Esfandi Kambiz, He Xiong Z, Wang Qiao
School of Agriculture and Environment, Massey University, Private Bag 11222, Palmerston North, New Zealand.
The New Zealand Institute for Plant & Food Research Limited, Private Bag 11600, Palmerston North, New Zealand.
Curr Zool. 2020 Jun;66(3):285-292. doi: 10.1093/cz/zoz048. Epub 2019 Oct 11.
Theories predict that in polyandrous species, the focal male should increase sperm allocation per mate in the presence of rivals to gain greater share of paternity, but in the presence of additional mates, he should reduce sperm allocation per mate to save sperm for insemination of more mates. However, empirical findings are often inconsistent and reasons behind are unclear. Furthermore, many studies use copulation duration as an estimate of the number of sperm transferred. Yet, empirical evidence for such assumption is largely lacking. Here, we used a sperm heteromorphic insect whose males produce two types of sperm, eupyrenes (fertile) and apyrenes (nonfertile), to test these postulations. We allowed focal males to detect chemical and acoustic but no tactile cues from rivals or additional mates both before and during mating and measured copulation duration and sperm allocation in successive copulations. We demonstrate that males transfer significantly more eupyrenes per mate in the presence of rivals and that the sperm allocation pattern persists in successive copulations under this condition. However, males do not adjust apyrene allocation in response to rivals probably because apyrenes play a relatively minor role in male reproductive success. Contrary to a previous study, focal males do not respond to additional mates most likely due to the lack of tactile cues in the present study. We reveal that sperm allocation is not a function of copulation duration in this insect for spermatophore formation and delivery occupy most of copulation duration and sperm transfer is complete near the end of copulation.
理论预测，在一妻多夫制物种中，处于竞争环境下的焦点雄性应该增加对每个配偶的精子投入，以获得更大的父权份额，但在有额外配偶的情况下，他应该减少对每个配偶的精子投入，以便为更多配偶的授精节省精子。然而，实证研究结果往往不一致，背后的原因尚不清楚。此外，许多研究将交配持续时间作为精子转移数量的估计指标。然而，这种假设的实证证据在很大程度上是缺乏的。在这里，我们使用了一种精子异形昆虫，其雄性产生两种类型的精子，即真核精子（可育）和无核精子（不育），来检验这些假设。我们让焦点雄性在交配前和交配期间都能检测到来自竞争对手或额外配偶的化学和声学信号，但没有触觉信号，并测量了连续交配中的交配持续时间和精子分配情况。我们证明，在有竞争对手的情况下，雄性对每个配偶转移的真核精子显著更多，并且在这种情况下，精子分配模式在连续交配中持续存在。然而，雄性不会因竞争对手而调整无核精子的分配，这可能是因为无核精子在雄性繁殖成功中发挥的作用相对较小。与之前的一项研究相反，焦点雄性对额外配偶没有反应，最有可能是因为本研究中缺乏触觉信号。我们发现，在这种昆虫中，精子分配不是交配持续时间的函数，因为精包的形成和传递占据了大部分交配持续时间，而精子转移在交配接近尾声时完成。
