I study evolution in wild populations on a contemporary time scale. I am currently a postdoc in Dmitri Petrov's lab at Stanford, where I am investigating fluctuating selection on Drosophila spp. in response to seasonal variaiton. I am also sequencing and assembling the red squirrel genome. My PhD investigated the evolutionary maintenence of personality in a wild population of red squirrels. I was advised by Andrew McAdam at the University of Guelph and Kay Holekamp at Michigan State University.
My dissertation established that temporally fluctuating selection might help maintain variation in animal personality and that behavioral traits play important ecological and evolutionary roles in a wild population of red squirrels. It also highlighted the importance of considering potentially confounding sources of environmental variation in quantitative genetic analyses by showing that maternal effects can have important effects on personality.
ActivityI measured activity as the active response of a squirrel to a novel environment (i.e. an open-field arena). Here are two videos superimposed - only one squirrel was tested at a time - characterizing the range of activity levels displayed by individuals.
AggressionI measured aggression as the aggressive response of a squirrel to its mirror image. This is an aggressive squirrel - notice how it attacks the mirror. Non-aggressive individuals would not even approach the mirror (on the left wall).
A fundamental question – is personality heritable? The variation in heritable traits is due, by varying degrees, to genetic differences. If personalities are caused by genetic differences then they can evolve, but other sources of variation are also interesting. I showed that red squirrel behavioral traits are heritable, but also that other sources of variation can be important. For example, maternal effects contribute approximately twice the variation as additive genetic effects to the activity of a squirrel. These results also highlight the importance of considering potentially confounding sources of environmental variation in quantitative genetic analyses.
Temporal variation in selection has long been proposed as a mechanism by which genetic variation could be maintained despite strong directional selection. Fluctuating selection has also been invoked to explain the maintenance of consistent individual differences in behavior.
I tested the hypothesis that ecological changes through time lead to fluctuating selection, which could maintain variation in behavioral traits, in a wild population of North American red squirrels. Linear selection gradients on red squirrel dam aggression and activity significantly fluctuated in sign across years depending on the level of competition among juveniles. Selection on aggression and activity also differed among components of fitness, between the sexes and included nonlinear components between and within traits that also changed through time. These results suggest that repeatable and heritable individual differences in red squirrel behavior could be maintained by complex fluctuations in natural and sexual selection.
Mate choice allows individuals to select beneficial genes for their offspring, but which genes are beneficial may depend on the environment or compatibility with the chooser's genes. Red squirrels perform dynamic and demanding mating chases where up to a dozen males vie for opportunities to mate with females on her single day of estrus.
Selection on red squirrel behavior through offspring recruitment fluctuates in response to annual changes in the degree of competition among juveniles for territorial vacancies. I tested the hypotheses that mating chases provide the opportunity for both female and male red squirrels to select for context-dependent good genes and complementary genes for their offspring's recruitment. Specifically, I predicted that aggressive mates would be preferred in high-juvenile competition years, but disfavored in low competition years, and that mate choice for docility would be disassortative with low-docility squirrels preferring high-docility mates and vice-versa.
I did not find support for adaptive context-dependent mate choice by females, but I did find support for male mate choice for complementary genes that was mediated through which female mating chase males attended. Male red squirrels attended mating chases disassortatively by docility, which would enhance fitness due to stabilizing selection on docility during juvenile recruitment. I also found evidence for post-copulatory selection for less aggressive males. These results highlight that even in systems with very high operational sex ratios, males choice is a factor that needs to be considered.
- Taylor, R. W., Humphries, M. M., Boutin, S., Gorrell, J. C., Coltman, D. W., and McAdam, A. G. Disassortative mate-choice on behavior in red squirrels. In Preparation.
- Taylor, R. W., Humphries, M. M., Boutin, S., Gorrell, J. C., Coltman, D. W., and McAdam, A. G. Fluctuating and nonlinear selection on behaviour in a wild population of red squirrels. In Review.
- Shonfield, J., Taylor, R. W., Boutin, S., Humphries, M. M., McAdam, A. G. 2012. Territorial defence behaviour in red squirrels is influenced by local density. Behaviour 149: 369—390.
- Taylor, R. W., Boon, A. K., Dantzer, B., Réale, D., Humphries, M. M., Boutin, S., Gorrell, J. C., Coltman, D. W., and McAdam, A. G. 2012. Low heritabilities, but genetic and maternal correlations between red squirrel behaviours. Journal of Evolutionary Biology, 25(4), 614—624.
- McFarlane, S. E., Lane, J. E., Taylor, R. W., Gorrell, J. C., Coltman, D. W., Humphries, M. M., Boutin, S., et al. (2011). The heritability of multiple male mating in a promiscuous mammal. Biology Letters, 7(3), 368—371.