MEPS 276:209-222 (2004)  -  doi:10.3354/meps276209

Biogeographic differences in claw size and performance in an introduced crab predator Carcinus maenas

L. David Smith*

Department of Biological Sciences and Environmental Science and Policy Program, 235 Sabin-Reed Hall, Smith College, Northampton, Massachusetts 01063, USA

ABSTRACT: Introduced predators must forage effectively to persist in new areas, and effective resource use is correlated with a predator¹s trophic (feeding) structures. The extent to which trophic morphology responds to spatial variation in prey resistance, and the time scale of that response, however, are not well understood. The introduced European green crab Carcinus maenas, which has expanded its range in the northwest Atlantic Ocean over the last century and encountered a latitudinal cline in prey armor, offers an ideal opportunity to test for such post-invasion changes. In rocky intertidal habitats in the Gulf of Maine, southern populations of the snail Littorina obtusata are better defended than northern populations. To test for correlated differences in claw size and prey defense, green crabs and common molluscan prey were collected at southern and northern sites in the Gulf of Maine. C. maenas are heterochelous, and analyses revealed that crusher claws of crabs collected in the south were significantly larger than those of crabs from the north after adjusting for carapace width. The size of the cutter claw, however, did not differ between regions. Shell weights for similar-sized snails differed among sites for 3 of the 4 species examined, but did not differ by region. To test crushing performance, southern and northern crabs were presented with increasing sizes of southern or northern L. obtusata in the laboratory. For similar-sized individuals, southern crabs were able to crush significantly larger snails than northern crabs regardless of the geographic origin of the snails. Thus, patterns in claw size and performance strongly suggest trophic responses to geographic differences in prey armor. Rapid changes in trophic morphology could facilitate the spread of this invasive species and initiate an ecological arms race if both predator and prey respond ecophenotypically to each other.


KEY WORDS: Introduced species · Trophic polymorphism · Crab claws · Phenotypic plasticity · Rapid evolution · Ecological arms race · Carcinus maenas · Littorina obtusata


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