Evol Ecol Res 13: 589-605 (2011)     Full PDF if your library subscribes.

Pathogen-mediated selection for MHC variability in wild zebrafish

Carl Smith1, Markéta Ondračková2, Rowena Spence1, Sally Adams3, Donna S. Betts4 and Eamonn Mallon4

1School of Biology, University of St. Andrews, St. Andrews, UK, 2Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic, Brno, Czech Republic, 3Department of Life Sciences, University of Warwick, Coventry, UK and 4Department of Biology, University of Leicester, Leicester, UK

Correspondence: C. Smith, School of Biology, University of St. Andrews, St. Andrews, Fife KY16 8LB, UK.
e-mail: cs101@st-andrews.ac.uk


Hypothesis: Genes of the major histocompatibility complex (MHC) show high variability, which is believed to arise through pathogen-mediated selection.

Organism: Zebrafish (Danio rerio) from seven independent natural populations.

Location: Bangladesh: two sites in Khulna District in the River Ganges drainage, and five sites in Mymensingh District in the River Brahmaputra drainage.

Methods: We investigated the relationship of parasite abundance and diversity with allelic variability of the MHC class II B gene in natural populations of zebrafish. A sample of 120 zebrafish was screened for metazoan parasites, and a subsample of 77 was assessed for immunogenetic variation. In total, 2475 metazoan parasites from 23 taxa were identified and 13 unique MHC class IIB alleles were isolated.

Conclusion: We found no evidence for a heterozygote advantage, and overall there was lower than expected heterozygosity of MHC alleles. We identified lower parasite abundance and diversity with specific MHC alleles, and this pattern varied between geographic regions. Results suggest that MHC variability in zebrafish is maintained by frequency-dependent and fluctuating selection.

Keywords: digenean, frequency-dependent selection, heterozygote advantage, major histocompatibility complex, metazoan parasite, pathogen-driven selection.

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