Image 1: Hoopoe (Upupa epops)

Hoopoes are a remarkable bird species. