Data from: Female social preference for males that have evolved via monogamy: evidence of a trade-off between pre- and post-copulatory sexually selected traits?

When females mate with multiple males both pre- and post-copulatory sexual selections occur. It has been suggested that females benefit from polyandry when better-quality males are successful in sperm competition and sire high-quality offspring. Indeed, studies of experimental evolution have confirmed that sperm competition selects for both increased ejaculate quality and elevated offspring viability. Fewer investigations have explored whether these fitness benefits are evident beyond early life-history stages. Here, I used house mice (Mus domesticus) from selection lines that had been evolving for 25 generations under either polygamy or monogamy to test whether females preferred males from lines that had evolved with sperm competition. Males from the polygamous lines had previously been shown to achieve a fitness advantage under semi-natural conditions, deeming them to be of high genetic quality and leading to the a priori expectation that females would prefer males that had evolved with sperm competition compared with males that had not. Contrary to expectation, the data showed that sexually receptive females spent more time associating with males from the monogamous lines. This unexpected but interesting result is discussed in relation to sperm competition theory that predicts a trade-off between male investment in pre- and post-copulatory sexually selected traits.

当雌性与多个雄性交配时，交配前性选择（pre-copulatory sexual selection）与交配后性选择（post-copulatory sexual selection）均会发挥作用。有研究指出，当高质量雄性在精子竞争（sperm competition）中胜出并产下优质后代时，雌性可从一妻多夫制（polyandry）中获益。事实上，实验进化（experimental evolution）研究已证实，精子竞争可选择出提升射精质量（ejaculate quality）与后代存活力（offspring viability）的相关性状。目前少有研究探讨这类适合度收益（fitness benefits）是否会在生命史早期阶段之外依然显著。本研究以经历25代多配制（polygamy）或单配制（monogamy）演化的小家鼠（Mus domesticus）选择品系为实验对象，旨在检验雌性是否更偏好那些在精子竞争环境下演化而来的雄性。过往研究已证实，多配制品系的雄性在半自然条件（semi-natural conditions）下具备更高的适合度优势（fitness advantage），这表明其拥有较高的遗传质量（genetic quality），因此我们先验预期（a priori expectation）雌性会更偏好经历精子竞争演化的雄性，而非未经历该过程的雄性。但与预期相反，实验数据显示，处于性接受期的雌性会花费更多时间与单配制品系的雄性共处。针对这一意外却颇具研究价值的结果，本文结合雄性在交配前与交配后性选择相关性状上的投资存在权衡（trade-off）的精子竞争理论展开了讨论。