Meeting Abstract
As a result of habitat loss and fragmentation, many species now exist in smaller and more isolated populations which often results in decreased genetic variation and reduced fitness. One cause of lower fitness may arise from increased susceptibility to pathogens due to the loss of variation at immune genes, such as those of the major histocompatibility complex (MHC). MHC genes are well known for their critical role in the detection of pathogens and the activation of the adaptive immune system in vertebrates. In this gene complex the presence of specific alleles as well as the number of alleles within individuals is related to disease resistance. Therefore, it is important to examine how neutral (genetic drift) and non-neutral (selection) processes influence MHC variation in populations that vary in size and demographic history. To investigate the effects of genetic drift and selection on genetic variation, we compared variation at the MHC and six neutral microsatellite loci in six populations of greater prairie-chickens (Tympanuchus cupido) that varied in size (174 – 178,000 birds) across the geographic range. By examining these genetic markers, we found that small populations have lower MHC variation, consistent with the effects of genetic drift. However, there was also evidence that selection influenced MHC variation at multiple levels. At the sequence level, we found signatures of historical selection at specific sites across the MHC genes (dN/dS > 1). At the population level, there was greater population differentiation at the MHC than at microsatellite markers, suggesting that local adaptation to pathogens may be driving differences at the MHC among populations. In summary, we found each population contained a unique MHC repertoire, and that both genetic drift and selection are important mechanisms shaping MHC variation in prairie-chickens.
