Mothers and not genes determine inherited differences in cadmium sensitivities within unexposed populations of the freshwater crustacean Gammarus fossarum

Deciphering evolutionary processes occurring within contaminated populations is important for the ecological risk assessment of toxic chemicals. Whereas increased tolerance to contaminants is well documented in aquatic animal populations, whether such phenotypic changes occur through genetic adaptation is still debated. In that sense, several studies with the freshwater crustacean Gammarus concluded in a weak potential for genetic adaptation to cadmium (Cd), while others reported inheritable increased tolerance in Cd-contaminated populations. Using quantitative genetics and selection experiments, this study sought to further assess the potential of Gammarus populations to genetically adapt to Cd. By combining the control of the reproductive cycle of this species in the laboratory and protocols of individual Cd exposure, we conducted half-sib analyses to establish the genetic and environmental sources of variance in Cd sensitivity of neonates. Prior to experiments, computations allowed optimizing the experimental design in order to increase the power to detect additive genetic variance. The main findings are the existence of strong between-brood variability along with weak heritability of Cd sensitivity within Gammarus populations. This study also revealed a significant maternal effect on individual Cd sensitivity. This sheds new light on the importance of maternal influence in microevolutionary processes occurring in contaminated environments.

解析污染种群内的进化过程，对有毒化学品的生态风险评估具有重要价值。尽管水生动物种群对污染物的耐受性增强已被大量文献证实，但这类表型改变是否由遗传适应所驱动，目前仍存在争议。就此而言，针对淡水甲壳动物钩虾属（Gammarus）的多项研究认为，其对镉（Cd）的遗传适应潜力较弱，但另有研究在镉污染种群中发现了可遗传的耐受性提升现象。本研究采用数量遗传学与选择实验方法，旨在进一步评估钩虾种群对镉产生遗传适应的潜力。通过结合实验室中对该物种生殖周期的调控技术与个体镉暴露实验方案，本研究开展了半同胞分析，以明确幼体镉敏感性的遗传与环境方差来源。实验开展前，我们通过计算优化了实验设计，以提升检测加性遗传方差的统计效力。主要研究结果表明，钩虾种群内存在显著的窝间变异，同时幼体镉敏感性的遗传力较低。本研究还发现，母体对个体镉敏感性存在显著影响。该发现为理解污染环境中微进化过程内母体效应的重要性提供了全新视角。