The circadian clock is an endogenous regulator of many biological processes. The clock specifically integrates abiotic signals of the environment, including photoperiod and temperature, and enables adaptive timing of biological and physiological activities to diurnal changes. The clock is an important determinant of fitness and a 24-hr endogenous cycle is hypothesized to confer an advantage; yet, significant variation in clock period length exists among populations. Few studies have examined how genetic variation is partitioned among vs within natural populations. For this project, 20 populations of a local plant species (Boechera stricta) were selected to assess for circadian period by utilizing 20 family lines from each population. The populations were selected by their location in multiple mountain ranges and at varying elevations. Leaf movement assays were conducted to determine period for each family line.
Results/Conclusions
Across the selected distribution, the mean values among the populations ranged from 20.8h to 24.3h. The amount of variation within individual populations was up to 6 hours, exceeding the published global among-population values for other plant species. Most populations have a mean value close to 24 hours, but populations with low values are not spatially autocorrelated, instead associated with environmental values. Within the populations of B. stricta, the range of values track with elevation; at higher elevations, values for circadian period are constrained to less than 2 hours, contrasted with high intrapopulation variation for plants from lower elevations. Previous work has focused on single genotypes per site across large spatial scales, but our work highlights the amount of variation for circadian period harbored within single populations. As the clock affects important physiological traits and is generally thought to affect performance, the extent of intrapopulation genetic variation in the clock also affects the opportunity for adaptive evolution.