The importance of color and body size for reproductive decision making by males and females of the giant river prawn, Macrobrachium rosenbergii (de Man, 1879) (Decapoda, Caridea, Palaemonidae).

The selection and expression of conspicuous colorations in animals is often related to anti-predation strategies and sociosexual communication. The giant river prawn, Macrobrachium rosenbergii (de Man, 1879) is a species with three male morphotypes that vary in claws' coloration and the size of the animals. It has been suggested that male reproductive quality might be associated to their coloration, but evidence is still conflicting. In addition, a possible communication function of orange patches, that occupies a large portion of egg-bearing females' cephalothorax, has never been investigated before. For that matter, in this study, we evaluated the importance of visual cues for reproductive decision making by males and females of the giant river prawn. Through two-choice discrimination experiments, we verified whether: 1) females would be equally attracted to the presence of males expressing different claw colorations and body sizes; 2) female reproductive status and body size would influence males' decision making. Under the tested experimental conditions, females predominantly chose larger over smaller males, while males showed no significant preference for any kind of female. It is possible that body size is one of the cues that females use to identify males' morphotype. The choice of larger males could provide greater protection for females against harassment by other males. Further studies should employ visual cues in combination with chemical ones for a better understanding of mate choice in this species.