The Early Maternal Environment Shapes the Parental Response to Offspring UV Ornamentation

Parents allocate resources to offspring to increase their survival and to maximize their own fitness, while this investment implies costs to their condition and future reproduction. Parents are hence expected to optimally allocate their resources. They should invest equally in all their offspring under good conditions, but when parental capacity is limited, parents should invest in the offspring with the highest probability of survival. Such parental favouritism is facilitated by the fact that offspring have evolved condition-dependent traits to signal their quality to parents. In this study we explore whether the parental response to an offspring quality signal depends on the intrinsic capacity of the parents, here the female. We first manipulated the intrinsic capacity of blue tit ( Cyanistes caeruleus ) females through lutein-supplementation during egg laying, and we subsequently blocked the UV/yellow reflectance of breast feathers on half of the nestlings in each brood. However, we did not find evidence that the female intrinsic capacity shaped parental favouritism for offspring UV/yellow colouration, as there were no differences in parental feeding or sibling competition. However, we found that males were more responsive than females to nestling UV/yellow when rearing capacity was high, as indicated by the prey-testings (when a parent places a prey item into a nestling’s gape but removes it again). Furthermore, when considering a more integrative measure, offspring growth, we did find the expected interaction effect. In control nests, UV-blocked nestlings gained less body mass than their non-UV-blocked siblings, whereas in lutein-supplemented nests UV-blocked nestlings gained more mass than their siblings. Overall, our results emphasize the female’s environment at an early reproduction stage shaped the role of offspring UV/yellow during family interactions illustrating plasticity in parental feeding rules.