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.

线粒体序列的进化速率与线粒体基因组大小均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被提出，用以解释该类差异。本研究采用47种线虫（Nematoda）的公开线粒体DNA（mtDNA）基因组序列，对其中三类假说开展检验：1）寿命依赖选择假说（longevity-dependent selection）、2）功能约束假说（functional constraints）以及3）复制竞争假说（race for replication）。研究未发现体型（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关联，因此几乎未为首个假说提供有效支持证据。依据终宿主类型（变温宿主 vs. 恒温宿主）划分的不同热环境寄生线虫类群，其蛋白质进化速率并无显著差异，故第二个假说也未获得足够的支持证据。然而本研究发现，寄生于恒温动物的线虫的线粒体基因组（mitogenome）显著小于寄生于变温动物的线虫类群，这为复制竞争假说提供了有力支持。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，其线粒体DNA长度变异模式与各自宿主呈现出相似的特征。