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Shifts in bacterial communities of eggshells and antimicrobial activities in eggs during incubation in a ground-nesting passerine.

Grizard S, Versteegh MA, Ndithia HK, Salles JF, Tieleman BI - PLoS ONE (2015)

Bottom Line: Regarding the antimicrobials, we notice a decrease of pH and lysozyme concentration, while ovotransferrin concentration increases during incubation.Lastly, our results provide limited evidence of significant correlation between antimicrobial compounds and bacterial communities.Identifying invading microbes and their roles in embryo mortality, as well as understanding the role of the eggshell microbiome, might be key to better understand avian strategies of immune maternal investment.

View Article: PubMed Central - PubMed

Affiliation: Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands; Department of Microbial Ecology, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands.

ABSTRACT
Microbial invasion of egg contents is a cause of embryonic death. To counter infection risks, the embryo is protected physically by the eggshell and chemically by antimicrobial proteins. If microbial pressure drives embryo mortality, then females may have evolved, through natural selection, to adapt their immune investment into eggs. Although frequently hypothesized, this match between immune allocation and microorganisms has not been explored yet. To examine if correlations between microbes on eggs and immunity in eggs exist, we collected eggs from red-capped larks (Calandrella cinerea) and simultaneously examined their bacterial communities and antimicrobial components--pH, lysozyme and ovotransferrin--during natural incubation. Using molecular techniques, we find that bacterial communities are highly dynamic: bacterial abundance increases from the onset to late incubation, Shannon's α-diversity index increases during early incubation stages, and β-diversity analysis shows that communities from 1 day-old clutches are phylogenetically more similar to each other than the older ones. Regarding the antimicrobials, we notice a decrease of pH and lysozyme concentration, while ovotransferrin concentration increases during incubation. Interestingly, we show that two eggs of the same clutch share equivalent immune protection, independent of clutch age. Lastly, our results provide limited evidence of significant correlation between antimicrobial compounds and bacterial communities. Our study examined simultaneously, for the first time in a wild bird, the dynamics of bacterial communities present on eggshells and of albumen-associated antimicrobial components during incubation and investigated their relationship. However, the link between microorganisms and immunity of eggs remains to be elucidated further. Identifying invading microbes and their roles in embryo mortality, as well as understanding the role of the eggshell microbiome, might be key to better understand avian strategies of immune maternal investment.

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Related in: MedlinePlus

Phylogenetic β-diversity of eggshell bacterial communities at different clutch ages.Dots are plotted based on the weighted UniFrac distances among bacterial communities and visualized on a Principal Coordinates Analysis (PCoA) plot. The variability of those communities is based on the two first axes of the PCoA. The percentage of variation explained per axis is mentioned on the graph: PC1 explained 68.93% of variation among communities and PC2 explained 11.92%. Egg age is symbolized by: day 1 (red), 2 (orange), 3 (yellow), 5 (green), 8 (blue) and 11 (purple). Each dot represents the bacterial community associated with one eggshell.
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pone.0121716.g002: Phylogenetic β-diversity of eggshell bacterial communities at different clutch ages.Dots are plotted based on the weighted UniFrac distances among bacterial communities and visualized on a Principal Coordinates Analysis (PCoA) plot. The variability of those communities is based on the two first axes of the PCoA. The percentage of variation explained per axis is mentioned on the graph: PC1 explained 68.93% of variation among communities and PC2 explained 11.92%. Egg age is symbolized by: day 1 (red), 2 (orange), 3 (yellow), 5 (green), 8 (blue) and 11 (purple). Each dot represents the bacterial community associated with one eggshell.

Mentions: While examining 1 day-old eggs, based on weighted UniFrac, we noticed their communities were phylogenetically more similar (98.0% (±0.13)) among each other, than were the ones of 5 days-old (94.2% (±0.94)). The two clutch ages significantly differed from each other (t = 4.03, df = 9.3, P = 0.003). Moreover, we observed that 1 day-old eggs preferentially clustered together along the first axis of the PCoA plot (68.9% of the variability; Fig 2). Communities of 5 days-old eggs, and more generally of other ages, were more variable and broadly distributed along the first, second (11.9% of the variability; Fig 2), and third axis (7.11% of the variability; S4 Fig) of the plots, although five of twelve eggshells overlapped with the communities of 1 day-old eggs. Differences in phylogenetic similarities between 1 day- and 5 days-old eggs were also reported for unweighted UniFrac (t = 3.06, df = 14.13, P = 0.008) and similar relationships between eggshell communities at different clutch ages were observed along the three first axes of the PCoA plots (S4 Fig).


