Morphometric variation in allopatric populations of Aegla platensis (Crustacea: Decapoda: Anomura): possible evidence for cryptic speciation

Aegla platensis is a freshwater crustacean species that forms a nonmonophyletic group, which may indicate that the taxon is composed of cryptic species. Our objective was to test if allopatric populations of A. platensis differ in carapace shape, aiming to clarify the species situation. We used a geometric morphometric approach to analyze the carapace shape of 11 populations of A. platensis, four from Argentina and seven from Brazil. Our results showed that all the populations differ significantly in carapace shape, except two populations from Argentina and two from Brazil. The Argentinean and Brazilian populations formed two separate groups and were separated by high values of shape distance. This suggests the existence of reproductive isolation between the populations from the two groups. Shape distances between populations within each country were lower. Allopatric populations of A. platensis may be isolated from each other by the difficulty of migration, leading to interruption of gene flow and differentiation in carapace shape.