Genetic colour polymorphism represents a rare but particularly striking form of colour signalling in which discrete colour phenotypes (morphs) provide a direct visual link to the underlying genotype determining their expression. Theoreticians have long recognised the value of genetic colour polymorphisms in providing a window into the evolution of genetic diversity, adaptations and even speciation. In particular, through investigating the full range of effects of displaying alternative colour morphs (e.g. genetics, physiology, behaviour and other life-history parameters), polymorphic systems provide a particularly appropriate opportunity to examine the full interaction of environmental and genetic factors in the adaptive evolution of colour signals. Yet, in most polymorphic species it is largely unknown how such alternative morphs optimize their evolutionarily fitness.

 

The Gouldian finch is arguably one of the most brightly coloured passerines, which also possesses a genetically-determined colour polymorphism, where both males and females display three head morphs - black, red and yellow. The head colour polymorphism is determined by two genes (one sex-linked and one autosomal), which together stimulate or suppress the production of melanin and carotenoid plumage pigments, resulting in the three discrete head morphs. A truly discrete polymorphism such as this is extremely rare in birds, as most species display continuous, or at least overlapping, variation in colour/pattern expression. Furthermore, these multiple morphs naturally coexist together in all wild populations. I am currently investigating how the morphs optimise their evolutionarily fitness, by examining the interaction of genetics, physiology and behaviour and their influence on the evolution of alternative life-history strategies. In particular, I am interested in how mechanisms such as genetic pleiotrophy, sexual imprinting, alternative behaviours (e.g. mate choice and dominance) and negative frequency-dependent selection affect the stability of the colour polymorphism.

An optimal diet is a necessity for all animals. Yet, the optimal nutritional requirements of individual's change through their lives as they experience a number of different physiological demands. For example, birds may experience larger developmental and growth demands during moult, and heavier investment into locomotion and foraging activity during chick rearing, with nutritional needs changing accordingly (e.g. more protein or energy). But surprisingly little is known about the nutritional requirements of most birds, especially as they move through different stages of their lives (e.g. initial growth, moult, pre-mating development, mating, rearing offspring, etc.).

 

In a project spanning the usually disparate fields of aviculture, physiology, behavioural ecology, and animal nutrition, we are analysing the nutritional requirements of Gouldian finches at different physiologically challenging stages of their life-cycle (i.e. a longitudinal study through their life history). This includes considering the divergent nutritional requirements of both males and females and the three head colour morphs, as well as at the impact of social stress (density and frequency-dependence) on nutrition and health. This project is funded by an ARC Linkage grant in collaboration with Simon Griffith (UNSW) and Bill Buttemer (University of Wollongong).

One group of birds ideally suited for illustrating sexual selection, sexual dimorphism and the evolution of elaborate plumage ornaments are the highly polygynous African bishop and widowbirds (Euplectes spp). The ornamental tails of widowbirds have provided some of the most fascinating examples of sexual signalling, including the classic sexual selection experiment by Malte Andersson on long-tailed widowbirds. Along with elongated tail plumes, most species also produce conspicuous yellow to red colour patches on their wings or body. This colouration is based on carotenoid pigmentation, which because of its dependence on diet and health has become a prime example of condition-dependent signalling.

 

Understanding the adaptive significance and evolutionarily coexistence of these male ornaments was the main focus of my PhD research (Göteborg University). In particular, this work investigated how the two costly signals could be maintained rather than, as predicted by current models, converging on the single most efficient (honest) trait. In these birds, the coexistence of two costly ornaments is achieved through divergent selection pressures from female mates (for long tails) and male rivals (for red badges).