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.

线粒体DNA（mtDNA）的渐渗在动物类群中颇为常见，但获得全新线粒体基因组所带来的影响尚不明晰。本研究聚焦于两种蜥蜴——热生态位特化的<i>Urosaurus graciosus</i>与栖息于更广范围热环境的<i>U. ornatus</i>之间的线粒体基因组渐渗现象。作为变温动物，二者的代谢速率深受热环境调控；而线粒体与代谢速率密切相关，因此线粒体渐渗事件可能会对整体能量预算造成显著冲击。
本研究依托针对Cyt-B与ND1基因序列的贝叶斯分析构建的线粒体基因树，结合这两个物种19个种群的形态学数据与微卫星标记，旨在解答两个核心科学问题：其一，线粒体-核基因组不协调的方向与分布区域，是否符合由过往种群扩张引发的渐渗预测——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适合度紧密相关的体型大小？
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性：仅在携带<i>U. graciosus</i>亲本基因型的个体中发现了<i>U. ornatus</i>型线粒体DNA。这一结果与<i>U. graciosus</i>检测到的种群扩张现象相符，但与<i>U. ornatus</i>的种群情况不符。
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个体；而携带异种线粒体的雄性个体，其体重与体长的相关性也与携带同种线粒体的雄性个体存在显著差异。
上述变化表明，携带异种线粒体的个体可能存在选择劣势，这与“有害等位基因更易在扩张种群中留存”的理论预期相符。