Ecological Genetics and Evolution

Jeffrey Feder     Professor Director, GLOBES-IGERT Program (Global Linkages of Biology, the Environment, and Society) Ph.D. Michigan State University Postdoctoral, Princeton University , University of Chicago

e-mail | labpage

I am interested in understanding speciation, the process whereby one evolutionarily distinct gene pool is divided into two. My research has focused on true fruit flies belonging to the Rhagoletis pomonella sibling species complex. These flies are of interest to evolutionary biologist because they appear to speciate sympatrically (i.e. in the absence of geographic isolation) by shifting and adapting to new host plants. Recently, the species R. pomonella shifted from its native host hawthorn (Crataegus spp.) to introduced, domestic apples (Malus pumila). This shift, which occurred approximately 150 years ago in the northeastern United States, provides a unique historical context in which to examine the relationship between host specialization and speciation in Rhagoletis.

My laboratory uses a multi-disciplinary research strategy to study factors responsible for partially reproductively isolating hawthorn and apple fly "host races". This includes mark-recapture field studies to elucidate migration patterns and evaluate the importance of host plant fidelity in reducing gene flow between the races. Laboratory selection experiments are being conducted to determine the role that larval and pupal development rates play in isolating the races. My laboratory is also constructing a restriction site linkage map to genetically dissect host specialization traits. By integrating results from field, selection and molecular genetic studies, we will eventually understand the ecology and genetics of host race formation and speciation in Rhagoletis.

Recently, my laboratory has also begun studying the Jamaican click beetle, Pyrophorous plagiophthalamus (abbr. P. pl . ). These bioluminescent beetles provides a unique opportunity to investigate the entire adaptive recursion from enzyme structure and function to phenotype to gene frequency change in natural populations. P. pl. bioluminesces from a ventral light organ in the abdominal cleft and a pair of dorsal organs on the pronotum . P. pl. uses the light organs for mate recognition in a similar, but not identical, fashion as fireflies. Males fly at night and continuously display from their ventral organs, while females respond intermittently from the bush using their dorsal organs. What is unique about P. pl. is that different individuals bioluminesce different colors. For example, ventral organs can emit either green, yellow / green, yellow, yellow / orange or orange colored light, while the paired dorsal organs vary among beetles from green to yellow green. As such, P. pl. represents the only known instance of a color polymorphism for any bioluminescent organism. Moreover, the genetic basis for the color polymorphism is known and involves specific amino acid substitutions in the protein luciferase (all substitutions have an additive effect on bioluminescent color, with distinct classes of green, yellow / green, yellow and orange color alleles segregating for the ventral locus, and separate green and yellow / green genes controlling dorsal light color).

We have just completed a population / genomics / phylogenetic analysis of cloned ventral luciferase genes from P. pl. and related taxa . The results support an evolutionary progression (positive Darwinian selection) from shorter (green) to longer (orange) wavelength ventral emission occurring on the Jamaican beetle lineage. We are currently testing a biogeographic model that the most recently evolved orange allele - which displays little intra-allelic sequence variation, but differs from the next nearest (yellow) class of alleles by three non-synonymous substitutions - arose in an isolated subpopulation before rapidly spreading through Jamaica . Studies are also being designed to test the visual sensitivity of beetles to different wavelengths of light (potentially leading to the cloning of opsin genes) and to elucidate the ecological basis for the color polymorphism (e.g., sexual selection, differential predation, character displacement from fireflies), which will allow us to complete the adaptive recursion from gene to phenotype to evolutionary change for P. pl.