American Society of Naturalists

Collin B. Edwards and Louie H. Yang (Jan 2021)

A model simulating the evolution of phenological cueing strategies with climate data shows variable phenological shifts

Read the Article (Just Accepted)

As the climate changes, plants and animals are shifting the timing of their activities (“phenology”): many butterflies are now active earlier in the spring, for example, and many plants now flower weeks earlier than they used to. However, these changes are not always consistent: different species may shift their phenology very differently. In a study appearing in The American Naturalist, Dr. Collin Edwards (graduate student at Cornell University, now a postdoctoral researcher at Tufts University) and Dr. Louie Yang (associate professor at University of California, Davis) demonstrate how the evolution of cue use could produce these variable responses to climate change. They present a simulation study in which organisms can evolve to start their life activity (e.g. a plant can germinate or an insect can emerge) based on a combination of three environmental cues – the local temperature, the local precipitation, and the day of the year (photoperiod). By simulating populations of these organisms using real climate data from 78 locations across North America and Hawaii, the authors demonstrate two mechanisms that could lead to the variability seen in real species. First, they found that simulated species evolved to respond to different environmental cues in the different climates across North America, and the best strategy depended on how reliably different combinations of cues predicted favorable weather in the future. For example, simulated populations in Farmington, Maine generally relied on precipitation as a cue, while simulation populations in Davis, California did not. Surprisingly, they also find that for any given climate, there are often multiple strategies that are equally viable but rely on very different cues. For example, some populations simulated in the Davis climate relied almost entirely on temperature as a cue, while others relied almost entirely on day of year. When populations differed in strategy – either because they evolved in different climates or because they evolved different strategies in the same climate – they responded differently to simulated climate change, just as real species are responding differently. This study reveals a novel mechanism driving the evolution of phenological strategies, and suggests that as the climate continues to change, we should expect to see increasing variation between species in the timing of activities like germination, hatching, flowering, and mating.

---

Abstract

Several studies have documented a global pattern of phenological advancement that is consistent with ongoing climate change. However, the magnitude of these phenological shifts is highly variable across taxa and locations. This variability of phenological responses has been difficult to explain mechanistically. To examine how the evolution of multi-trait cueing strategies could produce variable responses to climate change, we constructed a model in which organisms evolve strategies that integrate multiple environmental cues to inform anticipatory phenological decisions. We simulated the evolution of phenological cueing strategies in multiple environments, using historic climate data from 78 locations in North America and Hawaii to capture features of climatic correlation structures in the real world. Organisms in our model evolved diverse strategies that were spatially autocorrelated across locations on a continental scale, showing that similar strategies tend to evolve in similar climates. Within locations, organisms often evolved a wide range of strategies that showed similar response phenotypes and fitness outcomes under historical conditions. However, these strategies responded differently to novel climatic conditions, with variable fitness consequences. Our model shows how the evolution of phenological cueing strategies can explain observed variation in phenological shifts and unexpected responses to climate change.