Detecting Cd adaptation footprint in C. riparius with a multi-genomic approach. Cd adaptation footprint in C. riparius

Evolutionary processes and acquired tolerance to toxicants are important factors governing how animals respond to chemical exposure. Evidence for increased tolerance to cadmium (Cd), a widely distributed toxic metal in aquatic environments, in Chironomus riparius is conflicting and still questioned if it happens through phenotypic plasticity or genetic adaptation. The present study considered the relevance of directional environmental changes by increasing contaminant concentration in a multigenerational selection experiment. Evaluation of measurable life-cycle traits, transcriptomic responses and quantitative genetics from an evolve and resequencing (E&R) experiment were integrated to assess the potential of C. riparius to adapt to Cd. Survival tests revealed some adaptation to Cd exposure. Genomic analyses showed a strong, genome-wide selective response in all replicates, emphasizing that even control laboratory conditions continually exert selective pressure. The integration of transcriptomic and genomic data could isolate the genes related to Cd acquired resistance. Those genes could be linked to an efflux of metals. Therefore, it is possible to conclude that C. riparius can endure long-term Cd exposure also through genetic adaptation.

演化过程与获得性毒物耐受性，是决定动物应对化学暴露方式的核心影响因素。关于摇蚊（Chironomus riparius）对镉（Cd，一种广泛分布于水生环境的有毒金属）耐受性增强的相关研究结论存在分歧，且其耐受性提升究竟源于表型可塑性还是遗传适应，目前仍存在争议。本研究通过多代选择实验逐步提升污染物浓度，以此考察定向环境变化的关联效应。本研究整合了进化重测序（evolve and resequencing, E&R）实验中可测定的生命周期性状、转录组响应及数量遗传学分析结果，以评估摇蚊适应镉胁迫的潜力。生存试验结果显示，摇蚊对镉暴露已产生一定适应性。基因组分析表明，所有重复实验样本均出现全基因组范围内的强烈选择响应，这提示即便实验室对照条件也会持续施加选择压力。通过整合转录组与基因组数据，可筛选出与镉获得性抗性相关的基因，此类基因可能参与金属外排过程。据此可得出结论：摇蚊亦可通过遗传适应机制耐受长期镉暴露。