Circadian clocks manifest adaptations to predictable 24-h fluctuations
in the exogenous environment, but it has yet to be determined why the
endogenous circadian period length in the wild varies genetically around
the hypothesized optimum of 24 h. We quantified genetic variation in
circadian period in leaf movement in 30 natural populations of the
Arabidopsis relative Boechera stricta sampled within only 1° of latitude
but across an elevational gradient spanning 2460−3300 m in the Rocky
Mountains. Measuring over 3800 plants from 473 maternal families (7−20
per population), we found genetic variation that was of similar
magnitude among vs. within populations, with population means varying
between 21.9−24.9 h and maternal family means within populations varying
by up to ~6 h. After statistically factoring out spatial
autocorrelation at the habitat extremes, we found that elevation
explained a significant proportion of genetic variation in circadian
period such that higher-elevation populations had shorter mean period
lengths and less within-population variation. Environmental data
indicate that these spatial trends could be related to steep regional
climatic gradients in temperature, precipitation, and their intra-annual
variability. Our findings provide evidence that spatially fine-grained
environmental heterogeneity contributes to naturally occurring genetic
diversity in circadian traits in wild populations.
Reproduction and genetic diversity of Juniperus squamata along an elevational gradient in the Hengduan Mountains
