Clock polymorphism in Pacific salmon: evidence for variable selection along a latitudinal gradient.

Area of Science:

• Evolutionary biology
• Genetics
• Chronobiology

Background:

• Seasonal timing of life-history events is crucial for species survival.
• Circadian clock genes, like Clock, regulate responses to environmental cues such as photoperiod.
• Pacific salmonids exhibit variations in migration and breeding timing influenced by photoperiod.

Purpose of the Study:

• To investigate the role of duplicated Clock genes in population-level differences in reproductive timing among Pacific salmonids.
• To examine geographical variation in the polyglutamine (PolyQ) domain of OtsClock1a and OtsClock1b across multiple salmon species.

Main Methods:

• Analyzed geographical variation in the PolyQ domain of OtsClock1a and OtsClock1b in 53 populations of chum, coho, and pink salmon.
• Employed regression trees to assess the influence of photoperiod (day length) and freshwater migration on OtsClock1b PolyQ domain variation.

Main Results:

• Found evidence of variable selection on OtsClock1b correlating with latitudinal differences in reproductive timing.
• Day length at spawning significantly explained OtsClock1b allele frequency variation in chum and Chinook salmon populations.
• The influence of day length on OtsClock1b variation differed among salmon species.

Conclusions:

• OtsClock1b plays a role in mediating seasonal adaptation in Pacific salmonids.
• OtsClock1b contributes to geographical variation in reproductive timing, particularly in relation to photoperiod cues.
• The genetic basis for seasonal timing varies among highly migratory salmon species.