Rank, N. E. 1992. A hierarchical analysis of genetic differentiation in a montane leaf beetle (Chrysomela aeneicollis). Evolution 46: 1097-1111.
Herbivorous insects which use the same host plants as larvae and adults can have a subdivided population structure that corresponds to the distribution of their hosts. Having a subdivided population structure favors local adaptation of sub-populations to small-scale environmental differences and it may promote their genetic divergence. In this paper, I present the results of a hierarchical study of population structure in a montane willow leaf beetle, Chrysomela aeneicollis (Coleoptera: Chrysomelidae). This species spends its entire life associated with the larval host (Salix spp.), which occurs in patches along high-elevation streams and in montane bogs. I analyzed the genetic differentiation of C. aeneicollis populations along three drainages in the Sierra Nevada mountains of California at five enzyme loci: ak-1, idh-2, mpi-1, pgi-1, and pgm-1, using Weir and Cockerham's (1984) modification of Wright's F-statistics. My results demonstrated significant differentiation (Fst = 0.043) among drainages that are less than 40 kilometers apart. One locus, pgi-1, showed much greater differentiation than the other four (Fst = 0.412), suggesting that it is under natural selection. C. aeneicollis populations were also subdivided within drainages, with significant differentiation 1) among patches of willows (spanning less than 3 kilometers) and 2) in some cases, among trees within a willow patch. My results demonstrate that this species has the capacity to adapt to local environmental variation at small spatial scales.
Key words.- Allozymes, Chrysomela aeneicollis, F-statistics, gene flow, genetic differentiation, insect population structure, natural selection, phosphoglucose isomerase
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