Sunday 8 January 2012

Parthenogenesis and Nessie

The latest news on the BBC about a "virgin birth" shark reminds me again on how a Nessie population is sustained in the relatively small volume of water that is Loch Ness.

To recap, in the absence of a male shark, this female shark in a Dubai aquarium, has produced offspring for the fourth year in a row. It seems the descendants are doing well. and are not exact clones having some minor DNA differences There is nothing new in this scenario as various fish, reptiles and amphibians are known to reproduce asexually. However, the process has not been observed naturally in mammals.

This form of reproduction can be "turned" on and off depending on various factors such as a lack of males, seasonal factors, conditions that favour rapid population growth and so on. It has its advantages and disadvantages compared to normal reproduction. There is the reduction of the gene pool diversity and concomitant susceptibility to new mutations and diseases but on the plus side, there is no need divert scarce resources to develop males which cannot reproduce offspring themselves.

But does this have any relevance to the Loch Ness Monster? Curiously, the Nessie portrayed in the 2007 film "The Water Horse" (below) was asexual with a population of exactly one creature whose progeny were propagated by a single egg it laid. No problem with food stocks there then!

They say that "life always finds a way" but when it comes to one or more large creatures in a 24 mile long loch, scepticism adds "but not in this case". The question frequently levelled at Nessie "believers" is that there is not enough food to sustain a viable population of large creatures. Firstly, I don't accept this and shy away from the two dimensional thinking that goes on in this matter. However, assume that there is a prey-predator ratio issue for the moment.

Asexual reproduction would reduce (perhaps significantly) the number of creatures in the Loch. Certainly and statistically, half of them (the males) can go (well, some are needed if the females switch out of asexuality).

It would also eliminate inbreeding brought on by generations of the same pool of creatures inter-breeding. However, what the minimum viable population may be for such a group of asexual Nessies is pretty unclear. But there is an opening there for lower creature numbers. But what about lack of genetic diversity? Well, how often do Nessies reproduce? Once a year? Once a decade? The longer the generations, the less the impact of genetic diversity. There is also the matter of how stable Loch Ness is to changes that expose lack of genetic diversity. So what has happened at Loch Ness in the last 10,000 years that may endanger a small gene pool of monsters?

But it is all speculation when it comes to this decidedly odd beast.

So, was it the case 10,000 years ago as the glaciers retreated in Scotland that one or a few female Nessies became trapped in Loch Ness as the land rose from the burden of immense amounts of ice? Did asexuality kick in to preserve the continuation of the species? Did the creatures switch between asexual and sexual across the millenia depending on various environmental factors?

Who can tell? But as I said, such a scenario is not mandatory to explain how the Loch Ness Monster has survived to this day. The creature was moving between the seas, land and other lochs long before man ever became inquiring enough to ask such questions.

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