Long-Term Decrease in Coloration: A Consequence of Climate Change?

TL;DR

This study shows that climate change has led to duller and less chromatic ornamental coloration in blue tits over 15 years, likely due to environmental plasticity rather than genetic evolution.

Contribution

It provides evidence that climate warming influences social and sexual traits in wild birds through phenotypic plasticity, not microevolution.

Findings

Coloration has become duller and less chromatic in blue tits.

Temperature increase at moult correlates with decreased coloration.

No microevolutionary change detected in color traits.

Abstract

Climate change has been shown to affect fitness-related traits in a wide range of taxa; for instance, warming leads to phenological advancements in many plant and animal species. The influence of climate change on social and secondary sexual traits, that are associated with fitness due to their role as quality signals, is however unknown. Here, we use more than 5800 observations collected on two Mediterranean blue tit subspecies (Cyanistes caeruleus caeruleus and C.c. ogliastrae) to explore whether blue crown and yellow breast patch colourations have changed over the past 15 years. Our data suggests that colouration has become duller and less chromatic in both sexes. In addition, in the Corsican C.c. ogliastrae, but not in the mainland C.c. caeruleus, the decrease is associated with an increase in temperature at moult. Quantitative genetic analyses do not reveal any microevolutionary change in the colour traits along the study period, strongly suggesting that the observed change over time was caused by a plastic response to the environmental conditions. Overall, this study suggests that ornamental colourations could become less conspicuous due to warming, revealing climate change effects on sexual and social ornaments and calling for further research on the proximate mechanisms behind these effects.