Preferência por cores e importância de pistas visuais e químicas para a interação sociossexual no camarão Macrobrachium rosenbergii

Abstract

The prawn Macrobrachium rosenbergii is a species of great economic importance. There are three male morphotypes in the species: small males can transform into orange claw males and these into blue claw males. There is little information about the sensory ecology of the species. Thus, this research analyzed the preference of the prawns for different colors of shelters in juveniles and adults, the importance of visual cues for mate choice in males and females, and the relative importance of visual and chemical cues for mate location in females. To analyze the preference for colors of shelters, we first modeled how the prawns would visualize different colors that could be used in the production of the shelters, in order to use colors that would allow us to assess whether the choice of the animals is based on chromaticity or brightness. Subsequently, we inserted the prawns in an aquarium containing shelters with the colors that we defined for the analysis of the attraction of the animals to them. Juveniles preferred the blue shelter and based the decision on the chromaticity of the shelters while adults preferred the darker gray shelters and showed an aversion to the lighter gray shelter, basing the decision on brightness. To analyze the importance of visual cues for mate choice, we first photographed the prawns and then created stimuli that corresponded to the prawns on a black background. We modified in Photoshop the color of the claws of the males, the color of the ovary of femalels visualized through the cephalothorax and the size of the prawns. We analyzed the preference of males for females of different sizes and reproductive status and the preference of females for males of different sizes and males with blue or orange claws introducing photographs on opposite sides of the aquarium. We also verified if females would be equally attracted to the photograph of the male and to the male himself present in an adjacent aquarium. Males did not show greater preference for any photograph of the female. Females did not show greater preference for males with blue or orange claws or for the real male or its photograph. However, they preferred the enlarged photograph to the diminished photograph of the male. To analyze the relative importance of male visual and chemical cues for attraction of the females, we used photograph of the male as a visual stimulus and water from the aquarium with the male as a chemical stimulus. We analyzed the attraction of females to males when only chemical cues were present, when chemical and visual cues were present on the same side of the aquarium, and when chemical and visual cues were present on opposite sides of the aquarium. Females were only attracted when there were chemical and visual cues present on the same side of the aquarium. Thus, we conclude that visual cues are used by the prawns in different contexts, such as when choosing shelters and, in the case of females, when choosing mates. Chemical cues were also important, allowing, along with visual cues, males to be located by females. Our results allow a better understanding of the sensorial ecology of the species and the improvement of the cultivation of these animals.