A project undertaken at Macquarie University, and supervised by A/Prof Darrell Kemp.
The spectacular diversity of butterfly wing colouration is easy for us to appreciate, yet relatively little is known about how butterflies themselves perceive different colours. The eyes of most butterfly species are thought to contain three different colour receptors, thereby affording the ability for trichromatic colour vision (akin to humans, albeit with a different range of colour sensitivity). Recent findings have however revealed that some butterflies possess an additional red colour receptor, and therefore have the ability for tetrachromatic vision.
These species should be able to make finer-scale judgements across a broader range of colours than their trichromatic counterparts. However, they are also likely to pay a cost in terms of sacrificed visual acuity by virtue of trade-offs in the way that light is handled by the eye. Our study will be the first broad-scale investigation of which butterfly species possess tetrachromatic vision and whether its presence has been driven by characteristic features of ecology and/or behaviour.
We will focus on Australian members the nymphaline subfamily. Butterflies across this group reside in diverse habitats and showcase a great diversity of wing colouration. Importantly, the males of different nymphaline species also characteristically pursue one of two different strategies for locating mates. The males of “perching” species seek to locate females from a stationary position, either on the ground or on fringing vegetation, whereas the males of “patrolling” species actively search by flying around their mating habitat.
Theoretically, these two different strategies are likely to demand different visual abilities. Whereas the detection of females from a stationary perch should demand high visual acuity and a ‘fast’ eye, the same task for patrolling species should instead place greater priority upon colour discrimination. We therefore predict that tetrachromatic vision should be more prevalent among patrolling species. We will also search for relationships between this phenomenon and species wing colouration, body size and visual features of their predominant mating habitat.
Our study will use detailed behavioural experiments to define the visual contexts and capacities of exemplar perching versus patrolling species. We will couple this with a broad phylogenetically-controlled investigation based upon eyeshine measurement, a new high-throughput method for assaying colour vision that overcomes the limitations of traditional electrophysiological and molecular methods. The data will provide important insights into the ecology and evolution of colour vision in butterflies, and offer principles for potential application in pest control, biomimicry and human communication.