Data from: Asymmetric energetic costs in reciprocal-cross hybrids between carnivorous mice (Onychomys)

Aerobic respiration is a fundamental physiological trait dependent on
coordinated interactions between gene products of the mitochondrial and
nuclear genomes. Mitonuclear mismatch in interspecific hybrids may
contribute to reproductive isolation by inducing reduced viability (or
even complete inviability) due to increased metabolic costs. However, few
studies have tested for effects of mitonuclear mismatch on respiration at
the whole organism level. We explored how hybridization affects metabolic
rates in closely related species of grasshopper mice (genus Onychomys) to
better understand the role of metabolic costs in reproductive isolation.
We measured metabolic rate across a range of temperatures to calculate
basal metabolic rates (BMR) and cold-induced metabolic rates (MRc) in O.
leucogaster, O. torridus, and O. arenicola, and in reciprocal F1 hybrids
between the latter two species. Within the genus, we found a negative
correlation between mass-specific BMR and body mass. Although O. arenicola
was smaller than O. torridus, hybrids from both directions of the cross
resembled O. arenicola in body mass. In contrast, hybrid BMR was strongly
influenced by the direction of the cross: reciprocal F1 hybrids were
different from each other but indistinguishable from the maternal species.
In addition, MRc was not significantly different between hybrids and
either parental species. These patterns indicate that metabolic costs are
not increased in Onychomys F1 hybrids and, while exposure of
incompatibilities in F2 hybrids cannot be ruled out, suggests that
mitonuclear mismatch does not act as a primary barrier to gene flow.
Maternal matching of BMR is suggestive of a strong effect of mitochondrial
genotype on metabolism in hybrids. Together, our findings provide insight
into the metabolic consequences of hybridization, a topic that is
understudied in mammals.