Increase in body size is correlated to warmer winters in a passerine bird as inferred from time series data.

Mats Björklund,Antoni Borras,Juan Carlos Senar,Josep Cabrera

doi:10.1002/ece3.1323

Abstract

Climate change is expected to affect natural populations in many ways. One way of getting an understanding of the effects of a changing climate is to analyze time series of natural populations. Therefore, we analyzed time series of 25 and 20 years, respectively, in two populations of the citril finch (Carduelis citrinella) to understand the background of a dramatic increase in wing length in this species over this period, ranging between 1.3 and 2.9 phenotypic standard deviations. We found that the increase in wing length is closely correlated to warmer winters and in one case to rain in relation to temperature in the summer. In order to understand the process of change, we implemented seven simulation models, ranging from two nonadaptive models (drift and sampling), and five adaptive models with selection and/or phenotypic plasticity involved and tested these models against the time series of males and females from the two population separately. The nonadaptive models were rejected in each case, but the results were mixed when it comes to the adaptive models. The difference in fit of the models was sometimes not significant indicating that the models were not different enough. In conclusion, the dramatic change in mean wing length can best be explained as an adaptive response to a changing climate.

Highlights

It is well established that the climate is changing with increasing temperatures as one of the factors that is changing
A great deal of effort has been devoted to test whether a change is plastic or due to a genetic change as a result of selection (Meril€a and Hendry 2014), and plasticity has been used as a null model against which genetic changes are tested
Wing length in La Bofia females was positively correlated to winter PC1 in the same year (Table 2), but in males from La Bofia and males and females from La Vansa, we found a positive correlation with winter PC1 and wing length the year after (Table 1)

Summary

Introduction

It is well established that the climate is changing with increasing temperatures as one of the factors that is changing. Given that the change in temperature may lead to selection, and the fact that most traits host measurable amounts of additive genetic variation, we would expect that populations respond to selection in an adaptive way, that is, by a genetic change due to selection. A dichotomization of either a genetic or a plastic change is not biologically realistic because in most cases, we have both factors acting at the same time to a varying relative extent. This is, for example, clearly expressed in the Price theorem where change between generations in traits means is the sum of selection and “transmission bias”, that is, factors such as plasticity (e.g., Rice 2004)

Methods

Results

Conclusion