Phylogeographic Analysis of the Major Histocompatibility Complex Class II b Alleles of the Trinidadian Guppy, Poecilia reticulata
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The Major Histocompatibility Complex (MHC) are a set of vertebrae immune genes, that act in defense from cellular parasites. In Poecilia reticulata MHC is shown to also affect coloration and mate choice. The guppy acts as a model system in studying MHC. Having multiple copies of the MHC gene, large populations, and short generation time are ideal for studying MHC diversity. Samples were collected from Trinidad as Trinidad’s water system offers an ideal living lab with many genetically distinct populations separated by watersheds, waterfalls, and different predation levels. MHC may be separated into groups, known as super types, based on like binding properties of the peptide binding region. Through the construction of maximum likelihood trees super types were compared to the phylogeny of all alleles together. These trees were then aligned with the geography of Trinidad to look for correlation between clades of the tree and clusters of sample sites. When looking at the full tree of MHC alleles, significant correlation between phylogenetic tree and sample sites were found, however only super types 3, 4, 7, 10, and 14 were found to have this correlation. I discuss the role of selection, both natural and sexual on the presence and absence of MHC alleles, the roll of the Guppy’s colonization history in Trinidad, and the role of temporal separation due to the age of the MHC genes themselves.