An ancient indirect sex model: single and mixed patterns in the evolution of scorpion genitalia

PERETTI, A. V.

THE EVOLUTION OF PRIMARY CHARACTERS IN ANIMALS

OXFORD UNIVERSITY PRESS

Lugar: New York; Año: 2010; p. 218 - 248

Like many other arachnids, sperm transfer in scorpions involves complex behavior patterns: the male usually grasps the female with his claws, locates a suitable site, and deposits a sclerotized spermatophore. Then the male induces the female to pick up the sperm from the spermatophore, and the partners separate. There are two types of spermatophores: ?flagelliform? and ?lamelliform?. The former is exclusive to the basal family Buthidae and the latter occurs in the rest of the derived scorpion families. In this chapter functional morphology of spermatophores and some evolutionary changes of some reproductive traits in scorpions are reviewed. Scorpion spermatophores offer an interesting opportunity to contribute new data to explain the evolution of male genitalia. Three hypotheses as the most often quoted to explain the coevolution of male and female genitalia: lock-and-key, intersexual conflict over control of copulation (e.g., morphologically forced insemination) and sexual selection by cryptic female choice (e.g., with presence of internal courtship by male). Previous studies in scorpion genitalia indicated that genitalic stimulation may be a widespread mechanism and also suggested that different evolutionary processes could occur together (even in a single species). Observations of mating among closely related species indicate that the lock-and-key hypothesis cannot be accepted to explain spermatophore diversity. These observations also indicate the spermatophores are not generally equipped with structures that ?force? the female to perform sperm transfer as would appear if a male-female conflict over control of copulation was taking place. In addition, sperm competition is another evolutionary force that drives adaptations in male reproductive characters, including spermatophores and spermatozoa. Aside from the data supporting more one hypothesis than others and the many aspects waiting for further analyses, the available data in scorpions show an important fact: the coexistence of some different, and apparently opposing, hypotheses.