Spatio-temporal variation in parasite communities maintains diversity at the major histocompatibility complex class II in the endangered Rio Grande Silvery Minnow

Authors: Megan Pilger Osborne, Lusk Tyler, Turner Joel, Megan Pilger Thomas

Year: 2016 (xlviii)

Abstract

We combined genetic (MHC Class II and microsatellites), parasitological and ecological data to explore the relationship between these factors in the remnant wild Rio Grande silvery minnow population, an endangered species found in the southwestern Unite d States. Fish were infected with multiple parasites on the gills and there was spatio-temporal variation in parasite communities and patterns of infection. Despite its highly endangered status and chronically low genetic effective size, Rio Grande silvery mi nnow had high allelic diversity at MHC Class II with more alleles recognised at the presumptive DAB1 locus compared to DAB3 locus. We identified significant associations between specific parasites and MHC alleles against a backdrop of generalist parasite prevalence. We also found that individuals with higher individual heterozygosity (at neutral loci) and higher amino acid divergence between MHC alleles had lower parasite abundance and diversity (as measured by an index of parasitization). Taken together, these results suggest a role for fluctuating selection imposed by spatio-temporal variation in pathogen communities and divergent allele advantage, in maintenance of high MHC polymorphism. Understanding the complex interaction of habitat, pathogens and immunity in protected species will require integrated genetic and field studies to ensure that sufficient diversity is maintained to respond to novel pathogens, and changing host-pathogen interactions.