Hard-female mating in the brachyuran crab Thalamita prymna (Portunidae)

Abstract

Intermolt (hard shelled) female Thalamita prymna, including ovigerous females, were observed to mate both in the field (N=2) and laboratory (N=13). In the laboratory, intermolt males and females showed characteristic stalking and maneuvering behaviors prior to copulation, with copulation lasting 34.5±2.4 minutes (mean±SD). During a 20 month field survey, no guarding behavior or sperm plugs which are characteristic of portunid soft-female mating behavior were observed. A female reared in isolation to maturity over a 6 month period from an immature instar successfully mated during the intermolt stage and produced a fertile egg brood ten days after the single mating. From these observations, hard-female mating is concluded to be the principal mating strategy in T. prymna. Females of the congeneric species T. sima also mate during the intermolt and the contrasting mating behaviors of these 2 species are discussed.