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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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Map showing the location of the 42 Chinook salmon populations from California to Alaska.
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fig1: Map showing the location of the 42 Chinook salmon populations from California to Alaska.

Mentions: Of the 42 populations included in this study, 40 are part of a standardized DNA collection established by the Chinook Technical Committee (CTC) of the Pacific Salmon Commission (figure 1; Seeb et al. 2007). Individuals from all CTC populations were previously genotyped at 13 microsatellite loci. For this study, we obtained DNA samples of approximately 48 individuals from each of the 40 populations. In June 2004, we collected 20 Chinook salmon liver samples from the remaining two populations, Alaska's Montana Creek and Situk River, and extracted genomic DNA using the DNeasy Tissue Kit (Qiagen).


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)

Map showing the location of the 42 Chinook salmon populations from California to Alaska.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Map showing the location of the 42 Chinook salmon populations from California to Alaska.
Mentions: Of the 42 populations included in this study, 40 are part of a standardized DNA collection established by the Chinook Technical Committee (CTC) of the Pacific Salmon Commission (figure 1; Seeb et al. 2007). Individuals from all CTC populations were previously genotyped at 13 microsatellite loci. For this study, we obtained DNA samples of approximately 48 individuals from each of the 40 populations. In June 2004, we collected 20 Chinook salmon liver samples from the remaining two populations, Alaska's Montana Creek and Situk River, and extracted genomic DNA using the DNeasy Tissue Kit (Qiagen).

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