大型蚤对五价砷抗性选择的响应

金属污染对栖息在该环境中的生物具有强大的选择力,生物若能进化出对该金属的抗性则能在该环境中生存下去,否则将会灭绝。人工模拟的选择方法可以用来研究生物对金属的抗性进化。为了探索大型蚤(Daphnia magna)是否能进化出对五价砷(As(Ⅴ))的抗性,采用多代选择的方法对其进行了As(Ⅴ)诱导的抗性响应研究。依据本实验室大型蚤对As(Ⅴ)的96h半致死浓度(4.25 mg·L~(-1)),试验选取As(Ⅴ)亚致死浓度(8.0 mg·L~(-1))对大型蚤进行选择,每代选择30%~50%对As(Ⅴ)耐受性高的大型蚤转移至不加As(Ⅴ)环境下继续繁殖得到下一代,并重复该选择过程至获得第五代(F5)终止试验。以选择组F5代及对照组F5代大型蚤为测试目标,考察其在As(Ⅴ)继续暴露下的存活时间以期获得具As(Ⅴ)抗性大型蚤。结果显示,在F5代中,选择组大型蚤在As(Ⅴ)(8.0 mg·L~(-1))暴露下的存活时间相比对照组显著延长175%,证实了大型蚤对As(Ⅴ)的进化抗性。进一步研究发现,选择组F5代与对照组F5代相比繁殖力下降19.96%,平均每批产仔量降低15.71%。这表明经过五代人工选择后,大型蚤能够进化出对As(Ⅴ)的抗性,而这种抗性的进化伴随以生物适应性参数的降低为代价。另外,大型蚤对这种抗性的获得机制(对As(Ⅴ)的累积和脱毒机制)仍需进一步研究。

Rapid Evolution of Resistance to As(V) in Daphnia magna

Metal contamination can exert a strong selection force on the populations inhabiting in the metal con￣taminated environments. The populations will either survive in the contaminated environments by evolving the resistance to the metal(s) or go extinction in such contaminated environments. Artificial selection approach can be used to study the potential of evolution of resistance to metals in organisms. To understand whether Daphniamagna can evolve the resistance to arsenate (As(V)), an artificial selection was used to study responses of daphnids to the selection of As(V) resistance in a multi￣generation selection regime. Based on the 96￣h LC50 of As(V) (4.25 mg?L￣1), D.magna were exposed to a sublethal concentration (8.0 mg?L￣1) of As(V). In each generation, survivors from the As(V) exposure (i.e., As￣tolerant individuals) (approximately 30%￣50%) were allowed to produce off￣spring in the next generation. The artificial selection was repeated for 5 generations. The resistance to As(V) was quantified and fitness costs associated with the resistance to As(V) were evaluated in the F5 generation. The results showed that the selected group had a longer (175%) time to death than that of control, implying that daphnids might have evolved the resistance to As(V). Comparison of the data on the fitness components showed that the As￣resistant daphnids had a reduced fecundity (19.96%) and a decreased average brood size (15.71%) than the control daphnids. It was concluded that the daphnids could have evolved the resistance to As(V) exposure even after five generations of artificial selection. And the rapid evolution of resistance to As(V) in D.magna might be associated with fitness costs. Further research is needed to elucidate the underlying mechanisms (including accumulation and the detoxification of As(V)) for this resistance in D.magna.