Range edges and the molecular divergence of Greya moth populations


John N. Thompson, Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064, USA.
E-mail: thompson@biology.ucsc.edu


Aim  We investigated the geographical pattern of genetic divergence and demographic history in the prodoxid moth Greya obscura throughout its entire geographical range in far western North America and compared it to the geographical patterns found in a previously studied species, Greya politella, which co-occurs over the same range, in the same habitats, and on the same host plants.

Location  The study included sites distributed throughout the California Floristic Province.

Methods  We used analysis of cytochrome c oxidase subunit I (COI) and amplified fragment length polymorphisms to evaluate the pattern and history of genetic continuity among populations.

Results Greya obscura populations show a history of spatial expansion with considerable haplotype diversity in the centre of the geographical range. As with G. politella, some range-edge populations of G. obscura are sufficiently divergent (6.7% in COI) to be considered as potentially cryptic species. Greya obscura and G. politella, however, differ in the specific range-edge sites showing greatest genetic divergence and cryptic speciation.

Main conclusions  These results corroborate the view that range edges are important cradles of divergence and speciation. In addition, the results indicate that the geographical pattern of divergence at edges may differ even among closely related species occupying the same habitats and using the same hosts.