Review articleEcoimmunology and microbial ecology: Contributions to avian behavior, physiology, and life history
Section snippets
Introduction: microbial ecology, immune defense, and co-evolution
Ever since birds first appeared in the Mesozoic era (Benson et al., 2014), they have coexisted with microbes, potentially coevolving with avian ontogeny, behavior, physiology and immune function. There is even a growing literature to suggest that microbes were instrumental in determining early feather coloration and structure (Carney et al., 2012, Moyer et al., 2014). To put the importance of microbes into perspective: the microbial community inhabiting the human gut (1014cells) is estimated to
Eggs and embryos
Eggs and embryos are associated with microbe communities present in nests, as well as on the skin, feathers and feces of parents. Birds utilize a wide variety of different nesting materials including with potentially distinct microbial communities and some materials may even have antimicrobial characteristics. Feathers have been proposed to have antimicrobial characteristics and can prevent or manipulate microbial colonization (Peralta-Sanchez et al., 2012, Ruiz-Castellano et al., 2016, Shawkey
Nestlings and juveniles
Bacterial nest densities and assemblages (Berger et al., 2003) are hypothesized to play an important role in determining nestling growth and development. Siblings share more similar bacterial assemblage composition than would be expected by chance, demonstrating the potential role of the nest environment in shaping immune development (Brandl et al., 2014). To understand relationships between nestling immune function and bacteria, it is important to understand how immune function development
Adult phases
Adult microbial exposure is hypothesized to be a function of species' ecology, behavior and life history strategy which interact to produce variation in the relative risk of pathogenic microbe exposure (Fig. 2). Both comparative studies and manipulative experiments that alter the microbial exposure of birds at various stages of their life history could reveal the nature of physiological trade-offs that might be relevant in mediating the cost of bacterial defense. For example, Evans et al. (2016)
Microbial biogeography
Global microbe diversity and density are predicted to follow latitudinal diversity trends (Fuhrman et al., 2008, Stephens et al., 2016) but biogeography of microorganisms is complicated by host associations (e.g. Altizer et al., 2007, Huang et al., 2015, O'Dwyer et al., 2012) and a release from some of the biogeographical processes that shape macroorganism diversity and distribution (Horner-Devine et al., 2007, Martiny et al., 2006). Within high latitude zones temperature predicts pathogen
Conclusion: key questions and techniques
Much remains to be revealed about the influence of microbes on avian immunology, endocrinology, and behavior. Here, we present the key questions to be pursued in avian microbial ecology if we are to understand this neglected influence on life history evolution.
Author contributions statement
JKE wrote the first draft of the Eggs and Embryos and Nestlings and Juveniles sections. BA wrote the first draft of the Adult Phases section. KLB and BA jointly wrote the Ecological Considerations sections. JKE and KCK developed Fig. 1. BA and KLB developed Fig. 2. JKE and BA jointly wrote the Introduction and Conclusion sections. KLB, SG, and KCK revised the subsequent manuscript drafts.
Acknowledgements
We wish to thank the editors of the special issue for the invitation to submit our review.
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