Abstract
The introduction of non-native populations can have dramatic effects on the native fauna as a result of interbreeding and aggressive interference between closely related species. This study investigates if female European lobsters Homarus gammarus would sexually interact and mate with male American lobsters Homarus americanus, recently introduced to Norwegian waters, if given the choice between the heterospecific and a conspecific male. Interactions between a mixed species pair of male lobsters and a single H. gammarus female were recorded during 1 wk periods in a large tank provided with 2 shelters. Trials included either dominant H. americanus or dominant H. gammarus males. The frequency and duration of social interactions such as aggression, shelter visits, shelter shar- ing, courtship and mating were analysed. Conspecific courtship occurred in 10 trials, and mating, in 5 trials. No sexual interactions occurred between species. H. gammarus females preferred to court and mate with a conspecific male irrespective of its dominance status. In addition, the H. americanus males showed no sexual response to the European females. Females visited conspecific male shelters more frequently than heterospecific male shelters. They received longer visits from the conspecific than from the heterospecific male. Conspecific pairs shared shelters more frequently and over longer peri- ods of time than heterospecific pairs. Conspecific shelter sharing often included courtship, while heterospecific interactions were generally of aggressive nature, with lobsters fighting over shelter. The results suggest that European lobsters are able to recognize conspecific mates, perhaps by chem- ical signals, and that these signals serve as pre-mating barriers preventing hybridisation.
Highlights
The introduction of organisms into new geographical regions can bring together formerly separated species to create new interactions that may be detrimental to the native species
The present study aims to assess the risk of interbreeding between female European lobsters and male American lobsters by investigating behavioural interactions
American male lobsters Homarus americanus were dominant in 6 out of 15 trials, whereas H. gammarus males were dominant in 7 trials (Table 1)
Summary
The introduction of organisms into new geographical regions can bring together formerly separated species to create new interactions that may be detrimental to the native species. Behavioural studies testing the potential for interbreeding are important to understand the impact of species introductions on closely related native species (Huxel 1999). European lobsters Homarus gammarus Linnaeus, 1758 and American lobsters H. americanus Milne Edwards, 1837 are closely related species with small but significant genetic differences (Hedgecock et al 1977). They have been geographically isolated since the Pleistocene epoch and appear to have only weak repro-
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