Every year since 2013 I have spent several weeks, during April and May, on an island in the Kimberley. I have been monitoring a population of Northern Quoll and, to be honest, I thought I knew a fair bit about these grouse little marsupials. But after my last trip I now know that all I know is that I know very little.
The truth is that field surveys are but a snap shot in time from which you can interpret very little. What you see over a couple of weeks (even if you visit year after year) may reveal something about a population, but it reveals little about the individuals that comprise that population. And when you are studying a highly evolved top order predator that lives faster and dies younger than James Dean, a couple of weeks a year is simply not enough time to comprehend what individuals must endure during their very short time on planet Koolan.
Northern Quoll are a great study species. This is not because they are an iconic, predatory mammal that is under severe threat of extinction, but because they have an amazing, complex and extremely brief life history.
A mother gives birth to several young, more than half of which are male. She nurtures them on the teat in the pouch for a few weeks and then deposits them in a den where she cares for them for several more weeks before they make their way out into the big bad world. Once independent they enjoy a very brief but accelerated period of growth as the bolster their body reserves before they hit sexual maturity and the breeding season begins. During the breeding season the females continue to build their body reserves while the males cease feeding and commence a copulatory marathon that will, ultimately, lead to their death within a few short months.
The ecological advantages for the population of male semelparity (death after a single year of mating) are obvious. The massive male die-off reduces competition for food between young emerging from the den and adults remaining in the population at the time of emergence.
The advantages of multiple matings are also pretty obvious. Multiple mating promotes sperm competition so only the best of the best swimmers make it to the egg. This should result in the fittest and strongest babies.
The cessation of feeding in males also reduces predation pressure and increase food availability right about the time that the females are trying to maximise their body condition in anticipation of parenting a batch of parasites that will literrally suck the life out of them.
The driver for multiple mating in the males is quite obviously a shift in hormone balance. But what happens when that balance shifts too far? Is it possible that the desire to mate multiple times in an effort to sire the greatest number of the fittest babies could decend into a voracious sex frenzy where females are seriously injured or even killed during sex?
As previously reported in this blog, the damaged caused by the males is intense, as they bite hard on the neck and grip the females tight in amplexus around the ribs, digging their claws in and causing quite significant injury. In 2016 I surveyed Northern Quoll in late June, no more than two months later than I normally would and I observed something that I had suspected; the males were merciless when it comes to copulation.
But what I saw in 2018 defies explanation and it sure as hell appears to serve absolutely no evolutionary purpose. During our survey we discovered a female that had been literally mated to death. The female was found in the immediate vicinity of a male; both were contained in a storage unit within which they had made their way. As the photos clearly show the female has bite marks all around the neck and bite marks on the tail. There are also wear marks around the neck and front limbs from what I can only imagine is a savage amplexus.
What benefit can the individual, the population or the species derive from this sort of behaviour?? Is this a common occurrence in the wild or did it occur purely as a function of the situation?? Is it a case of Fishers Runaway Sexual Selection gone wrong?? That is, the drivers behind semelapirity have simply gone past the point of no return. I dont know; I am not sure I want to know.
Who am I kidding, of course I want to know. Dont you?
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