Estimates of circadian period for family lines of Boechera stricta

Circadian clocks confer adaptation to predictable 24-h fluctuations in the
exogenous environment, but it has yet to be determined what ecological
factors maintain natural genetic variation in endogenous circadian period
outside of the hypothesized optimum of 24 h. We estimated quantitative
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 elevation gradient spanning 2460−3300 m
in the Rocky Mountains. Measuring ~3800 plants from 473 maternal families
(7−20 per population), we found that genetic variation 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 accounting for spatial autocorrelation
at a habitat extreme, 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 reduced
intrapopulation ranges. 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 suggest that spatially fine-grained environmental heterogeneity
contributes to naturally occurring genetic variation in circadian traits
in wild populations.