By Julie Old, Associate Professor, Biology, Zoology, Animal Science, Western Sydney University
If you look at where wombats deposit their poo, you realize that they must be capable of some surprising acrobatics. It always surprised me to see wombat shoots on top of tufts of grass or logs, because I always wondered how the fat creatures must have maneuvered to put it there.
It turns out that these robust marsupials also engage in another kind of acrobatics: we recently received a video from Lyndell Giuliano and Andy Carnahan in Tomboye, New South Wales, who had filmed two wombats in the wild “doing wild”!
Although we know it happens, because there are baby wombats that replenish the population over time, it's not often people get to witness such an event.
A rare observation of intimacy above ground
Researchers have previously documented wombat sex in any detail. Prior to the sightings noted in the review, it was thought to occur underground in the privacy of the burrow, which is probably why it was rarely observed.
Although we still don't know much about what wombats get up to underground, wombats have been seen mating above ground in the open!
In this scenario, the male wombat has been described to chase the female wombat, often biting her and pushing her on her side, before also laying on her side and mating with her.
In this recorded “rom-com”, only the male seems to be on his side during mating.
Violence and death
Other marsupials are also quite aggressive during mating. The Tasmanian devil, which probably got its name not unsurprisingly, is particularly aggressive. Males draw females into their burrow and hold them captive, sometimes for days.
Among the small, rodent-like antechinus and phascogales, the males are so determined to mate with as many females as they can that it results in a huge increase in stress hormones, leading to complete organ failure, and then death.
This reproductive strategy, called “semelparity”, also occurs in salmon and some frogs and lizards – but it is extremely rare among mammals.
And in the insect kingdom, it is not uncommon for males to die after mating, although the causes are often quite different.
Female praying mantises attract males and after the incident decapitate their male companion and devour them. This cannibalism strategy allows females to produce more eggs. Males that are consumed are given a reproductive advantage through potentially increased numbers of offspring.
Male bees (drones) mate with females (queens) in the air. In some species, during the height of the “process”, the end of the male's barbed endophallus is ejected from his body and retained with his sperm inside the queen. His work done, the male then falls from the sky dead.
Subterfuge and fusion
Many animals use pheromones, essentially chemical messengers between members of the same species.
Some orchids have utilized these chemicals, mimic pheromones of female wasps. Male wasps are tricked into thinking they have found their female, and when they mate with the flower, they are coated in pollen. These wasps then mate with another orchid and thus transfer the pollen, and then the orchid is fertilized.
There are some even more bizarre mating encounters in the animal world. The female deep sea fish allows the male to fuse with her, and sometimes even more than one male will fuse with the same female.
In exchange for sperm, the male monkfish receives nutrients from the female via its fused circulatory system. A true 'till death do us part' relationship.
Survival of the fittest
Among marsupials, some species (polyprotodonts) give birth to many more young than they can support. These so-called “supernumerary” young then compete to reach a teat first, in what is essentially survival of the fittest.
The maximum number of young that can survive is therefore determined by the maximum number of teats.
The Virginia opossum has 13 teats and can give birth to up to 56 young (although the average is more like 21), so many newborns die shortly after birth, unable to find and attach to a teat. Tasmanian devils also produce an average of 39 young, but only have four teats, so the maximum surviving devil litter size is four.
Wombats are not polyprotodonts and have only two teats. But they usually only have one joey at a time.
Much can be said about the phalluses in the animal world. None more than echidna penis with their four heads, of which they only use two at a time.
Sharks likewise have two claspers, extensions of the pelvic fins that support internal fertilization, of which they use only one during mating. Whale penises have been said to have been mistaken for deep-sea monsters, or perhaps kraken tentacles, which have been observed grappling with their whale prey.
In order not to be outdone by the males, female marsupials have three vaginas and two uteruses. Two of the three vaginas are used for reproduction to allow sperm to travel up to fertilize the eggs. The third vagina, which lies between the other two, is for giving birth.
Female platypuses and echidnas have two uteri and two ovaries. However, in platypuses only the left ovary is functional, and therefore they use only one side of their reproductive tract to produce young.
Back to wombats
As we have seen, there is a wide variety of strategies that animals use to produce young. Some reproductive strategies are familiar to us, others are deadly.
That puts the wombat video into perspective: our correspondents report that the creatures walked away from the scenario unscathed, albeit with a few love bites. At least everyone survived.
The authors do not work for, consult with, own stock in, or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
Originally published in The conversation.
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