Different strategies and shapes: the relationship between mating system and sexual dimorphism in two freshwater prawn species

Caridean prawns show five different types of mating systems and may show specific morphological characters depending on the reproductive strategy, resulting in sexual dimorphism between males and females. The present study aimed to analyse the sexual dimorphism in the freshwater prawns Macrobrachium pantanalense and Macrobrachium iheringi, two species that presumably have different mating systems. Our predictions are that the pattern of sexual dimorphism shows differences between the species, which may be related to its mating system and sexual behavior. Sexual dimorphism was analysed by geometric morphometrics using the carapace (CA), second pleonal pleuron (SPP) and cheliped propodus (CP). The geometric morphometrics analysis showed differences between the sexes in the shape of CA and SPP of M. pantanalense. In M. iheringi, differences between sexes were observed only in the shape of SPP. The sexual dimorphism in the size of CA and CP diverged between the species, while in M. pantanalense the females showed the largest sizes, in M. iheringi the males showed the largest sizes. The patterns observed between size and shape of structures in each species reinforce the presence of relationships between mating system and sexual dimorphism in caridean prawn species. http://zoobank.org/urn:lsid:zoobank.org:pub:03DE0D3E-598A-46929771-79EA449D92EA