Circadian rhythmicity is an endogenous biological cycle of about 24 h, which exists in cyanobacteria and fungi,
plants and animals. Circadian rhythms improve the adaptability of organisms in both constant and changing environments.
The cryptochrome (CRY) is a key element of the circadian system in various animal groups including
fishes.
We studied evolution of cryptochromes in the phylogenetically and ecologically diverse fish taxa. The phylogenetic
tree of fish Cry features two major clades: Cry1 and Cry2. Teleosts possess extra copies of Cry1 due to the
genome duplication, which resulted in 3 main paralogous subfamilies (1A, 1B and 1C). Cry1 experienced further
diversification through additional duplications in some taxa. 1A of Cry1 ismore conserved than the other paralogs
(dN = 0.010 ± 0.003, π = 0.119 ± 0.058). The analysis of selection indicated that, while the Cry homologs in
fish evolved under the different levels of selection pressure, strong purifying selection (averageω=0.017) dominated
in their evolution.