Knief Ulrich, Forstmeier Wolfgang, Kempenaers Bart, Wolf Jochen B W
Division of Evolutionary Biology, Faculty of Biology, Ludwig Maximilian University of Munich, Planegg-Martinsried 82152, Germany.
Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, Seewiesen 82319, Germany.
R Soc Open Sci. 2021 Sep 1;8(9):211025. doi: 10.1098/rsos.211025. eCollection 2021 Sep.
The propulsion of sperm cells via movement of the flagellum is of vital importance for successful fertilization. While the exact mechanism of energy production for this movement varies between species, in avian species energy is thought to come predominantly from the mitochondria located in the sperm midpiece. Larger midpieces may contain more mitochondria, which should enhance the energetic capacity and possibly promote mobility. Due to an inversion polymorphism on their sex chromosome , zebra finches () exhibit large within-species variation in sperm midpiece length, and those sperm with the longest midpieces swim the fastest. Here, we test through quantitative real-time PCR in zebra finch ejaculates whether the inversion genotype has an effect on the copy number of mitochondrial DNA (mtDNA). We find that zebra finches carrying the derived allele (correlated with longer sperm midpieces) have more copies of the mtDNA in their ejaculates than those homozygous for the ancestral allele (shorter midpieces). We suggest downstream effects of mtDNA copy number variation on the rate of adenosine triphosphate production, which in turn may influence sperm swimming speed and fertilization success. Central components of gamete energy metabolism may thus be the proximate cause for a fitness-relevant genetic polymorphism, stabilizing a megabase-scale inversion at an intermediate allele frequency in the wild.
精子通过鞭毛运动实现推进，这对成功受精至关重要。虽然不同物种中这种运动产生能量的确切机制有所不同，但在鸟类中，能量被认为主要来自精子中段的线粒体。较大的中段可能含有更多的线粒体，这应该会增强能量产生能力，并可能促进精子的运动能力。由于其性染色体上存在倒位多态性，斑胸草雀（）的精子中段长度在种内存在很大差异，并且中段最长的精子游动速度最快。在此，我们通过对斑胸草雀射精样本进行定量实时PCR，来测试倒位基因型是否对线粒体DNA（mtDNA）的拷贝数有影响。我们发现，携带衍生等位基因（与较长的精子中段相关）的斑胸草雀，其射精样本中的mtDNA拷贝数比那些祖先等位基因纯合（中段较短）的个体更多。我们推测mtDNA拷贝数变异对三磷酸腺苷产生速率具有下游效应，进而可能影响精子的游动速度和受精成功率。因此，配子能量代谢的核心成分可能是一种与适应性相关的遗传多态性的直接原因，使得一个兆碱基规模的倒位在野外以中等等位基因频率稳定存在。
