Sminthopsis) are so hyperactive—like shrews—that, in order to supply their high energy needs, they must devour their own weight in food (chiefly insects) each day. The numbat uses its remarkable wormlike tongue to lap up termites and ants. Many Australian possums, bandicoots, and American opossums have a mixed diet of plants and insects. Wombats and many other marsupials are strictly vegetarian. The small honey possum (Tarsipes rostratus) is specialized to feed on the nectar of flowers, and other marsupials also may serve as important pollinators in that way. Few large carnivores have ever evolved in Australia, because of the low productivity of its environment. The most-recent large carnivorous marsupials to evolve—the Tasmanian devil and the now-extinct thylacine, or Tasmanian wolf (Thylacinus cynocephalus)—were both displaced on the mainland by the dingo.

Marsupials are notably less intelligent than placental mammals, partly because of their simpler brains. Compared with that of placentals, the brain of marsupials differs markedly in both structure and bulk. Most notably, it lacks a corpus callosum, the part of the placental brain that connects the two cerebral halves. The marsupial brain is also smaller relative to overall body size for example, a quoll has about half as much brain tissue as a placental cat of similar skull size. It is not surprising, therefore, to find that marsupial behaviour differs somewhat from that of placentals. One peculiarity that may stem from that underdevelopment is restricted vocal ability. Although marsupials are not entirely silent, few emit loud sounds of excitement or distress apparently, none utters grunts of contentment or even cries of hunger when young. Their vocalizing is more limited and less variable than that of placentals. The ferocious-sounding rutting roars of male koalas are a dramatic and unexpected exception.

There seems to be little permanent social organization among most marsupials beyond short-lived pair bonds during mating. Many of the grazing marsupials, such as kangaroos and wallabies, move in feeding groups called mobs, but those associations are not true social groups, as there is no attention paid to any leaders or elders. Only the lesser gliders (Petaurus) have permanent cohesive social groupings.

The life cycle of marsupials exhibits peculiarities that have long been considered primitive compared with those of placental mammals but are more likely adaptations to low-productivity environments. The uterine cycle of the female marsupial has no secretory phase, and the uterine wall is not specialized for embryo implantation, although a transitory placenta does exist in the bandicoots. The period of intrauterine development in marsupials ranges from about 12 days in the bilby (Macrotis lagotis) to 38 days in the swamp wallaby (Wallabia bicolor).

The young, born in a vulnerable embryonic condition, make their own way to the shelter, warmth, and nourishment of the pouch in pouchless marsupials the young simply cling to the teats. Those fortunate enough to survive that arduous journey may succeed in attaching themselves to the mother’s nipples, which then swell and become firmly fastened—almost physically fused—to the mouth tissues of the young. In that condition the young continue their development for weeks or months, after which they are weaned and begin to look after themselves. Frequently, the partially developed young outnumber the available teats, and the excess individuals perish.


How does this even WORK?

At some point in their evolution, these species became locked on a runaway train of extreme “sperm competition” – whichever males put the most energy into making and sowing their seed had the most offspring, even if it killed them.

So the whole lives of these little insectivores became geared towards baby-making. Hardly any of them survive past their first year. By six months, the males reach full maturity, and devote the next five months to bulking up – they need to gain as much weight as possible before the females become fertile. Once that happens, they won’t have time to eat. They’ll be entirely dependent on stored energy for weeks as they run from female to female, engaging in marathon sex.

In fact, mating season drives them to such energy-saving extremes, they stop producing sperm about a month before the females even become receptive. All the sperm they will ever make in their lifetime gets stored in the plumbing while the testicles themselves atrophy. This isn’t the best location for safekeeping – they immediately start losing sperm in their urine. This puts them in dire straights – they have irreversibly committed to the next breeding season, and the clock is ticking.

Their eggs (so to speak) are all in one basket, and spoiling rapidly. No wonder they’re so frantic to mate until they drop.

Luckily for them, fathering little antechinuses is not a “him or him” proposition – each litter can have young from more than one dad. It doesn’t matter which male gets to a particular female first, as long as he gets to her eventually. This is because the female hasn’t even ovulated yet when mating begins – instead, she stores all the sperm from the season in her ovaries, then ovulates after the breeding season is done. It’s a bit of bet-hedging on her part. If she has offspring with many different dads, her own genes are more likely to be passed on to her grandkids.


That opossum in your yard: They may be ugly but they aren't dumb

Unlike the cliche, familiarity doesn't seem to breed contempt. It breeds indifference instead.

Why else would we take so little interest in one of the most fascinating of Alabama's wildife - the opossum?

