Island hopping introduces Polynesian field crickets to novel environments, genetic bottlenecks and rapid evolution.

Teleogryllus oceanicus, a cricket native to Australia, was introduced to Hawaii where it encounters a novel natural enemy responsible for their recent rapid evolutionary loss of singing ability. To explore how genetic diversity varies across their broad range, their mode of introduction to Hawaii and nonadaptive influences on the sexual signalling system, we assessed variation at seven microsatellite loci in 19 Australian and island populations. Genetic variability was highest in Australia, intermediate in Oceania and lowest in Hawaii, and differentiation among local populations was a clear function of geographical distance. Hawaiian populations are most closely related to those from the Society Islands and Cook Islands, and a neighbour-joining tree based on D(A) is consistent with movement by Polynesian settlers. We found evidence of bottlenecks in six island populations (including three Hawaiian populations), supporting previous findings in which bottlenecks were implicated in the crickets' loss of singing ability.