Guest essay by Eric Worrall
A new study claims climate stress is making some birds lose their mating ornamentation.
Climate change ecology: Hot under the collar
A 34-year study of collared flycatchers demonstrates that males are evolving to be less ornamented in response to rising temperatures.
For male collared flycatchers (Ficedula albicollis; pictured), having a large white patch on your forehead signals that you are a fearsome rival, and an attractive mate. But while large patch size was thought to give males an evolutionary advantage, it seems that climate change is turning this advantage on its head. In this issue of Nature Ecology & Evolution, Evans and Gustafsson report that the collared flycatcher’s forehead patch has declined in size because large patch males have lower fitness as the climate warms.
In many animals, males have ornamental features that are used to attract mates, and to signal to rivals during territorial interactions. While these ‘sexually selected’ ornaments can increase a male’s mating success, they can also impose a variety of costs on their bearers. Ornaments such as bright colouration can increase susceptibility to predators, or they can predispose males to competing for larger territories and more mates, at the expense of providing care for their offspring. As a result, ornamental traits are hypothesized to evolve only when the benefits of being ornamented outweigh the costs.
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While the authors demonstrate a strong link between climate warming and selection on male ornamentation, they were not able to determine the mechanism behind this link.
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Certainly, there are good theoretical reasons why climatic changes could influence animal ornamentation across the globe. As Evans and Gustafsson show, some ornaments will decline in response to environmental change, and it is conceivable that some ornaments could disappear altogether. However, there are also reasons to predict that climate change will drive the evolution of new, or exaggerated, ornaments in some species. Just as climate change will lead to winners and losers in terms of species’ abundance and distribution, it seems it may also lead to winners and losers in the global beauty pageant.
