Similarities in butterfly emergence dates among populations suggest local adaptation to climate

Abstract

Phenology shifts are the most widely cited examples of the biological impact of climate change, yet there are few assessments of potential effects on the fitness of individual organisms or the persistence of populations. Despite extensive evidence of climate‐driven advances in phenological events over recent decades, comparable patterns across species' geographic ranges have seldom been described. Even fewer studies have quantified concurrent spatial gradients and temporal trends between phenology and climate. Here we analyse a large data set (~129 000 phenology measures) over 37 years across the UK to provide the first phylogenetic comparative analysis of the relative roles of plasticity and local adaptation in generating spatial and temporal patterns in butterfly mean flight dates. Although populations of all species exhibit a plastic response to temperature, with adult emergence dates earlier in warmer years by an average of 6.4 days per °C, among‐population differences are significantly lower on average, at 4.3 days per °C. Emergence dates of most species are more synchronised over their geographic range than is predicted by their relationship between mean flight date and temperature over time, suggesting local adaptation. Biological traits of species only weakly explained the variation in differences between space‐temperature and time‐temperature phenological responses, suggesting that multiple mechanisms may operate to maintain local adaptation. As niche models assume constant relationships between occurrence and environmental conditions across a species' entire range, an important implication of the temperature‐mediated local adaptation detected here is that populations of insects are much more sensitive to future climate changes than current projections suggest.

Winter chilling speeds spring development of temperate butterflies

“…() and Roy et al . () to our UK data for the period 1976–2013, we detected a statistically significant countergradient variation in the UK for A. cardamines , with a steeper among year slope of phenology against average spring temperature (over 120 days) than between‐population (over space) slope (Table S6), which is similar to what has previously been found by Phillimore et al . () and Roy et al .…”

“…() and Roy et al . (). This MCMCglmm approach can be extended to include winter cold duration as an environmental variable.…”

“…() and Roy et al . (). The aim of these two analyses was to investigate population structure of the butterflies using a statistical method based on quantitative genetics.…”

“…() and Roy et al . (), but extended to include winter cold duration as a variable and ran the model as a trivariate analysis with winter duration, spring temperature and butterfly phenology as response variables. We used a similar method to Phillimore et al .…”

“…In spite of this, many studies that aim to predict future changes of the phenology of wild species use correlations with only spring temperature, estimated as an average temperature over one or several months (Roy et al . ). Although this approach can reveal interesting patterns, it ignores potentially important effects of other variables on phenology, including effects of winter chilling.…”