Vahed Karim, Gilbert James D J, Weissman David B, Barrientos-Lozano Ludivina
Department of Biological and Forensic Sciences, College of Life and Natural Sciences, University of Derby, Kedleston Rd, Derby, DE22 1GB, United Kingdom.
Evolution. 2014 Jul;68(7):2052-65. doi: 10.1111/evo.12421. Epub 2014 May 21.
The function of nuptial gifts has generated longstanding debate. Nuptial gifts consumed during ejaculate transfer may allow males to transfer more ejaculate than is optimal for females. However, gifts may simultaneously represent male investment in offspring. Evolutionary loss of nuptial gifts can help elucidate pressures driving their evolution. In most katydids (Orthoptera: Tettigoniidae), males transfer a spermatophore comprising two parts: the ejaculate-containing ampulla and the spermatophylax-a gelatinous gift that females eat during ejaculate transfer. Many species, however, have reduced or no spermatophylaces and many have prolonged copulation. Across 44 katydid species, we tested whether spermatophylaces and prolonged copulation following spermatophore transfer are alternative adaptations to protect the ejaculate. We also tested whether prolonged copulation was associated with (i) male cercal adaptations, helping prevent female disengagement, and (ii) female resistance behavior. As predicted, prolonged copulation following (but not before) spermatophore transfer was associated with reduced nuptial gifts, differences in the functional morphology of male cerci, and behavioral resistance by females during copulation. Furthermore, longer copulation following spermatophore transfer was associated with larger ejaculates, across species with reduced nuptial gifts. Our results demonstrate that nuptial gifts and the use of grasping cerci to prolong ejaculate transfer are functionally equivalent.
婚飞礼物的功能引发了长期的争论。在射精转移过程中消耗的婚飞礼物可能使雄性转移的精液量超过对雌性最适宜的量。然而，礼物可能同时代表雄性对后代的投资。婚飞礼物的进化丧失有助于阐明推动其进化的压力。在大多数螽斯（直翅目：螽斯科）中，雄性传递一个精包，精包由两部分组成：含有精液的壶腹和精包叶——一种凝胶状礼物，雌性在射精转移过程中食用。然而，许多物种的精包叶已经减少或没有，并且许多物种的交配时间延长。在44种螽斯物种中，我们测试了精包叶以及精包转移后的长时间交配是否是保护精液的替代适应方式。我们还测试了长时间交配是否与（i）雄性尾须适应有关，有助于防止雌性脱离，以及（ii）雌性抵抗行为有关。正如预测的那样，精包转移后（而非之前）的长时间交配与婚飞礼物减少、雄性尾须功能形态的差异以及雌性在交配过程中的行为抵抗有关。此外，在婚飞礼物减少的物种中，精包转移后的交配时间越长，精液量越大。我们的结果表明，婚飞礼物和利用抓握尾须来延长射精转移在功能上是等效的。
