Hybridization, adaptation and ecological opportunity

Abstract: A fundamental theory of quantitative genetics predicts that the amount of standing genetic variation is crucial to adaptation and the generation of diversity. My research shows that hybridization between distant species instantaneously elevates levels of genetic variation and can lead to adaptive advantages of hybrids under stressful conditions. I used Saccharomyces yeast to generate hybrid populations of vast genetic and phenotypic variation and tested their evolutionary potential under different environmental scenarios. I found that transgressive segregation generates extreme hybrid phenotypes that were between 1.5 and 3-fold fitter than the mid-parent, enabling them to colonize novel environments lethal to parental populations. The extent of hybrid transgression was correlated to the genetic and phenotypic crossing distance between their parents, consistent with the prediction that allelic complementation and/or epistasis in hybrids become more frequent the longer two parental lineages have evolved independently from each other. Using experimental evolution in gradually deteriorating environments, I further show that hybridization can lead to the evolutionary rescue of populations. Hybrids adapted to more degraded environments than non-hybrids, resulting in survival rates far exceeding those of their ancestors. The resilience of populations to habitat degradation is a major concern for biodiversity conservation. My research shows that hybridization can increase evolutionary responsiveness and that taxa able to exchanges genes with distant relatives may better survive rapid environmental change. This may be useful in a world where hybridization is becoming increasingly common due to the relocation of plants and animals by humans.