That's opossum with an "o" and that "o" is important. To be technically correct, it's the Virginia - as in the State - opossum and that "Virginia" is important too.

The Virginia opossum got this common name from its Algonquian Indian name "apasum," meaning "white beast," and from the state where it was first given an English name in the early 1600's by Captain John Smith of the Jamestown Colony and Pocahantas fame.

The "o" is important because when British explorer James Cook, on his first voyage to Australia some 150 years after Captain Smith named them, encountered other cat-sized animals that nurtured their young in a pouch, his ship's naturalist erroneously assumed they were the same, or at least similar, species and called them opossums too.

It turns out that the Australian marsupials are not closely related to our opossums, so to prevent confusion, scientists now call all Australian species possums - no "o" -- to distinguish them from our opossums.

The "Virginia" is important because although we only have one marsupial species in the United States, more than 70 more species occur throughout Central and South America.

So in addition to our Virginia opossum, there are mouse opossums, slender opossums, water opossums, pygmy opossums, and woolly opossums, not to mention fat-, short-, thick-, and bushy-tailed opossums, plus my favorite -- four-eyed opossums.

They are all marsupials though -- animals that give birth to still developing embryonic pups and rear them for months in a pouch.

Virginia opossums are pregnant for only 12 days before giving birth to 10 to 50 of these pups, each about the size of a small bee or large ant. In order to survive, these deaf, blind, hairless fetuses have to crawl unaided the inch or so from their mother's birth canal into her pouch and find one of her 13 nipples.

As only 5-7 young are typically raised, many pups are lost along the way. For those lucky enough to find and attach to a nipple, their lips soon fuse together and for the next two months they remain fastened to that nipple 24/7. If dislodged, they will be unable to re-attach and will die.

Life is no picnic for an opossum pup.

By the time they are 3 to 4 months old, opossums have left the pouch for good and are on their own. Also by this time, they've acquired all those traits which make them such endearing creatures.

They have all 50 of their teeth - most of any American mammal -- which they use to eat your garbage, your pet's food if you leave it outdoors, or just about any food that won't eat them first. They have hind feet with opposable thumbs, and they are the only mammal native to the United States with a grasping prehensile tail.

Even as newly independent pups, they have all the intelligence they will ever have. What's that, you say? Opossum intelligence?

Yes, despite their undeserved reputation for stupidity and a brain that is only one-fifth the size of a cat's, opossums are better at remembering where food is hidden than are dogs, cats, or rats.

Opossums are probably most famous for "playing 'possum," that is pretending to be dead when threatened. Actually, as someone who has trapped, tagged, and released hundreds of opossums, I can say with some authority that they are much more likely to hiss, growl, and flash those 50 teeth than they are to collapse in a heap and play dead.

But for all their bluster, they are surprisingly hesitant to bite. They seldom bite pets and despite handling many, I've never been bitten, although not all my field assistants can say the same.

If this threat doesn't work, they may indeed keel over, drool, excrete foul-smelling liquid from their anal glands, and play dead.

They will continue to play dead pretty much regardless of what you do to them. Whether they really have fallen into some sort of opossum trance, fainted, or are just pretending, isn't clear. Electronic monitoring of their heart and brain activity shows no differences when they are playing dead compared to when they are normally active, so maybe they are just superb and dedicated actors.

One thing opossums don't have to play dead for is snakes. They are virtually immune to snake venom, thanks to a unique protein in their blood. So copperheads, water moccasins, and even large rattlesnakes are part of the standard opossum diet. Remember this the next time that you aren't bitten by a large rattlesnake. It's the opossum's form of public service.

Opossums need to get about the business of reproducing quickly - and they can do so as soon as 6 months of age -- because they won't live for long. For reasons that we don't understand they undergo a sort of accelerated aging, so that by the time they are 2 years old, they begin to show classic signs of aging such as wasting muscles, a declining immune system, and the development of cataracts.

Most wild opossums are actually dead before they are two years old and of more than one hundred I've put radio collars on and monitored throughout their lives, none has so far lived more than 3 years.

Despite these fascinating traits, opossums will no doubt continue to get little respect. I'm not sure why.

They do not carry rabies or other diseases that people need to worry about. With their long snouts, toothy snarl, naked ears and rat-like tail, they certainly fail the "cute" test.

Maybe it's no more complicated than that.

Steven Austad is Chair of the Biology Department at UAB. Before becoming a research scientist, he had various lives as an English major, a newspaper reporter, a New York City taxi driver, and a Hollywood wild animal trainer. Living now in Birmingham with his veterinarian wife, 6 dogs, 2 parrots, and a cat, he enjoys nothing more than communicating how science works to the general public.

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