When we look around, the decrease in biodiversity becomes a concern as we realize that we are in the midst of another great extinction. This has an increased poignancy when we think how long these species have been around. Even more so when we think about the long low evolutionary process that we learned about some years ago. Things are not quite as settled as they seem though. Le Page (1) has put together a wide range of examples of very rapid speciation into one general article.
Evolutionary adaption can go in spurts in one direction and sometimes back again. A drought on one of the Galapagos Islands in 1977 wiped out plants that produced small seeds putting great pressure on large beak size that could tackle larger seeds. In a few years the average beak size was 4% larger, until 1983 when the weather went back to a wet cycle. Beak sizes went smaller again as small seeds became available and the food abundance pressure was reversed.
Small islands are good places to observe changes. A nice example comes from Kauai in the Hawaiian Islands when in the ‘90s a parasitic fly that targets crickets was introduced. Crickets get ultra noisy when looking for girlfriends and the loud chirps gave their location away to the fly, which would then pounce and lay an egg on the romantic cricket. The hatched larva would get stuck into it meal-ready-to-eat and munch its way through the live cricket.
The Kauai crickets went into evolutionary overdrive. Now nearly all the males have different shaped wings that don’t make chirping sounds. The parasitic fly population has dropped. The corollary is that the large number of stealth male crickets could have a particularly arid love life. But they developed a strategy. Now the stealth males cluster around the few chirpers that are still around. The females crowd in to attend the raves and nature has found a way to maintain romance on the island.
A chirping cricket is still a target for the fly, but the numbers are small and the few genetic stick-in-the-muds can hold the line. Would that the building environmental pressures could give us an evolutionary spurt in the brain department.
1. http://www.newscientist.com/article/mg21028061.300
