Applied Zoology, Faculty of Biology, Technische Universität Dresden, D-01062 Dresden, Germany
Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
J Exp Biol. 2019 Jun 19;222(Pt 12):jeb206136. doi: 10.1242/jeb.206136.
Attachment to surfaces is a major aspect of an animal's interaction with the environment. Consequently, shaping of the attachment system in relation to weight load and substrate is considered to have occurred mainly by natural selection. However, sexual selection may also be important because many animals attach to their partner during mating. The two hypotheses generate opposing predictions in species where males are smaller than females. Natural selection predicts that attachment ability will scale positively with load, and hence body size, and so will be larger in females than males. Sexual selection predicts attachment forces in males will be larger than those in females, despite the males' smaller size because males benefit from uninterrupted copulation by stronger attachment to the female. We tested these predictions in the common bedbug , a species in which both sexes, as well as nymphs, regularly carry large loads: blood meals of up to 3 times their body weight. By measuring attachment forces to smooth surfaces and analysing fixed copulating pairs and the morphology of attachment devices, we show that: (i) males generate twice the attachment force of females, despite weighing 15% less; (ii) males adhere to females during copulation using hairy tibial adhesive pads; (iii) there are more setae, and more setae per unit area, in the pads of males than in those of females but there is no difference in the shape of the tarsal setae; and (iv) there is an absence of hairy tibial attachment pads and a low attachment force in nymphs. These results are consistent with a sexually selected function of attachment in bedbugs. Controlling sperm transfer and mate guarding by attaching to females during copulation may also shape the evolution of male attachment structures in other species. More generally, we hypothesise the existence of an arms race in terms of male attachment structures and female counterparts to impede attachment, which may result in a similar evolutionary diversification to male genitalia.
动物与环境的相互作用主要体现在对表面的附着上。因此，附着系统的形成与体重和基质有关，这被认为主要是通过自然选择实现的。然而，性选择也可能很重要，因为许多动物在交配时会附着在它们的伴侣身上。这两个假设在雄性比雌性小的物种中产生了相反的预测。自然选择预测，附着能力将与负载（即身体大小）呈正相关，因此雌性的附着能力将大于雄性。性选择预测，尽管雄性体型较小，但由于雄性通过更强的与雌性的附着而获得不间断的交配，雄性的附着力将大于雌性的附着力。我们在普通床虱中测试了这些预测，在这种物种中，两性以及若虫都经常携带大量的负载：高达其体重 3 倍的血餐。通过测量光滑表面的附着力，分析固定交配对以及附着装置的形态，我们表明：（i）尽管体重轻 15%，但雄性产生的附着力是雌性的两倍；（ii）雄性在交配时使用毛状胫骨粘性垫附着在雌性身上；（iii）雄性胫骨粘性垫上的刚毛数量更多，单位面积的刚毛数量也更多，但跗节刚毛的形状没有差异；（iv）若虫没有毛胫骨附着垫，附着力也较低。这些结果与性选择在床虱附着中的功能一致。在交配时附着在雌性身上来控制精子转移和配偶保护，也可能塑造其他物种中雄性附着结构的进化。更普遍地，我们假设存在一个关于雄性附着结构和雌性附着结构的军备竞赛，以阻止附着，这可能导致类似的雄性生殖器的进化多样化。
