Deleterious Epistatic Interactions Between Electron Transport System Protein-Coding Loci in the Copepod Tigriopus californicus

Abstract

The nature of epistatic interactions between genes encoding interacting proteins in hybrid organisms can have important implications for the evolution of postzygotic reproductive isolation and speciation. At this point very little is known about the fitness differences caused by specific closely interacting but evolutionarily divergent proteins in hybrids between populations or species. The intertidal copepod Tigriopus californicus provides an excellent model in which to study such interactions because the species range includes numerous genetically divergent populations that are still capable of being crossed in the laboratory. Here, the effect on fitness due to the interactions of three complex III proteins of the electron transport system in F 2 hybrid copepods resulting from crosses of a pair of divergent populations is examined. Significant deviations from Mendelian inheritance are observed for each of the three genes in F 2 hybrid adults but not in nauplii (larvae). The two-way interactions between these genes also have a significant impact upon the viability of these hybrid copepods. Dominance appears to play an important role in mediating the interactions between these loci as deviations are caused by heterozygote/homozygote deleterious interactions. These results suggest that the fitness consequences of the interactions of these three complex III-associated genes could influence reproductive isolation in this system.

The nature of interactions that contribute to postzygotic reproductive isolation in hybrid copepods

“…Similar to the results found for CYC in the set of three crosses and reciprocal crosses between the AB, SD, and SCN populations, for both RISP and CYC1 in most crosses there are significant deviations from Mendelian inheritance at each locus in the F 2 adults and no deviations in F 2 nauplii in any of these crosses (Willett 2006(Willett , 2008b. Although it appears then that these regions of the genome are impacting hybrid fitness, the favored homozygous genotypic class does not in general match the mtDNA-type in a cross suggesting that under these conditions there is not a simple pattern of genomic coadaptation between either of these two genes and mtDNA.…”

A Linkage Map Reveals a Complex Basis for Segregation Distortion in an Interpopulation Cross in the Moss Ceratodon purpureus

“…This observation suggests that some NY two-locus genotypes may have had deleterious interactions with an additional Ec factor that was not linked to any segregating marker in our mapping population; such factors may have been absent either due to chance or, more likely, because they were maternally inherited cytoplasmic elements (Burke and Arnold 2001;Willett and Burton 2001;Levin 2003;Fishman and Willis 2006;Harrison and Burton 2006;Willett 2006;Chase 2007). This model implies that these genetic interactions involve multiple complementary loci, where the presence of a homospecific allele at either autosomal locus is sufficient for proper function.…”

Cytonuclear Genic Incompatibilities Cause Increased Mortality in Male F2 Hybrids of Nasonia giraulti and N. vitripennis

“…Nuclear genes of the OXPHOS system are therefore promising candidates for being incompatible with a heterospecific mitochondrion. However, so far only a few studies have addressed the possible role of cytonuclear genic incompatibilities in hybrid breakdown (e.g., Hutter 2002Hutter , 2007Rawson and Burton 2002;Sackton et al 2003;Burton et al 2006;Ellison and Burton 2006;Harrison and Burton 2006;Willett 2006). The short generation time of Nasonia species, its haplodipolid sex determination, and availability of the genome sequence makes Nasonia a suitable model system for studying these interactions in further detail.…”