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

Abstract

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.

Relative growth and morphological sexual maturity of the caridean prawn Macrobrachium villosimanus (Tiwari, 1949) (Decapoda: Palaemonidae)

“…This finding is consistent with other studies (Berglund, 1981; Boschi, 1974; Cartaxana, 2003; Kim, 2005; Koshy, 1969) that reported males of the palaemonid species are generally larger, with a highly evident sexual dimorphism. Several other studies reported this size predominant is frequently observed in species of Macrobrachium Spence Bate, 1868, mainly being associated with size and form of the chelipeds of adult males (Boschi, 1974; Nogueira et al, 2023; Nogueira, Mossolin, et al, 2022; Rossi et al, 2022; Santos et al, 2022). Bauer et al (2014) reported that, for many caridean species, males are significantly larger than females for ‘temporary mate guarding’ or ‘neighborhood of dominance’ mating systems, and that they use hypertrophied weapons (major chelipeds, third maxillipeds) to fight for and defend females.…”

Morphological Diversity of Different Male Morphotypes of Giant Freshwater Prawn Macrobrachium rosenbergii (De Man, 1879)

“…This could explain why the OBC males' bodies do not develop as much as in other larger morphotypes. The OBC is a special male individual, with a major cheliped more developed than the normal BC type [51].…”

“…The characteristics of each morphotype's chelipeds impart a distinct role in the population and the environment in which it lives. The differential pattern in cheliped size, color, and spination certainly has an impact on the intraspecific interactions as well as the male's interaction with the environment [5,51]. The use of spines to differentiate male morphotypes is common in Macrobrachium species [5,10], as well as in other genera, such as Rhynchocinetes [45,46].…”