Data from: Introgression of mtDNA in Urosaurus lizards: historical and ecological processes

Introgression of mtDNA appears common in animals but the implications of acquiring a novel mitochondrial genome are not well known. This study investigates mito-genome introgression between the lizard species (Urosaurus graciosus), a thermal specialist, and <i>U. ornatus</i>, a species that occupies a wider range of thermal environments. As ectotherms, their metabolic rate is strongly influenced by the thermal environment; with mitochondria being linked to metabolic rates, overall energy budgets could be impacted by introgression. I use mitochondrial gene trees, inferred from Bayesian analyses of Cyt-B and ND1 gene sequences, along with morphology and microsatellites from nineteen populations of these two species to address if the direction and location of mito-nuclear discordance match predictions of introgression resulting from past population expansions. MtDNA is expected to move from resident species into expanding or invading species. Second, does having a heterospecific form of mitochondria impact body size, a trait strongly associated with fitness? Multiple independent introgression events of historic origin were detected. All introgression was unidirectional with <i>U. ornatus</i>-type mtDNA found in <i>U. graciosus</i> parental type individuals. This result was consistent with population expansions detected in <i>U. graciosus</i> but not <i>U. ornatus</i>. Females with heterospecific mtDNA were significantly smaller than homospecific forms and heterospecific males had a different relationship of body mass to body length than those with homospecific mtDNA. These changes indicate a potential selective disadvantage for individuals with heterospecific mitochondria and are consistent with the theoretical expectation that deleterious alleles are more likely to persist in expanding populations.