Flickering from green to blue, red and yellow in the blink of an eye, panther chameleons (Furcifer pardalis) turn up the colour for a range of reasons, from warning off intruders to evading predators. Some chameleons even increase the thermostat by shifting to a darker shade when they are chilly. But it wasn't clear whether certain aspects of colour are also the key to female chameleon hearts. ‘To date, the role of physiological colour change in mate choice is poorly understood’, says Alexis Dollion from the Université de Paris, France. Together, Sandrine Meylan and Anthony Herrel, with colleagues from the Sorbonne Université and Muséum national d'Histoire naturelle and Olivier Marquis from the Parc Zoologique de Paris, France, set up chameleon speed dates while monitoring the males’ appearance to find out if any particular skin hue, colour intensity and brilliance (which combine to produce colour saturation) and brightness changes might make a male irresistible.
But the team also needed to make sure that the mood lighting was just right. ‘Chameleon vision extends into the ultraviolet, which some animals, like humans, cannot see’, he says; females could miss out on essential aspects of the males’ vivid serenades if the lighting wasn't sufficiently natural and the UV shades were lost. Setting up a bank of lamps, ranging from incandescent bulbs and LED lights to a UV fluorescent tube, the team photographed male panther chameleons every two minutes during the throes of courtship to capture their appearance in the moments before the female audience succumbed to their charms.
Comparing pixels in images recorded from several locations on each male's body as he wooed his would-be sweetheart, the team realised that the females were impressed by males that changed the brightness least. In addition, the males that pushed the boat out and went for the most dramatic colour changes seemed to have better success with the females than more conservative suitors, whose shades remained similar to their initial palette. However, when the team compared the effects of colour changes in different regions of the males’ skins, the females preferred males that kept the brightness of the band along their side fairly steady. Also, the males that played it safe and retained similar hues in their stripes and background skin, and those that changed the saturation, seemed to attract more female attention.
Turning their attention to the UV ‘before’ and ‘after’ shots, the scientists could see that the attractive male chameleons also alter their appearance by increasing the brightness of their UV shades and switching their UV colours more. In fact, the males that did not splash out on ostentatious UV displays seemed to be actively avoiding catching the eye of nearby ladies, probably because they prefer the quiet life by evading predators and other unwanted attention.
In short, the male panther chameleon's cutaneous pyrotechnic displays seem to fan the flames of female ardour and the team is curious to find out whether different portions of the reptiles’ skins convey different information that the females use when selecting Mr Right.