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Incubation reduces microbial growth on eggshells and the opportunity for trans-shell infection

Authors

  • Mark I. Cook,

    1. Ecosystem Sciences Division, Department of Environmental Science, Policy and Management, 151 Hilgard Hall No. 3110, University of California, Berkeley, CA 94720, USA
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    • Present address: South Florida Water Management District, 3301 Gun Club Rd., PO Box 24680, West Palm Beach, FL 33416, USA

  • Steven R. Beissinger,

    Corresponding author
    1. Ecosystem Sciences Division, Department of Environmental Science, Policy and Management, 151 Hilgard Hall No. 3110, University of California, Berkeley, CA 94720, USA
      E-mail: beis@nature.berkeley.edu
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  • Gary A. Toranzos,

    1. Department of Biology, PO Box 23360, University of Puerto Rico, San Juan, PR 0093, Puerto Rico
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  • Wayne J. Arendt

    1. USDA Forest Service, International Institute of Tropical Forestry, Sabana Research Station, HC2 Box 6205, Luquillo PR 00773, Puerto Rico
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E-mail: beis@nature.berkeley.edu

Abstract

Avian eggshells harbour microbes shortly after laying, and under appropriate ambient conditions they can multiply rapidly, penetrate through shell pores, infect egg contents and cause embryo mortality. We experimentally examined how incubation affects bacterial processes on the eggshells of pearl-eyed thrashers Margarops fuscatus nesting in tropical montane and lowland forests in Puerto Rico. Bacteria and fungi grew rapidly on shells of newly laid, unincubated eggs exposed to ambient conditions, but declined to low levels on shells of eggs incubated by thrashers. Divergence in bacterial growth between incubated and exposed eggs was more marked at the montane forest than at the lowland site. Pathogenic microorganisms became increasingly dominant on shells of exposed eggs, but these groups were relatively rare on incubated eggs, where more benign, less invasive groups prevailed. Some incubation during laying may be necessary to decrease the probability of trans-shell infection by reducing the growth of harmful bacteria and fungi on eggshells, although it may increase hatching asynchrony and the likelihood of brood reduction.

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