School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
Evolution. 2010 Sep;64(9):2746-57. doi: 10.1111/j.1558-5646.2010.01022.x.
Understanding the selection pressures shaping components of male reproductive success is essential for assessing the role of sexual selection on phenotypic evolution. A male's competitive reproductive success is often measured in sequential mating tests by recording P1 (first mating male) and P2 (second mating male) paternity scores. How each of these scores relates to a male's overall fitness, for example, lifetime reproductive success is, however, not known. This information is needed to determine whether males benefit from maximizing both P1 and P2 or by trading off P1 against P2 ability. We measured P1, P2, and an index of lifetime reproductive success (LRS(i) , a male's competitive reproductive success measured over 12 days) for individual male Drosophila melanogaster. We found no evidence for phenotypic correlations between P1 and P2. In addition, whereas both P1 and P2 were associated with relative LRS(i) , only P2 predicted absolute LRS(i) . The results suggest that P2 was most closely linked to LRS(i) in the wild-type population studied, a finding which may be common to species with strong second male sperm precedence. The study illustrates how P1 and P2 can have differing relationships with a male's overall reproductive success, and highlights the importance of understanding commonly used measures of sperm competition in the currency of fitness.
了解塑造雄性生殖成功的选择压力对于评估性选择对表型进化的作用至关重要。雄性的竞争生殖成功通常通过记录 P1（第一次交配的雄性）和 P2（第二次交配的雄性）亲权得分，在连续交配试验中进行衡量。然而，这些得分中的每一个与雄性的整体适应度（例如，终生生殖成功）的关系并不清楚。需要这些信息来确定雄性是否受益于最大化 P1 和 P2，还是通过权衡 P1 与 P2 能力来实现。我们测量了个体黑腹果蝇雄性的 P1、P2 和终生生殖成功指数（LRS(i)，在 12 天内衡量雄性的竞争生殖成功）。我们没有发现 P1 和 P2 之间存在表型相关性的证据。此外，虽然 P1 和 P2 都与相对 LRS(i)相关，但只有 P2 可以预测绝对 LRS(i)。研究结果表明，在研究的野生型群体中，P2 与 LRS(i)的联系最为密切，这一发现可能在具有强烈第二雄性精子优势的物种中很常见。该研究说明了 P1 和 P2 如何与雄性的整体生殖成功有不同的关系，并强调了理解常用的精子竞争衡量标准在适应度货币中的重要性。
