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Cultivation medium is one of the first aspects to be considered in zooplankton laboratory cultivation. The use of artificial media does not concern to reproduce natural conditions to the cultivations, which may be achieved by using natural organic compounds like humic substances (HS). This study aimed to evaluate the effects of a concentrate of dissolved organic carbon (DOC) from the Negro River (NR(1)) and an extraction of humic acids (HA) from humus produced by Eisenia andrei on the life history traits of laboratory-based Latonopsis australis SARS (1888). A cohort life table approach was used to provide information about the effectiveness of NR and HA as supplements for the artificial cultivation of L. australis. Additionally, we seek to observe a maximization of L. australis artificial cultivation fitness by expanding the range of HS concentrations. The first experiment demonstrated that the females of L. australis reared under NR10 (mgDOCL(-1)) may have experienced an acceleration of the population life cycle, as the females have proportionally reproduced more and lived shorter than controls. By contrast, the use of the HA did not improve life history traits considered. The expansion of the concentration range (5, 10, 20 and 50 mgDOCL(-1)) corroborated the patterns observed on the first assay. Results for the fitness estimates combined with shorter lifespans than controls demonstrated trade-offs between reproductive output and female longevity reared under NR conditions, with NR20 been suggested as the best L. australis cultivation medium. This response might be associated with hormone-like effects., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Field populations of daphnids historically-stressed by metal contamination may show increased resistance to those contaminants. This study was undertaken aiming to confirm/infirm three main hypotheses: (1) field populations living in historically-impacted environments are more tolerant to metal stress than populations from reference sites; (2) resistance differences are genetically-determined, i.e., differences persist after controlling for environmental and maternal effects, by acclimating cloned lineages to similar conditions; and (3) resistance to stress in field populations living in historically-impacted environments is due to the disappearance of sensitive individuals rather than the appearance of highly resistant ones, i.e., the shift in the central tendency of resistance is linked to a decrease in the range of population resistance and not to an increased upper limit of the population resistance. Three populations of the cladoceran Ceriodaphnia pulchella Sars in Southern Portugal were sampled; one of which has been historically-stressed by acid mine drainage (AMD) from an abandoned cupric-pyrite mine and two from reference sites within the same watershed. To assess if resistance differences were genetically-determined, the three populations were acclimated for at least five generations under the same controlled conditions. Assays with AMD contaminated water samples were performed with both non-acclimated and acclimated individuals from all studied populations. Reproduction results in sub-lethal assays revealed significant differences between the reference and stressed populations. Significant differences in resistance to lethal levels of toxicity were observed for both non-acclimated and acclimated populations, individuals from population I being more resistant than those from reference populations. The existence of genetically-determined sensitivity differences was attested by the presence of significant differences in resistance to lethal levels of toxicity in acclimated individuals from reference and stressed populations. Results from cumulative mortality assays revealed that sensitive individuals were most probably present in the original population, but no conclusion could be draw about the presence of extreme resistant individuals in the historically-stressed population. Finally, it was shown that responses among populations converged from high to low levels of contamination.