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Red squirrels
Stan Boutin and his students have been monitoring red squirrels in the southwest Yukon since 1987. Over this 17-year period roughly 5000 squirrels have been permanently tagged and monitored throughout their lifetime (up to 8 years of age). As a result, we have a fairly detailed understanding of the ecology of this population. For more details [ click here ].
Maternal effects and microevolution ( back to top ) Maternal effects are widespread and can have dramatic influences on evolutionary dynamics, but their genetic basis is measured rarely in natural populations. In the breeding seasons of both 1999 and 2000, I used cross-fostering techniques to estimate both direct (heritability) and indirect (maternal) influences on the potential for evolutionary change. Juvenile growth in both body mass and size had significant amounts of genetic variation, but experienced large, heritable maternal effects. The consideration of these indirect genetic effects revealed a greater than three-fold increase in the potential for evolution of growth in body mass relative to that predicted by heritability alone. Survival data for 1, 352 juveniles born over the last 12 years in this population indicated that selection on juvenile growth rates varied in intensity and direction from one year to the next. Phenotypic changes in juvenile growth rates across years cannot be explained adequately by simple evolutionary genetic equations (response = selection x heritability). Instead, changes in juvenile growth rates are influenced both directly by contemporary selection as well as indirectly via maternal effects. These data indicate that maternal effects have played a very important role in the evolution of juvenile growth rates in this population over the past 12 years. The ability to manipulate individual squirrels of known pedigree (15 years, ~750 females, paternity currently unknown but see below) within a relatively large population provides an elegant system for examining short-term evolution in a natural mammalian population. Climate change and the timing of breeding ( back to top ) Spring temperatures in the southwest Yukon have increased by roughly 2 °C over the last 27 years and the abundance of spruce cones in our study area has increased dramatically over the last 10 years. Collaborative work with Stan Boutin, Denis Réale and Dominique Berteaux has shown that mean lifetime parturition date in our population of squirrels has advanced by 18 days over this same time period. Much of this advancement in the timing of breeding can be explained by the large degree of phenotypic plasticity for this trait. However, there has also been consistent directional selection favouring earlier breeding (i = -0.17). Analysis of our existing squirrel pedigree using a maximum likelihood 'animal model' (DFREML) revealed significant additive genetic variation in parturition date (h2 = 0.16) and indicated that breeding values for parturition date had advanced by nearly 3 days over this 10-year period, which agrees with predictions from the breeder's equation. It appears therefore, that this large phenotypic response in the squirrels to changes in environmental conditions was the result of both phenotypic plasticity and a genetic response to directional selection. Media reports on this work can be found at: CBC, New Scientist & The Guardian
Paternity ( back to top ) Hair samples have been collected from roughly 2000 squirrels in this population since 1998. Microsatellite primers for red squirrels are currently being developed and tested in Dave Coltman's lab at the University of Sheffield. We will use these samples to add patrilines to our existing pedigree. Jeff Lane a Ph.D. student in the Boutin lab will be using a combination of behavioural and genetic techniques to examine patterns of male reproductive success in this population.
Food experiment ( back to top ) Red squirrels in the southwest Yukon feed almost exclusively on the seeds of white spruce (Picea glauca) cones. The abundance of spruce cones varies annually over three orders of magnitude. Recent work in this population suggests that many aspects of red squirrel behaviour, physiology, life history and genetics are shaped by this large amount of variation in food abundance. We have recently initiated an ambitious large-scale food supplementation experiment whereby an entire population of squirrels will be continuously supplemented with food for the next 5-7 years. Collaborative work with Stan Boutin, Murray Humphries, Dave Coltman and Jon Slate will investigate the population, behavioural, physiological and genetic responses of the red squirrels to this experimental manipulation. My particular interest in this experiment concerns the supplementation effects on natural selection, genetic architecture and evolutionary responses to selection.
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