Sunday, 4 October 2015

Lessons From The Dordogne - Evolving Insects

Here are some examples of one of the important drivers in evolution - the need to avoid being eaten. I took these pictures on our recent holiday in France but you don't need to go all the way to France to find similar ones. You can probably find several in your back yard or any roadside verge or hedgerow.

The first, on the right is of a grasshopper. It's slightly above dead center.

Can't see it? Well, that's rather the point. Zoom in to find it.

This species lives in grassland and, if it keeps still, looks just like a piece of brown vegetation, even having marks that mimic the shadows cast by blades of grass.

Scroll down for a close up.

Now for something I fished out of our swimming pool. I noticed what looked like a leaf which was moving just a little too purposefully, and it seemed to be producing little ripples.

In fact, this is a slightly unusual form as most are green, although of the three we had in the garden around our pool, only one was green. But then I might have missed the others. Never-the-less, this one's disguise (as a twig) seems to work fairly well. In this case, not only is it trying to avoid being seen by a predator but also by its prey. It is of course a mantis, which depends on stealth to capture just about anything that comes within striking distance of its viciously clawed front legs. This one even struck at a dead piece of the buddleia flower fluttering in the breeze near where it was standing.

A question at this point for those creationists who claim not to be able to understand how evolution works.

Which do you think will produce the most offspring, a mantis which a potential predator overlooks and which potential prey doesn't see, or one which gets eaten and finds catching food difficult because its potential dinner sees it coming? No! Don't look in a Bronze Age book, or a website run by Ken Ham for the answer; just apply a little logic and see if you can work it out for yourself.

This next one is a probably an example of Batesian mimicry.

Batesian mimicry is where a species benefits by mimicking a harmful or distasteful species when it isn't itself harmful or distasteful. This depends on a potential prey either mistaking it for a species it's learn to avoid or at least not taking the risk. The 'once bitten; twice shy' strategy.

It's a day-flying hummingbird hawkmoth, feeding on wild clary. To a human it looks like a small hummingbird but to a bird it might look like a big bumblebee, especially with those flashes of orange on its hind wings. There is a relative of this moth - the bee hawkmoth - that even more closely resembles a bumblebee.

The hummingbird 'mimicry' itself is probably a case of convergent evolution as both hummingbirds and these hawkmoths feed on the nectar of flowers with long tubes and both use the same strategy of hovering in front of the flower while inserting a proboscis or a tongue into the flower.

The relationship between flowers and their pollinator species is a whole different subject for evolution but here I'm looking at mimicry or cryptic colouration.

Another question now for creationists. If even one in a thousand predators mistake those flashes of orange for a bumblebee do you think this improves or decreases the chances of the moth surviving and breeding successfully? Will this be increased the more closely the moth resembles a bee or decreased and will those moths which have a better chance of breeding tend to leave more descendants with that colouration or fewer? Again use logic and common sense, not a creationist website or an old book.

Lastly, this is an example of the exact opposite of camouflage; conspicuous colouration.

It's a heteropteran bug which revels in the Latin name Graphosoma italicum. It probably doesn't have an English name because it is absent from Britain but it is abundant in places in France. I found four in about one square yard near the banks of the Dordogne river. It uses the 'if you've got it, flaunt it' strategy. In this case what it's got is a foul taste. This is the sort of species which might be copied by a different species using Batesian mimicry.

The question here for evolutionists is how does this system arise? For that we would need to know the evolutionary history of the species because some forms of cryptic camouflage would have arisen not for the current ecosystem but for an earlier one with different predators with different visual acuity and colour perception. Is the foul taste a product of adaptive evolution or just a fortuitous accident?

This foul taste/conspicuous colour system must have depended on altruism (though not conscious altruism of course) in that some individuals would need to have been eaten for predator species to learn to reject it. In terms of selfish genes of course this isn't a problem. A few getting eaten, so programming the predators to reject others, will benefit the genes for colouration and (maybe) taste in the long term.

It is known that many species, including humans, have evolved the ability to detect some toxins by their bitter taste. In fact, the ability to detect 'bitter' probably evolved partly for that purpose. It seems likely that insects like Graphosoma italicum have exploited this and evolved especially 'toxic' taste. Once this happened, the selective pressure to advertise it is obvious.

Other tastes which many species have evolved to be repelled by are the tastes of feces, for obvious reasons. This again could have been exploited by these foul-tasting species.

The close-up on the right is the grasshopper from the first photograph. Did you spot it?

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