Resumo O estudo dos aspectos populacionais e reprodutivos providenciam informações sobre a estrutura ecológica das populações naturais. Este estudo teve como objetivo caracterizar aspectos populacionais e reprodutivos de Hyalella palmeirensis de uma lagoa do sul do Brasil. Os anfípodos foram amostrados mensalmente (agosto/2012 a julho/2013) por uma pessoa com o auxílio de puçá por 20 minutos. Fêmeas ovígeras e casais em comportamento pré-copulatório foram individualizados no campo. Um total de 12.325 indivíduos foram amostrados, sendo 1.421 machos, 6.983 fêmeas (incluindo 215 fêmeas ovígeras) e 3.921 juvenis. Machos pareados e não pareados são significativamente maiores em tamanho do que as fêmeas. Houve uma correlação positiva entre o tamanho do corpo (CC) de machos e fêmeas pareados. Machos e fêmeas apresentaram distribuição bimodal. A proporção sexual total favoreceu as fêmeas, e estas foram mais frequentes em quase todos os meses. Fêmeas ovígeras e casais em pré-cópula foram amostrados ao longo do ano, mas com elevada frequência no inverno e outono, respectivamente, caracterizando uma reprodução sazonal. Os juvenis foram amostrados ao longo do ano, com maior intensidade na primavera. A fecundidade média foi de 19,6 ± 4,34 ovos. Não houve redução no número de ovos durante o desenvolvimento embrionário. Os resultados observados em H. palmeirensis demonstram que esta espécie possui uma dinâmica populacional e reprodutiva muito similar a outras espécies de Hyalella já analisadas no sul do Brasil. Além disto, apesar de H. palmeirensis ocorrer num ambiente com influência antrópica (cultivo de soja), sua população está conseguindo se manter na área, com reprodução e recrutamento na maioria dos meses do ano..

Abstract The study of population and reproductive traits provides information about the ecological structure of natural populations. This study aimed to characterize dynamics and reproductive traits of Hyalella palmeirensis from a natural pond from southern Brazil. The amphipods were sampled monthly (August 2012 to July 2013) by a person with the aid of a hand net for 20 minutes. Ovigerous females and pre-copulatory pairs were individualized in the field. A total of 12,325 individuals were sampled, being 1,421 males, 6,983 females (including 215 ovigerous females) and 3,921 juveniles. Paired and unpaired males were significantly greater in size than females. There was a positive correlation between body size (CL) of paired males and females. Males and females showed bimodal distribution. Total sex ratio favored females, and these were more frequent in almost all months. Ovigerous females and precopulatory pairs were found throughout the year, but with high frequency in winter and autumn, respectively, characterizing a seasonal reproduction. Juveniles were sampled throughout the year, with greater intensity in the spring. The mean fecundity was 19.6 ± 4.34 eggs. No reduction in the number of eggs was observed during embryonic development. The results observed in H. palmeirensis demonstrate that this species has a population and reproductive dynamics very similar to other species of Hyalella already analyzed in southern Brazil. Moreover, it can be seen that although the H. palmeirensis occurs in an environment with anthropic influence (soy cultivation,) the population is managing to remain in the area, with reproduction and recruitment in most months of year.

Abstract Two recently described amphipods species from southern Brazil, Hyalella georginae Streck and Castiglioni, 2017 and Hyalella gauchensis Streck and Castiglioni, 2017, had their population structures characterized by sex, females’ ovigerous condition, cephalothorax length (mm), size-class frequency distribution, sex-ratio, reproductive period, and recruitment. The specimens were collected with a dip net from a stream source (H. georginae) and from a water reservoir (H. gauchensis) in the Palmeira das Missões municipality, state of Rio Grande do Sul, Brazil, from August 2012 to July 2013 (12 months). Both species showed a bimodal frequency distribution for total and seasonal size classes, with males larger than females. Overall, the sex ratio favored females when analyzed monthly and seasonally. Ovigerous females were recorded throughout the year, with higher frequency in spring (H. georginae) and summer (H. gauchensis), characterizing a seasonal reproduction. Both species showed continuous recruitment, with greater intensity in the spring. The population structure of these two Hyalella species had similar features, showing continuous recruitment and seasonal reproduction related to their life-history strategies, which promote adaptations to their habitat.