Transgenerational retention and maternal transfer of selenium in Daphnia magna

We examined transgenerational retention and maternal transfer of selenium (Se) in three consecutive generations (F0, F1, and F2) of Daphnia magna. The F0 generation was exposed to dietary selenium (as selenite) only, and the F1 and F2 generations received only the maternally derived selenium from F0 and F1, respectively. Algal food Scenedesmus obilquus was radiolabeled with 0.56 microM Se, and the finial Se concentration in the algae was 115.6 microg Se/g dry weight. After 10 d feeding, the initial Se concentration in the F0 prior to depuration was 0.72 microg Se/g wet weight. The Se retention within the same generation was comparable at different food concentrations, but it increased across the consecutive generations regardless of the food concentration, suggesting that Se elimination was dependent on the source of Se accumulation (dietary vs maternally derived). Retention was also comparable among different batches of offspring within the same generation. Reproduction rate increased with increasing food concentration but decreased across the successive batches in F1. The 10-d overall maternal transfer efficiency increased with increasing food concentration in all generations. Approximately 19 to 24% of Se in F0 was transferred maternally to F1 during reproductive events, but the-efficiency decreased considerably from F1 to F2. Maternal transfer also decreased in the later batches of F1. The transfer efficiency to each neonate showed a negative relationship with food concentration in both F0 and F1, suggesting that the Se transfer to the offspring was compromised by the reproduction rate. We concluded that dietary-derived Se (from F0) was more efficiently transferred to the offspring (F1) than the maternally derived Se (from F1) transferred to F2; thus it is necessary to separate the dietary and maternal contributions to the overall Se accumulation in Daphnia.