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 U. ornatus, 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 U. ornatus-type mtDNA found in U. graciosus parental type individuals. This result was consistent with population expansions detected in U. graciosus but not U. ornatus. 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.

线粒体DNA（mtDNA）渐渗在动物类群中颇为常见，但获取异种线粒体基因组所带来的演化影响仍未被充分厘清。本研究以两种蜥蜴为研究对象：热环境特化种优雅优肢龙（Urosaurus graciosus）与栖息热环境跨度更广的饰纹优肢龙（U. ornatus），旨在探究二者之间的线粒体基因组渐渗现象。作为变温动物，二者的代谢速率强烈受环境温度调控；而线粒体代谢功能与代谢速率直接相关，因此线粒体渐渗事件可能对个体的整体能量预算产生影响。本研究通过对细胞色素b（Cyt-B）与烟酰胺腺嘌呤二核苷酸脱氢酶亚基1（ND1）基因序列进行贝叶斯分析，构建线粒体基因树，并结合两个物种19个种群的形态学数据与微卫星标记（microsatellites），旨在解答两个科学问题：其一，核质不一致（mitonuclear discordance）的方向与分布模式是否符合过往种群扩张引发渐渗的理论预测——即线粒体DNA会从定居物种向扩张或入侵物种流动；其二，携带异种线粒体是否会影响与个体适合度紧密相关的体型性状？本研究检测到多起独立的远古渐渗事件，且所有渐渗均为单向：仅在携带U. graciosus亲本型的个体中，检测到了U. ornatus型线粒体DNA。这一结果与U. graciosus的种群扩张信号相符，却与U. ornatus的种群动态不符。进一步分析显示，携带异种线粒体的雌性个体体型显著小于携带同种线粒体的雌性；而携带异种线粒体的雄性个体，其体质量与体长的相关性模式也与携带同种线粒体的雄性存在显著差异。上述结果表明，携带异种线粒体的个体可能存在潜在的选择劣势，这与有害等位基因（deleterious alleles）更易在扩张种群中留存的理论预期相一致。