Effect of Incubation on Bacterial Communities of Eggshells in a Temperate Bird, the Eurasian Magpie (Pica pica)

Abstract

Inhibitory effect of incubation on microbial growth has extensively been studied in wild bird populations using culture-based methods and conflicting results exist on whether incubation selectively affects the growth of microbes on the egg surface. In this study, we employed culture-independent methods, quantitative PCR and 16S rRNA gene pyrosequencing, to elucidate the effect of incubation on the bacterial abundance and bacterial community composition on the eggshells of the Eurasian Magpie (Pica pica). We found that total bacterial abundance increased and diversity decreased on incubated eggs while there were no changes on non-incubated eggs. Interestingly, Gram-positive Bacillus, which include mostly harmless species, became dominant and genus Pseudomonas, which include opportunistic avian egg pathogens, were significantly reduced after incubation. These results suggest that avian incubation in temperate regions may promote the growth of harmless (or benevolent) bacteria and suppress the growth of pathogenic bacterial taxa and consequently reduce the diversity of microbes on the egg surface. We hypothesize that this may occur due to difference in sensitivity to dehydration on the egg surface among microbes, combined with the introduction of Bacillus from bird feathers and due to the presence of antibiotics that certain bacteria produce.

The Bacterial Community Found on the surface Purple Martin (Progne subis) Eggs

“…Our bacterial findings were similar to those of other studies examining bacterial communities lining the eggshells of Pied Flycatcher [8], House Wren [13], and Eurasian Magpies [14]. However, our findings differ from those in a study by Wang et al [11] examining the microbial eggshell communities of Tree and Violet-Green Swallows, which are in the same family as Purple Martins.…”

“…Our data implies that similar selective influences must be present within Purple Martins, Pied-Flycatchers and House Wrens because of the predominance of Pseudomonas within the bacterial eggshell communties [8,13,14]. Differences in breeding habitat, diet, nest construction, and incubation behaviors have been tried in previous studies to explain differences in bacterial profiles associated with avian species [27,28], but it is hard to align the above avian species as similar based on these factors and different from other avian species such as American Kestrels and Tree and Violet-Green Swallows that have different bacterial communities lining their eggshell.…”

“…This genus comprises a large and diverse group of microorganisms found in terrestrial, freshwater, and marine environments [19]. Predominance of Pseudomonas has also been observed in nests of Blue and Great Tits [20], the plumage of Eastern Bluebirds [21] and American Redstarts [22], and on the surface of Pied Flycatcher [8], House Wren [13], and Eurasian Magpie [14] eggs. The predominance of Pseudomonas may stem from their ability to produce antibiotic substances referred to as pyocins [23], which can provide them with a competitive advantage over other bacteria.…”

“…Thus, the first step in understanding the microbial communities lining the eggshell is to identify the bacterial components of closely related and diverse avian species. To date, studies have focused on the Pearly-eyed Thrasher [10], Western Bluebird, Tree Swallow, Violet-Green Swallow [11], Pied Flycatcher [12], House Wren [13], Eurasian Magpie [14], and American Kestrel [15]. This list includes a diverse set of species, but it does not include closely related species within the same family (data for Tree and Violet-Green Swallows were presented together with no discrimination between species).…”

Partial incubation during egg laying reduces eggshell microbial loads in a temperate‐breeding passerine

“…Bacteria and fungi are pervasive in the nests of birds (Baggott and Graeme-Cook 2002) and have the potential to impact egg viability through trans-shell infection (Cook et al 2003(Cook et al , 2005b. Eggshell microbes originate from a number of sources, including nest material (Lee et al 2014, Martínez-García et al 2016, nest boxes and the female's cloaca (Ruiz-de-Castañeda et al 2011b). Extensive work on poultry has demonstrated the physical and biochemical defenses of eggs against eggshell microbes (reviewed by Bruce and Drysdale 1994, Berrang et al 1999, Svobodová and Tůmová 2014, including at the level of the cuticle Halls 1973, Bruce andDrysdale 1991; see also Wellman-Labadie et al 2008).…”