Understanding colour polymorphism in birds
Many species show a variety of different phenotypes. How this diversity is maintained is one of the main questions in evolutionary biology. Researchers have long been fascinated by this phenomenon because the occurrence of two or more phenotypes in the same population runs counter to the notion that selective pressure should favour the optimal form for an environment, and any lesser quality individuals should be quickly eliminated through natural selection. Colour polymorphism occurs where a population of animals displays different colour morphs that are unrelated to age or sex and occur too frequently to be due to recurrent mutation. Colour polymorphism is rare in birds, occurring in around 3.5% of species. However, it is more common in raptors and particularly within Accipiter hawks where about 25% of species are polymorphic.
Our research in this field focuses primarily on the Black Sparrowhawk Accipiter melanoleucus. We use this model species to test various hypotheses for the occurrence and maintenance of colour polymorphism in bird species. Our study population breeds on the Cape Peninsula and is unusual in that most adults consist are the rarer dark morph. The main focus of our research has been attempting to explore the occurrence and persistent of this unusual morph ratio in this area.
In addition, we have been investigating the use of images sourced through internet search engines to document the distribution of visual phenotypes such as colour morphs in animal species.
Activities in 2016
- Gareth Tate submitted his PhD ‘Exploring the maintenance of plumage polymorphism in the Black Sparrowhawk’.
- Sanjo Rose's BSc Hons dissertation explored whether the morphs of Black Sparrowhawks are distributed differently according to the degree of urbanisation.
- Edmund Rodseth (MSc candidate in Molecular and Cell Biology, UCT) continued to make good progress on his study to identify the genetic pathway for colour polymorphism in Black Sparrowhawks.
- In collaboration with Dr Christopher Briggs in the United States, we are using MORPHIC to describe the distribution of morphs of Swainson's Hawks Buteo swainsoni across North America.
- In another collaboration led by Dr Chiara Morosinotto, University of Turku, including the research group of Prof. Jon Brommer and Dr Patrik Karell in Finland, Dr Rui Lourenço in Portugal and Dr Anita Gamauf in Austria, we are using MORPHIC to describe spatial distribution of Tawny Owls Strix aluco across Europe in relation to climate, habitat, anthropogenic impact and diet.
- We presented our research at the Pan-African Ornithological Congress (PAOC), Dakar, Senegal; and the North American Ornitho-logical Conference (NAOC), Washington DC, United States.
- We ran a workshop at the British Ornithologist Union (BOU) conference held in Leicester, UK, to demonstrate the use of the MORPHIC web app.
- Gareth Tate was awarded his PhD and has since been appointed as Manager of the Endangered Wildlife Trust’s Birds of Prey Programme.
- Gareth published a paper which examined differential hunting success between the two morphs in relation to ambient light levels in the leading ecology journal Ecology Letters. This paper was highlighted as a recommended paper by Faculty 1000.
- Gareth published a paper from his thesis which explored the breeding performance of pairs consisting of either different or like morphs in the Journal of Avian Biology.
- Gareth submitted a paper to Scientific Reports which is currently in review. This paper uses information on GPS tracked male Black Sparrowhawks to explore whether the two morphs spend different amounts of time foraging in different habitats or in varying light levels.
- Petra Sumasgutner published a paper examining recruitment and survival rates of offspring of different morph parents in the Journal of Animal Ecology.
- Gabriella Leighton published her BSc Hons dissertation in Methods in Ecology and Evolution This research demonstrated the successful use of Google images to describe the spatial distribution of colour morphs, and included the development of the freely available web app MORPHIC which facilitates the capture of this information from the web. This paper was awarded the prize for the best paper by an Early Career Researcher published in this journal in 2016.
Impact of the project
This project will add to our understanding and theory about the maintenance of genetic diversity in populations. It provided the first empirical evidence for the light level hypothesis for the maintenance of colour polymorphism in birds. Our demonstration that Google Images can provide robust unbiased information on the spatial distribution of visible phenotypes, and the development of the MORPHIC web app, has opened up a whole new approach for research in this field.
DST-NRF CoE grant; Claude Leon Foundation; UCT URC grant.
Dr Arjun Amar (FIAO, UCT)
Dr Jacqui Bishop (Biological Sciences, UCT)
Dr Rob Ingle (MCB, UCT)
Dr Petra Sumasgutner (FIAO, UCT)
Ann Koeslag (Volunteer)
Pierre Hugo (Comp Sci, UCT)
Prof. Alex Roulin (UNIL, Switzerland)
Students: Gareth Tate (PhD, UCT); Edmund Rodseth (MSc, MCB, UCT), Gabriella Leighton (BSc Hons, UCT); Sanjo Rose (BSc Hons, UCT)
Dr Gareth Tate graduated at the end of 2016 and is now employed by the Endangered Wildlife Trust as Manager of their Birds of Prey Programme (Photo: Ann Koeslag)