The reproductive anatomy of male freshwater prawnsMacrobrachium australiense(Holthuis, 1890) in southeast Queensland

Male reproductive system of the freshwater prawn Macrobrachium brasiliense (Decapoda: Palaemonidae): Notes on spermatophore formation and sperm count

Studies on the morphology of the reproductive system are essential for understanding the reproduction processes of species or even within genera or families. The present study aimed to describe the functional morphology of the male reproductive system, spermatophore formation, and sperm count of Macrobrachium brasiliense. The anatomy of the reproductive system consists of a pair of testes from which the vasa deferentia (VD) starts, extending to the fifth pair of pereopods. The VD is divided into three regions: proximal (PVD), middle (MVD), and distal (DVD). In the PVD, there is a prominent fold, the typhlosole, formed by columnar cells. The typhlosole disappears in the MVD, being incorporated into one of the faces of the VD wall, identified by its simple columnar epithelium while the remainder of the vessel wall is formed by squamous or simple cubic epithelium. Columnar cells produce type-II and III secretion. The epithelium in the DVD is made up only of cubic cells. Low sperm concentration was observed when compared to other species of the genus Macrobrachium. In conclusion, the typhlosole and columnar epithelium are responsible for the asymmetric spermatophore, which seems the pattern of Macrobrachium that is probably shared with other caridean shrimps.

Is there a trade-off between sperm production and sexual weaponry in the Amazon River prawn Macrobrachium amazonicum (Heller, 1862)?

The Amazon River prawn Macrobrachium amazonicum shows populations with four well-defined morphotypes in males. Dominant males of morphotypes green claw 1 (GC1) and green claw 2 (GC2) have large bodies and chelipeds and a higher reproductive success in comparison with the submissive morphotypes - translucent claw (TC) and cinnamon claw (CC). However, recently, some populations of the species do not have dominant morphotypes. Here, we compared the patterns of spermatic production and concentration among morphotypes and populations with three different phenotypes: (i) large-size amphidromous prawns, and (ii) large-size ("i" and "ii" with dominant morphotypes) and (iii) small-size hololimnetic prawns (without morphotypes). We described the spermatogenesis and the histochemical features of vasa deferentia (VD) and evaluated the relationship between the investment in spermatic production and sexual weapons acquisition in males of different phenotypes. The spermatic production and concentration in populations with four morphotypes were similar between morphotypes. The exception was the CC morphotype in which males had the seminiferous tubules filled with spermatocytes and low spermatic concentration. The spermatogenesis, spermiogenesis, and VD structure were not different among the studied phenotypes and populations. The seminal fluid of M. amazonicum is comprised by glycoproteins and by concentric layers of secretions of types I, II (basophilic), and III (eosinophilic). We could infer that males of dominant morphotypes allocate a higher amount of energy to the development of strong sexual weapons at the expense of the energy allocated to the reproductive system during the sequential growth. Inversely, small-size males direct more energy toward the spermatic production and transference at the expense of sexual weapons. Therefore, there is a clear trade-off between the investment in the gonadal and sexual weapons development in males of M. amazonicum.

Morphology of the male reproductive system of freshwater prawn Macrobrachium carcinus (Decapoda, Caridea): Functional and comparative aspects

Testes and vasa deferentia are parts of the male reproductive system of decapod crustaceans. Both organs show morphological differences among decapod species in terms of anatomical and histological patterns reflecting the diversity of this group. Describing these features may assist in systematics, phylogenetics, and studies of reproductive behavior, especially for species of commercial interest, such as Macrobrachium carcinus, a native American species that, unusually for this genus, has no precopulation courting behavior. This study aims to describe the reproductive morphology and spermatogenesis of the male freshwater prawn M. carcinus. The male reproductive system of this species consisted of lobed testes connected to the vasa deferentia. The testis of M. carcinus was divided into several lobules. Each lobule was formed by a cluster of germ cells surrounded by connective tissue and nurse cells. This microscopic anatomy and histology of the testicular histoarchitecture has been described for many species of Decapoda and may represent a derived design of the testes. Unlike that in other decapod species, spermatogenesis proceeds in short transitory phases that produce spermatozoa at high concentrations and frequencies, corroborating the uncommon male reproductive behavior of this species. In the spermatic pathway, the lobules develop and fuse before releasing spermatozoa from the testes; however, this process has not been observed in decapods, yet. The neutral compounds secreted by the vas deferens are important for sperm nutrition as females secrete a substance for spermatophore adhesion during reproduction. This study presents different features and dynamics of the spermatogenic process in the male reproductive system of M. carcinus that have not yet been presented in the literature for decapods.