Impact of environmental variation and temporal autocorrelation on underlying genetics
Research on the evolutionary effect of environmental variability and autocorrelation is often framed in terms of increasing frequencies of novel and unfavourable environments [60]. Greater environmental variability and lower temporal autocorrelation expose individuals to environments that are novel and often unfavourable, and their impact on the evolutionary response is mixed depending on other factors at play. One direct consequence of higher variability and lower autocorrelation is that individuals and populations spend less time in temporal refugia [31], which reduces fitness. On the other hand, exposure to unfavourable environments driven by higher variability and lower temporal autocorrelation can also lead to increased additive genetic variance, thereby increasing the evolutionary potential of a trait[26,61,61,62,62–67]. The hypotheses for why such an increase in genetic variance could occur are reviewed in [60]. One is that selection is ineffective in removing mutations that are maladaptive only in rare environments[68]. Thus, exposure to novel environments will increase genetic variation and therefore heritability[26,69]. Determining the magnitude and frequency of this phenomenon in natural populations is an important focus for research, as the opposite effect is also known to occur[65,66,70–75].
The effect of environmental novelty on heritability, selection, and genetic variance depends also on the system-specific evolutionary history and relationship between environmental and genetic effects in producing phenotypes[60]. Contrary to above for example, some studies show that both environmental novelty and harshness can decrease additive genetic variance[65,66,70–75]. This decrease may occur if an unfavourable condition prevents individuals from expressing the underlying genetically determined benefits from a trait, for example due to lack of nutrition[71]. In such cases, selection could favour the regulation of gene expression such that alleles are not expressed in an unfavourable environment, for example by decreasing the heritability of traits underpinned by associated alleles[60]. In turn, depending on the mechanisms at play, evolutionary tracking may be either facilitated or hindered in environments with an increasing rate of change, variation, and/or autocorrelation. Whether or not a population is likely to successfully track a moving environmental optimum will in part determine the ability of plasticity to help bridge this gap.