Mikko Koskinen, Thrond Haugen & Craig Primmer

1. The relative role of drift and selection in life-history evolution: a case study from recently founded populations of grayling Mikko Koskinen, Thrond Haugen & Craig Primmer

2. Outline • Background to ‘Darwinian’ vs ‘neutral’ evolutionary theories • Presentation of the framework of this study • Results and conclusions

3. Natural Selection vs Random Drift? • Transplantation experiments suggest that selection is an efficient evolutionary force - Anolis lizards were introduced onto small islands - Populations differentiated from each other over 10-14 years according to the recipient island’s vegetation (Losos et al. 1997, Nature)

4. Natural Selection vs Random Drift? • Comparisons of phenotypic differentiation and selectively neutral differentiation (e.g. from non-coding DNA microsatellites) suggest that selection is an efficient evolutionary force 1 -Mean quantitative genetic (QST) differentiation generally exceeded neutral marker gene (FST) differentiation (Merilä & Crnokrak 2001, J. Evol. Biol.) QST 0.1 0.01 0.01 0.1 1 FST

5. Natural Selection vs Random Drift? S. Wright • In stark contrast with the Darwinian view, influential theories (e.g. Wright 1931, Kimura 1995) suggest that drift is the dominant evolutionary force in finite populations • It is fair to say that the ‘neutral drift hypothesis’ has been among the most controversial issues in evolutionary biology in the last 50 years, and is empirically understudied

6. Outline • Background to ‘Darwinian’ vs ‘neutral’ evolutionary theories • Presentation of the framework of this study • Results and conclusions

7. Study system European grayling, Thymallus thymallus Norway

8. The ‘plan’ • To measure quantitative genetic differences (QST) between the populations using ‘common-garden’ experiments (six early life-history traits) • Three temperatures, three populations with half-sib design • Four unique females mated with each male (28 families per population) (Spitze et al 1993, Genetics) Variance components from mixed-model Anova 95% CI from non-parametric bootstrapping • To measure neutral genetic differences (FST), i.e. the effect of drift, using 17 microsatellite DNA loci

9. The ‘plan’ • To investigate the demographic history of the populations using microsatellites, and to use that for interpreting how the results relate to the ‘Darwinian’ vs ‘neutral’ evolutionary theories • To test the null-hypothesis of neutral evolution of the six traits using: (Lande 1976, Evolution) -Ne = effective population size (maximum-likelihood estimate from microsatellite data) -s2GB = additive genetic variance between populations -s2GW = additive genetic variance within populations (among sire var comp) -h2 = narrow-sense heritability in a given population and environment -t = divergence time of populations

10. Outline • Background to ‘Darwinian’ vs ‘neutral’ evolutionary theories • Presentation of the framework of this study • Results and conclusions

11. Results - neutrality tests • Neutral evolution was rejected for the majority of the trait • Recall:

12. Results - neutrality tests • Extremely low Ne estimates, not compatible with sexual reproduction, would have been required for drift to dominate over selection F1,  = 3.84 for P  0.05

13. Results - QST vs FST • Population differences based on quantitative traits (QST) often strikingly exceeded the analogous measures based on microsatellites (FST) Les vs Ht FST length at termination yolk-sac volume growth rate incubation time swim-up length hatching length 0.0 0.5 1.0

14. Results - demographic history • Effective sizes of the populations were small • Microsatellite diversity within populations was low • The populations have historically experienced severe ‘bottlenecks’ Show examples of Ne sampling distributions and likewise for N0/N1

15. Conclusions • The evolution of the phenotypic differences between the populations was dominantly due to natural selection -neutrality tests [F-test and Ne(sign) estimates] -QST vs FST comparisons • Provide Fst/Qst+Fst

16. Conclusions • However, also drift had a notable effect (FST = 0.05-0.21) • The dominating effect of selection is interesting in the light of the demographic history of the populations. • According to the influential ‘neutral theory’, the low Nes and bottlenecks should have emphasized the effect of drift

17. Acknowledgements • Thanks to Juha Merilä, Mark Beaumont, Asbjørn Vøllestad, Peter Crnokrak, Andrew Hendry, Martin Lascoux and Nick Smith for helpful comments!