Our Work

Our research in Zambia addresses the general theme of how interactions between species shape evolution and generate biological diversity. We are all passionate naturalists and our work is all inspired by natural history and field observations, and depends heavily on experiments in the field. With the help of interdisciplinary collaborations, we also integrate fieldwork with techniques drawn from other fields such as evolutionary genetics, sensory biology, physiology, and applied mathematics.

We primarily study brood-parasitic birds, which are a wonderful system for researching coevolution in the wild. This is because they are locked into coevolutionary interactions with their hosts, demanding continual adaptation and counter-adaptation in both parties. They are also very tractable to field experiments. Africa is an excellent place to study brood parasites as it contains the greatest diversity of brood parasites in the world. These interactions between tropical species are often oldest and therefore most revealing of general evolutionary processes.

Much of our research addresses two general themes:

Research - egg circle

1. How do signals of identity evolve?

We are interested in understanding how coevolution shapes sophisticated signals of identity. Our work has shown that parasitism by cuckoos and cuckoo finches has driven hosts to evolve visual ‘signatures’ of identity on their eggs, made up of different combinations of colours, spots and scribbles. The astonishing beauty and diversity of egg signatures is thus the outcome of a coevolutionary arms race between signatures and forgeries: hosts are driven to escape mimicry by evolving new egg types, but are constantly pursued by the parasite. A current research focus is to ask what are the design hallmarks (both phenotypic and genetic) of a perfect signature, and reciprocally, those of a perfect forgery.

Research - egg pairs

2. How is specialisation to different coevolutionary partners maintained?

Reciprocally, coevolution has shaped ancient genetic specialisation in parasites. Our work In collaboration with Prof Michael Sorenson at Boston University, has shown that ancient host-specific genetic lineages exist within certain parasitic species. These lineages have been shaped by coevolution with hosts and allow the integrity of intricate host-specific adaptations to be preserved. For example, in greater honeyguides, we have found that different strains of females within a single parasite species transmit the genes for egg mimicry from mother to daughter via the W chromosome (that in birds is carried only by females), and have thus remained perfectly faithful to different host species for several million years. Our research has also highlighted how phenotypically plastic processes such as imprinting can be associated with highly specialised chick mimicry in parasitic finches, by facilitating speciation.

More generally, we are intrigued by how the mechanistic basis of coevolutionary adaptations and counter-adaptations might shape the trajectory of evolutionary arms races. Together with our collaborators, we are currently further exploring how cognition, genetics, biophysics, biochemistry and physiology might promote or constrain coevolutionary diversification.

Zambia is a particularly wonderful place to address these questions in part because of its remarkable diversity of brood-parasitic birds: 31 species occur, representing four of the seven groups in which brood parasitism has independently evolved in birds. Our work focusses particularly on eight species from three of these independently evolved groups: four species of parasitic finch from the genera Anomalospiza and Vidua (Viduidae), two species of honeyguides (Indicatoridae), and two species of Cuculinae cuckoos.

The Study Systems pages on this website give an overview of the natural history of each of these bird families, and summarise some of our past findings.

On the Study Systems pages,  you will also find information on two other research topics we have investigated at our study site in Zambia, with links to the theme of species interactions: first, how does the winter ecology of migratory birds allow them to exploit a radically different biotic and abiotic environment on their African non-breeding grounds? Second, how does predator vision shape the evolution of nest camouflage in ground-nesting birds?

All these research themes also benefit from cooperation with other Zambian biologists, and we work closely with colleagues at Copperbelt University, the Livingstone Museum and (forthcoming in 2021) the Choma Museum on collaborative research, capacity-building, and public outreach.

Our work also depends crucially on the field skills and hospitality of the local community where we work, in the Choma District of southern Zambia (see The Team and Thanks).

Please also visit our sister research project in Mozambique, which seeks to understand the other side of the life of one of our brood-parasitic study species, the Greater Honeyguide, as a cooperative partner of our own species: www.africanhoneyguides.com.

News

New paper published on Weber’s Law and mimicry

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. 

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New paper on evolution of egg signatures

Our paper “Hosts elevate either within-clutch consistency or between-clutch distinctiveness of egg phenotypes in defence against brood parasites” has just been published in the journal Proceedings of the Royal Society of London B. In this study, led by Eleanor Caves, we asked how host eggs evolve adaptations that allow them better to discriminate their own eggs from parasitic eggs. Theoretically, hosts can generate their own individually-distinctive egg ‘signatures’ by laying eggs that appear similar to one another (consistency) but look very different from other individuals’ eggs (distinctiveness). In this new study, we show that host species of two African brood parasites deploy either consistency or distinctiveness, but not both, as defences, and achieve distinctiveness by combining egg colours and patterns in unpredictable combinations.

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Mairenn Attwood awarded Cambridge teaching prize

Congratulations to Mairenn Attwood for being awarded the Janet Moore Prize for teaching in the Department of Zoology at the University of Cambridge, for her outstanding tutorial supervision of final-year undergraduate students, who praised her breadth and depth of knowledge, enthusiasm, and friendliness.  Mairenn follows in the footsteps of Tanmay Dixit who was awarded the Janet Moore Prize in 2020. Well done both for inspiring the next generation of behavioural ecologists!

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