title: Very low levels of direct additive genetic variance in fitness and fitness components in a red squirrel population.
abstract: A trait must genetically correlate with fitness in order to evolve in response to natural selection, but theory suggests that strong directional selection should erode additive genetic variance in fitness and limit future evolutionary potential. Balancing selection has been proposed as a mechanism that could maintain genetic variance if fitness components trade off with one another and has been invoked to account for empirical observations of higher levels of additive genetic variance in fitness components than would be expected from mutation-selection balance. Here, we used a long-term study of an individually marked population of North American red squirrels (Tamiasciurus hudsonicus) to look for evidence of (1) additive genetic variance in lifetime reproductive success and (2) fitness trade-offs between fitness components, such as male and female fitness or fitness in high- and low-resource environments. "Animal model" analyses of a multigenerational pedigree revealed modest maternal effects on fitness, but very low levels of additive genetic variance in lifetime reproductive success overall as well as fitness measures within each sex and environment. It therefore appears that there are very low levels of direct genetic variance in fitness and fitness components in red squirrels to facilitate contemporary adaptation in this population.
authors: Department of Integrative Biology, University of Guelph Guelph, ON, N1G 2W1, Canada.
authors: S Eryn
authors: SE
authors: McFarlane
authors: Department of Biological Sciences, University of Alberta Edmonton, AB, T6G 2E9, Canada.
authors: Jamieson C
authors: JC
authors: Gorrell
authors: Department of Biological Sciences, University of Alberta Edmonton, AB, T6G 2E9, Canada.
authors: David W
authors: DW
authors: Coltman
authors: Department of Natural Resource Sciences, McGill University, Macdonald Campus Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada.
authors: Murray M
authors: MM
authors: Humphries
authors: Department of Biological Sciences, University of Alberta Edmonton, AB, T6G 2E9, Canada.
authors: Stan
authors: S
authors: Boutin
authors: Department of Integrative Biology, University of Guelph Guelph, ON, N1G 2W1, Canada.
authors: Andrew G
authors: AG
authors: McAdam
keywords: Genetic covariance; Robertson–Price identity; heritability; sexual antagonism; temporal fluctuations in selection