Maintenance of ecological polymorphism by frequency-dependent selection

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Most species have a single general type of individual in their populations, but in some species, several quite different types co-exist. The most obvious examples is that two sexes coexist, which occurs because both are required for reproduction. My research is asking how different types persist within each sex, in cases where the different types occur due to strong genetic differences. More than one kind of male, or female, are not necessary for reproduction. Why doesn't one type outcompete the other, driving it to extinction? I am exploring these questions by taking advantage of large differences body size, appearance and behaviour that are caused by single genetic differences in an extraordinary shorebird called the ruff. Most male ruffs have fancy breeding plumages, but, uniquely among birds, these are as individually variable as the coat colours of domestic cats. Birds of different colours behave differently. Dark birds are territorial, while light birds share breeding territories with owners. Females are smaller, and lack fancy plumage. Remarkably, about 1% of males, called `female mimics', have small body sizes, lack fancy plumage, do not display to females, but nonetheless achieve breeding success. I have previously learned that development into one or another male type is controlled by differences at only two genes. Such dramatic effects are unusual. In most cases many interacting genes determine large differences in such characteristics. My studies with this intriguing species ask: (1) What are the exact genes that control development into one kind of male or another, for behaviour, plumage, and body size? Extraordinary advances in the technology for processing DNA is enabling us to 'find genes' that control such functions. (2) How do these same genes express themselves differently in males and females? The gene that makes 'female mimics' also slows down breeding by females that carry it, which seems disadvantageous. Possibly as a result, a higher proportion of birds than expected that carry this gene are males. (3) What controls the sex ratio differences of birds of different types? (4) How do different types of males co-exist in the population? Why doesn't one type out compete the others? My findings will help us understand demonstrate fundamental mechanisms controlling dramatic body size, appearance, and behavioural differences in a vertebrate. These are easier to study in ruffs than in most other animals because they are caused by known genetic differences.