MATE COMPETITION IN THE VELVET SWIMMING CRAB NECORA PUBER - EFFECTS OF PERCEIVED RESOURCE VALUE ON MALE AGONISTIC BEHAVIOR

Male velvet swimming crabs [Necora puber (L.)] were observed to engage in long and vigorous agonistic interactions to gain possession of a s exually receptive female. The role of agonistic behaviour in male mate competition in this species was examined by investigating the effect of the perceived presence of sexually receptive females on interaction s between males. Exposing male crabs to water conditioned by sexually receptive females resulted in prolonged interactions, with a greater i ncidence of potentially injurious behaviour than interactions between control crabs, exposed only to sea water. Male-conditioned water also resulted in more offensive behaviour, but these interactions were of s horter duration and not significantly different from sea water control s. Agonistic superiority was strongly correlated with contestant relat ive size when males were exposed to male-conditioned water or sea wate r, but not when exposed to female-conditioned water. Overall, the resu lts conformed with the general predictions of game theoretic models in relation to the influence of resource value on agonistic behaviour. C rabs were more persistent and probably incurred greater fitness costs in the perceived presence of a sexually receptive female, when interac tions may have been resolved on the basis of factors more closely rela ted to actual fighting ability than the relative body sizes of contest ants.