RESUMO
Sperm transfer in spiders is achieved by copulatory organs on the male pedipalps (i.e., copulatory bulbs), which can be simple or a complex set of sclerites and membranes. During copulation, these sclerites can be used to anchor in corresponding structures in the female genitalia by means of hydraulic pressure. In the most diverse group of Entelegynae spiders, the retrolateral tibial apophysis clade, the female role in the coupling of genitalia is considered rather passive, as conformational changes of the female genital plate (i.e., the epigyne) during copulation are scarce. Here, we reconstruct the genital mechanics of two closely related species belonging to the Aysha prospera group (Anyphaenidae) that bear a membranous, wrinkled epigyne and male pedipalps with complex tibial structures. By using microcomputed tomography data of a cryofixed mating pair, we reveal that most of the epigyne remains greatly inflated during genital coupling, and that the male tibial structures are coupled to the epigyne by the inflation of a tibial hematodocha. We propose that a turgent female vulva is a prerequisite for the genital coupling, which could implicate a female control device, and that the structures from the male copulatory bulb have been functionally replaced by tibial structures in these species. Furthermore, we show that the conspicuous median apophysis is maintained in spite of being functionally redundant, posing a puzzling situation.
Assuntos
Aranhas , Masculino , Feminino , Animais , Microtomografia por Raio-X , Sêmen , Genitália , Genitália Feminina/diagnóstico por imagem , Copulação , Genitália Masculina/diagnóstico por imagemRESUMO
Genital traits are among the fastest to evolve, and the processes that drive their evolution are intensively studied. Spiders are characterized by complex genitalia, but the functional role of the different structures during genital coupling is largely unknown. Members of one of the largest spider groups, the retrolateral tibial apophysis (RTA) clade, are characterized by a RTA on the male palp, which is thought to play a crucial role during genital coupling. However, the RTA was lost in several families including the species-rich wolf spiders (Lycosidae) leading to the hypothesis that the genital coupling is achieved by alternative mechanisms. Here, we investigate the genital interactions during copulation in the wolf spider Agalenocosa pirity (Zoicinae) on cryofixed mating pairs using electron, optical and X-ray microscopy and compare our findings with other lycosids and entelegyne spiders. We found an unprecedented coupling mechanism for lycosid spiders involving the palea and a membranous cuticle folding adjacent to the epigynal plate. Additionally, we show an uncommon coupling between the median apophysis and the contralateral genital opening, and confirmed that the terminal apophysis acts as functional conductor, as previously hypothesized for males of Zoicinae. Phylogenetic mapping of RTA indicated that the basal tibial process found in Agalenocosa is a secondary acquisition rather than a modified RTA.