Changes in food quality can dramatically impair zooplankton fitness, especially in eutrophic water bodies where cyanobacteria are usually predominant. Cyanobacteria are considered a food with low nutritional value, besides some species can produce bioactive secondary metabolites reported as toxic to zooplankton. Considering that cyanobacteria can limit survival, growth and reproduction of zooplankton, we hypothesized that the adverse effects of the dietary exposure of Daphnia species to saxitoxin-producing cyanobacteria depend on the relative abundance of nutitious food source in the diet. Life table experiments were conducted with different diets: 1) without nutritional restriction, where neonates were fed with diets at a constant green algae (Monoraphidium capricornutum) biomass as a nutritious food source, and increasing cyanobacterial concentration (STX-producing Raphidiopsis raciborskii), and 2) with diets consisting of different proportions of M. capricornutum (nutritious) and R. raciborskii (poor food) at a total biomass 1.0 mg C L 1. In general, the presence of high proportions of cyanobacteria promoted a decrease in Daphnia somatic growth, reproduction and intrinsic rate of population increase (r) in both diets with more pronounced effects in the nutritionally restricted diet (90% R. raciborskii). Two-way ANOVA revealed significant effects of species/clone and treatments in both assays, with significant interaction between those factors only in the second assay. Regarding the grazing assay, only D. laevis was negatively affected by increased cyanobacterial proportions in the diet. In the life table assay with constant edible food, a reduction in the reproduction parameters and the intrinsic rate of population increase (r) of all species was observed, In conclusion, we found adverse effects of the toxic cyanobacterial strain R. raciborskii on Daphnia fitness, regardless of the constant amount of nutritious food available, proving the toxic effect of R. raciborskii and the nutritional quality of the food has a greater influence on the fitness of these animals.
Changes in food quality can dramatically impair zooplankton fitness, especially in eutrophic water bodies where cyanobacteria are usually predominant. Cyanobacteria are considered a food with low nutritional value, and some species can produce bioactive secondary metabolites reported as toxic to zooplankton. Considering that cyanobacteria can limit the survival, growth and reproduction of zooplankton, we hypothesized that the dietary exposure of neotropical Daphnia species (D. laevis and D. gessneri) to saxitoxin-producing cyanobacteria impairs Daphnia feeding rates and fitness regardless of a high availability of nutritious algae. Life table and grazing assays were conducted with different diets: (1) without nutritional restriction, where neonates were fed with diets at a constant green algae biomass (as a nutritious food source), and an increasing cyanobacterial concentration (toxic and poor food source), and (2) with diets consisting of different proportions of green algae (nutritious) and cyanobacteria (poor food) at a total biomass 1.0 mg C L−1. In general, the presence of high proportions of cyanobacteria promoted a decrease in Daphnia somatic growth, reproduction and the intrinsic rate of population increase (r) in both diets with more pronounced effects in the nutritionally restricted diet (90% R. raciborskii). A two-way ANOVA revealed the significant effects of species/clone and treatments in both assays, with significant interaction between those factors only in the second assay. Regarding the grazing assay, only D. laevis was negatively affected by increased cyanobacterial proportions in the diet. In the life table assay with constant nutritious food, a reduction in the reproduction and the intrinsic rate of the population increase (r) of all species were observed. In conclusion, we found adverse effects of the toxic cyanobacterial strain R. raciborskii on Daphnia fitness, regardless of the constant amount of nutritious food available, proving the toxic effect of R. raciborskii and that the nutritional quality of the food has a greater influence on the fitness of these animals.
INTRODUÇÃO:O presente estudo realizou uma análise do efeito transgeracional de uma espécie de cianobactéria tóxica sobre espécie de microcrustáceo: Daphnia laevis, clone Ibirité (ambiente aquático brasileiro). OBJETIVOS: Avaliar a aptidão de uma população de Daphnia, através dos seguintes parâmetros: sobrevivência, crescimento somático, fecundidade e taxa intrínseca de aumento populacional (r), em duas gerações (F0 e F 1 ) mediante exposição à dieta com adição da cianobactéria Raphidiopsis raciborskii (cepa LETC-CY-05). METODOLOGIA: Fêmeas de D. laevis foram expostas a dois tratamentos com a cepa tóxica (proporções de 20% e 50%) e um grupo controle com a espécie alimentada 100% com microalga verde. Na F0 e F 1 os ciclos de vida foram avaliados, sendo possível analisar a aptidão (r) entre populações de diferentes gerações. RESULTADOS: Os resultados revelaram diferentes respostas de D. laevis aos parâmetros analisados. Analisando os resultados da geração F 1 de D. laevis, ou seja, a prole advinda da geração F0, podemos notar que a idade da primeira reprodução foi maior nas concentrações com adição da cepa tóxica de cianobactéria, assim como observado na geração F0, porém, na F 1 a idade da primeira reprodução diminuiu em todas as concentrações em relação à F0. Comparando os resultados da geração F 1 a respeito do total de neonatos produzidos com os resultados da F0, podemos constatar que a produção de neonatos de F 1 foi maior do que a F0. A taxa intrínseca de crescimento populacional (r) da F 1 também sofreu um leve aumento quando comparamos com F0. Ao observamos o parâmetro de fecundidade média da F 1 e comparamos com F0, notamos houve um aumento sutil no número médio de neonatos. Porém, na concentração de 50%, a fecundidade média de F 1 foi menor do que na de 20% e do grupo controle alimentado apenas com clorofícea. CONCLUSÃO: O presente trabalho demonstrou que a F0 de D. laevis se mostrou mais tolerante na dieta mista com 20% de cianobactéria e que a geração de neonatos de mães expostas à cianobactéria (F 1 ) demonstrou que são mais tolerantes do que a F0 já que as mães se alimentaram de cianobactéria e podem ter transferido tolerância à prole.
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