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Incubation reduces microbial growth on eggshells and the opportunity for trans-shell infection
Mark I Cook1, Steven R Beissinger, Gary A Toranzos
1Ecosystem Sciences Division, Department of Environmental Science, Policy and Management, 151 Hilgard Hall No. 3110, University of California, Berkeley, CA 94720, USA Department of Biology, PO Box 23360, University of Puerto Rico, San Juan, PR 0093, Puerto Rico USDA Forest Service, International Institute of Tropical Forestry, Sabana Research Station, HC2 Box 6205, Luquillo PR 00773, Puerto Rico.
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.
Insights
Incubation of avian eggs reduces harmful bacteria and fungi on shells, preventing embryo mortality. This microbial shift is more pronounced in montane forests, highlighting incubation
Area of Science:
- Microbiology
- Avian Ecology
- Evolutionary Biology
Background:
- Avian eggshells are susceptible to microbial colonization post-laying.
- Rapid microbial growth on unincubated eggs can lead to embryo mortality via trans-shell infection.
- Understanding microbial dynamics on eggshells is crucial for avian reproductive success.
Discussion:
- Incubation by parent birds significantly reduces bacterial and fungal load on eggshells.
- The effect of incubation on microbial communities is more pronounced in montane compared to lowland tropical forests.
- Incubation favors benign microbial communities, suppressing pathogenic and invasive microorganisms on eggshells.
Key Insights:
- Parental incubation is a critical factor in regulating eggshell microbial communities.
- Reduced pathogenic microbial growth on incubated eggs likely lowers infection risk.
- Environmental factors, such as forest type, modulate the impact of incubation on eggshell microbes.
Outlook:
- Further research could explore the specific mechanisms by which incubation suppresses harmful microbes.
- Investigating the long-term consequences of altered microbial communities on hatchling health is warranted.
- This study provides a foundation for understanding host-microbe interactions in avian reproduction.
