Intraspecific shape variation in horseshoe crabs: The importance of sexual and natural selection for local adaptation |
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Authors: | Søren Faurby Kasper Sauer Kollerup Nielsen Itsara Intanai Cino Pertoldi Peter Funch |
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Institution: | a Department of Ecology and Evolutionary Biology, University of California Los Angeles, 621 Charles E. Young Dr. South, 90024 Los Angeles, USAb Ecology and Genetics, Department of Biological Sciences, Aarhus University, Ny Munkegade 114-116, 8000 Århus C, Denmarkc National Science Museum, Technopolis, Klong 5, Klong Luang, Pathumthani 12120, Thailandd Faculty of Science and Technology, Prince of Songkla University, Pattani 94000,Thailande Department of Environmental Sciences, College of Environmental Sciences, College of Environment and Natural Resources, Cantho University, 3/2 Street, Cantho City, Vietnamf Mammal Research Institute, Polish Academy of Sciences, Waszkiewicza 1c, 17-230 Bia?owie?a, Bialowieza, Poland |
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Abstract: | A morphometric analysis of the body shape of three species of horseshoe crabs was undertaken in order to infer the importance of natural and sexual selection. It was expected that natural selection would be most intense, leading to highest regional differentiation, in the American species Limulus polyphemus, which has the largest climatic differences between different populations. Local adaptation driven by sexual selection was expected in males but not females because horseshoe crab mating behaviour leads to competition between males, but not between females. Three hundred fifty-nine horseshoe crabs from nine populations, representing three species, were analyzed using a digitizer to position sixty morphometric landmarks in a three-dimensional space. Discriminant analysis revealed strong regional structuring within a species, which suggests strong philopatry, and showed the existence of geographically-based intraspecific variation. An admixture analysis showed regional intraspecific differentiation for males and females of L. polyphemus and males of the Asian horseshoe crab Carcinoscorpius rotundicauda, but not for females of C. rotundicauda and another Asian horseshoe crab, Tachypleus gigas. Differences in shape variation between sexes were tested with F-tests, which showed lower intrapopulation morphometric variation in males than females. These results indicate a lower degree of local adaptation on body shape in C. rotundicauda and T. gigas than in L. polyphemus and a lower degree of local adaptation in females than in males. |
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Keywords: | Admixture analysis Carcinoscorpius rotundicauda Limulus polyphemus Morphometrics Sexual selection Tachypleus gigas |
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