Circadian clocks and adaptation in Arabidopsis

Jan 15, 2011Molecular ecology

Internal daily clocks and how Arabidopsis plants adjust to their environment

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Abstract

F2 plants with endogenous rhythms that closely match the environmental T-cycle produce relatively more viable offspring in the F3 generation.

Arabidopsis thaliana plants were modified to create genetic variance for circadian rhythmicity.
Selection was applied to F2 plants with varying circadian periods under different competition strengths.
The average circadian rhythm period of resulting F3 plants showed a strong positive correlation with the T-cycle growth conditions of competing F2 plants.
The frequency of long-period alleles in F3 plants was altered based on circadian phenotypes.
These findings suggest that a circadian clock aligned with environmental cycles may confer a fitness advantage.

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Endogenous circadian rhythms are almost ubiquitous among organisms from cyanobacteria to mammals and regulate diverse physiological processes. It has been suggested that having an endogenous circadian system enables an organism to anticipate periodic environmental changes and adapt its physiological and developmental states accordingly, thus conferring a fitness advantage. However, it is hard to measure fitness directly and there is, to date, only limited evidence supporting the assumption that having a circadian system can increase fitness and therefore be adaptive. In this article, we report an evolutionary approach to examine the adaptive significance of a circadian system. By crossing Arabidopsis thaliana plants containing mutations that cause changes in circadian rhythms, we have created heterozygous 'Mother' (F1) plants with genetic variance for circadian rhythmicity. The segregating F2 offspring present a range of circadian rhythm periods. We have applied a selection to the F2 plants of short and long T-cycles under different competition strengths and found that the average phenotype of circadian period of the resulting F3 plants show a strong positive correlation with the T-cycle growth conditions for the competing F2 plants. Consistent with their circadian phenotypes, the frequency of long-period alleles was altered in the F3 plants. Our results show that F2 plants with endogenous rhythms that more closely match the environmental T-cycle are fitter, producing relatively more viable offspring in the F3 population. Thus, having a circadian clock that matches with the environment is adaptive in Arabidopsis.

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Circadian clocks and adaptation in Arabidopsis

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