Local adaptation and maternal effects in two species of marine gastropod (genus Crepidula) that differ in dispersal potential

Adaptation to local conditions should be less likely in species with wide dispersal since periodic immigration from populations not under selection would counteract the short-term results of local selection. To test this hypothesis, we used 2 species of sympatric marine gastropods of the genus Crepidula that have vastly different early life dispersal stages. Offspring of C. fornicata emerge as long-lived free-swimming larvae, whereas offspring of C. convexa emerge as benthic juveniles. We investigated the local adaptation of each species at 2 locations by assessing their tolerance to the toxic metal copper in the laboratory. We conducted 96 h acute copper toxicity tests with juveniles of C. convexa and larvae of C. fornicata released in the laboratory by adults collected from a reference site (Lynn Harbor, Nahant, Massachusetts, USA) or a polluted site (New Bedford Harbor, Fairhaven, Massachusetts). To test for maternal effects, we also raised C. fornicata released in the laboratory (F-1 generation) to sexual maturity and tested for differences in copper tolerance of their offspring (F-2). As expected, juveniles of C. convexa from the polluted site were significantly more copper tolerant than juveniles from the reference site (p <= 0.05), suggesting local adaptation at the polluted site. Contrary to expectations, F-1 larvae of C. fornicata from the polluted site were not equally copper tolerant, but less copper tolerant than F-1 larvae from the reference site. However, copper tolerance did not differ for F-2 larvae of C. fornicata from the 2 sites. Our results suggest that populations of C. convexa can adapt to locally high metal concentrations, while populations of C. fornicata cannot, probably because of the periodic input of C. fornicata larvae from distant populations that do not experience high metal stress. Also, long-term exposure of C. fornicata adults to pollutants apparently decreased the copper tolerance of their offspring (F-1 generation), an effect not seen in the laboratory-propagated F-2 generation.