Reproductive strategies of a population of a freshwater amphipod (Crustacea, Amhipoda, Hyalellidae) from southern Brazil

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.

摘要：本研究旨在表征巴西南部阿根廷钩虾（Hyalella bonariensis）种群的繁殖策略。本研究评估了配对成功率、雌雄个体的繁殖周期、繁殖力以及繁殖起始时的体型大小。研究人员于2012年8月、2012年10月、2013年1月及2013年4月共开展4次采样，由单人使用孔径250 µm的捞网采集20分钟。野外现场将预配对个体与抱卵雌虾单独分离。实验室环节中，研究人员测量了样本的头胸甲长（cephalothorax length, CL），并从雌虾的育幼囊中取出卵与幼体进行计数。配对雌雄个体的平均头胸甲长显著高于未配对个体。该种群存在体型性二态——无论是否处于配对状态，雄性体型均大于雌性。推测体型更大的雄性在预配对行为过程中失去配偶的概率更高。观察到配对雌雄个体的体型存在显著相关性：体型较大的雄性通常与体型较大的雌性交配，小型雄性则与小型雌性交配（相关系数r = 0.81）。雄性的配对成功率随体型增大而提升，由此可推测所有体型等级的雄性均有机会找到配偶。雌性的配对成功率与体型无关——配对与未配对雌性的平均头胸甲长无显著差异。雌雄个体的繁殖成功率均随体型增大而提升，该趋势在雄性中更为显著。体型最大等级的雌性繁殖成功率为零。本研究结果证实了“体型更大的雌性虽可产出更多卵粒，但相较于小型雌性，其找到配偶的概率更低”这一假说。因此，小型雌性拥有更高的配对成功率，因为它们可与比例更高的雄性完成交配。阿根廷钩虾的平均繁殖力估算值为17.4（±3.89）枚卵/幼体。本研究结果与巴西境内其他钩虾属（Hyalella）物种的相关研究结果一致。