Published online by Cambridge University Press: 20 July 2015
The present study tests hypotheses about sexual dimorphism in body size and morphology versus differential mating behaviours of three male ontogenetic stages (typus, intermedius and robustus morphotypes) of the hingebeak shrimp Rhynchocinetes durbanensis Gordon using canonical discriminant analysis. There is strong sexual dimorphism in this species, in that robustus morphotypes are greater in size and with larger appendages (extended third maxillipeds and major [first] chelipeds) than females. As typus males grow bigger in size, their third maxillipeds and major chelipeds become proportionately larger than those of females, and the numbers of corneous spines on the terminal segment of the maxillipeds are reduced. Although there is no sexual dimorphism in body size between typus and intermedius males and females, the robustus males are often substantially larger than females. During mating and spermatophore transfer, all male morphotypes performed similar behaviours (touching, overlapping and holding), but only intermedius and robustus morphotypes appeared to fertilize the broods of the females successfully. Robustus males were faster in approaching as well as mating with receptive females than subordinate males. When mating with robustus males, females spawned more quickly than after mating with typus and intermedius males. Additionally, the time taken for spermatophore transfer by typus males was longer. Rejection by females during the initial approach by typus males often resulted in unsuccessful spermatophore attachment. Results of this study suggest a dominance hierarchy in R. durbanensis similar to certain other rhynchocinetid species in which females appear to prefer mating with the larger robustus males.