Intraspecific shape variation in horseshoe crabs: the importance of sexual and natural selection for local adaptation

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  • Søren Faurby, Denmark
  • Kasper Sauer Kollerup Nielsen, Aarhus Universitet, Denmark
  • Somchai Bussarawit, National Science Museum, Thailand
  • Itsara Intanai, Prince of Songkla University, Thailand
  • Nguyen van Cong, Denmark
  • Cino Pertoldi
  • Peter Funch
  • Department of Biological Sciences, Genetics and Ecology

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.

Original languageEnglish
JournalJournal of Experimental Marine Biology and Ecology
Volume407
Pages (from-to)131-138
ISSN0022-0981
DOIs
Publication statusPublished - 2011

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