When you think of colour-changing animals, what comes to mind? A slowmoving chameleon barely distinguishable from its spot in a tree? Or maybe an octopus camouflaging itself on the ocean floor? What about hundreds of bright yellow male Asian common toads (Duttaphrynus melanostictus) gathering to fight each other for the company of their somewhat drab, brown-coloured mates? During monsoon rains, the toads gather in groups of over 200 individuals at breeding sites throughout South and Southeast Asia. Before congregating, the male toads swiftly change colour to a conspicuous yellow, signalling to other males that they are ready to fight - and to distinguish themselves to potential female mates. Unsurprisingly, hormones associated with the 'fight or flight' response are high during these 'explosive breeding' events thanks to the stressful monsoon rains that coincide with the mating season and fighting for partners. Could these hormones have something to do with the toads' striking colour change? Susanne Stückler and Doris Preininger from the University of Vienna, Austria, and their colleague Matthew Fuxjager from Brown University, USA, decided to investigate.
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