Phylogeography and reproductive variation of the poecilogonous polychaete Boccardia proboscidea (Annelida: Spionidae) along the West Coast of North America

The ability to produce more than one kind of offspring, or poecilogony, is a striking example of reproductive variability. Traditionally, larval nutrition has been classified as a dichotomy: if offspring obtain nutrition from their mothers (lecithotrophy), there is lower fecundity and greater chance of offspring survival than when they get their nutrition from plankton (planktotrophy). The polychaete Boccardia proboscidea (Spionidae) produces both types of embryos using three different reproductive strategies. In this study, we examined the roles of genetic history and phenotypic plasticity on explaining natural variation in B. proboscidea along the Pacific coast of the United States using two genetic mitochondrial markers, 16S rDNA and Cyt b, and common garden experiments. These data show a single North American West Coast network that is structured, geographically, by the well-documented biogeographic break near Point Concep- tion, California. The southern group within this network cov- ers a smaller range, but has larger haplotype diversity, than the northern group. Some individuals differing in reproduc- tive type had the same haplotype, indicating independence of these features; however, differences between laboratory and field data suggest additional geographic variation within one of the reproductive types. Females from higher latitudes provide offspring with larger supplies of extra embryonic nu- trition than females from southern latitudes. Results herein suggest that both genetic history and developmental plastic- ity are playing a role in the maintenance of this reproductive polymorphism.