Mitonuclear effects on sex ratio persist across generations in interpopulation hybrids

Eukaryotic energy production requires tight coordination between nuclear
and mitochondrial gene products. Because males and females often have
different energetic strategies, optimal mitonuclear coordination may be
sex-specific. Previous work found evidence for sex-specific mitonuclear
effects in the copepod Tigriopus californicus by comparing two parental
lines and their reciprocal F1 crosses. However, an alternative hypothesis
is that the patterns were driven by the parental source of nuclear
alleles. Here we test this alternative hypothesis by extending the same
cross to F2 hybrids, who receive both maternal and paternal nuclear
alleles from F1 hybrids. Results confirm mitonuclear effects on sex ratio,
with distorted ratios persisting from the F1 to F2 generations, despite
reduced fitness in F2 hybrids. No sex by cross interactions was found for
other phenotypic traits measured. Mitochondrial DNA content was higher in
females. Both routine metabolic rate and oxidative DNA damage were lower
in F2 hybrids than in parentals. The persistence of sex-specific
mitonuclear effects, even in the face of F2 hybrid breakdown, attests to
the magnitude of these effects, which contribute to the maintenance of
within-population mitochondrial DNA polymorphisms.