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Are colourful signals honest?

Colourful signals are widespread throughout the animal world, providing a wide range of information to potential mates, rivals, and predators. But what is the mechanism behind the rapid colour change of a bearded dragon? How do we know that the animal with the most intense signal colouration is the healthiest, the strongest, or the best potential mate? To answer these questions one needs to turn their attention to just beyond the skin’s surface. Recently our lab has been investigating how changes in an animal’s environment translate to changes in their colouration, and how this process ensures that a colourful signal always sends an honest message.

Animals that are stressed out can’t perform at their best. So how do tawny dragons know who to mate with, who to challenge, and who to avoid? We have shown that tawny dragons experiencing stress produce paler signal colouration over time and that others can tell the difference. What we see on the surface however, only tells half the story. Using transmission electron microscopy (see image inset), we were able to look at skin tissue in fine detail and analyse the structure of the ‘dermal chromatophore unit’ to reveal how small differences below can produce big differences on the surface. To truly prove that dragons can’t just fake it till they make it, producing their eye-catching signals regardless of their condition, we aim to uncover a clear mechanism by which stress hormone elevation and other physiological changes act directly on these pigment cells to alter colouration.

– Anna Lewis

Anna completed her Masters of Science on the effects of stress on colour expression in tawny dragon lizards, and how it alters the structural components of colour expression using electron microscopy. Read more about her findings here!