The role of sexual signal evolution in speciation and species coexistence

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Nowhere is the diversity of life more apparent than in the astonishing array of colours and sounds animals use to communicate with each other. Similar to human language, animals use signals to identify relatives, defend territories and attract mates. However, the types of signals used by individuals can be very different from one species to the next. For example, male peacocks attract females using their technicoloured tail feathers, whereas the redwing blackbird displays a red wing spot with a yellow stripe to win mates. But why does this spectacular diversity exist and how did it arise? On top of this, the evolution of new signals over millions of years can lead to the breakdown of communication between related populations, and is therefore predicted to promote the formation of new species with different ways of communicating. For centuries, evolutionary biologists including Charles Darwin have questioned why animals use so many different signals to communicate, and whether the evolution of new signals leads to the formation of new species. Yet, despite this long-standing interest, answering these fundamental questions still remains a major challenge.For the first time, it is now possible to measure the diversity of communication signals across thousands of animal species using new technologies, including ultraviolet digital photography and sound recording. Birds are famous for their striking plumage colour and song, and with almost 10,000 different species, they provide a unique opportunity to test these ideas on a global scale. Birds perceive the world in a very different way to humans and other animals, as their eyes are sensitive to ultraviolet light, allowing them to see colours invisible to the human eye. I will generate novel datasets capturing the full spectrum of diversity in visual and acoustic signals across all birds. The power of my approach lies in the fact that I will be able to reconstruct how birds themselves hear songs and see plumage colour-the two main ways that birds communicate with each other. I will use these novel datasets to compare signals across species in order to understand how and why signals change over time, and whether new signals coincide with the origin of new species. I will combine this with detailed observations of natural bird populations in one of the most biodiverse regions on Earth, the Himalayas. This will make it possible to study the present-day consequences of changes in communication signals for interactions among species and the factors promoting biodiversity.Together, my research will shed light on unresolved evolutionary questions by exploring how and why signals change over millions of years across species, and the consequences of this for the origin and maintenance of new species. My research will significantly advance our knowledge of the processes underlying the evolution of animal communication signals and ultimately the role that such signals play in promoting and maintaining the diversity of life on Earth.