Integrated morphometric and molecular analyses indicate three male morphotypes in the freshwater prawn Macrobrachium olfersii (Decapoda, Palaemonidae) along the Brazilian neotropical region

Males of Macrobrachium olfersii have a large cheliped (second pereiopod) with individual variations in shape and ornamentation, and they vary in size within and between populations. Some misidentification or doubts about taxonomic validity occur due to this morphological variability throughout their geographic distribution. We carried out a morphometric analysis to detect specific patterns and the potential occurrence of morphotypes in M. olfersii from different populations. Our data set included 52 females and 109 males collected in the Neotropical region, between the north and south limits of Brazilian territory, in coastal rivers from the states of Rio Grande do Norte, Bahia, Espírito Santo, Rio de Janeiro, São Paulo, Paraná and Santa Catarina. Body measurements were size standardized by allometric methods and explored by the principal component analysis (PCA) and non-hierarchical analysis of K-means clustering and canonical variate analysis (CVA). Our results suggested three distinct morphological groups (morphotypes) only for males in M. olfersii. Furthermore, the confirmation of monophyly of the different populations of M. olfersii was accomplished by sequences of 16S rDNA. Additional studies about relative growth in other populations and the analysis of the entire ontogenetic development of males in the laboratory will be important to complement the knowledge about morphotypes in this species.