Meeting Abstract
Epigenetic potential, or the capacity for epigenetically-mediated phenotypic plasticity, may play an important role during range expansions. As range-expanding populations face comparatively novel ecological challenges and can be genetically constrained due to bottlenecks and/or founder effects, they might often rely on phenotypic plasticity via epigenetic mechanisms to rapidly cope with these challenges. Here, we asked whether one proxy for epigenetic potential (i.e. the abundance and/or position of CpG sites within gene promoters) varied among three native and three introduced populations of house sparrows (Passer domesticus). DNA methylation primarily occurs at CpG sites and we recently discovered that methylation at one CpG site within the putative promoter region of a microbial surveillance gene (Toll-like receptor 4, TLR-4) was a strong predictor of TLR-4 expression in house sparrows. We characterized i) total CpG sites, ii) SNPs in CpG sites, and iii) overall SNP variation within the putative promoter region of TLR-4. We hypothesize that SNP variants represent genetic assimilation of initially pure (environmental) epigenetic effects, particularly when they occur within or near CpG sites. We found more unmodified CpGs (those lacking SNPs) and fewer SNPs overall in birds from introduced populations. Moreover, we found greater variation in the number of SNPs among CpG sites in native populations, suggesting selection against some SNPs in introduced populations and/or assimilation of previously epigenetic effects in native ones. These results support a role for epigenetic potential in the range expansions of this species, and have instigated a more intensive study using epi- and ddRADseq.
