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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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Plot of latitude in degrees (x-axis) against frequencies of alleles for (a) 335 bp (R2=0.407, p=0.0001; y=1.52+−0.016x) and (b) 359 bp (y-axis) (R2=0.285, p=0.0003; y=−0.39+0.012x).
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fig5: Plot of latitude in degrees (x-axis) against frequencies of alleles for (a) 335 bp (R2=0.407, p=0.0001; y=1.52+−0.016x) and (b) 359 bp (y-axis) (R2=0.285, p=0.0003; y=−0.39+0.012x).

Mentions: We found a significant association between average allele length of OtsClock1b PolyQ variants and latitude using linear regression (R2=0.516, p<0.0001, regression coefficient=0.514; figure 4). Examination of the two most common OtsClock1b alleles (335 and 359 bp) revealed a significant association between frequency and latitude albeit in the opposite direction. The short 335 bp allele increases in frequency at lower latitudes (R2=0.407, p<0.0001, regression coefficient=−0.016) while the long 359 bp allele increases in frequency at higher latitudes (R2=0.285, p=0.0003, regression coefficient=0.013) (figure 5a,b).


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)

Plot of latitude in degrees (x-axis) against frequencies of alleles for (a) 335 bp (R2=0.407, p=0.0001; y=1.52+−0.016x) and (b) 359 bp (y-axis) (R2=0.285, p=0.0003; y=−0.39+0.012x).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Plot of latitude in degrees (x-axis) against frequencies of alleles for (a) 335 bp (R2=0.407, p=0.0001; y=1.52+−0.016x) and (b) 359 bp (y-axis) (R2=0.285, p=0.0003; y=−0.39+0.012x).
Mentions: We found a significant association between average allele length of OtsClock1b PolyQ variants and latitude using linear regression (R2=0.516, p<0.0001, regression coefficient=0.514; figure 4). Examination of the two most common OtsClock1b alleles (335 and 359 bp) revealed a significant association between frequency and latitude albeit in the opposite direction. The short 335 bp allele increases in frequency at lower latitudes (R2=0.407, p<0.0001, regression coefficient=−0.016) while the long 359 bp allele increases in frequency at higher latitudes (R2=0.285, p=0.0003, regression coefficient=0.013) (figure 5a,b).

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