Dissecting the Contributions of Plasticity and Local Adaptation to the Phenology of a Butterfly and Its Host Plants

Abstract

Phenology affects the abiotic and biotic conditions that an organism encounters and, consequently, its fitness. For populations of high-latitude species, spring phenology often occurs earlier in warmer years and regions. Here we apply a novel approach, a comparison of slope of phenology on temperature over space versus over time, to identify the relative roles of plasticity and local adaptation in generating spatial phenological variation in three interacting species, a butterfly, Anthocharis cardamines, and its two host plants, Cardamine pratensis and Alliaria petiolata. All three species overlap in the time window over which mean temperatures best predict variation in phenology, and we find little evidence that a day length requirement causes the sensitive time window to be delayed as latitude increases. The focal species all show pronounced temperature-mediated phenological plasticity of similar magnitude. While we find no evidence for local adaptation in the flowering times of the plants, geographic variation in the phenology of the butterfly is consistent with countergradient local adaptation. The butterfly's phenology appears to be better predicted by temperature than it is by the flowering times of either host plant, and we find no evidence that coevolution has generated geographic variation in adaptive phenological plasticity.

Effect of winter cold duration on spring phenology of the orange tip butterfly, Anthocharis cardamines

“…More generally, the statistical method used to detect local adaptation by Phillimore et al. (2012), and also by Roy et al. (2015), allows for the time of emergence to covary with only one environmental variable (e.g., spring temperature), whereas the combined experimental results of this study and Stålhandske et al.…”

“…Thus, the seeming discrepancy in geographic patterns of phenology between Phillimore et al. (2012) and Stålhandske et al. (2014) could be the result of geographic differences in winter chilling.…”

“…(2012) detected a countergradient pattern. They found a latitudinal gradient with the northern UK population appearing to respond more strongly to spring warmth.…”

Estimating the ability of plants to plastically track temperature‐mediated shifts in the spring phenological optimum

“…First dates are also sensitive to sampling effort and species abundance; if either covaries with spring temperatures over time and/or space, this can bias any of our slope estimates up or down (appendix A in Phillimore et al, 2012). window) was identical to the best performing temp model for each species.…”

“…We obtained an estimate of the variance-covariance between response variables for each random effect (r): (Phillimore et al, 2012). When year was the random effect, we obtained a temporal slope (i.e.…”