Impact of the rate of environmental change on underlying genetics
When the rate of environmental change is too slow, selection is weak and can be ineffective in part due to lag load [50–52]. As the rate of environmental change increases, selection strengthens, and the population can track the moving optimum with a consistent phenotypic lag[53]. In this range of environmental change, in some contexts additive genetic variance and heritability can also increase[50,54]. In this case, up to a certain intermediate rate of environmental change, genetic variation and evolutionary potential may be expected to increase simply from an increase in standing variation available to selection. However, phenotypic lag can become too large for the rate of selection to follow if the environment, and thus the optimal trait, changes too quickly[50,53,55]. Here, the gap between the mean trait in the population and the optimal trait increases, which can lead to decreased fitness and eventually extinction[56]. As such, the mean time to extinction in a natural population decreases as the rate of environmental change increases beyond the optimal rate[50].
Studies that directly assess the role of environmental variability and temporal autocorrelation on genetic variation and heritability are limited. However, increasing environmental variability, similar to the rate of change, elicits a maximal response to selection at an intermediate magnitude that optimizes selection and ultimately evolutionary tracking [57,58]. In contrast, the ability of populations to evolutionarily track a shifting adaptive peak increases with greater temporal autocorrelation because that implies increased predictability of future environments[41,56]. Moreover, positively autocorrelated environmental fluctuations can increase additive genetic variance[59]. Thus, evolutionary potential may be higher in temporally autocorrelated environments.