How did 500 species of a fish form in a lake? Dramatically different body clocks

Despite the dramatic difference between day and nightlife, how fish exploit different times of day has not been studied systematically. Scientists explored alterations in the circadian timing of activity and the duration of rest-wake cycles in Lake Malawi's cichlids and identified the first single nocturnal species. Timing and duration of rest and activity varies dramatically, and continuously, between populations of Lake Malawi cichlids, providing a system for exploring the molecular and neural basis underlying variation in nocturnal activity.

from Latest Science News -- ScienceDaily https://www.sciencedaily.com/releases/2021/04/210408112355.htm