Hydrobates spp. – Circadian locomotor output cycles kaput (Clock) gene poly-glutamine repeats

Annual cues in the environment result in physiological changes that allow
organisms to time reproduction during periods of optimal resource
availability. Understanding how circadian rhythm genes sense these
environmental cues and stimulate the appropriate physiological changes in
response is important for determining the adaptability of species,
especially in the advent of changing climate. A first step involves
characterizing the environmental correlates of natural variation in these
genes. Band-rumped and Leach’s storm-petrels (Hydrobates spp.) are pelagic
seabirds that breed across a wide range of latitudes. Importantly, some
populations have undergone allochronic divergence, in which sympatric
populations use the same breeding sites at different times of year. We
investigated the relationship between variation in key functional regions
of four genes that play an integral role in the cellular clock mechanism –
Clock, Bmal1, Cry2 and Per2 – with both breeding season and absolute
latitude in these two species complexes.  We discovered that
allele frequencies in two genes, Clock and Bmal1, differed between
seasonal populations in one archipelago, and also correlated with absolute
latitude of breeding colonies. These results indicate that variation in
these circadian rhythm genes may be involved in allochronic speciation, as
well as adaptation to photoperiod at breeding locations.