The Background

Species that use colour for communication often show remarkable divergence across their range, with each population possessing a unique colour form that has, over evolutionary time, been the most successful in that particular environment.

In rare cases, however, two or more alternative colour forms can persist within a population, resulting in a state known as “colour polymorphism”. This population state is of considerable interest and importance to evolutionary biology as requires the origin and maintenance of an alternative communication signal which, under evolutionary theory, should not be allowed to occur.

Even more remarkable are instances in which colour polymorphism is found in many independent populations of the same species, where the local visual environment, population history and animal behaviour can contribute to the maintenance of colour polymorphism while also driving population divergence.

The System

The Ornate Rainbowfish, Rhadinocentrus ornatus provides a unique opportunity to study this evolutionary paradox of multiple colour forms and population divergence.

Populations from Cooloola and Fraser Island, Queensland, display considerable variation in colouration and body shape, even among neighbouring creeks. Furthermore, individuals vary in the amount of red colouration they display and the exact colour of their red pigment.

The majority of creeks harbour both red and blue colour forms, which are represented in both males and females, but vary considerable in the frequency of each. Creeks also vary extensively in their visual habitat, largely in the colour of the water, which can be anything from highly tannin-stained (dominated by red light) to crystal clear (dominated by white light).

The Approach

At each population of Ornate Rainbowfish we catch a representative sample of the adults at that location (between 50 and 100 individuals), photograph them, take caudal fin clips from 30 for genetic analysis and release them back into their habitat.

The photographs serve as a record of the ratio of red to blue fish at the site, and are analysed to calculate the amount of red an individual displays, how intense the red pigment is, and examine divergence in body shape among populations.

Genetic material allows us to construct phylogenetic trees using all populations included in the study to assess whether historical relationships or contemporary gene flow influence the patterns observed among populations.

At each location we also take a number of measurements of the visual habitat using a spectromoter, including the colour of the water, the light moving downwards and sideways through the water column, and the visual background.

 

Publications:

Hancox, D., Hoskin, C. J. & Wilson, R. S. 2010. Evening up the score: sexual selection favours both alternatives in the colour polymorphic ornate rainbowfish. Animal Behaviour, 80, 845-851.

 

Project Funding:

Ecological Society of Australia

Student Research Grant-     $750

Queensland Department of Environmental Research Management

Cliff Thompson Memorial Scholarship-      $10,000