What doesn’t kill you makes you stronger: detoxification ability as
mechanism of honesty in a sexually selected signal
Sexual selection maintains colourful signals. The metabolic pathways to
produce them often involve toxic byproducts that can reduce survival.
However, rather than discarding these otherwise harmful byproducts,
animals may use them by integrating them into sexually-selected traits.
We tested this using the damselfly Hetaerina americana, where males bear
a red wing spot evolved by intrasexual competition. We determined that
red wing spots are generated by ommochrome pigments derived from the
toxic metabolite, 3-hydroxy-kynurenine (3-Hk). We also found that males
treated with 3-Hk had more ommochromes than controls but similar
survival, suggesting that deposition of ommochromes counteracts the 3-HK
toxicity. Thus, we report that sexually selected signals involve the
treatment of excreted compounds that could otherwise have lethal
effects, a hypothesis we call “detoxifying ability signalling”. Our
results provide new insights about the evolution of sexual signals,
elucidating a mechanism of honest indicators that could have arisen due
to natural selection.