Seven ephemeral pools on the coastal plain of southern Brazil were found to be inhabited by three annual and 22 non-annual fish species. Two common annual species (Austrolebias minuano and Cynopoecilus fulgens) exhibited clear seasonal dynamics, with the appearance of young fishes in the austral autumn (May to June) and a decline in abundance over the seasonal cycle. The third annual species, Austrolebias wolterstorffii, was rare. No seasonal dynamics were observed in non-annual fishes. The relative abundance of non-annual fishes compared with annual fishes increased over the seasonal cycle, but they coexisted widely. The size structure of annual fishes suggested the presence of a single age cohort in most pools though a second age cohort was registered in one pool in August, coinciding with a large flooding. Strong sexual dimorphism in body size was found in C. fulgens throughout the seasonal cycle, while no sexual dimorphism in body size was found in A. minuano. Female-biased sex ratios were recorded in both common annual fish species in the last three sampling dates (in spring), but not during the first two sampling dates (in winter). The natural lifespan of annual fishes was <8 months. Annual fishes disappeared before habitat desiccation in half of the pools, while non-annual fishes were still present.

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Predation and population density have fundamental size-and sex-specific effects on individual survival and demographic parameters. Given the overlap and interactions between different age cohorts in natural populations, separating the factors related to differential survival and growth based on longitudinal field-collected data is problematic. Using a Neotropical annual fish (Austrolebias minuano) with a single age cohort per generation, we used replicated field enclosures to experimentally test the roles of avian predation and fish population density on survival and growth over adult lifespan. We found that mortality risk was higher in larger males and smaller females when predation was experimentally excluded. Exposure to avian predation eliminated this sex-specific effect of body size on survival. No overall sex difference in survival was found in the experiment, despite a female-biased sex ratio in natural populations. Individually based growth rates were highest in enclosures at low population density with no predation risk. Overall, we demonstrate that annual fish suffer high sex-dependent size-specific mortality that is more strongly related to predation than to density-dependent processes. This has important implications for our understanding of the evolution of senescence and other life history traits in annual fishes.

Questions: Are organic rice crops better than convention crops for aquatic plant conservation? We tested three hypotheses: (1) richness, diversity and biomass of aquatic macrophytes are higher in organic rice fields than in conventional ones;(2) aquatic macrophyte species composition in organic rice fields is more similar to that of natural wetlands than to conventional rice fields; and (3) aquatic macrophyte richness, diversity, biomass and species composition in natural wetlands will differ from those of organic and conventional rice fields.Location: Coastal plain of southern Brazil. Methods:We sampled macrophytes at four conventional crops, four organic crops and four natural intermittent wetlands. We sampled at six different times at each site throughout the rice cultivation cycle.Results: A total of 55 species was recorded in natural wetlands and 36 species in rice fields, with 23 found in conventional crops and 27 found in organic crops. The richness, biomass and species composition of macrophytes was similar in the two rice production systems and lower than that of natural wetlands over the cultivation cycle studied. Species composition of natural wetlands differed from that of rice crops mainly through the presence of hydrophytes and rushes.Conclusions: Some macrophyte species used rice crops as a complementary habitat, but diversity was lower and composition was different from that of natural wetlands. Both conventional and organic systems negatively impacted macrophyte biodiversity. However, the similar richness and biomass of plants in organic and conventional crops indicated that natural techniques with less impact could be efficient in reducing undesirable plant diversity in agricultural systems.

Oxidative stress plays an important role in the evolution of aging and life history. High investments in life-history traits and environmental conditions can be associated with increased oxidative stress and aging process. However, to date, most studies that investigated variations in oxidative status were performed with long-lived vertebrates. Studies with short-lived vertebrates in wild are nonexistent. Annual killifishes have the shortest lifespans among vertebrates and inhabit temporary ponds subject to large variations in environmental conditions. In this sense, we investigated whether the high investment in growth and reproduction in a short-lived vertebrate and the large variations in environment has any cost in susceptibility to oxidative stress. We assessed the seasonal variation and the environmental correlates of four different oxidative status markers (lipid peroxidation and activity of the antioxidant enzymes Superoxide Dismutase, Catalase and Glutathione S-Transferase) along the life cycle of wild individuals of the Neotropical annual fish Austrolebias minuano. Males showed reduction in all biomarkers (except proteins) along their life cycle, while females showed increased oxidative stress only in the growth period. In addition, we showed that water physicochemical parameters, habitat structure and presence of cooccurring killifish species influenced the seasonal variation of the biomarkers. A. minuano showed an efficient antioxidant system for most part of their life cycle (mainly in males), suggesting a well-developed oxidative stress regulation system. We also show that annual fish mortality (mainly in males) apparently is not related to oxidative stress. Thus, environmental factors should drive annual fish aging and mortality.