title: Are antimicrobial defences in bird eggs related to climatic conditions associated with risk of trans-shell microbial infection?
abstract: BACKGROUND
  All 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.
  
  
  RESULTS
  Contrary 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.
  
  
  CONCLUSIONS
  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.
authors: Animal Ecology Group, Centre for Ecological & Evolutionary Studies, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands ; Department of Zoology, University of Cambridge, Downing Street, CB2 3EJ Cambridge, UK.
authors: Nicholas Pc
authors: NP
authors: Horrocks
authors: Animal Ecology Group, Centre for Ecological & Evolutionary Studies, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands.
authors: Kathryn
authors: K
authors: Hine
authors: Animal Ecology Group, Centre for Ecological & Evolutionary Studies, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands.
authors: Arne
authors: A
authors: Hegemann
authors: Animal Ecology Group, Centre for Ecological & Evolutionary Studies, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands ; Department of Ornithology, National Museums of Kenya, PO Box 40658, Nairobi, Kenya.
authors: Henry K
authors: HK
authors: Ndithia
authors: Biology Department, Science College, Taif University, P.O. Box 888, 21974 Taif, Saudi Arabia.
authors: Mohammed
authors: M
authors: Shobrak
authors: Wildlife Conservation Society, 2300 Southern Boulevard, 10460 Bronx, NY, USA.
authors: Stéphane
authors: S
authors: Ostrowski
authors: Department of Evolution, Ecology & Organismal Biology, Ohio State University, 43210 Columbus, OH, USA.
authors: Joseph B
authors: JB
authors: Williams
authors: Animal Ecology Group, Centre for Ecological & Evolutionary Studies, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands.
authors: Kevin D
authors: KD
authors: Matson
authors: Animal Ecology Group, Centre for Ecological & Evolutionary Studies, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands.
authors: B Irene
authors: BI
authors: Tieleman
keywords: Antimicrobial; Aridity; Egg albumen; Humidity; Lark; Lysozyme; Ovotransferrin