The Hawaiian Islands have long been known as a natural laboratory for studying evolution. Zuk et al. have assessed the effect of the selective pressure of parasitoid flies on Teleogryllus field crickets introduced to the island of Kauai. Female flies locate male crickets when they call to female crickets, and lay their eggs on the cricket; the larvae burrow into the host and consume it from within, eventually killing it. Over just 20 generations, the singing males dwindled in abundance owing to the selective pressure from the parasitoid, and a new, silent type of male--known as flatwings--became prevalent. Given that the song functions as a signal to potential mates, how do the flatwing males attract female partners? Field experiments suggest that the silent males congregate around the few remaining singers, increasing the chance of intercepting inquisitive females (who have possibly relaxed their requirement that the male keep singing up to the moment of mating). Thus, natural selection has not only had a rapid population genetic effect; there has been a behavioral response as well. It remains to be seen, however, if the singing males are now too rare to support the local parasitoid population, or if the singing males will disappear entirely (and, if so, whether the crickets will find a new solution to the problem of finding mates). -- AMS
Biol. Lett. 2, 10.1098/rsbl.2006.0539 (2006).
