| Summary: | The ability of individuals to change breeding time is predicted to be an important aspect of adapting to climate change. Changes in breeding time could occur through either behavioural adjustment of breeding time or evolution. To date, few studies have investigated these processes in Arctic environments, where temperature is rising at a greater rate than the global mean. I evaluated the contribution of behavioural adjustment of breeding time and evolution to changes in breeding time associated with annual variation in snow melt and female breeding age over a 42-year dataset from an Arctic population of Black Guillemots (Cepphus grylle mandtii). I used an Animal Model to decompose the variance observed in breeding time and I used three fitness metrics in a bivariate Animal Model to estimate selection on clutch initiation DOY. Finally, I examined the temporal trend in the genetic component of variation in clutch initiation date to determine if evolution contributed to the shift in breeding time. During the study period mean clutch initiation date advanced 7.8 days, snow melt date advanced 7.6 days, and the average female breeding age increased by 4.7 years. Earlier clutch initiation was associated with experienced mothers, earlier snow melt, and higher fitness. Individuals advanced clutch initiation at different rates as they aged but responded similarly to variation in snow melt. Heritability of clutch initiation date was negligible (h2 = 0.04, 95% CI [0.00-0.11]), and there was no evidence of evolution contributing to the change in breeding time. My results suggest that covariation between clutch initiation date and fitness is driven by environmental, but not genetic factors. Consequently, changes of breeding time in Black Guillemots are likely driven by plastic behavioural adjustment with limited potential for evolutionary change. M.Sc.
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