Data from: Evolution to environmental contamination ablates the circadian clock of an aquatic sentinel species

Environmental contamination is a common cause of rapid evolution. Recent work has shown that Daphnia pulex, an important freshwater species, can rapidly evolve increased tolerance to a common contaminant, sodium chloride (NaCl) road salt. While such rapid evolution can benefit organisms, allowing them to adapt to new environmental conditions, it can also be associated with unforeseen tradeoffs. Given that exposure to environmental contaminants can cause circadian disruption, we investigated whether the circadian clock was affected by evolving a tolerance to high levels of road salt. By tracking the oscillations of a putative clock gene, period, we demonstrated that D. pulex express per mRNA with approximately 20-hour oscillations under control conditions. This putative circadian rhythm was ablated in response to high levels of salinity; populations adapted to high NaCl concentrations exhibited an ablation of period oscillation. Moreover, we showed that while gene expression is increased in several other genes, including clock, actin, and Na+/K+-ATPase, upon the adaptation to high levels of salinity, per expression is unique among the genes we tracked in that it is the only gene repressed in response to salt adaptation. These results suggest that rapid evolution of salt tolerance occurs with the tradeoff of suppressed circadian function. The resultant circadian disruption may have profound consequences to individuals, populations, and aquatic food webs by affecting species interactions. In addition, our research suggests that circadian clocks may also be disrupted by the adaptation to other environmental contaminants.环境污染是驱动生物快速演化的常见诱因。近期研究表明，作为重要淡水物种的蚤状溞（Daphnia pulex）能够快速演化出对常见污染物——氯化钠（sodium chloride, NaCl，道路融雪盐）的耐受性提升。尽管这类快速演化可使生物获益，帮助其适应新的环境条件，但同时也可能伴随难以预见的权衡效应。鉴于环境污染物暴露可引发昼夜节律紊乱，本研究探究了演化获得高浓度道路盐耐受性是否会对昼夜节律钟（circadian clock）产生影响。通过追踪推定的生物钟核心基因period（简称per）的振荡表达模式，我们证实：在对照组条件下，蚤状溞的per mRNA呈现约20小时的振荡表达。在高盐度胁迫下，这种推定的昼夜节律会被消除；适应了高浓度NaCl的蚤状溞种群，其period基因的振荡表达完全消失。此外，本研究发现：在适应高盐环境后，包括时钟基因（clock）、肌动蛋白（actin）以及钠钾腺苷三磷酸酶（Na+/K+-ATPase）在内的多个其他基因的表达均会上调，但在所检测的基因中，per基因的表达是唯一被盐适应抑制的基因，这一特征具有独特性。上述结果表明，盐耐受性的快速演化，会以昼夜节律功能受抑制作为权衡代价。由此产生的昼夜节律紊乱，可能通过影响物种间相互作用，对个体、种群以及水生食物网造成深远影响。此外，本研究还表明，针对其他环境污染物的适应性演化，同样可能扰乱昼夜节律钟。