Patterns of trait divergence between populations of the meadow grasshopper, Chorthippus parallelus

To understand the process of speciation, we need to identify the evolutiona ry phenomena associated with divergence between populations of the same spe cies. A powerful approach is to compare patterns of trait differences betwe en populations differing in their evolutionary histories. A recent study of genetic divergence between populations of the meadow grasshopper Chorthipp us parallelus, from different locations around Europe has allowed us to use this species to investigate which aspects of evolutionary history are asso ciated with divergence in morphology and mating signals. During the last gl aciation C. parallelus was confined to a number of refugia in southern Euro pe and has subsequently recolonized the northern part of the continent. Thi s process of isolation followed by range expansion has created populations differing markedly in their evolutionary pasts-some have been isolated from one another for thousands of years, others have undergone repeated founder events, and others now live in sympatry with a closely related species. Us ing laboratory-reared grasshoppers from 12 different populations with a ran ge of evolutionary histories, we quantify differences in morphology, chemic al signals, and male calling-song. The observed pattern of divergence betwe en these populations is then compared with the pattern predicted by hypothe ses about what drives divergence. This comparison reveals that long periods in allopatry and processes associated with repeated founder events are bot h strongly associated with divergence.