Evolution and maintenance of a larval dimorphism in the polychaete, Streblospio benedicti
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The maintenance of multiple life history strategies in a single species may represent either a transitional form or an evolutionarily stable strategy that can maximize potential for both local adaptation and dispersal. The spionid polychaete Streblospio benedicti has been studied extensively and contains two morphologically distinct and heritable larval types. The major difference in these two larval modes is their development time, and thus, potential for dispersal. The amount of effective migration between larval types and geographic populations will affect colonization ability, population genetic structure, inbreeding depression, and population extinction rates. This research addresses life history dichotomies by determining if differences in dispersal are adequate to explain the maintenance of two distinct larval modes. Using single nucleotide polymorphism markers, I determine genetic structure in populations of S. benedicti and determine the extent that they are reflective of both dispersal ability and the amount of gene flow that occurs between individuals of both larval types. I find that there is a large amount of genetic structure between populations on the East Coast, and this structure is dictated predominately by geography rather than developmental type.