Plasticidade comportamental e morfológica em Aegla longirostri (Decapoda: anomura)

Abstract

This study was divided in two papers, which addressed the antipredator behavior and sexual selection in Aegla longirostri. To evaluate the Aegla longirostri antipredator behavior we performed three experiments subdivided in two treatments each. In the first experiment the animals were fasting for a week; they had 20 minutes to move in an experimental aquarium with food and shelter, firstly with no risk treatment and, after a week, they were exposed to treatment with predation risk (the risk consisted of a crushed conspecific in water). In the second experiment, they were not fasting and were submitted to both treatments. In the third experiment, we tested the behavior of prey relative to the presence of a fish known to be a natural Aegla predator. Data showed that individuals chose to keep their foraging efforts, even with risk or not. However, in treatments with risk signaling there was a balance in the actions because they also looked for shelter. However the time spent with feeding was bigger than with sheltering. The animals strongly responded to the cues of conspecifics, sheltering more, suggesting that the cue is recognized as a real threat of predation. This boldness against predation threat can be related to bigger benefits gained by these individuals, that increase their fitness, including: partners, shelters and food. In the second article, we verified whether the A. longirostri chelipeds are sexually selected traits (SST), by analyzing: 1) if sexes invest differently in chelipeds size and shape; 2) if male chelipeds of four populations differ in size and shape and 3) if chelipeds show greater variation than the second pereiopod. To investigate sexual dimorphism we used data of geometric morphometrics of chelipeds and we compared the centroid size (CS) between sexes using Wilcoxon test, the shape using MANOVA and interactions between chelipeds and CS using ANCOVA. To compare male chelipeds of four populations, we used ANOVA to analyze differences of CS and MANOVA to compare the shapes. PCA and Relative warps were used to verify greater trends in shape variation. Lastly, we used traditional morphometrics to compare the variation between sexual traits (chelipeds) and a non-sexual trait (pereiopod), using ANOVA. The results showed that the right chelipeds do not differ between sexes, but the left chelipeds do, and males invest differently between their chelipeds, but females do not. Males of four populations differ in their chelipeds and pereiopods, and traditional morphometrics shows that SST are more variable than the pereiopod, but do not differ from each other. These results indicated that left cheliped is a SST, because there is a clear investment only from males in this appendage, the shape differing accordingly to the environment competition where they live. Furthermore, SST are highly condition dependent and vary much more than non-sexually selected traits, what was corroborated in this study.