Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman St., Box G-W, Providence, RI 02912, USA.
Mol Ecol. 2011 Nov;20(21):4503-20. doi: 10.1111/j.1365-294X.2011.05290.x. Epub 2011 Oct 10.
The physiological link between oxygen availability and mitochondrial function is well established. However, whether or not fitness variation is associated with mitochondrial genotypes in the field remains a contested topic in evolutionary biology. In this study, we draw on a population of the teleost fish, Fundulus heteroclitus, where functionally distinct subspecies hybridize, likely as a result of past glacial events. We had two specific aims: (i) to determine the effect of mtDNA genotype on survivorship of male and female fish under hypoxic stress and (ii) to determine the effect of hypoxic stress, sex and mtDNA genotype on gene expression. We found an unexpected and highly significant effect of sex on survivorship under hypoxic conditions, but no significant effect of mtDNA genotype. Gene expression analyses revealed hundreds of transcripts differentially regulated by sex and hypoxia. Mitochondrial transcripts and other predicted pathways were among those influenced by hypoxic stress, and a transcript corresponding to the mtDNA control region was the most highly suppressed transcript under the conditions of hypoxia. An RT-PCR experiment on the control region was consistent with microarray results. Effects of mtDNA sequence variation on genome expression were limited; however, a potentially important epistasis between mtDNA sequence and expression of a nuclear-encoded mitochondrial translation protein was discovered. Overall, these results confirm that mitochondrial regulation is a major component of hypoxia tolerance and further suggest that purifying selection has been the predominant selective force on mitochondrial genomes in these two subspecies.
氧可用性和线粒体功能之间的生理联系已得到充分证实。然而，在野外，适应度的变化是否与线粒体基因型有关，这在进化生物学中仍是一个有争议的话题。在这项研究中，我们利用了一种硬骨鱼，即虹鳉（Fundulus heteroclitus）的种群，其中功能不同的亚种杂交，可能是过去冰川事件的结果。我们有两个具体目标：（i）确定 mtDNA 基因型对雄性和雌性鱼类在缺氧应激下存活的影响；（ii）确定缺氧应激、性别和 mtDNA 基因型对基因表达的影响。我们发现了一个出乎意料的、高度显著的性别对缺氧条件下存活的影响，但 mtDNA 基因型没有显著影响。基因表达分析揭示了数百个受性别和缺氧调节的转录本。受缺氧应激影响的转录本包括线粒体转录本和其他预测途径，而对应于 mtDNA 控制区的转录本是在缺氧条件下受抑制程度最高的转录本。对控制区的 RT-PCR 实验与微阵列结果一致。mtDNA 序列变异对基因组表达的影响有限；然而，我们发现了 mtDNA 序列与核编码线粒体翻译蛋白表达之间的一个潜在重要的上位性。总的来说，这些结果证实了线粒体的调控是缺氧耐受的一个主要组成部分，并进一步表明，在这两个亚种中，纯化选择一直是线粒体基因组的主要选择力量。
