The price of sex appeal

Guppies have spots along their flanks that vary in colour, size, position and reflectivity. In 1980, J A Endler found that, over several generations, male colour patterns adapted to the local risk of predation. Fortunately, for the species, guppy genes that code for male skin decoration exist in several forms (alleles). As the predation environment changes, guppies with the ‘wrong’ alleles get a raw deal: with no predators around, it’s the other guys who mostly get the girls; and in predator-infested waters, they get eaten first. In either case, their alleles tend not to get passed on.

The things that drive girl guppies dotty
Are guppy males whose skins are spotty.
But guppy guys know decoration
Makes them targets for predation.

If predators nearby are feeding,
Big, flashy spots, though good for breeding,
Can make a chap an easy meal –
It’s just the price of sex appeal.

So what’s a guppy guy to do?
Well, nature’s got a trick or two:
It’s learned just how a guppy feels,
And given it some cool alleles.

The genes that program guppy spots
Have different forms – in fact, there’s lots:
One ‘spot’ allele may code for many,
While others dish out hardly any;

Some make red spots, some make blue,
Some an iridescent hue;
Small spots, big spots. All these may
Be expressed by DNA.

Thus, guppy genes have quite a range
Of possibilities for change.
Those who survive, it’s evident,
Can change with the environment.

It means that guppies can adapt
To life, instead of getting trapped.
The trouble is, adapting means
Survival of the fittest genes.

So some within the population
Are destined for extermination:
Those guppy blokes who find they’re stuck
Without the right allele – tough luck!

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