Female lizards roll over to avoid sex
Female Lake Eyre dragons have evolved remarkable adaptations to avoid sex. To avoid male harassment and unwanted copulation attempts, female Lake Eyre dragons flip over onto their backs, exposing bright orange colour patches on their throats and bellies.
Lake Eyre dragon lizards live only on the barren salt crusts of dry lakes in Australia’s arid interior. During the breeding season, males persistently harass females and bite their necks during mating, which can cause injury and even death. Females attempt to run away or aggressively display to harassing males but, as a last resort, flip over onto their backs. Although it seems counter-intuitive that a female should flip over to avoid sex, this position prevents mating, which can only occur when males are mounted on the female’s back.
Flipping over exposes bright orange patches on the throat and belly, which only the females develop during the breeding season (the male belly and throat remain white). Flipping over and showing a bright orange belly leaves females obvious and vulnerable to predators such as birds of prey. So why did the orange patches and odd behaviour of female Lake Eyre dragons evolve?
Our research revealed that females develop orange patches to signal that they are sexually receptive and males court and harass females with the orange patches more than females without orange. Why, then, do females retain the orange patches when no longer receptive (i.e. when they are pregnant) and rejecting male courtship? We discovered that predators are less likely to attack flipped over females with bright orange patches, perhaps because they are not recognised by predators as potential prey. Contrary to what was previously assumed, the conspicuous ‘female-only’ ornamentation in Lake Eyre dragons actually decreases predation risk, rather than increasing it, when females are flipped over.
To learn more, read the full papers here:
Chan, R., Stuart-Fox, D. and Jessop, T.S. 2009. Why are females ornamented? A test of the courtship stimulation and courtship rejection hypotheses. Behavioral Ecology, 20: 1334-1342. PDF
Jessop, T.S., Chan, R. and Stuart-Fox, D. 2009. Sex steroid correlates of female-specific coloration, behaviour and reproductive state in Lake Eyre dragons, Ctenophorus maculosus. Journal of Comparative Physiology A 195: 619-630. PDF
Mclean, C.A., Moussalli, A. and Stuart-Fox, D. 2010. The predation cost of female resistance. Behavioural Ecology, 21: 861-867. PDF
Or view the media coverage of the study:
Aussie lizard rolls over to avoid sex – ABC News (29 April 2009)
Photo credit: Devi Stuart-Fox