Some decapod species have intraspecific morphological variations that result in distinct adult morphotypes that influence the population structure, social dominance, and reproduction of the population. Here we investigated whether this differentiation into morphotypes occurs in adult males of Macrobrachium brasiliense, through the analysis of relative growth and morphology. Specimens were collected in the region of Uberlândia, Minas Gerais state, southeastern Brazil. Seven dimensions of each male were measured: carapace length (CL), ischium length, merus length, carpus length, propodus length, dactylus length, and major cheliped length. Principal component analysis, clustering, and discriminant analyses were used to identify possible morphotypes. The analysis of relative growth was employed to estimate the growth patterns of body structures (dependent variables) in relation to the CL (independent variable). Two morphotypes were identified: Mirim, which has less developed chelipeds (23.31 ± 3.08 mm) with fewer spines, and Açu, which has larger chelipeds (41.39 ± 8.14 mm) with many well‐developed spines, especially in the merus. Most morphometric relationships differed significantly (p < .01) between the two morphotypes. The chelipeds were useful characters for the identification of the morphotypes of M. brasiliense, corroborating previous descriptions of the genus. We provide a detailed description of the main macroscopic characteristics that differed between morphotypes, which will enable their identification in future studies. Our results contribute to the knowledge of the population biology of M. brasiliense and should be considered in future investigations, since the presence of these male morphotypes probably influences the reproductive biology and population ecology of the species.

The main objective of this study was to estimate the morphological sexual maturity of Macrobrachium brasiliense (Heller, 1862) and to analyze the relative growth of the species. During one year of sampling, from July 2012 to June 2013, 199 specimens were collected in a stream located in a Cerrado biome, in the Triângulo Mineiro region, state of Minas Gerais. Once identified and sexed, the length of the carapace, the length of the segments of the chelipeds (ischium, merus, carpus, propodus and dactyl) and width of the pleura were measured (mm). The maximum and mean sizes of the carapace length measured 20.5 mm (Mean: 9.6 ± 4.2 mm) and 20.1 mm (Mean: 7.7 ± 3.4 mm) for males and females, respectively. The propodus length for males, and the pleura width for females, were used for the classification of the specimens into juvenile and adult, using K-means analysis and discriminant analysis. The relative growth of the species was also evaluated through covariance analysis for all structures (ANCOVA, α = 0.05). In females, the growth of most structures occurred equally between juveniles and adults, with the exception of the merus and pleura structures. On the other hand, the growth of almost all structures of males differed between juveniles and adults. Only the carpus and the pleura growth were similar. We also estimated the size at onset of morphological sexual maturity at 8.64 mm CL for males (CL50% r = 1.71) and 8.03 mm CL for females (CL50% r = 0.07). Our results contribute to the understanding of some important questions related to the reproductive biology of M. brasiliense. We noted that males grow differently from females and become the largest individuals in the population, resulting in a sexual dimorphism. Such sexual dimorphism might promote the development of the temporary mating guarding behavior, a reproductive strategy very important for caridean shrimps.

During the ontogenetic development of crustaceans, the relative growth of some structures may change, especially during the transition from juvenile to adult. This study describes the relative growth of body structures of Macrobrachium iheringi, and provides information on its population dynamics, such as structure, fecundity, and morphological sexual maturity. The sampling of M. iheringi was carried out in “Ribeirão da Hortelã”, in Botucatu (SP, Brazil). The length of the carapace (CL), abdomen (AL), and ischium (IL), merus (ML), carpus (CrL), propodus (PpL), and dactyl (DcL) of the second right pereopod were measured. In addition, the width of the second abdominal pleura (PW) and propodus height (PpH) were included in analyses. The relationships that best demonstrated the changes in the allometric coefficient were CL vs PpL in males and females. The CL, in which males and females reach morphological sexual maturity, was estimated as 13.3 mm and 11.1 mm, respectively. The sex-ratio differed from the expected 1:1 and was skewed towards females. Precipitation and temperature influenced the abundance of different demographic classes. Macrobrachium iheringi has few but large eggs, which is expected since this species has an abbreviated larval development. Based on these results, we conclude that the propodus are good indicators of the size at onset of morphological sexual maturity. In addition, important information was obtained on the biology of M. iheringi, including its life cycle pattern, reproduction and influence of abiotic factors.

Abstract:The main objective of this study was to analyze the choice behavior of adult individuals of Macrobrachium brasiliense (Decapoda, Palaemonidae) with regard to different substrates and microhabitats in two distinct experiments. The first experiment offered the prawns three samples of substrates with different granulometries: fine sand, coarse sand, and gravel. The second experiment offered three types of microhabitats: aquatic macrophytes, wood fragments, and rocks. In general, the prawns chose the fine substrate, to a significant extent (ANOVA, p < 0.01). In the microhabitat experiment, the prawns selected the wood fragments (ANOVA, p < 0.01). In general, these results show that substrates with fine sand and microhabitats composed of fragments of wood might provide direct benefits for M. brasiliense, such as protection against predators and food availability through biofilm formation.

Animal weapons are generally complex systems composed of more than one structure. A crab’s claw, for instance, is composed of a dactyl (a movable finger) and a propodus (where the muscle resides). Any weapon feature that increases winning probability also increases an individual’s fitness, meaning that all moving parts of a weapon will be under the same selective force—increasing their integration. By comparing weapons to homologous structures not used for fighting, we can test whether fighting increases morphological integration. Here, we tested that hypothesis by comparing the right (non-fighting) and left (fighting) claws of males of Aegla. First, we tested if the shape and size of the propodus and dactyl differed between claws. Then, we compared the degree of morphological integration. We showed that claws differed in their shape and size, but both claws showed similarly high levels of integration. This pattern can occur if selection favours an adequate squeeze on both claws, even though squeezing performance might differ between the claws. Nevertheless, the dactyl is important in determining the integration of a claw but it has been greatly ignored in crustacean studies and its study might increase our knowledge of claw evolution.

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The present study aims to describe the population structure of the freshwater prawn Macrobrachium brasiliense and to analyze whether it varies seasonally, with emphasis on abundance variation by demographic category, sex ratio, size, and morphotypes, in addition to analyzing the recruitment period and its relationship with rainfall. The collections of M. brasiliense were carried out in a Cerrado region, in the southeastern region of Brazil. The population structure was analyzed according to the size, sex, and life stage. The density of morphotypes was calculated by the proportion of each morphotype in the population. Male and female prawns were more abundant in the largest and smallest size classes, respectively. The juvenile morphotype was the most abundant among males (45.9 %), while the "Mirim" and "Açu" morphotypes occurred in a similar proportion (27.87 % and 26.23 %, respectively). The population structure varied significantly between seasons (dry and rainy). A relationship of juvenile abundance with rainfall was recorded. The recruitment period was observed between the end of the rainy season and the beginning of the dry season, while adults were more abundant at the end of the dry season and the beginning of the rainy season. The information in this study contributes to the knowledge of the influence of seasonality and

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