Submitted to: Molecular Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/22/2007
Publication Date: 7/1/2007
Citation: Scheffer, S.J., Hawthorne, D.J. 2007. Molecular evidence of host-associated genetic divergence in the holly leafminer phytomyza glabricola (diptera: agromyzidae): apparent discordance among marker systems. Molecular Ecology. 16:2627-2637. Interpretive Summary: Leafmining flies are responsible for millions of dollars of losses to U.S. farmers and horticulturists each year. The holly leafminers attack several species of holly, reducing their commercial value and aesthetic appeal. This study uses molecular markers to show that the holly leafminer is comprised of two host races, each feeding on a different holly species. Knowledge of host races within pest species is important for management efforts as host races may differ in many biological attributes. Information on host races in P. glabricola will be of interest to ecologists and evolutionary biologists as well as to horticulturists and commercial growers.
Technical Abstract: Sympatric host races play a central role in the debate surrounding the feasibility and prevalence of sympatric speciation in diversification of phytophagous insects. Of greatest interest are host races that have recently diverged, but finding genetic evidence for very recently diverged host races may prove difficult as initially only a few loci are expected to evolve diagnostic differences. The holly leafminer Phytomyza glabricola feeds on two hollies, Ilex glabra and I. coriacea, and exhibits a dramatic life history difference on the two hosts suggesting that host races may be present. We collected 1393 bp of mitochondrial cytochrome oxidase I sequence data and amplified fragment length polymorphism (AFLP) data (45 polymorphic bands) from sympatric populations of flies reared from the two hosts. Neither marker system found fixed difference in the populations studied. Phylogenetic and frequency analysis of mitochondrial cytochrome oxidase I sequence data uncovered considerable variation but no structuring by either host plant or geographic location. In contrast, analysis of AFLP frequency data found a significant effect of host plant, but no effect of geographic location. Likewise, neighbor-joining analysis of AFLP data resulted in clustering by host plant. The AFLP data indicate that P. glabricola is either comprised of host races or is, at least, experiencing strong selection on the two host plants. The lack of fixed differences in mitochondrial or AFLP data, suggest that host-associated divergence is very recent. Phytomyza glabricola provides a new sympatric system for exploring the role of geography and ecological specialization in speciation of phytophagous insects.