Male reproductive systems of <i>Macrobrachium pantanalense</i> Dos Santos, Hayd &amp; Anger, 2013 and <i>M. amazonicum</i> (Heller, 1862) (Decapoda: Caridea: Palaemonidae): new insights into the morphology of the spermatozoa of decapod crustaceans

Abstract Studies on the male reproductive system (MRS) and the ultrastructure of spermatozoa may provide key information about the reproductive biology and phylogenetic relationships between crustacean species. We describe the functional anatomy of the MRS and the ultrastructure and morphometry of spermatozoa of two closely related freshwater shrimps, Macrobrachium pantanalenseDos Santos, Hayd &amp; Anger, 2013 (MP) and M. amazonicum (Heller, 1862) (MA) to detect possible interspecific differences. We introduce geometric morphometrics as a new tool to analyze the caridean spermatozoa for closely related species. The main differences in the anatomy of the MRS of the two species are related to the positive reaction to acid polysaccharides in the distal region of the vas deferens of M. pantanalense and the shape and size of their spermatozoa. SEM and TEM analyses confirmed variations in the shape of spermatozoa of both species and this variation was found to be significant by the use of geometric morphometrics. These tools can highlight differences among caridean shrimps, mainly in cases of closely related species. It becomes clear that MA and MP, despite being two closely related taxa that evolved separately relatively recently, are distinctly different taxa with differences found mainly in the spermatozoa.