Uhl Gabriele, Nessler Stefan Heinz, Schneider Jutta
Department of Neuroethology, Institute of Zoology, University of Bonn, Endenicher Allee 11-13, D-53115, Bonn, Germany.
Zoology (Jena). 2007;110(5):398-408. doi: 10.1016/j.zool.2007.07.003. Epub 2007 Sep 14.
Genitalia are among the fastest evolving morphological traits as evidenced by their common function as diagnostic traits in species identification. Even though the main function of genitalia is the successful transfer of spermatozoa, the presence of diverse structures that are obviously not necessary for this suggests that genitalia are a target of sexual selection. The male genitalia of many spider species are extremely complex and equipped with numerous sclerites, plates and spines whose functions are largely unknown. Selection on male genitalia may be particularly strong in sexually cannibalistic spiders, where mating success of males is restricted to a single female. We investigated the copulatory mechanism of the sexually cannibalistic orb weaving spider Argiope bruennichi by shock freezing mating pairs and revealed a complicated interaction between the appendices and sclerites that make up the male gonopods (paired pedipalps). The plate that covers the female genital opening (scape) is secured between two appendices of the male genital bulb, while three sclerites that bear the sperm duct are unfolded and extended into the female copulatory opening. During copulation, females attack and cannibalise the male and males mutilate their genitalia in about 80% of cases. Our study demonstrates that (i) genital coupling is largely accomplished on the external part of the female genitalia, (ii) that the mechanism requires an interaction between several non-sperm-transferring structures and (iii) that there are two predetermined breaking points in the male genitalia. Further comparative work on the genus Argiope will test if the copulatory mechanism with genital mutilation indeed is an adaptation to sexual cannibalism or if cannibalism is a female counter adaptation to male monopolisation through genital plugging.
生殖器是进化最快的形态特征之一，这在物种鉴定中作为诊断特征的常见功能中得到了证明。尽管生殖器的主要功能是成功转移精子，但存在各种显然并非必需的结构，这表明生殖器是性选择的目标。许多蜘蛛物种的雄性生殖器极其复杂，配备有众多的骨片、板和刺，其功能大多未知。在性食同类蜘蛛中，对雄性生殖器的选择可能特别强烈，在这类蜘蛛中，雄性的交配成功仅限于与单一雌性。我们通过对交配中的蜘蛛对进行速冻，研究了性食同类圆蛛Argiope bruennichi的交配机制，揭示了构成雄性生殖肢（成对的须肢）的附器和骨片之间复杂的相互作用。覆盖雌性生殖孔的板（scape）固定在雄性生殖球的两个附器之间，而带有输精管的三个骨片展开并延伸到雌性交配孔中。在交配过程中，雌性会攻击并吃掉雄性，并且在大约80%的情况下，雄性会自残其生殖器。我们的研究表明：（i）生殖器的耦合在很大程度上是在雌性生殖器的外部完成的；（ii）该机制需要几个非精子转移结构之间的相互作用；（iii）雄性生殖器中有两个预定的断裂点。对Argiope属的进一步比较研究将检验带有生殖器自残的交配机制是否确实是对性食同类的一种适应，或者食同类行为是否是雌性对雄性通过生殖器堵塞进行垄断的一种反适应。
