Repeated Adaptive Introgression at a Gene under Multiallelic Balancing Selection

• DOI: 10.1371/journal.pgen.1000168
• Publication Date: 2011-04-17T22:13:56Z
• Authors: Vincent Castric; Jesper Bechsgaard; Mikkel H. Schierup; Xavier Vekemans
• Keywords: Introgression; Balancing selection

Recently diverged species typically have incomplete reproductive barriers, allowing introgression of genetic material from one into the genomic background other. The role natural selection in preventing or promoting remains contentious. Because co-adaptation, some chromosomal fragments are expected to be selected against new and resist introgression. In contrast, should favor for alleles at genes evolving under multi-allelic balancing selection, such as MHC vertebrates, disease resistance, self-incompatibility plants. Here, we test prediction that negative, frequency-dependent on gene controlling pistil specificity two closely related species, Arabidopsis halleri A. lyrata, caused this locus a higher rate than background. Polymorphism is largely shared, identified 18 pairs S-alleles only slightly divergent between species. For these S-alleles, divergence four-fold degenerate sites (K = 0.0193) about four times lower 0.0743). We demonstrate difference cannot explained by differences effective population size types loci. Rather, our data most consistent with five-fold increase rates compared background, making study first documented example adaptive facilitated selection. suggest process plays an important maintenance high allelic diversity S-locus flowering plant families. among last stop introgressing, their comparison provides lower-bound estimate time since stopped forming fertile hybrids, thereby complementing average portrait provided data.