WEAVERBIRD_DEFENCE · Unravelling an extended phenotype: sexual selection and the evolution of nest architecture in weaverbird defence against brood parasitism

Unravelling an extended phenotype: sexual selection and the evolution of nest architecture in weaverbird defence against brood parasitism

Why is nature so diverse? In the natural world, the same problems recur but nature’s solutions manifest in strikingly different forms. As evolutionary biologists, we are interested in understanding the processes and mechanisms that lead to this variation. And increasingly, as scientists and as a society, we are turning to nature for inspiration to solve human problems and to counteract the consequences of human activity. One dominant force in nature is coevolution, which often leads to escalating arms races of adaptations and counteradaptations. Cuckoos and their hosts provide a textbook example of coevolution, by reciprocally selecting for better parasitic tricks (to fool hosts into rearing cuckoo offspring) or better host defences (to avoid rearing a cuckoo chick). However, we know much less about how these arms races between species interact with the social selection pressures within species. The weavers (Ploceidae) provide a unique opportunity to investigate such questions. These small birds produce conspicuous, enclosed nests that vary both across and within species. The males produce the nests and the females choose their preferred nests in which to lay eggs. Weavers are also host species of the brood parasitic Diederik cuckoo (Chrysococcyx caprius) and the architectural design of weaver nests is thought to be an important barrier in keeping the cuckoo out of the nest, but we have a surprisingly limited understanding of this fascinating evolutionary interaction. This project had two main objectives: (1) Uncover evolutionary mechanisms that explain weaver nest structure: (a) is weaver nest architecture a defence against brood parasitism and if so, how do nests repel cuckoos? (b) to characterise the extent to which female preference for nest characteristics interacts with nest defences against cuckoos; (c) to document and examine the effects of variation in nest defences on host egg patterning (information used by hosts when making decisions about egg rejection), since nest structure influences the light environment in which host and cuckoo eggs are observed by the host. (2) To draw inspiration from natural structures using interdisciplinary approaches that could provide bio-inspired solutions to problems faced by humans. Unfortunately, work towards each of these outputs was severely curtailed owing to enduring direct and indirect effects of the global covid pandemic. Nevertheless some progress was achieved.The project grew from two strands of previous work by the the Researcher, and these continued to provide background detail to the project supported by the Marie Curie Fellowship. One previous strand examined how the appearance of a brood parasite contributes to provoking defences against parasitism by the host. The second strand of work investigated the breeding biology of weaverbirds. Even though it proved impossible to reach any conclusions about the two main objectives of the current project, five papers / preprints were produced in relation to these preliminary strands of work.

Data: CORDIS, © European Union