Phenotypic Evolution of Circadian Rhythms in Arabidopsis thaliana

Wakefield, Stephanie
Circadian rhythms are internal, repeating rhythms that can be set by environmental inputs such as temperature and light; because the diurnal cycle on earth is close to 24 hours, circadian cycles close to 24 hours are thought to be adaptive. I tested whether circadian rhythms evolved in the manner predicted, such that genotypes with period lengths greater than or less than 24 hours are at a selective disadvantage. I assayed 80 genotypes in total: 40 Arabidopsis thaliana genotypes produced from a cross between two natural ecotypes and 40 genotypes derived from the original set that have undergone several generations of selection in the field. I quantified both sets for circadian period using a reporter gene approach. The genotypes showed significant genetic variation in circadian period, ranging from 24 to 27 hours. There was no significant difference in circadian period between the two sets of lines, but there appears to be a trend toward longer periods in the field evolved lines. Since the genotypes used in the original study contain allele combinations not present in natural populations, we can better understand how natural selection has acted on circadian phenotypes by comparing the original versus the field evolved lines.
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