Interplay between selection, drift, and history: MHC polimorphism in two South American subterranean rodents (Ctenomys australis and C. talarum).

ANA P. CUTRERA; EILEEN A. LACEY; MATÍAS S. MORA

Amherst, University of Massachusetts

Congreso; The American Society of Mammalogists: 86th Annual Meeting.; 2006

American Society of Mammalogists (ASM)

The genes of The Histocompatibility Complex (MHC) are among the most variable functional loci known in vertebrates. Variation at these genes, which are involved in detection of and response to pathogens, is through to be maintained primary by balancing selection. At the same time, MHC genes are subject to the same processes that affect variation at neutral loci, raising intriguing questions regarding the interplay between selection and other determinants of genetic structure at MHC loci. To explore the effects of current selection versus historical demography, we compared patterns of the MHC variability in two species of subterranean rodents: Ctenomys australis and C. talarum. Although these species co-occur in the same geographic area, they have undergone different historical regimes; while mtDNA analysis of C. talarum reveal a stable pattern of differentiation by genetic drift and limited gene flow. C. australis has experience a recent demographic expansion following Quaternary sea level changes. Compariison of two MHC Class II genes, DRB and DQA, revealed that allelic variability is lower but heterozygosity is higher for C. talarum. Significant population-level evidence of selection was found for DQA in C. talarum. Significant molecular-level evidence of selection was obtained for DRB from C. talarum and DQA from C. australis. For C. australis, estimates of Tajima’s D were significantly negative for both loci, as expected under balancing selection. These results are discussed in light of the interplay between balancing selection and drift, as mediated by the different historical regimes experienced by populations of these species.