Kaehlert, Sarah (2015) Larval reproduction - a life history trait exemplified by the American comb jelly Mnemiopsis leidyi A. Agassiz, 1865. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 85 pp.

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Abstract

The rate of marine invasions has lately been shown to increase as a consequence of growing anthropogenic transport, increasing globalization and partly due to global change. A prominent example of a marine invasive species is the comb jelly Mnemiopsis leidyi, which successfully invaded northern and southern Europe in two independent invasion events. The species shares a rare life history trait, namely paedogenesis in which larvae reproduce. In this study egg production rates and growth of two invasive populations of M. leidyi from the Baltic and the Caspian Sea were measured, respectively. The approach was organized around answering the following questions:
- Do invasive populations of M. leidyi perform larval reproduction?
- What is the proportion of larval reproduction within an invasive population?
- What could be the trigger to larval reproduction?
- What potential ecological impact could larval reproduction have on the invasion potential of the species?
We found reproducing larvae in both invasive populations from a size starting at 2 mm oral - aboral length without a so far described pause in reproduction during metamorphosis. The fraction of reproducing larvae between both populations differed and was 3.3 % and 25.5 % for Baltic Sea and Caspian Sea populations, respectively. Both invasive populations showed judging on the location of reproductive tissue, adult reproduction already in the transitional stage. These results are in contrast to previous findings. Additionally, larvae were found to survive food shortage for longer periods. Larvae of M. leidyi are therefore recognized as potentially playing a key role in the invasion success of M. leidyi as we shall not forget that they are also more robust in comparison to adults because of their great healing and regeneration potential.

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