Shifts in bacterial communities of eggshells and antimicrobial activities in eggs during incubation in a ground-nesting passerine.

Grizard S, Versteegh MA, Ndithia HK, Salles JF, Tieleman BI - PLoS ONE (2015)

Phylogenetic β-diversity of eggshell bacterial communities at different clutch ages.Dots are plotted based on the weighted UniFrac distances among bacterial communities and visualized on a Principal Coordinates Analysis (PCoA) plot. The variability of those communities is based on the two first axes of the PCoA. The percentage of variation explained per axis is mentioned on the graph: PC1 explained 68.93% of variation among communities and PC2 explained 11.92%. Egg age is symbolized by: day 1 (red), 2 (orange), 3 (yellow), 5 (green), 8 (blue) and 11 (purple). Each dot represents the bacterial community associated with one eggshell.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4400097&req=5

pone.0121716.g002: Phylogenetic β-diversity of eggshell bacterial communities at different clutch ages.Dots are plotted based on the weighted UniFrac distances among bacterial communities and visualized on a Principal Coordinates Analysis (PCoA) plot. The variability of those communities is based on the two first axes of the PCoA. The percentage of variation explained per axis is mentioned on the graph: PC1 explained 68.93% of variation among communities and PC2 explained 11.92%. Egg age is symbolized by: day 1 (red), 2 (orange), 3 (yellow), 5 (green), 8 (blue) and 11 (purple). Each dot represents the bacterial community associated with one eggshell.
Mentions: While examining 1 day-old eggs, based on weighted UniFrac, we noticed their communities were phylogenetically more similar (98.0% (±0.13)) among each other, than were the ones of 5 days-old (94.2% (±0.94)). The two clutch ages significantly differed from each other (t = 4.03, df = 9.3, P = 0.003). Moreover, we observed that 1 day-old eggs preferentially clustered together along the first axis of the PCoA plot (68.9% of the variability; Fig 2). Communities of 5 days-old eggs, and more generally of other ages, were more variable and broadly distributed along the first, second (11.9% of the variability; Fig 2), and third axis (7.11% of the variability; S4 Fig) of the plots, although five of twelve eggshells overlapped with the communities of 1 day-old eggs. Differences in phylogenetic similarities between 1 day- and 5 days-old eggs were also reported for unweighted UniFrac (t = 3.06, df = 14.13, P = 0.008) and similar relationships between eggshell communities at different clutch ages were observed along the three first axes of the PCoA plots (S4 Fig).

Bottom Line: Regarding the antimicrobials, we notice a decrease of pH and lysozyme concentration, while ovotransferrin concentration increases during incubation.Lastly, our results provide limited evidence of significant correlation between antimicrobial compounds and bacterial communities.Identifying invading microbes and their roles in embryo mortality, as well as understanding the role of the eggshell microbiome, might be key to better understand avian strategies of immune maternal investment.

View Article: PubMed Central - PubMed

Affiliation: Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands; Department of Microbial Ecology, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands.

ABSTRACT
Microbial invasion of egg contents is a cause of embryonic death. To counter infection risks, the embryo is protected physically by the eggshell and chemically by antimicrobial proteins. If microbial pressure drives embryo mortality, then females may have evolved, through natural selection, to adapt their immune investment into eggs. Although frequently hypothesized, this match between immune allocation and microorganisms has not been explored yet. To examine if correlations between microbes on eggs and immunity in eggs exist, we collected eggs from red-capped larks (Calandrella cinerea) and simultaneously examined their bacterial communities and antimicrobial components--pH, lysozyme and ovotransferrin--during natural incubation. Using molecular techniques, we find that bacterial communities are highly dynamic: bacterial abundance increases from the onset to late incubation, Shannon's α-diversity index increases during early incubation stages, and β-diversity analysis shows that communities from 1 day-old clutches are phylogenetically more similar to each other than the older ones. Regarding the antimicrobials, we notice a decrease of pH and lysozyme concentration, while ovotransferrin concentration increases during incubation. Interestingly, we show that two eggs of the same clutch share equivalent immune protection, independent of clutch age. Lastly, our results provide limited evidence of significant correlation between antimicrobial compounds and bacterial communities. Our study examined simultaneously, for the first time in a wild bird, the dynamics of bacterial communities present on eggshells and of albumen-associated antimicrobial components during incubation and investigated their relationship. However, the link between microorganisms and immunity of eggs remains to be elucidated further. Identifying invading microbes and their roles in embryo mortality, as well as understanding the role of the eggshell microbiome, might be key to better understand avian strategies of immune maternal investment.

Show MeSH
Related in: MedlinePlus