MCMULLIN, E.R.; MARSH, A.G.; University of Delaware, Lewes, DE: Poecilogony in the polychaete Streblospio benedictii: incipient speciation or maintained polymorphism?

Most benthic marine invertebrate species exhibit only a single developmental mode. Poecilogony, or the occurrence of multiple developmental modes within a species, is very rare, and molecular genetic studies often reveal suspected cases to be the result of cryptic sibling species. Streblospio benedictii is a spionid polychaete found along the coast of North America, producing either large numbers of small actively swimming and feeding larvae , or a small number of large nonfeeding larvae. Developmental mode in this species is a highly heritable trait, but the two developmental morphs of S. benedictii can successfully interbreed, producing viable offspring with an intermediate larval morphology. Cytochrome oxidase I DNA sequence analysis also suggests that planktotroph and lecithotroph S. benedictii are members of the same species. Poecilogony in S. benedictii could result from spatial or temporal heterogeneity in survival of the two morphs or from a very recent speciation event with a subsequent reintegration of two previously isolated (geographically/genetically) populations. AFLP markers were developed to generate genomic fingerprints of lecithotrophic and planktotrophic S. benedictii. These markers will be used to estimate interbreeding (geneflow) between field populations of the two developmental morphs to assess whether there is any evidence of speciation.