G-Santoyo, Isaac; Gonzalez-Tokman, Daniel; Tapia-Rodríguez, Miguel; Cordoba, Alex
What is the role of colourful traits in animals? Quite often these traits are used by adult males to assess each other when competing over mating territories. This function is linked to a second question of what such colours are made of. We used to know that these colourful traits contained key dietetic elements also used for the animal’s development and survival. However, food can also come with toxic compounds. One untested idea is that rather than discarding these harmful elements, animals integrate them to construct their colourful traits. We tested this idea using the American rubyspot damselfly whose adult males bear a red wing spot that communicates the ability to fight for and defend a mating territory against other males. We determined that the red spot is generated by ommochrome pigments derived from the toxic tryptophan metabolite, 3-hydroxy-kynurenine (3-Hk). Males treated with 3-Hk ended up with more ommochromes than control males but had a similar survival, suggesting that the allocation of ommochrome to the wing counteracts the 3-Hk toxicity. This implies that colourful traits may work to store toxic compounds, a hypothesis we have called “detoxifying ability signalling”. In this sense, only males capable of storing large toxic amounts, are able to produce a large red spot. This mechanism is entirely new for colourful and other sexual traits.