Condition Dependence and Fitness Consequences of Sexual Traits in Zebra Finches

The developmental stress hypothesis offers a mechanism to maintain honesty of sexually selected traits, since only high genetic quality individuals will be able to fully develop ornaments in the face of early stress. The zebra finch has become a model species in studies of developmental stress. However, results have been mixed and a unifying perspective is missing. Using a quantitative genetic approach, we study the effect of the sometimes dramatic differences in early growth conditions experienced by a total of 413 cross-fostered male and 395 female zebra finches on 20 male and 14 female traits. We find moderate effects of growth conditions on body size, mass and fat deposition (mean r = 0.22), weak effects on beak colour (mean r = 0.10) and no effect on song or plumage characters. Looking at possible life-history trade-offs, we found a weak effect on the success at fertilising eggs under aviary conditions, in males, but no effects on longevity in either sex. We conclude that zebra finches are remarkably resilient to early developmental stress. Our results do not support the hypothesis that sexually selected traits show heightened condition dependence as compared to non-sexually selected traits.