Reproductive anatomy and receptivity of the female Cyrtograpsus angulatus (Brachyura: Varunidae): Implications for the mating system

Abstract

The study of the functional anatomy of the female reproductive organs of Brachyura is often used in the classification and establishment of phylogenetic relationships. Besides, it allows us to draw inferences about the reproductive strategies and mating systems of crabs. Using histology and scanning electron microscopy we assessed the reproductive biology of Cyrtograpsus angulatus females by studying: the vulvae morphology, the receptive period duration, the spawning capacity and its relation to the seminal receptacle weight or carapace width, and the anatomy of the seminal receptacle. The vagina was of the concave type with an operculate vulva whose hinge became mobile when the female was receptive. The presence of striae in the vulvae hinge were related to the carapace width and maturity stage. Receptivity occurred during the intermolt period and lasted from 5 to 7 days. The duration of receptivity was independent of the seminal receptacle weight. Large females had seminal receptacles full of sperm and more frequently spawned a brood of eggs compared to small females. The seminal receptacle showed a threshold filling capacity. The histological anatomy of the seminal receptacle corresponds to the general pattern described for other Brachyura. A ventral connection of the ovary to the seminal receptacle was found. The presence of an oviduct valve at the junction of the ovary and the seminal receptacle was evident in non receptive females, but not evident in receptive ones. The seminal receptacle contained an unstructured mass of sperm with no evidence of separate ejaculates. As a result, a female centered competitive mating system is suggested in this species.