Abstract: The aim of this study was to characterize the reproductive strategies of a population of Hyalella bonariensis from southern Brazil. Pairing success, reproductive period of males and females, fecundity, and body size at the onset of reproduction were evaluated. Animals were sampled four times (August 2012, October 2012, January 2013, and April 2013) with the 250 µm-mesh dip net during 20 minutes by only one person. In the field, precopulatory pairs and ovigerous females were individualized. In the laboratory, cephalothorax length (CL) were measured and eggs and juveniles were removed from the females' marsupium and counted. The mean CL of paired males and females was significantly higher than that of non-paired males and females. A sexual dimorphism in body size was observed in the population - both paired and non-paired males were larger than females. Probably larger males have a higher probability of losing females during precopulatory behavior. A significant correlation was observed between the size of paired males and females - larger males often paired with larger females and smaller males paired with smaller females (r = 0.81). The pairing success of males increased with body size and we can assume that males from all size classes are able to find mates. The pairing success of females was independent of body size - paired and non-paired females had similar mean CL. The reproductive success increased with body size in males and females, and was more evident in males. Females from the largest size classes had null reproductive success. The idea that larger females can produce more eggs but might have a lower probability of finding a mate than smaller females was corroborated by our results. Therefore, smaller females have higher pairing success because they are capable of mating with a higher percentage of males. The estimated mean fecundity of H. bonariensis was 17.4 (± 3.89) eggs/juveniles. Our results are similar to those of other species of Hyalella from Brazil.
Resumo: Este trabalho teve por objetivo caracterizar as estratégias reprodutivas de uma população de Hyalella bonariensis no sul do Brasil, avaliando o sucesso de pareamento, o período reprodutivo de machos e fêmeas, a fecundidade e o tamanho corporal dos indivíduos durante a reprodução. Para isso foram realizadas quatro amostragens (Agosto/2012, Outubro/2012, Janeiro/2013 e Abril/2013) utilizando-se uma rede de mão, com malha de 250 µm, durante 20 minutos por um coletor. Em campo, os casais e as fêmeas ovígeras foram individualizados e em laboratório os mesmos foram mensurados quanto ao comprimento do cefalotórax (CC) (mm) e os ovos ou juvenis encontrados dentro do marsúpio foram contados. O CC médio dos machos e fêmeas pareados foi significativamente superior ao dos machos e fêmeas não pareados. Um dimorfismo sexual no tamanho corpóreo foi observado na população - ambos machos pareados e não pareados foram maiores do que as fêmeas. Aparentemente os machos maiores têm uma maior probabilidade de perder fêmeas durante o comportamento precopulatório. Foi observada correlação positiva entre o tamanho dos machos e fêmeas que foram encontrados formando casais - machos maiores geralmente pareiam com fêmeas maiores e machos menores com fêmeas menores (r=0,81). O sucesso de pareamento dos machos aumentou com o tamanho corpóreo e podemos assumir que os machos de todas as classes de tamanho são capazes de encontrar parceiras sexuais; entretanto, o sucesso de pareamento das fêmeas não depende do tamanho das mesmas, sendo que as fêmeas pareadas e não pareadas apresentaram CC médio semelhante. O sucesso reprodutivo da espécie aumentou com o tamanho corpóreo em machos e fêmeas, sendo mais pronunciado nos machos. As fêmeas pertencentes às maiores classes de tamanho apresentaram sucesso reprodutivo nulo. Os resultados suportam a ideia que as fêmeas grandes poderiam ter uma baixa probabilidade de encontrar parceiro para formar par pré-copulatório, quando comparada às fêmeas de tamanhos inferiores, apesar das fêmeas maiores serem mais fecundas. Neste sentido, as menores fêmeas possuem um sucesso de pareamento maior, pois elas são capazes de copular com uma elevada proporção de machos. A fecundidade média da espécie foi estimada em 17,4 (± 3,89) ovos/juvenis. Os resultados observados no presente trabalho assemelham-se aos encontrados para outras espécies do gênero já analisadas no sul do Brasil.
There are 68 known species of Hyalella worldwide, with 23 occurring in Brazil. The state of Rio Grande do Sul, Southern Brazil, has the largest diversity of the genus in the country, with nine species recorded. The current study aimed to describe two new species of Hyalella from state of Rio Grande do Sul, both of them in the Northwest region of the state, one found in a small spring and another in an artificial pond. Hyalella georginae n. sp. presents several clusters of simple setae on antenna 2, maxilliped very slender, gnathopod 2 dactylus not reaching the lobe of propodus, pleopods rami with short plumose setae and a peculiar pattern of setae on uropods and telson. Hyalella gauchensis n. sp. presents antenna 2 with few setae, maxilliped very slender, gnathopod 2 dactylus reaching the lobe of propodus and pleopods rami with long plumose setae. From this work, the number of Hyalella species found in Brazil increases to 25 and 70 for the genus.
Amphipoda , Animals , Brazil
A new species of the freshwater amphipod Hyalella Smith, 1874 is described for the plateau of the Itatiaia National Park, located between the states of Minas Gerais and Rio de Janeiro, southeastern Brazil. This is the first Brazilian species of Hyalella found at more than 2,200 meters of altitude. The specimens were found in a small stream, buried under rocks, in the higher area of the Park. The main morphological characteristics that differentiate the new species are the extreme reduction of the size of the uropod 3, absence of apical setae on telson, absence of comb-scales on gnatopods 1 and 2, absence of curved seta on inner ramus of uropod 1 and sternal gills tubular on pereonites 3 to 7. The new species presents similarities with some cave species of the genus, apparently being troglophile and that is the process of adaptation to the hypogean habitat. The importance of creating new protected areas for the conservation of Hyalella in Brazil is discussed.
Amphipoda , Altitude , Animals , Brazil , Fresh Water , Parks, Recreational
The freshwater crustaceans from the order Amphipoda occur mainly in cold and temperate climates. However, in the tropics, these animals can be more abundant in subterranean environments, where the temperatures are milder than in surface. Despite being accepted that the number of species of freshwater amphipods in South America is lower when compared to other regions, recent descriptions have shown that its diversity is certainly underestimated. In this study, a new species of the genus Hyalella is described for Brazil, the fourth troglobiotic species of Hyalella for the country and the sixth in the world. The new species was found on the epikarst of a cave in São Paulo state, Southeastern Brazil. Besides, the new species shows typical characteristics from organisms adapted to the subterranean environments, a pattern also observed in the other troglobiotic species of the genus.
Amphipoda/anatomy & histology , Amphipoda/classification , Animal Distribution , Animal Structures/anatomy & histology , Animals , Brazil , Caves , Ecosystem , Female , Male
