Abstract

The extent to which mitochondrial DNA (mtDNA) variation 25 is involved in
adaptive evolutionary change is currently being reevaluated. In particular,
emerging evidence suggests that mtDNA genes coevolve with the nuclear
genes with which they interact to form the energy producing enzyme
complexes in the mitochondria. This suggests that intergenomic epistasis
30 between mitochondrial and nuclear genes may affect whole-organism
metabolic phenotypes. Here, we use crossed combinations of mitochondrial
and nuclear lineages of the seed beetle Callosobruchus maculatus and assay
metabolic rate under two different temperature regimes. Metabolic rate was
affected by an interaction between the mitochondrial and nuclear lineages and
35 the temperature regime. Sequence data suggests that mitochondrial genetic
variation has a role in determining the outcome of this interaction. Our genetic
dissection of metabolic rate reveals a high level of complexity, encompassing
genetic interactions over two genomes, and genotype × genotype ×
environment interactions. The evolutionary implications of these results are
40 twofold. First, because metabolic rate is at the root of life histories, our results
provide insights into the complexity of life history evolution in general, and
thermal adaptation in particular. Second, our results suggest a mechanism
that could contribute to the maintenance of non-neutral mtDNA polymorphism.
Evolution Page 2 of 37