Natural variation in yolk fatty acids, but not androgens, predicts offspring fitness in a wild bird

Lucia Mentesana,Stefania Casagrande,Martin N Andersson,Michaela Hau,Wolfgang Goymann,Caroline Isaksson

doi:10.1186/s12983-021-00422-z

Lucia Mentesana, Stefania Casagrande + Show 4 more

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https://doi.org/10.1186/s12983-021-00422-z

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Abstract

BackgroundIn egg-laying animals, mothers can influence the developmental environment and thus the phenotype of their offspring by secreting various substances into the egg yolk. In birds, recent studies have demonstrated that different yolk substances can interactively affect offspring phenotype, but the implications of such effects for offspring fitness and phenotype in natural populations have remained unclear. We measured natural variation in the content of 31 yolk components known to shape offspring phenotypes including steroid hormones, antioxidants and fatty acids in eggs of free-living great tits (Parus major) during two breeding seasons. We tested for relationships between yolk component groupings and offspring fitness and phenotypes.ResultsVariation in hatchling and fledgling numbers was primarily explained by yolk fatty acids (including saturated, mono- and polyunsaturated fatty acids) - but not by androgen hormones and carotenoids, components previously considered to be major determinants of offspring phenotype. Fatty acids were also better predictors of variation in nestling oxidative status and size than androgens and carotenoids.ConclusionsOur results suggest that fatty acids are important yolk substances that contribute to shaping offspring fitness and phenotype in free-living populations. Since polyunsaturated fatty acids cannot be produced de novo by the mother, but have to be obtained from the diet, these findings highlight potential mechanisms (e.g., weather, habitat quality, foraging ability) through which environmental variation may shape maternal effects and consequences for offspring. Our study represents an important first step towards unraveling interactive effects of multiple yolk substances on offspring fitness and phenotypes in free-living populations. It provides the basis for future experiments that will establish the pathways by which yolk components, singly and/or interactively, mediate maternal effects in natural populations.

Highlights

In egg-laying animals, mothers can influence the developmental environment and the phenotype of their offspring by secreting various substances into the egg yolk
As almost all monounsaturated fatty acid (MUFA) were included in PC2, whereas only one or two were present in PC1 and PC3, and the effects of different groups fatty acids are more relevant to our research question rather than specific fatty acids, the effects of MUFAs on nestling phenotype are discussed primarily based on results for PC2
Our study suggests a novel link between natural variation in yolk fatty acid content and offspring fitness and phenotype in a wild bird population

Summary

Introduction

In egg-laying animals, mothers can influence the developmental environment and the phenotype of their offspring by secreting various substances into the egg yolk. Yolk steroid hormones, such as androgens and glucocorticoids, can influence offspring growth, competitive ability and survival (e.g., Ficedula albicollis; [17, 18] and reviewed by [19]), but they can increase chick susceptibility to oxidative stress by increasing the production of reactive oxygen species or by impairing antioxidant defenses (e.g., Gallus gallus; [20, 21]). Yolk fatty acids have been shown to vary with environmental conditions in free-living birds (Cyanistes caeruleus, Parus major [31, 32]), but it remains unclear whether they play a role in shaping offspring fitness and phenotype in natural populations that experience frequent fluctuations in food availability and weather conditions

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