Dietary carotenoid supplementation facilitates egg laying in a wild passerine

Abstract

During egg laying, females face a trade‐off between self‐maintenance and investment into current reproduction, since providing eggs with resources is energetically demanding, in particular if females lay one egg per day. However, the costs of egg laying not only relate to energetic requirements, but also depend on the availability of specific resources that are vital for egg production and embryonic development. One of these compounds are carotenoids, pigments with immuno‐stimulatory properties, which are crucial during embryonic development. In this study, we explore how carotenoid availability alleviates this trade‐off and facilitates egg laying in a small bird species, the blue tit (Cyanistes caeruleus). Blue tits have among the largest clutch size of all European passerines and they usually lay one egg per day, although laying interruptions are frequent. We performed a lutein supplementation experiment and measured potential consequences for egg laying capacity and egg quality. We found that lutein‐supplemented females had less laying interruptions and thus completed their clutch faster than control females. No effects of treatment were found on the onset of egg laying or clutch size. Experimentally enhanced carotenoid availability did not elevate yolk carotenoid levels or egg mass, but negatively affected eggshell thickness. Our results provide hence evidence on the limiting role of carotenoids during egg laying. However, the benefits of laying faster following lutein supplementation were counterbalanced by a lower accumulation of calcium in the eggshell. Thus, even though single components may constrain egg laying, it is the combined availability of a range of different resources which ultimately determines egg quality and thus embryonic development.

The early maternal environment shapes the parental response to offspring UV ornamentation

“…Each dosage was mixed with 5 g of commercial bird fat with nuts (GRANA Oryx), whereas the same amount of bird fat without lutein was provided to nests in the control treatment. We confirmed through direct observations that males rarely visited the nest during nest construction and we can thus assume that the supplement was mainly consumed by females 30 .…”

“…Lutein-supplemented females completed their clutch faster than control females, as the treatment reduced the occurrence of egg-laying interruptions 30 . Two days before the expected hatching date, we performed a full-brood cross-fostering by exchanging clutches between nests in a fashion that allowed both lutein-supplemented females (n = 24) and control females (n = 23) to raise a control clutch.…”

“…At the start of the breeding season, we visited nest-boxes every two days to record the beginning of nest construction, laying date and hatching date (day 0). Once nest construction was finished in a given nest, that is, when the moss cup was well defined but not filled with feathers and hair, we started lutein supplementation in that nest (see Lutein supplementation section below; for more details, see also 30 ). We continued supplementing blue tit females during egg laying and finished once incubation started.…”

“…At the end of nest construction, we visited nests every two days and lutein was supplied in experimental nests using a dose of 50 mg of Versele Laga Yel-lux Oropharma (lutein 8000 mg/kg), which corresponds to 0.4 mg of lutein and which is within the natural limits consumed by blue tit females (for a detailed explanation, see 30 ). Each dosage was mixed with 5 g of commercial bird fat with nuts (GRANA Oryx), whereas the same amount of bird fat without lutein was provided to nests in the control treatment.…”

“…To test our hypothesis, we first experimentally manipulated the availability of a specific micronutrient (i.e., lutein) for blue tit females at egg laying, which is the most energy-demanding stage of the females` life. Indeed, we have previously found that lutein supplementation facilitated egg laying, thus improving the female’s intrinsic capacity 30 . Additionally, we experimentally manipulated in half of the nestlings within each brood a nestling quality signal, the UV/yellow breast plumage colouration 35 .…”