Early life and transgenerational stressors impact secondary sexual traits and fitness

Developmental stress from early life challenges impacts adult phenotype across a range of species. However, the potential transgenerational consequences for adult phenotype are largely unknown. Additionally, the possible impacts of natural hatch/birth order and natal brood composition in unmanipulated broods/litters on adult performance has been understudied. This experiment takes a novel approach to studying developmental stress by integrating and assessing multiple potential stressors and multiple secondary sexual traits simultaneously in order to determine how these influence both social and genetic reproductive success. Male zebra finches were colony-reared on high- or low-quality diets; as adults, they reproduced competitively on an intermediate diet. Male visual ornaments (beak color and cheek patch size) were found to be reliable signals of developmental stress, since they showed high sensitivity to multiple early conditions and predicted reproductive success. Contrary to the nutritional stress hypothesis, early diet did not impact song traits investigated. Male reproductive success was impacted by diet history, male hatch order, and natal brood traits of males’ fathers, with daughter and son production sensitive to different subsets of identified reproductive stressors. Notably, diet influenced only son production and the hatch orders of males and their fathers influenced only daughter production. Findings suggest that the sexes respond differently to early life conditions, which may influence subsequent sex allocation patterns. Despite good general correspondence in patterns of social and genetic reproductive success, males that sired 1 or more extra-pair offspring achieved higher fitness through greater son production.