Fitness effects of gene flow (both advantageous and deleterious) have garnered plenty of recent press and scientific exploration. At the population level, the concepts and consequences are notoriously familiar. In the context of immigration, they reduce to existing genetic variation, and new variation introduced into the recipient “sink” population, or conversely, homogenizing effects, and loss of overall biodiversity at the species level. Emigration on the other hand (gene flow to a new environment) could result in local adaptation, and eventual speciation, or loss of genomic diversity due to pervasive inbreeding, and eventual extinction. Three recent manuscripts attempt to summarize/study these concepts, and provide neat springboards for future explorations
- Genetic rescue to the rescue – Whiteley et al. (2015) TREE
Genetic Rescue (GR) can be advantageous to small inbred populations in many ways, due to increased genetic diversity introduced into the “sink” population, often increasing fitness of the population, and its ability to evolve adaptively. But the central debate in the efficacy of genetic rescue lies in whether it delivers on its promise above, or results in what’s known as “outbreeding depression” – the overall reduction of genetic diversity (at the species level), leading to more homogenous populations with reduced diversity. Whiteley et al. (2015) in this excellent TREE review assess numerous studies that have measured population fitness in the context of genetic rescue in several taxa. They also provide an excellent review of the state of the science in utilizing genetic rescue for conservation efforts.
GR may not save imperiled populations over the long term (ultimately, sufficient habitat is required for that), but recent results show that GR can buy time by improving their fitness and increasing population sizes in the short term.