Bat signal (of selection) summons evolutionary hope in face of epidemic disease: an example of the power and promise of genetic monitoring.

Abstract

A long-standing question in evolutionary biology is the extent to which adaptation to novel stressors can buffer populations from extinction. This question is arguably one of the most important questions for evolutionary biologists to answer in this age of rapid global change. Knowledge of how best to manage genetic variation in organisms faced with dramatic changes in their abiotic or biotic environment, such as those associated with anthropogenic climate change or emerging infectious disease, is critical for mitigating these threats. Genetic responses to rapid environmental changes are often characterized by selective sweeps, whereby a newly beneficial allele increases in frequency and becomes fixed in response to selection imposed by the novel stressor. The classic example of a selective sweep is referred to as a hard sweep , which is when a de novo mutation increases rapidly in frequency, resulting in a significant decrease in genetic diversity in and adjacent to the selected locus. A soft sweep , in contrast, is when a relatively more common neutral allele becomes beneficial in the new environment. Because such a previously neutral allele tends to be present in multiple haplotype blocks, genetic diversity is often maintained as the newly beneficial allele increases in frequency. Detection of hard sweeps is typically straightforward; however, soft sweeps can be challenging to detect due to the relative lack of gametic disequilibrium between the beneficial mutation and the nearby genomic background. In this issue of Molecular Ecology, Gignoux-Wolfsohn et al. (2021) test for subtle signatures of selection in bat populations recovering from mass-mortality events caused by white-nose syndrome (WNS). By combining long-term population monitoring, timely sampling, whole genome sequencing, and sensitive analytical approaches, the authors reveal evidence of population recovery driven by selection acting on standing genetic variation, characterized by soft sweeps and numerous loci of small effect. In doing so, the authors demonstrate an exemplary framework for uncovering adaptive responses to novel and dramatic stressors - knowledge that is essential to our efforts to preserve biodiversity in the face of rapid environmental change.