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Origin and functions of iridescent colours in hummingbirds

Abstract : The study of colour can offer valuable insights into the fine details of evolutionary mechanisms. It is indeed a complex trait, which can evolve along several dimensions, and which is controlled by multiple selective pressures with often opposed effects. Yet, there is one class of colours that has received few attention from evolutionary biologists: iridescent colours. This is due to the inherent complexity of these colours and the fact that their sole quantitative measurement is a challenge in itself. During my PhD, I worked with physicists and biologists and I used optical theory to propose a new measurement method for iridescent colours. I then validated this method empirically by showing that it produced reliable and repeatable estimates for both hummingbirds and \textit{Morpho} butterflies. My work during these three years has also focused on the development of other methodological tools and software for the study of colours. I also focused more precisely on iridescent colours in hummingbirds. I mainly investigated two sides of this topic and tried to find out (i) the proximate causes of iridescence in hummingbirds: how do they produce the striking colours they are renowned for? (ii) the ultimate causes of iridescence: what are the evolutionary mechanisms which control the evolution of iridescence at the community level? I found out that the structures producing iridescence in hummingbirds are way more diverse than what we previously thought. They even display an usual type of structure which has not been described in any other group yet. I also showed that at the interspecific level, iridescent colours on the back of hummingbirds tend to be similar among species occupying the same communities, which suggests a possible role of the environment in the evolution of these colours, possibly for camouflage against predators. On the other hand, colours on the belly tend to be more similar than expected by change among co-occurring species, which suggests a role of selection for communication.
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Hugo Gruson. Origin and functions of iridescent colours in hummingbirds. Populations and Evolution [q-bio.PE]. Université de Montpellier, 2019. English. ⟨tel-02465397⟩

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