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A latitudinal cline in the Chinook salmon (Oncorhynchus tshawytscha) Clock gene: evidence for selection on PolyQ length variants.

O'Malley KG, Banks MA - Proc. Biol. Sci. (2008)

Bottom Line: We found evidence of a latitudinal cline in average allele length and frequency of the two most common OtsClock1b alleles.Comparison to 13 microsatellite loci showed that 335 and 359 bp deviate significantly from neutral expectations.Our findings suggest that length polymorphisms in OtsClock1b PolyQ may be maintained by selection and reflect an adaptation to ecological factors correlated with latitude, such as the seasonally changing day length.

View Article: PubMed Central - PubMed

Affiliation: Coastal Oregon Marine Experiment Station, Department of Fisheries and Wildlife, Hatfield Marine Science Center, Oregon State University, Newport, OR 97365, USA. kathleen.omalley@noaa.gov

ABSTRACT
A critical seasonal event for anadromous Chinook salmon (Oncorhynchus tshawytscha) is the time at which adults migrate from the ocean to breed in freshwater. We investigated whether allelic variation at the circadian rhythm genes, OtsClock1a and OtsClock1b, underlies genetic control of migration timing among 42 populations in North America. We identified eight length variants of the functionally important polyglutamine repeat motif (PolyQ) of OtsClock1b while OtsClock1a PolyQ was highly conserved. We found evidence of a latitudinal cline in average allele length and frequency of the two most common OtsClock1b alleles. The shorter 335 bp allele increases in frequency with decreasing latitude while the longer 359 bp allele increases in frequency at higher latitudes. Comparison to 13 microsatellite loci showed that 335 and 359 bp deviate significantly from neutral expectations. Furthermore, a hierarchical gene diversity analysis based on OtsClock1b PolyQ variation revealed that run timing explains 40.9 per cent of the overall genetic variance among populations. By contrast, an analysis based on 13 microsatellite loci showed that run timing explains only 13.2 per cent of the overall genetic variance. Our findings suggest that length polymorphisms in OtsClock1b PolyQ may be maintained by selection and reflect an adaptation to ecological factors correlated with latitude, such as the seasonally changing day length.

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Nucleic and amino acid sequence of OtsClock1a PolyQ locus.
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fig2: Nucleic and amino acid sequence of OtsClock1a PolyQ locus.

Mentions: We found no evidence of length polymorphism in the OtsClock1a PolyQ domain among the Chinook salmon populations as all individuals were homozygous for the 199 bp allele. The OtsClock1a PolyQ fragment consists of 52 amino acid residues flanked by 36 and 11 bp of non-coding sequence (figure 2).


A latitudinal cline in the Chinook salmon (Oncorhynchus tshawytscha) Clock gene: evidence for selection on PolyQ length variants.

O'Malley KG, Banks MA - Proc. Biol. Sci. (2008)

Nucleic and amino acid sequence of OtsClock1a PolyQ locus.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2572187&req=5

fig2: Nucleic and amino acid sequence of OtsClock1a PolyQ locus.
Mentions: We found no evidence of length polymorphism in the OtsClock1a PolyQ domain among the Chinook salmon populations as all individuals were homozygous for the 199 bp allele. The OtsClock1a PolyQ fragment consists of 52 amino acid residues flanked by 36 and 11 bp of non-coding sequence (figure 2).

Bottom Line: We found evidence of a latitudinal cline in average allele length and frequency of the two most common OtsClock1b alleles.Comparison to 13 microsatellite loci showed that 335 and 359 bp deviate significantly from neutral expectations.Our findings suggest that length polymorphisms in OtsClock1b PolyQ may be maintained by selection and reflect an adaptation to ecological factors correlated with latitude, such as the seasonally changing day length.

View Article: PubMed Central - PubMed

Affiliation: Coastal Oregon Marine Experiment Station, Department of Fisheries and Wildlife, Hatfield Marine Science Center, Oregon State University, Newport, OR 97365, USA. kathleen.omalley@noaa.gov

ABSTRACT
A critical seasonal event for anadromous Chinook salmon (Oncorhynchus tshawytscha) is the time at which adults migrate from the ocean to breed in freshwater. We investigated whether allelic variation at the circadian rhythm genes, OtsClock1a and OtsClock1b, underlies genetic control of migration timing among 42 populations in North America. We identified eight length variants of the functionally important polyglutamine repeat motif (PolyQ) of OtsClock1b while OtsClock1a PolyQ was highly conserved. We found evidence of a latitudinal cline in average allele length and frequency of the two most common OtsClock1b alleles. The shorter 335 bp allele increases in frequency with decreasing latitude while the longer 359 bp allele increases in frequency at higher latitudes. Comparison to 13 microsatellite loci showed that 335 and 359 bp deviate significantly from neutral expectations. Furthermore, a hierarchical gene diversity analysis based on OtsClock1b PolyQ variation revealed that run timing explains 40.9 per cent of the overall genetic variance among populations. By contrast, an analysis based on 13 microsatellite loci showed that run timing explains only 13.2 per cent of the overall genetic variance. Our findings suggest that length polymorphisms in OtsClock1b PolyQ may be maintained by selection and reflect an adaptation to ecological factors correlated with latitude, such as the seasonally changing day length.

Show MeSH