MCCOY, Adam M.; Harvard University: The acoel Convoluta convoluta: A natural experiment for the investigation of barriers to marine invasions

Although biological invasions of macrofaunal organisms are recognized as a major problem in marine and terrestrial ecosystems, the importance and extent of invasions of microorganisms in marine environments remain largely unexplored. Species interactions are a potential barrier to dispersal in terrestrial systems, but little is understood about these barriers in the marine environment. Certain marine invertebrates rely on specific microbial interactions ranging from settlement cues to nutritional relationships, but almost nothing is known about the distribution of these microbes in the environment. The recent invasion in the Gulf of Maine by the symbiotic acoel Convoluta convoluta provides a natural experiment to investigate this barrier. European populations of C. convoluta have an obligate relationship with endosymbiotic diatoms of the genus Licmophora that must be reestablished each generation. Is the success of C. convoluta as an invader due to an undetected prior invasion of the symbiotic diatom, introduction to the environment of symbiotic Licmophora sp. from adult hosts, or acquisition of a different symbiont? The 18S sequences of free living Licmophora sp. from unialgal culture isolates and by PCR amplification of field collected cells, show the most abundant free living Licmophora sp. differs from the cells found within C. convoluta hosts from the same locale. In contrast, symbionts from Gulf of Maine and European populations of C. convoluta are indistinguishable at this locus. I have used a variety of molecular genetic techniques using the more variable ITS region to investigate the abundance of the free-living form of the symbiont, the population structure of the symbionts, and how that structure has changed over time.