Are antimicrobial defences in bird eggs related to climatic conditions associated with risk of trans-shell microbial infection?

Nicholas Pc Horrocks,Arne Hegemann,Kathryn Hine,Mohammed Shobrak,Kevin D Matson,B Tieleman,Stéphane Ostrowski,Joseph B Williams,Henry K Ndithia

doi:10.1186/1742-9994-11-49

Abstract

IntroductionAll bird eggs are exposed to microbes in the environment, which if transmitted to the developing embryo, could cause hatching failure. However, the risk of trans-shell infection varies with environmental conditions and is higher for eggs laid in wetter environments. This might relate to generally higher microbial abundances and diversity in more humid environments, including on the surface of eggshells, as well as the need for moisture to facilitate microbial penetration of the eggshell. To protect against microbial infection, the albumen of avian eggs contains antimicrobial proteins, including lysozyme and ovotransferrin. We tested whether lysozyme and ovotransferrin activities varied in eggs of larks (Alaudidae) living along an arid-mesic gradient of environmental aridity, which we used as a proxy for risk of trans-shell infection.ResultsContrary to expectations, lysozyme activity was highest in eggs from hotter, more arid locations, where we predicted the risk of trans-shell infection would be lower. Ovotransferrin concentrations did not vary with climatic factors. Temperature was a much better predictor of antimicrobial protein activity than precipitation, a result inconsistent with studies stressing the importance of moisture for trans-shell infection.ConclusionsOur study raises interesting questions about the links between temperature and lysozyme activity in eggs, but we find no support for the hypothesis that antimicrobial protein deposition is higher in eggs laid in wetter environments.

Highlights

All bird eggs are exposed to microbes in the environment, which if transmitted to the developing embryo, could cause hatching failure
Our study raises interesting questions about the links between temperature and lysozyme activity in eggs, but we find no support for the hypothesis that antimicrobial protein deposition is higher in eggs laid in wetter environments
We hypothesised that if antimicrobial defences have evolved to match the risk of microbial infection [36,37,38,39,40] concentrations of antimicrobial proteins in eggs should vary with those environmental conditions that predict the risk of trans-shell infection

Summary

Introduction

All bird eggs are exposed to microbes in the environment, which if transmitted to the developing embryo, could cause hatching failure. The risk of trans-shell infection varies with environmental conditions and is higher for eggs laid in wetter environments. To minimise infection by microbes, eggs possess physical barriers such as the shell and membranes, and chemical barriers in the form of antimicrobial proteins and peptides [29,30] These barriers are set by the mother during egg formation, allowing her to transmit her experience of the wider environment to her offspring, thereby influencing offspring phenotype and survival [31,32]. We hypothesised that if antimicrobial defences have evolved to match the risk of microbial infection [36,37,38,39,40] concentrations of antimicrobial proteins in eggs should vary with those environmental conditions that predict the risk of trans-shell infection

Methods

Results

Conclusion