Sperm morphology, adenosine triphosphate (ATP) concentration and swimming velocity: unexpected relationships in a passerine bird

The relationship between sperm energetics and sperm function is poorly known, but is central to our understanding of the evolution of sperm traits. The aim of this study was to examine how sperm morphology and ATP content affect sperm swimming velocity in the zebra finch Taeniopygia guttata. We exploited the high inter-male variation in this species and created extra experimental power by increasing the number of individuals with very long or short sperm through artificial selection. We found a pronounced quadratic relationship between total sperm length and swimming velocity, with velocity increasing with length up to a point, but declining in the very longest sperm. We also found an unexpected negative association between midpiece length and ATP content: sperm with a short midpiece generally contained the highest concentration of ATP. Low intracellular ATP is therefore unlikely to explain reduced swimming velocity among the very longest sperm (which tend to have a shorter midpiece).

精子能量代谢与精子功能之间的关联目前尚未得到充分阐明，却是我们理解精子性状演化的核心所在。本研究旨在探究斑胸草雀（Taeniopygia guttata）的精子形态与三磷酸腺苷（ATP）含量如何影响其精子游动速度。我们利用该物种极高的个体间变异，并通过人工选育增加具有极长或极短精子的个体数量，以此提升实验统计效力。研究发现，精子总长度与游动速度之间存在显著的二次曲线关系：随着长度增加，游动速度先上升至临界点，随后在极长精子中出现下降。我们还发现了一个意料之外的负相关关系：精子中段长度与ATP含量呈负相关，中段较短的精子通常拥有最高的ATP浓度。因此，细胞内ATP含量较低并不能解释极长精子（其中段通常较短）游动速度降低的现象。