How can we stay together? ― A review of copulatory mechanics in entelegyne spiders

MICHALIK, P.; POY, DANTE; RAMÍREZ, M. J.; PIACENTINI, L. N.

Capital Federal (on line)

Congreso; VI Congreso Latinoamericano de Aracnología; 2020

Spider´s unique mating system is marked by a key challenge: how can their genital organs remain attached efficiently during copula? This apparently simple aspect of spider´s reproductive biology was tackled by an amazing variety of strategies, probably fueled by sexual selection. Here, we review copulatory mechanics in spiders in a phylogenetic context, identifying functional patterns at different taxonomic levels and detecting innovations, regularities and atypical coupling strategies. We focused on Entelegynae, the group of spiders where copulatory mechanics diversified most. Our review indicates that primary locking (i.e., the initial mechanical engaging of male and female genitalia that allows full expansion of the copulatory bulb) structures in males are located in the retrolateral margin of their pedipalps, and confirm that an ipsilateral insertion pattern (left embolus in left copulatory opening and vice versa) is the most common among entelegynes. Also, most araneoid males usually utilize combinations of their conductor, paracymbium or median apophysis to achieve primary locking in highly variable mechanisms. In contrast, males of the RTA clade generally use the RTA to that end, or a variety of bulb sclerites when the RTA is absent. For example, our results from species of Anyphaenidae lacking a RTA suggest that many species rely on their conductors to achieve primary locking, in a highly conserved manner. After full expansion, the final positioning of the copulatory bulb relative to the epigynum as well as the leading of the embolus into the copulatory duct are secured by a remarkable variety of structures in male and female organs. Our review highlights that, in spite of the impressive diversity of spider genitalia, generalizations about the basic functioning of it can be made at different taxonomic levels, and that high quality observations made over one (or few) species can be extrapolated, at some extent, to other related and morphologically homogeneous species.