Population features, sexual dimorphism and handedness of the primary freshwater crab Trichodactylus cf. fluviatilis (Brachyura: Trichodactylidae) from southeastern Brazil

Recent molecular analyses characterized the freshwater crab Trichodactylus fluviatilis as a species complex. Considering this new scenario, studies about the population features are fundamental to understanding the biology of species belongs to this complex. We investigated the population from southeastern Brazil identify as Trichodactylus cf. fluviatilis, testing the hypotheses that sex ratio differs from the expected 1:1, and that the species shows sexual dimorphism in size, weaponry and body weight. The reproductive period and handedness were also investigated. Population features were determined based on the size-frequency distribution, gonadal development and sex ratio. Sexual dimorphism was analysed comparing the average size and the allometric coefficient. Handedness was verified according to the proportion of right and left chelipeds. Sex ratio skewed towards males and the reproduction was continuous. The sexual dimorphism in T. cf. fluviatilis was found in structures related to weaponry and reproduction. In weaponry, sexual dimorphism was demonstrated by robust chelipeds and high allometric values in males. In females, a high allometric was recorded to the abdomen, structure directly related to reproduction. The right-handedness was observed to the species. All these results contribute to a better understanding of the species’ life history.