Data from: You are where you live: parasitic nematode mitochondrial genome size is associated with the thermal environment generated by hosts

There exists remarkable interspecific variation in mitochondrial sequence evolution rates and in mitochondrial genome sizes. A number of hypotheses based on the forces of mutation and selection have been proposed to explain this variation. Among such hypotheses, we test three: 1) the ‘longevity-dependent selection’, 2) the ‘functional constraints’ and 3) the ‘race for replication’ hypotheses, using published mtDNA genomic sequences of 47 Nematoda species. We did not find any relationship between body size (used as a proxy for longevity) and genome size or the substitution rate of protein sequences, providing little evidence for the first hypothesis. Parasitic species from different thermal habitats, as determined by their definitive host type (ectothermal vs. endothermal), did not differ in their rates of protein evolution. Therefore, little support was obtained for the second hypothesis. However, we revealed that mitogenomes of parasites of endotherms were significantly smaller than those of parasites of ectotherms, supporting the race for replication hypothesis. As mitochondrial genomes of endothermal animals are usually more compact than those of ectothermal animals, intriguingly, nematode parasites of endotherms and ectotherms exhibit similar patterns of mtDNA length variation to their hosts.

线粒体序列进化速率与线粒体基因组大小存在显著的种间差异。目前已有诸多基于突变与选择压力的假说，旨在解释这一现象。本研究利用已发表的47种线虫动物门（Nematoda）物种的线粒体DNA（mitochondrial DNA，mtDNA）基因组序列，对其中三类假说开展检验：1）‘寿命依赖选择’（longevity-dependent selection）假说，2）‘功能约束’（functional constraints）假说，以及3）‘复制竞赛’（race for replication）假说。
研究未发现体型大小（作为寿命的替代指标）与基因组大小或蛋白质序列替换速率之间存在任何关联，这为第一种假说提供的支持十分有限。根据终宿主类型（变温动物vs.恒温动物）划分的不同热环境栖息地的寄生线虫类群，其蛋白质进化速率并无显著差异，因此第二种假说也未获得足够的实验支撑。
不过，本研究发现寄生于恒温动物的线虫线粒体基因组显著小于寄生于变温动物的线虫，这一结果支持了‘复制竞赛’假说。值得注意的是，由于恒温动物的线粒体基因组通常较变温动物更为紧凑，寄生于恒温动物与变温动物的线虫类寄生虫，其线粒体DNA长度变异模式与其宿主呈现出高度相似的特征。