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...