Population dynamics in Daphnia magna as modified by chronic tetradifon stress

Two Daphnia magna offsprings (animals from the first and third brood) whose parentals (F-0-generation) were exposed during 21 days to different tetrad ifon (4-chlorophenyl 2,4,5-trichlophenyl sulfone) concentrations, were tran sferred to a pesticide free medium during 21 days (recovery period). The al gae Nannochloris oculata (5 x 10(5) cells/ml) was used as food. In this rec overy study, survival, growth and reproduction (mean total young per female , mean brood size, onset of reproduction and mean number broods per female) were assessed as individual parameters and the intrinsic rate of natural i ncrease (r) as population parameter, for F-1 generation (1st and 3rd broods ). Reproduction was still reduced in F-1 (1st and 3rd broods) generation da phnids from parentals (F-0) exposed to 0.18 mg/L tetradifon and higher conc entrations even after 21 days in clean water. However, survival was not sig nificantly different (p>0.05) in those F1 offsprings from parentals pre-exp osed to the acaricide. Growth was still reduced in F1 daphnids from parenta ls pre-exposed to 0.10-0.44 mg/L tetradifon. The intrinsic rate of natural increase (r) was still affected in F1 generation daphnids, specially in tho se from the third brood. Therefore, F1 generation D, magna offsprings from a parental generation (F0) previously exposed to the acaricide tetradifon w ere not able to recuperate completely when a recovery period of 21 days was allowed.