Life-history consequences of adaptation to pollution. Daphnia longispina clones historically exposed to copper

The present study was conducted to assess life history effects of adaptation to pollution in Daphnia longispina clones historically exposed to an acid mine drainage from an abandoned pyrite mine. Four sensitive and resistant clones from reference and impacted populations were exposed to a range of copper exposure levels and their life history and physiological responses in terms of survival, reproduction, respiration and feeding rates compared. The most resistant clone was from 16 to 48 fold more tolerant to copper in terms of LC50 and population growth rates than sensitive ones, respectively. The genetic differences between the resistant and sensitive clones were that in the polluted environment individuals of the resistant clone survived 50% better, reproduced 3 days earlier, grew 20% better, produced three more offspring per day and had population growth rates 45% greater. In the unpolluted environment, however, individuals from the resistant clone had the lowest reproduction and somatic growth rates but equivalent population growth rates, than sensitive daphnids. Thus, these life history changes did not translate into lower fitness in unpolluted environments in terms of population growth rates. Observed higher respiration rates of the most resistant clone support in part the energy cost hypothesis of tolerance, whereas increase feeding, reproduction and growth rates across copper exposure levels may also, indicate that resistant individuals need copper to fulfil they physiological demands thus supporting the metal deficiency hypothesis as well.