Friday, 13 September 2013

Evolving A Quickie

Related species, Gambusia puncticulata, showing the gonopodium
A lovely piece of research published in the Journal of Evolutionary Biology today illustrates perfectly how environmental differences can quickly lead to genetic divergence. It doesn't seem to be available online yet but is reported on in a New Scientist article by Victoria Druce

It was published by Justa Heinen-Kay of North Carolina State University who does most of her research in the Bahamas on the mosquitofish, Gambusia hubbsi, a small, promiscuous, live-bearing fish that inhabits blue holes. Mosquitofish eggs are fertilised internally and males have modified anal fins called gonopodia with which to deposit sperm into females in an act of copulation. The problem is, a big gonopodium makes fast swimming difficult and copulating pairs of fish are vulnerable to predators because they make a larger target and may well be distracted.

Typical blue hole
The blue holes in which these fish are found are vertical caves which filled with water when the sea-level rose at the end of the last ice-age, some 10,000 years ago. All blue holes have acquired their fauna since that time. They are also found in Mexico and Belize. Some of these holes have also acquired a large predator fish, the bigmouth sleeper (Gobiomorus dormitor), while others have remained predator free. Thus we have a ready-made laboratory test-bed to see what happens when a species is subject to predation while a control group is free to evolve without predators.

Heinen-Kay and her team caught and examined specimens of Ga. hubbsi and noticed that where predation was present, males had smaller gonopodia than those found in predator-free blue holes. She explains the idea in her profile:

In order to gain genetic benefits for their offspring, females should prefer males that are successful in their local environment. But, the most important type of whole-organism performance will depend on local selection pressures. Rapid-burst escape swimming speed is of utmost importance for Bahamas mosquitofish living with predatory fish, yet that performance is irrelevant in blue holes without predators. At the same time, although resource availability does not differ between high- and low-predation blue holes, low-predation populations have much greater population densities, so competition for resources and foraging efficiency will be more intense than in populations with predators.


Basically, when predators are present, it produces more descendants if mating is quick and fast swimming is possible. In predator-free environments, female selection for large gonopodia will ensure mating is more successful and so well-endowed males will produce more offspring.

To anyone with even a basic understanding of evolutionary biology and how the resulting phenotype is the product of several competing factors, this is probably astoundingly obvious, but to a creationist who believes an omni-benevolent magic man magicked everything into existence and everything is descended from a couple of ancestors who lived on a boat, is must seem incomprehensible.

Why would this magic man have given some varieties of Ga. hubbsi smaller gonopodia so they could get mating over with quickly to escape the predators he put there to eat them? Did this creator have a day when he was in favour of Go. dormitor, so he put them in blue holes with food in, then the next day, changed sides and gave Ga. hubbsi smaller gonopodia so they could avoid becoming Go. dormitor food?

And how on Earth can this be described as Intelligent Design by anyone with even a modicum of intelligence?

References:
Victoria Druce, Mosquitofish are efficient lovers New Scientist 14 September 2013, Magazine issue 2934.


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