Occurrence of male morphotypes in the freshwater prawn Macrobrachium acanthurus Wiegmann, 1836 (Decapoda, Palaemonidae)
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This study tested the hypothesis of the existence of male morphotypes in Macrobrachium acanthurus, a species of recognized economic potential, with an extensive geographic distribution. The collections occurred on eight occasions between July 2016 and March 2018 at seven points along the Jequitinhonha River, state of Bahia, Brazil. The identification of male morphotypes occurred through morphological and morphometric analyses. In total, 297 males were collected. The carapace length (CL) ranged from 4.6 to 41.81 mm, with a size at onset of maturity estimated at 11.85 mm. The morphological and morphometric analyses confirmed our hypothesis with the distinction of three morphotypes: M1, M2, and M3. M1 was characterized by males with chelipeds similar to those of females: relatively small, with tiny spines and without pubescence in the dactylus; M2 males had chelipeds larger than those of M1, as well as larger and denser spines, with little pubescence in the dactylus; and M3 individuals had considerably more robust chelipeds, very prominent spines and a thick layer of pubescence when compared to those of the previous morphotype. Our results suggest a social hierarchy where M1 is subordinate, M2 subdominant, and M3 the dominant morphotype. However, behavioural studies are needed to confirm this.