Brood-parasitic birds lay eggs that mimic those of other species, to trick hosts into incubating their egg and raising their chick. Hosts often fight back by evolving egg colours and patterns that look different from those of their parasites, making an impostor easier to spot. In this study, we tested whether natural selection also drives hosts to evolve eggs that look different from those of other hosts, to avoid being susceptible to their neighbour’s specialist parasites when several host species live side by side. Using data from Major John Colebrook-Robjent‘s wonderful egg collection, we find evidence for this in the hosts of African brood-parasitic birds, which have evolved astonishingly diverse eggs. Read more in the full paper is published in Proceedings of the Royal Society of London B, by Eleanor Caves (former MPhil student), Martin Stevens and Claire Spottiswoode; see also a news article about this research in The Economist.
Our paper ‘Why and how to apply Weber’s Law to coevolution and mimicry’ has been published in the journal Evolution. This perspectives paper, written by Tanmay Dixit, Eleanor Caves, Claire Spottiswoode, and Nicholas Horrocks, argues that Weber’s Law of proportional processing can lead to otherwise counterintuitive predictions about the evolutionary trajectories of mimicry systems. Weber’s Law states that when the magnitude of a stimulus is large, it is more difficult to discriminate a change or difference from that stimulus. In other words, relative differences are more salient than absolute differences. We show that Weber’s Law could have implications for mimicry: when stimulus magnitudes are high, it should be more difficult to discriminate a model from a mimic. This leads to testable predictions about evolutionary trajectories of models and mimics. We also present a framework for testing Weber’s Law and its implications for coevolution.