Phenotypic Plasticity and the Evolution of Marine Invertebrate Larvae

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Are genes leaders or followers in evolution? When Mary Jane West-Eberhard posed this question a decade ago, she drew our attention to a fundamental point. While genetic divergence is important in speciation, most organisms exhibit considerable phenotypic variation that does not involve changes in gene sequence, but rather changes in gene expression. The study of heritable changes in gene expression, termed epigenetics, has a long history in cell differentiation and disease. Only recently have epigenetic tools been applied within an evolutionary context, and it is revolutionizing our ideas on the origins and persistence of phenotypic diversity. My students and I study phenotypic plasticity in polychaetes, a group of marine invertebrates. These species produce both small planktonic larvae and large benthic juveniles, offspring that are dimorphic in morphology, behavior and habitat. This allows us to investigate the mechanisms that shape evolutionary transitions in larval form, with broad implications as the majority of Metazoa produce a larval stage. I propose to investigate the potential role of epigenetics in this case of phenotypic plasticity. Epigenetic mechanisms, such as histone and DNA methylation, are fast, reversible, responsive to environment and capable of producing alternate phenotypes that can be passed down over generations. We will test the hypothesis that dimorphisms in larval development evolved through epigenetics by: 1) using immunohistochemistry to map differences in histone modifications to differences in phenotype between larval morphs; 2) using in situ hybridization to study de novo methylation events in embryos to identify when larval morph is established in development; and, 3) identifying factors in the worms' habitat that act as epigenetic marks and change the morphology and life history of young. This will be one of very few studies to investigate the molecular link between environment and phenotype in a non-model species. This research will provide valuable training opportunities for young scientists in an exciting and newly emerging field.