Host use pattern of the pea crab Afropinnotheres monodi: potential effects on its reproductive success and geographical expansion

摘要

The successful settlement of the African pea crab Afropinnotheres monodi in the Bay of Cadiz was analysed to gain new insights into the evolution of pea crab parasite life history traits. The pea crab lives symbiotically and with high prevalence in the bivalves Cerastoderma glaucum and Mytilus galloprovincialis, and with low prevalence in Scrobicularia plana. A remarkable monopolisation of the host (1 crab per bivalve) occurred irrespective of host species and crab demographic categories (males, hard females, soft females), probably as an optimisation of resources in small hosts. However, there was a clear asymmetry in host use by the different crab categories. A 1:1 sex ratio was found in crabs harboured by C. glaucum and S. plana, with most of the female crabs being small and hard specimens, whereas crabs inhabiting M. galloprovincialis were primarily large reproductive females. Ovigerous females were found throughout the year in M. galloprovincialis, and there was a strong correlation between female size and fecundity, suggesting that the females harboured by this host were the major contributors to the reproductive effort of the studied population. Conversely, most of the new crabs recruiting to the population were harboured by the remaining 2 host species. We hypothesise that such a generalist but asymmetrical usage of bivalve hosts by pea crabs may have clear benefits for species such as A. monodi, that are undergoing geographical expansion, facilitating their dispersal to new locations and their successful settlement in sheltered systems, such as the Bay of Cadiz.