Carotenoid-based coloration predicts both longevity and lifetime fecundity in male birds, but testosterone disrupts signal reliability

Abstract

<p>Sexual selection promotes the evolution of conspicuous animal ornaments. To evolve as</p><p>signals, these traits must reliably express the “quality” of the bearer, an indicator of individual</p><p>fitness. Direct estimates of individual fitness may include the contribution of longevity and</p><p>fecundity. However, evidence of a correlation between the level of signal expression and</p><p>these two fitness components are scarce, at least among vertebrates. Relative fitness is dif-</p><p>ficult to assess in the wild as age at death and extra-pair paternity rates are often unknown.</p><p>Here, in captive male red-legged partridges, we show that carotenoid-based ornament</p><p>expression, i.e., redness of the bill and eye rings, at the beginning of reproductive life pre-</p><p>dicts both longevity (1–7 years) and lifetime breeding output (offspring number and hatching</p><p>success). The recently proposed link between the individual capacity to produce red (keto)</p><p>carotenoid pigments and the efficiency of cell respiration could, ultimately, explain the</p><p>correlation with lifespan and, indirectly, fecundity. Nonetheless, in males of avian species,</p><p>carotenoid-based coloration in bare parts is also partially controlled by testosterone. We</p><p>also manipulated androgen levels throughout life by treating males with testosterone or anti-</p><p>androgen compounds. Treatments caused correlations between signal levels and both fit-</p><p>ness components to disappear, thus making the signals unreliable. This suggests that</p><p>the evolution of carotenoid-based sexual signals requires a tightly-controlled steroid</p><p>metabolism.</p>