Habitat loss is splitting the world?s plants and animals into smaller and more isolated fragments. At the same time, many organisms also have to withstand rapid and stressful changes to their environment. Combined, these factors can increase extinction risk. One possible escape from extinction is through adaptation. Yet, small populations with low genetic diversity may be unable to adapt in time to keep pace with environmental change. An approach sometimes used to increase genetic diversity is to move individuals from one site to another. In theory, this method could prevent extinction by increasing the potential and speed of adaptation. But, it is unknown how this occurs, or how often it works. This project will determine whether small populations that received new genes can adapt faster to a stressful environment and avoid extinction compared to those that have not. This project will focus on studying eastern mosquitofish in outdoor tanks. These fish tanks will have different amounts and types of genetic diversity, and some will be heated to make their environment stressful. The researchers will measure changes in genes and in the number of fish in each tank over several years. At the end of the experiment they will determine whether fish from heated tanks can resist heat better than fish from unheated tanks. Genes involved in adaptation to heat will be identified, and the researchers will assess whether tanks that received new fish were less likely to go extinct. This project will reveal the genetic factors that contribute to adaptation versus extinction. Importantly, outcomes from this work will inform management decisions and improve biodiversity conservation. Broader Impacts include K-12 outreach through teacher training and summer camp activities for students. A postdoctoral researcher and several graduate and undergraduate students will be trained as part of this project.
Rapid adaptation has the potential to rescue populations facing novel, stressful environments. Yet, this will only happen if populations can survive under stressful conditions and also have sufficient genetic variation to respond to selection. Most of the evolutionary rescue literature focuses on the roles of local standing variation or de novo mutation, largely ignoring the beneficial or constraining roles of gene flow and genetic drift. Recent evidence suggests that gene flow may be an important source of variation that can result in increased population growth, especially when recipient populations are small and inbred. However, direct evidence that gene flow can prevent extinction is lacking from natural populations, and long-term benefits of gene flow such as increased adaptive potential have almost never been shown. The proposed research will investigate how differences in recent evolutionary history (i.e., genetic drift and gene flow) affect adaptive response and persistence in the face of novel stress. The project will generate experimental populations of eastern mosquitofish with different recent evolutionary histories. The researchers will use acute stress experiments to test the effects of evolutionary history on initial and evolved thermal tolerance. A multigenerational mesocosm experiment will be used to test how evolutionary history affects individual fitness, population dynamics, and extinction probability in populations exposed to chronic novel stress (near-lethal heat) compared to a benign environment. Finally, the researchers will generate whole genome sequence data from wild populations and from a time series collected from the mesocosm populations to identify genomic mechanisms underlying adaptation and demography. This project will provide a unique mechanistic view of the eco-evolutionary roles of genetic drift and gene flow and may fundamentally change generally accepted expectations about the role of gene flow in contemporary populations.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
