The term “natural selection” brings to mind the idea of a species gradually looking, acting, and being different. This has been documented countless times over thousands of years, ever since humans started killing things they didn’t like. Comparatively little studying has been documented on the genetic mechanism for evolution, or more specifically the evolution of genes. Recently, however, evidence has been found which cleanly and clearly displays the effects of evolution on genes, and those genes back on evolution.
This evidence comes in the gene called distal-less which expresses itself in the development of insect limbs. Generally, when this gene is partially removed, the affected insect develops shorter limbs. After the limbs are fully grown, distal-less is no longer needed. One insect, however, still uses distal-less after its limbs have become fully grown: the water strider. The limbs affected in this bug, after the normal cycle, are not really limbs at all, but antennae. The male water striders grow large, hooked appendages, which are used to increase personal “fitness” (the term used in “survival of the fittest” meaning the relative number of offspring a single organism has in its lifetime) by increasing the likelihood of a male to mate with a struggling female. The antennae work by hooking onto a female, so as not to be thrown off.
The females struggle because they are able to store sperm, and have no need for any more. The males, on the other hand, want to mate with every single female around. In addition, the females are in danger of getting a disease through contact, or being eaten from below. If you think these hooks are cruel to the females, don’t, because on average only 12% of males’ attempts succeed. The females are extraordinarily good at getting away, and the males need all the help they can get.
The genetics comes from experiments done around these bugs. In one experiment, the distal-less was lessened during the time that it grew the antennae and the antennae essentially traveled back in evolutionary time. What I found most interesting was that the effectiveness of the “modified” males made a smooth curve from 12% to 0%, rather than jumping suddenly. This allowed the researchers to map the evolutionary path the males must have undergone to reach the antennae size that they have now, keeping in mind that the females did also undergo an evolutionary change, becoming more effective at kicking the males off.
What is most interesting to me is the rate of genetic change in this population: any moderately effective trait to help the male hang on better will be extremely helpful, and that change will become widespread. I am also interested in what would happen if the distal-less was increased, rather than decreased.
Sources: http://www.cbc.ca/quirks/ (May 12, 2012 edition),