Evolutionary Ecology of Mnemiopsis leidyi invasion into North and Baltic Sea
Final Report Abstract
As biological invasion continue to homogenize biota across ecosystems, marine habitats are especially affected by species translocations through high capacity vectors such as ballast water. Here we have identified two independent invasions of the American ctenophore M. leidyi into Eurasian Seas. Given the low genetic diversity between native and invaded range in Northern Europe and the introduction history in Southern Europe, M. leidyi was almost certainly introduced via ballast water. We were able to reconstruct two independent waves into Northern and Southern Eurasian Sea, with very different patterns of invasion. In the older southern invasion we propose a direct introduction from the Gulf of Mexico into the Black Sea, followed by secondary introductions into the Caspian and Mediterranean Sea, according to a "stepping stone" mode of invasive range expansion. This invasion wave was accompanied by stepwise losses of neutral genetic diversity. For Northern Europe we have identified a direct introduction into North and Baltic Sea, resulting only in moderate losses of diversity in the North Sea and no reduction in the Baltic. With a population genetic time series of theses northern sites were furthermore able to reconstruct how diversity and divergence develop shortly after the invasion establishment. We show that the surprisingly high divergence between recently invaded North and Baltic Sea persist and demonstrate that diversity stays virtually unchanged at its discriminate levels in North Sea and Western Baltic. Furthermore our population genetic measures supported the conclusion that towards the distribution margin in the Central Baltic, M. leidyi formed sink populations. Our results demonstrate that population genetic measures are a vital tool to reconstruct population history and invasion events in gelatinous Zooplankton. Combining experimental infections with next generation sequencing we have generated the first EST-libraries of immune relevant genes in a ctenophore. Given that M. leidyi will be the first ctenophore with a sequenced genome and its unique ecological relevance, our data will help to understand the evolution of immune defense and ecological interaction with parasites and infections. Based on the EST-libraries a Q-RT-PCR assay for specifically upregulated immune genes was developed. Applying this assay to a second immune experimeni, we could demonstrate that the ctenophore M. leidyi is capable of specific immune priming. It is the first description of immune priming in the phylum Ctenophora and has important implication in linking the immune repertoire of these basal organisms to actual expression upon infection and ultimately ecological performance in variable habitats.
Publications
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(2010) Microsatellites reveal origin and genetic diversity of Eurasian invasions by one of the world's most notorious marine invader, Mnemiopsis leidyi (Ctenophora). Molecular Ecology 19:2690-2699
Reusch TBH, Bolte S, Sparwel M, Moss AG, Javidpour J
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(2012) Ctenophore population recruits entirely through larval reproduction in the central Baltic Sea. Biology Letters 8:809-812
Jaspers C, Haraldsson M, Bolte S, Reusch TBH, Thygesen UH, Kiorboe T
