Abstract
Several studies have documented a global pattern of phenological advancement across multiple taxa that is consistent with ongoing climate change1–3. However, the magnitude of these phenological shifts is highly variable across taxa and locations2–4. This variability of phenological responses disrupts species interactions under climate change5–9, but has been difficult to explain mechanistically10–13. To understand how climate change could evoke such variable responses in different groups of organisms, we constructed a model for the evolution of phenological cueing strategies using historic climate data from 78 locations in North America and Hawaii. Here we show how phenological cueing strategies can evolve in predictable ways, but still express highly variable responses to climate change. Across locations, organisms in our model evolved diverse strategies that reflected geographic differences in the reliability of different environmental cues for predicting future conditions. Within locations, a wide range of evolved strategies showed similar emergence phenotypes under historical conditions. However, these same strategies revealed previously hidden and variable responses under novel climatic conditions, with strong fitness consequences. These cryptic differences in cueing strategies evolved under historical conditions because epistasis and non-additive genotype × environment interactions among years resulted in weak selection gradients across an extensive region of trait space. These findings show how the evolution of integrated phenological cueing strategies can explain observed variation in phenological shifts and unexpected responses to climate change.