Cryptic species in marine polychaete and their independent introduction from North America to Europe |
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Authors: | Bastrop R; Jurss K; Sturmbauer C |
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Institution: | Department of Zoology, University of Rostock, Germany. |
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Abstract: | The vast body of ballast water carried across oceans by freight ships
represents a major source for the introduction of foreign species into
marine ecosystems. The worm Marenzelleria viridis, originally found only in
North America, appeared in estuaries of the North Sea in 1979 and 6 years
later also in the Baltic, where it has developed into a major faunal
element. Two competing hypotheses are discussed here: either both
populations owe their presence to a single introductory event in the North
Sea, or each population originated from a separate introduction. Our
phylogeographic analysis of Baltic, North Sea and American Marenzelleria,
based on mitochondrial 16S rDNA sequences (326- bp segment) of 98
individuals from 17 localities on the North American, North Sea, and Baltic
coasts not only favors the two-event hypothesis, but also separates the
locations of origin for the introductions. Eighteen mitochondrial genotypes
were identified altogether. In agreement with allozyme data, three lineages
were identified: genotypes assigned to the same lineage differed from each
other by up to 5 point mutations, and those assigned to different lineages
differed by up to 17. The existence of three morphologically
indistinguishable, and thus cryptic, species is therefore suggested. The
individuals from the Baltic Sea probably originated from the Atlantic coast
of the United States between Chesapeake Bay and Georgia, and the North Sea
populations may stem from the U.S. coast region north of Chesapeake Bay to
Nova Scotia. Despite their similar morphologies, the two European
Marenzelleria species may differ ecologically with respect to their
preference for habitat salinity. Assuming that transport via ballast water
occurs quite frequently, we hypothesize that both European cryptic species
of Marenzelleria may originally have been introduced to both the North Sea
and the Baltic Sea but that neither of them was able to proliferate in both
water bodies owing to their differential physiological performances at high
and low salinities.
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