Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Nedlands, WA 6009, Australia.
Heredity (Edinb). 2011 May;106(5):869-75. doi: 10.1038/hdy.2010.130. Epub 2010 Oct 20.
Ejaculates comprise multiple and potentially interacting traits that determine male fertility and sperm competitiveness. Consequently, selection on these traits is likely to be intense, but the efficacy of selection will depend critically on patterns of genetic variation and covariation underlying their expression. In this study, I provide a prospective quantitative genetic analysis of ejaculate traits in the guppy Poecilia reticulata, a highly promiscuous live-bearing fish. I used a standard paternal half-sibling breeding design to characterize patterns of genetic (co)variation in components of sperm length and in vitro sperm performance. All traits exhibited high levels of phenotypic and additive genetic variation, and in several cases, patterns of genetic variation was consistent with Y-linkage. There were also highly significant negative genetic correlations between the various measures of sperm length and sperm performance. In particular, the length of the sperm's midpiece was strongly, negatively and genetically correlated with sperm's swimming velocity-an important determinant of sperm competitiveness in this and other species. Other components of sperm length, including the flagellum and head, were independently and negatively genetically correlated with the proportion of live sperm in the ejaculate (sperm viability). Whether these relationships represent evolutionary trade-offs depends on the precise relationships between these traits and competitive fertilization rates, which have yet to be fully resolved in this (and indeed most) species. Nevertheless, these prospective analyses point to potential constraints on ejaculate evolution and may explain the high level of phenotypic variability in ejaculate traits in this species.
精液包含多个潜在相互作用的特征，这些特征决定了雄性的生育能力和精子竞争力。因此，对这些特征的选择很可能是强烈的，但选择的效果将取决于决定其表达的遗传变异和协变模式。在这项研究中，我对虹鳉（Poecilia reticulata）的精液特征进行了前瞻性的定量遗传分析，虹鳉是一种高度滥交的胎生鱼类。我使用标准的父系半同胞繁殖设计来描述精子长度和体外精子性能的组成部分的遗传（协变）模式。所有特征都表现出高水平的表型和加性遗传变异，在某些情况下，遗传变异模式与 Y 连锁一致。各种精子长度和精子性能的测量值之间也存在高度显著的负遗传相关性。特别是，精子中段的长度与精子的游动速度呈强烈、负相关和遗传相关，这是精子竞争力的重要决定因素，在这种和其他物种中也是如此。精子长度的其他组成部分，包括鞭毛和头部，与精液中活精子的比例（精子活力）独立且负相关。这些关系是否代表进化上的权衡，取决于这些特征与竞争受精率之间的精确关系，而这些关系在这种（甚至大多数）物种中尚未完全解决。尽管如此，这些前瞻性分析表明了对精液进化的潜在限制，并可能解释了该物种精液特征中高水平的表型可变性。
