Lizards and the language of colour changehttp://adf.ly/Q0Fvh

Devi Stuart-Fox is an evolutionary biologist at the University of Melbourne who has spent the past decade investigating colour change in lizards. She’s now leading an international team of researchers in an investigation into how they achieve colour change, why they do it, and what it costs them. I had a chat to her about what she’s discovered, and what she hopes to discover, about the incredibly complex language of colour change in nature.

Your research showed that the primary use of colour change in chameleons isn’t camouflage. What is it?

There are a lot of species of chameleon, and some have really advanced capacities for colour change, and in others it’s really very limited. So the big question was, why has this ability evolved to such a remarkable degree in some species and not in others?

What we were able to show is the species that do change colour the most actually have the most conspicuous social displays. So there’s been selection for them to use these really bright, flashy colours in their communication and social displays, therefore there was selection on their ability to change colour. We suggested that the ability to change colour evolved for that reason, rather than simply for camouflage. Because why change colours, why not just be very camouflaged against your backgrounds?

We were wondering whether the ability to change colour could be related to the number of different backgrounds they would need to match, or the particular habitat they are found in. We found that there is no relationship, so that’s why we said it hasn’t been driven by camouflage. They obviously use it for camouflage – they match very well – but it’s a limited range of colours they have to match. Whereas in their social displays when they change colours, they’ve got pinks and oranges, greens and blues, and a wide range of ultraviolet colours that are visible to chameleons but not to us.

Do bearded dragons use colour change in a similar way?

Females use colour to signal whether they’ll accept courtship or aggressively reject male advances, and the males use it in territorial displays and also in courtship displays to female. We don’t know what specific colours mean, in some cases dark colours can be a symbol of submission, but in other cases, like the black beard in [Central bearded dragon] males, it’s a symbol of dominance. So different colours mean different things in different contexts.

It’s interesting that the female dragons have developed a specific mechanism based on a colour signal to ward off the males.
I’m particularly interested in precisely that. I’ve been studying it in the Lake Eyre dragons – they occur only in the Lake Eyre salt pan, which is the most barren habitat you could be in. Usually it’s the males that are a brighter version of the females, but in this species both sexes are really well matched to their backgrounds, and in the breeding season, the females develop really bright patches of orange on their bellies. What was in the literature before was that these patches develop when the females are rejecting the males, but what we showed was that the patches developed when they’re receptive, and the males see the orange on the female’s throat and absolutely harass them.
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Lizards and the language of colour change

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