MCCOY, Adam M; Harvard University: Host-Symbiont Specificity:A Means to Predict a Biological Invasion

Despite recognition of the potential ecological consequences of biological invasions, factors that determine the ability of exotics to successfully invade remain largely unknown. Many species in the marine environment rely on specific interactions with microbes for a variety of processes including settlement cues and nutritional interactions. Specificity in interactions of this type can be a potential barrier to invasion. Just as invaders sometime gain a competitive advantage by �escaping� specific parasites, absence of a beneficial partner imposes a competitive cost upon potential invaders. Unfortunately, the extent of invasions of microorganisms in natural environments remains largely unexplored. The symbiotic acoel Convoluta convoluta is an excellent model system for an investigation into these broad phenomena. C. convoluta has an apparently obligate endosymbiont, it must acquire from the environment with each generation, but has still been a successful invader in the Gulf of Maine. The range of C. convoluta has expanded southward over the past several years, and the range of the free-living �symbiont� has preceded the C. convoluta expansion. The extent of species invasions has likely been underestimated due to the lack of investigation of microbial invaders. Also, this potential barrier, an obligate interaction with a specific microbial partner, can become a mechanism to facilitate invasion if the microbial partner invades; however, it also suggests an important area for future study. With a better understanding of the composition of marine microbial communities we may gain a better ability to predict future invasions. This association is currently unique in that knowledge of the �symbiont� distribution allows prediction of where the C. convoluta will, and will not invade in subsequent years.