Abstract The Parapaguridae comprises hermit crabs that inhabit deep-water environments. In these environments, shell availability can be limited, mostly consisting of small and fragile-shelled gastropods. Thus, different strategies have evolved to mitigate this limited shell supply. Sympagurus dimorphus (Studer, 1883) lives in association with a zoanthid cnidarian that creates a pseudo-shell that grows with the hermit crab. In contrast, Oncopagurus gracilis (Henderson, 1888) inhabits small, calcified gastropod shells. Therefore, we selected these two species as models to test sexual dimorphism and shape patterns of their chelipeds and cephalothoracic shield, due to their different shelter acquisition methods. We photographed the animals and digitized the images to employ comparative geometric morphometric techniques. We tested the differences in shape between the sexes within each species, and also tested sexual size dimorphism based on centroid size. For O. gracilis, we found shape differences for the chelipeds and cephalothoracic shield, however, we only observed sexual size dimorphism for the chelipeds. For S. dimorphus, an inverse pattern was found, in which females presented more robust chelipeds, and sexual size dimorphism was present in which males were larger. These differences can be reasonably explained by their shelter acquisition methods, in which O. gracilis depends on small shells that limit growth, while S. dimorphus grows with its cnidarian pseudo-shell. The robustness found in the shape patterns may also be related to their behaviors, e.g., in addition to competition for shells, they also fight during mating. However, we emphasize that future studies with other populations of these species are needed for comparative purposes.

Resumen En el presente estudio se analizaron los parámetros de crecimiento y longevidad de machos y hembras de Macrobrachium brasiliense. Las muestras se obtuvieron mensualmente desde julio/2012 hasta junio/2013 en la región de Triângulo Mineiro, Minas Gerais, Brasil. Un total de 199 camarones adultos (97 machos, 102 hembras) fueron analizados y medidos según la longitud del caparazón (CL, mm). Los machos (9.64 ± 4.17 mm, CL) fueron más grandes que las hembras (7.7 ± 3.39 mm, CL). Las curvas de crecimiento para CL por el modelo de von Bertalanffy se describen mediante las ecuaciones: CL = 21.0 [1 - e -0.00446 (t)] para los machos y CL = 20.0 [1 - e -0.00454 (t)] para las hembras. Al comparar las curvas de crecimiento con la prueba tipo F, no hubo diferencias entre los coeficientes de crecimiento (K) de machos y hembras (GL22; F3.16 = 2.476; p = 0.088). La longevidad se estimó en 2.83 años para los machos y 2.78 años para las hembras. En general, la longevidad observada es similar a la de las especies de Macrobrachium.

Abstract Growth and longevity parameters of males and females of Macrobrachium brasiliense were analyzed. Sampling was carried out monthly from July 2012 to June 2013 in Triângulo Mineiro region, Minas Gerais, Brazil. A total of 199 adult prawns (97 males and 102 females) were analyzed and measured according to the carapace length (CL, mm). Males (9.64 ± 4.17 mm, CL) were larger than females (7.7 ± 3.39 mm, CL). CL growth curves by the von Bertalanffy model are described by the equations CL = 21.0 [1 - e -0.00446 (t)] for males and CL = 20.0 [1 - e -0.00454 (t)] for females. Comparison of the growth curves by performing the F-type test, showed that there was no difference between the growth coefficients (K) of males and females (GL22; F3.16 = 2.476; p = 0.088). Longevity was estimated as 2.83 years for males and 2.78 years for females. In general, the observed longevity is similar to that of other Macrobrachium species.

Abstract The aim of this study was to analyze the reproductive period, fecundity, egg size and reproductive output (RO) of a hololimnetic population of Macrobrachium amazonicum. The prawns were collected monthly, from May 2017 to April 2018, in a water reservoir isolated from river connections, in Severínia (20º49’31.92” S, 48º49’39.55” W), São Paulo, Brazil. Ovigerous females were preserved individually in 70% ethanol. The reproductive period was calculated based on the monthly percentage of ovigerous females. The egg mass was weighed and partially measured. The eggs were counted and classified according to the embryonic developmental stage. The reproductive output was calculated individually by dividing the dry weight of females without eggs by the mass of eggs. The reproductive period was continuous, with peaks in the dry season. Egg volume differed among stages and seasons (ANCOVA, p < 0.05), being larger in the rainy season. The reproductive output differed between seasons (rainy: 12.5 ± 4.8%; dry: 13.9 ± 5.4%, p < 0.05), as well as fecundity (rainy: 585 ± 304 eggs; dry: 613 ± 306 eggs, p < 0.05). We concluded that the reproductive traits of this population differ from those of other populations of M. amazonicum previously studied, and that these differences may be consequences of the isolation of this population.

Resumen El objetivo de este estudio fue analizar el período reproductivo, la fecundidad, el tamaño del huevo y el esfuerzo reproductivo (RO) de una población hololimnética de Macrobrachium amazonicum. Los camarones fueron recolectados mensualmente, de mayo de 2017 hasta abril de 2018, en un embalse aislado de las conexiones fluviales, en Severínia (20º49’31.92” S, 48º49’39.55” O), São Paulo, Brasil. Las hembras ovígeras fueron conservadas individualmente en etanol al 70%. El período reproductivo se calculó con base en el porcentaje mensual de hembras ovígeras. La masa de huevos se pesó y midió parcialmente. Los huevos se contaron y clasificaron de acuerdo con la etapa de desarrollo embrionario. El esfuerzo reproductivo se calculó individualmente dividiendo el peso seco de las hembras sin huevos por la masa de los huevos. El período reproductivo fue continuo, con picos en la estación seca. El volumen del huevo difirió entre las etapas y las estaciones (Ancova, p < 0.05), siendo mayor en la estación lluviosa. El esfuerzo reproductivo difirió entre las estaciones (lluviosa: 12.5 ± 4.8%; seca: 13.9 ± 5.4%, p < 0.05), así como la fecundidad (lluviosa: 585 ± 304 huevos; seca: 613 ± 306 huevos, p < 0.05). Concluimos que los rasgos reproductivos de esta población difieren de los de otras poblaciones de M. amazonicum estudiadas previamente, y que estas diferencias pueden ser consecuencias del aislamiento de esta población.