Sexual maturity and ontogenetic shape variations in the freshwater anomuran crab,Aegla uruguayana(Decapoda, Aeglidae)

Summary Sexual maturity is marked by morphological changes in freshwater anomuran crabs. Specific modifications to the dorsal and ventral forms of the cephalothorax and the coxa of the fifth pereiopod in males indicate reproductive maturity. Here, we describe changes in cephalothorax and coxa that develop during sexual maturity in the freshwater anomuran, Aegla uruguayana. To evaluate shape, the dorsal and ventral cephalothorax and the coxa of the fifth pereiopod of this species were digitally photographed. With specific landmarks as reference points, the crab shape was analyzed for each of the three body parts. Relative warps analysis were performed revealing shape differences among the size forms and sexes. The dorsal cephalothorax and the coxa of the fifth pereiopod are different between juveniles, males and females. Individuals of 12–16 mm cephalothorax length have a shape closest to the “consensus configuration” in the population, which is correlated with the onset of sexual maturity in males. Additionally, there are size and shape differences among juveniles and adult individuals of the population. The shape differences were observed mainly in the coxa of the fifth pereiopod of males, as the length of the sexual tube increases during sexual development. Moreover, sexual maturity occurred simultaneously with cephalothorax and coxa development. These results show that multiple cohorts of A. uruguayana coexist in the population and that individuals can have a different reproductive capacity within the active sexual population.