Abstract
Similar patterns of dispersal and gene flow between closelyassociated organisms may promote local adaptation andcoevolutionary processes. We compare the genetic structures of thetwo species of a plant genus (Roridula gorgonias and R. dentata)and their respective obligately associated hemipteran mutualists(Pameridea roridulae and P. marlothi) using allozymes. Inaddition, we determine whether genetic structure is related todifferences in host choice by Pameridea. Allozyme variation wasfound to be very structured among plant populations but less soamong hemipteran populations. Strong genetic structuring amonghemipteran populations was only evident when large distancesisolated the plant populations on which they live. Althoughgenetic distances among plant populations were correlated withgenetic distances among hemipteran populations, genetic distancesof both plants and hemipterans were better correlated withgeographic distance. Because Roridula and Pameridea have differentscales of gene flow, adaptation at the local population level isunlikely. However, the restricted gene flow of both plants andhemipterans could enable adaptation to occur at a regional level.In choice experiments, the hemipteran (Pameridea) has a strongpreference for its carnivorous host plant (Roridula) aboveunrelated host plants. Pameridea also prefers its host species toits closely related sister species. Specialization at the specificlevel is likely to reinforce cospeciation processes in thismutualism. However, Pameridea does not exhibit intraspecificpreferences toward plants from their natal populations aboveplants from isolated, non-natal populations.