Shape variation of the prawn Macrobrachium jelskii (Palaemonidae: Decapoda) in the Neotropical semiarid drainages: an intra- and inter-basin investigation

The present study aims to show the intra- and inter-basin body-shape variations of the freshwater prawn Macrobrachium jelskii (Miers, 1877) in Brazilian Neotropical semiarid basins, quantifying relations to address if its occurrence is old and natural or recent and artificial (anthropic). We used a geometric-morphometric tool to explore patterns of shape variation of the cephalothorax, abdomen and cheliped regarding eco-evolutionary traces (sexual dimorphism, hydrodynamism and geographical isolation) among the drainages. The sexual shape dimorphism was observed in cephalothorax and abdomen of females, which presented more horizontally stretched than in males, possibly favouring gonadal development, vitellogenesis and egg attachment. No apparent hydrodynamic trend was observed in the morpho-space. Moreover, no consensus was shown in the morpho-space about the geographic isolation in semiarid basins regarding the three body-structure planes. However, the abdominal plane indicates a low population/basin structure, which can be an indirect reflection of variations of vitellogenesis in eggs modulated by environmental factors. Furthermore, morphometric variations show low phenotypic plasticity, which is supported by the literature, indicating a scenario of non-natural distribution.