The indisputable scarcity of asexual vertebrates alludes to an inherent cost incurred in asexual reproduction. Cellular respiration, the mechanism by which eukaryotes generate energy in the form of ATP, functions by harnessing subatomic energy via an electron transport system made up of co-evolved protein subunits of mitochondrial and nuclear origin. Asexual lineages lack the ability to efficiently filter autosomal alleles via genetic recombination, and thus are predicted to gradually lose compatibility between mitochondrial and nuclear genomes. The universal need for energy among eukaryotes suggests that this intragenomic network may contribute to the scarcity of asexual vertebrates. Alternative hypotheses include genomic incompatibilities due to the hybrid origins of essentially all parthenogenetic vertebrates. With asexuals constituting one third of its ~45 species, the genus Aspidoscelis (whiptail lizards) is a great model system for testing costs of asexuality. Here we measure endurance capacity in five species of Aspidoscelis and examine mitochondrial respiration between sexual and asexual species using live mitochondria respirometry. Our results show reduced endurance and mitochondrial respiration in asexual lineages compared to parental sexual lineages. We discuss these findings in the context of evolutionary history and mitonuclear co-evolution.