Evolutionary Biology Centre/Evolutionary Biology, University of Uppsala, Uppsala, Sweden.
J Evol Biol. 2011 Jan;24(1):111-20. doi: 10.1111/j.1420-9101.2010.02142.x. Epub 2010 Oct 28.
The evolutionary sequence of events in the evolution of reproductive barriers between species is at the core of speciation biology. Where premating barriers fail, post-mating barriers, such as conspecific sperm precedence (CSP), gamete incompatibility (GI) and hybrid inviability (HI) may evolve to prevent the production of (often) costly hybrid offspring with reduced fitness. We tested the role of post-mating mechanisms for the reproductive isolation between two sunfish species [bluegill (BG) Lepomis macrochirus and pumpkinseed (PS) Lepomis gibbosus] and their first-generation hybrids. Performing in vitro sperm competition experiments, we observed asymmetric CSP as main post-mating isolation mechanism when BG and PS sperm were competing for PS eggs, whereas when sperm from both species were competing for BG eggs it was HI. Furthermore, hybrid sperm--although fertile in the absence of competition--were outcompeted by sperm of either parental species. This result may at least partly explain previous observations that natural hybridization in the study system is unidirectional.
物种间生殖隔离的进化事件序列是物种形成生物学的核心。在交配前障碍失败的情况下，交配后障碍，如同种精子优先（CSP）、配子不相容（GI）和杂种不育（HI），可能会进化以防止产生（通常）具有较低适应性的昂贵杂种后代。我们测试了两种太阳鱼物种（蓝鳃太阳鱼 [BG] Lepomis macrochirus 和南瓜籽太阳鱼 [PS] Lepomis gibbosus）及其第一代杂种之间的生殖隔离的交配后机制的作用。通过进行体外精子竞争实验，我们观察到当 BG 和 PS 精子竞争 PS 卵子时，不对称 CSP 是主要的交配后隔离机制，而当两种物种的精子竞争 BG 卵子时，是 HI。此外，杂种精子——尽管在没有竞争的情况下是可育的——但仍被来自任一亲本性别的精子所竞争淘汰。这一结果至少可以部分解释之前的观察结果，即在研究系统中，自然杂交是单向的。
