Discussion:
A mounting body of work has suggested that mitonuclear incompatibilities are among the first genetic barriers to evolve at early stages of population divergence across taxa (Burton & Barreto 2012; Burtonet al. 2013; Hill 2016; Sloan et al. 2017; 2018; Hillet al. 2018), affecting multiple life history traits that render hybrids unfit. Nevertheless, it is still unclear whether such BDMIs involve a few nuclear regions in a localized part of the genome, or if they involve many regions throughout the nuclear genome. Understanding the genetic architecture of mitonuclear incompatibilities can benefit from the “evolve-and-resequence” approach developed for model organisms (Burke et al. 2014; Schlotterer et al. 2015), where adaptation to divergent environments stems from standing genetic variation generated from an initial hybrid population. In this study, we evolved sickly F2 hybrids of the copepod Tigriopus californicus , where parental nuclear alleles are represented at similar frequencies, and monitor change in these allele frequencies after experimental evolution under two divergent mitochondrial backgrounds. We hypothesize that recovery of hybrid fitness will primarily result from selection favoring mitonuclear compatibility and that allelic frequency changes across the genome will reveal locations where such selection has acted.