Animal signals are used in a variety of contexts including mate-choice, parent-offspring interactions, foraging, predator deterrence, and territory defence. Lizards signal in a variety of ways. Some, like skinks, use olfactory cues through scent-marking. However, the dragon lizards and the closely related iguanas, communicate primarily through visual displays centred on push-ups and head-nods.

Lizards have proved to be very useful model systems for studying the design and function of movement-based visual signals. A useful context in which to study movement-based signals is that of animal conflicts, which do not always escalate into fights. Exchanges of territorial displays often allow rivals to ascertain relative status from a distance, so that physical combat can be avoided.

The diversity we see in display structure directly reflects ecological factors including habitat choice, resource distribution, presence of sympatric congeners, and predation threat. Effective signals are those that have a high ‘signal-to-noise ratio’. The physical habitat acts as background noise that sets a minimum structure for reliable detection, in terms of the spectral characteristics, and relative movement of, the signal and wind-blown plants. The environment will also influence the degree to which the signal degrades over viewing distance. As a consequence, relatively simple displays are favoured when longer transmission distances are required. However, the need to remain inconspicuous to predators imposes an important constraint on display structure. Simple displays are also more common when resource defence is rare, as is likely to be true for many herbivorous lizard populations. Conversely, when resources are limiting, we typically see more complex signals, driven by higher levels of male-male competition.

Stereotypy is a common property of many types of signals because it serves to increase the reliability of detection. The displays of iguanid lizard species are highly stereotyped. Lizards use either a single species-specific display, or one chosen from a limited repertoire. However, most feature a core, predictable sequence of motor patterns. These can be highly consistent within a species, or show significant individual differences. Low variation in display patterns probably evolved for species recognition. Selection pressure is therefore likely to be greater in the presence of sympatric congeners. Furthermore, when the influence of female mate choice is negligible (as appears to be the case in iguanian lizards) the level of display divergence may reflect the extent of differential resource use, with more similar displays being retained when resource requirements overlap and are competed for between species. In contrast, displays that show considerable inter-species variation would imply a species recognition role.

Jacky dragon visual signals

Jacky dragons have several displays in their repertoire. However, we are only beginning to understand their function in social interactions.

The PUSH-UP DISPLAY by male Jacky dragons (a putative aggressive signal) is composed of a stereotyped series of discrete motor patterns, delivered in an obligatory sequence. The display begins with a period of tail-flicking, followed by backward and forward arm-waves, a push-up and a body-rock. Some or all of the components are often then repeated one or more times.

Jacky dragons also perform displays which are antithetical to the jerky push-up display. Both SLOW ARM-WAVES and SLOW HEAD-NODS are performed in response to push-up displays. We suspect that these function as appeasal signals, although this is at best an educated guess.

Rare display motor pattern(s): sometimes the single arm used in backward and forward arm-waves is replaced by a TWO-ARM WAVE.

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