Communicating with movement

Many animals use signals defined by movement to communicate. Compared with sounds and colour, however, much less is known about the evolution of movement-based signalling. I study the signalling behaviour of the Jacky lizard (Amphibolurus muricatus) as a model system for understanding the design of such signals. These lizards rely on motion for communicating during territorial disputes: a rapid sequence of motor patterns during aggressive displays ; and the complete antithesis to signal submission.
The aggressive displays of these Jacky lizards begin with tail flicking. A flicking tail is, therefore, the motion signal that a receiver must detect among other competing motion signals in the environment. For Jacky lizards, this is mostly in the form of wind-blown plants. The focus of my current work has been to explore the relationship between plant motion and Jacky lizard tail flicking:

Each microhabitat reflects distinct image motion environments. At all locations, image motion became more directional and angular speed increased as wind speeds increased. The magnitude of these changes and the spatial distribution of image motion, however, varied between locations. Plant motion noise also strongly depends on the depth-structure of the environment (J Comp Physiol A 2008)
Based on ongoing modelling work, the separation of tail flick image motion from plant image motion (based on motion information alone) is NOT trivial
Indeed, lizards take longer to detect a tail flick signal when wind blows plants in the environment (Biology Letters 2008)
To compensate for increased plant motion, they tail flick for longer and switch to intermittent motion (Current Biology 2007)
- see also a video clip illustrating the change in signalling behaviour.
Also, in collaboration with Terry Ord at the University of California, Davis, the displays of some Caribbean lizards were found to be faster as plant motion angular speed increased. (Proceedings of the Royal Society of London B 2007)

Quantifying image motion

Underlying this work is the need to be able to quantify the structure of signals and noise in a manner that allows for direct comparison across different types of visual motion. I use gradient detectors that quantify changes in image intensity. More details can be found here.

Experiments

To complement quantitative analyses of visual motion, I also run behavioural experiments to test specific aspects of signal design. I have used radio-controlled models and digital video playback incorporating 3D animations to understand the relative effectiveness of different motor patterns at attracting attention, as well as studies conducted in naturalistic enclosures outside to explore variation in signal production as the motion environment varies due to differences in wind conditions.

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Last updated: April 3, 2008