Jakob C. Mueller

Genetic population structure of two cryptic Gammarus fossarum types across a contact zone

Previous studies have revealed inconsistent results about the taxonomic status of European Gammarus fossarum forms. The variability in morphology and hybridization ability has not shown clear geographic patterns, whereas on a genetical basis two Central European G. fossarum forms have been proposed.

A STUDY OF POPULATION GENETICS IN THE EUROPEAN LOBSTER, HOMARUS GAMMARUS (DECAPODA, NEPHROPIDAE)

By means of an RAPD analysis, the degree of genetic variation in the European lobster, Homarus gammarus, was assessed. We focused our attention on the Helgoland population, which is isolated by its geographical location. By comparison with seven other European lobster populations we demonstrated that the Helgoland lobster is genetically widely separated from other European lobster stocks. However, all populations investigated showed high values of genetic distance, indicating that genetic exchange among European populations of Homarus gammarus may be restricted. The European lobster populations appeared to be isolated by distance since the pattern of genetic relationships reflects their geographic location. We thus suggest a distinct, genetical population structure, possibly maintained by genetic drift within relatively isolated local populations and restricted gene flow between them. This contrasts to the homogeneous population structure of the American lobster, Homarus americanus. Mit Hilfe der RAPD Analyse wurde der Grad der genetischen Variation bei Homarus gammarus, dem Europaischen Hummer, bestimmt. Dabei konzentrierten wir unser Interesse auf den Helgolander Hummer, eine Population, die durch ihre geographische Lage isoliert ist. Durch Vergleich mit sieben anderen europaischen Hummerpopulationen zeigten wir, das der Helgolander Hummer genetisch deutlich von anderen europaischen Hummerstocks getrennt ist. Alle untersuchten Populationen zeigten relativ grose genetische Distanzen untereinander. Dieses Resultat deutet darauf hin, das der genetische Austausch zwischen den Populationen des Europaischen Hummers eingeschrankt sein konnte. Die untersuchten Populationen des Europaischen Hummers scheinen durch ihre raumliche Distanz genetisch voneinander getrennt zu sein, da die beobachteten genetischen Muster ihre geographische Verteilung widerspiegeln. Aus diesem Grund vermuten wir eine charakteristische genetische Populationsstruktur, die moglicherweise durch eine genetische Drift innerhalb mehr oder weniger isolierten lokalen Populationen und dem damit verbundenen eingeschrankten Genflus zwischen solchen Populationen hervorgerufen wird. Dieses Resultat steht im Gegensatz zu der homogenen Populationsstruktur des Amerikanischen Hummers, Homarus americanus.

Genetics on invasive species

Genetic markers are especially appropriate to reveal historical processes, as for example regarding biological invasions. Phylogenetic and population genetic methods enable to identify the taxa involved in an invasion (native and non-native species) and often lead to the perception of multiple or cryptic invasions. Phylogeographic and multi-locus approaches have been developed to assign individual invaders to potential source populations. The results may have implications for management measures. However, little is known about the genetic architecture of newly colonised populations. We introduce here genetic models for colonisations in linear habitats like rivers or coastlines. The expectations about the neutral genetic population structure in relation to different invasion modes are compared to European field data of Dikerogammarus villosus (Amphipoda) and Dreissena polymorpha (Bivalvia). Finally, a potential correlation between genetic diversity and invasion success is discussed.