Meeting Abstract
The genomes of mitochondria, plastids, and other endosymbionts have long been hypothesized to play a role in creating reproductive isolation between species. One general mechanism to explain the role of mitochondrial (mt) genomes in creating reproductive isolation is the propensity for mt genomes to accumulate slightly deleterious mutations. If mt mutations exert selective pressure for corresponding changes in nuclear-encoded genes (i.e., mitonuclear coevolution), then coadapted mitonuclear genotypes would arise within lineages. Epistatic interactions among coadapted mt- and nuclear-encoded genes might therefore be compromised in hybrids, leading to hybrid breakdown and reproductive isolation. We have previously documented pervasive signatures of mitonuclear coevolution in the angiosperm genus Silene, and here we explore whether compromised mitonuclear interactions in Silene hybrids cause reduced fitness and mt function. Through backcrossing experiments, hybrids were generated that possess either control or “mismatched” cytonuclear genotypes. Survival, growth, and reproduction were then quantified in the resulting hybrids. Detailed measurements of substrate-coupled respiration and other metrics of mt function were also performed in isolated mitochondria. Although there was variation between genotypes in organismal fitness and mt function, none of our measurements indicated that mismatched hybrids had reduced fitness or altered mt function. While these results do not rule out the possibility of a role for cytonuclear interactions in reproductive isolation (even within Silene), they highlight important questions that have been raised about the ubiquity of cytonuclear coevolution in the creation of species boundaries.
