Lopes Isabel, Baird Donald J, Ribeiro Rui
Instituto do Ambiente e Vida, Departamento de Zoologia da Universidade de Coimbra, Largo Marquês de Pombal, 3004-517 Coimbra, Portugal.
Chemosphere. 2005 Dec;61(8):1189-97. doi: 10.1016/j.chemosphere.2005.02.072. Epub 2005 Apr 19.
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.
长期受到金属污染压力的水蚤野外种群可能对这些污染物表现出更高的抗性。本研究旨在证实/证伪三个主要假设：（1）生活在历史受影响环境中的野外种群比来自参考地点的种群对金属胁迫更具耐受性；（2）抗性差异是由基因决定的，即通过使克隆谱系适应相似条件来控制环境和母体效应后，差异仍然存在；（3）生活在历史受影响环境中的野外种群对胁迫的抗性是由于敏感个体的消失而非高抗性个体的出现，即抗性中心趋势的变化与种群抗性范围的减小有关，而非种群抗性上限的增加。对葡萄牙南部的三种枝角类美丽角突网纹溞种群进行了采样；其中一个种群长期受到来自废弃铜硫矿的酸性矿山排水（AMD）的压力，另外两个来自同一流域内的参考地点。为了评估抗性差异是否由基因决定，将这三个种群在相同的受控条件下适应至少五代。对所有研究种群的未适应和适应个体都进行了AMD污染水样的试验。亚致死试验中的繁殖结果显示参考种群和受胁迫种群之间存在显著差异。在未适应和适应种群中均观察到对致死毒性水平的抗性存在显著差异，种群I的个体比参考种群的个体更具抗性。参考种群和受胁迫种群的适应个体对致死毒性水平的抗性存在显著差异，证明了基因决定的敏感性差异的存在。累积死亡率试验结果表明，敏感个体很可能存在于原始种群中，但对于历史受胁迫种群中是否存在极端抗性个体无法得出结论。最后，结果表明种群之间的反应从高污染水平到低污染水平趋于一致。
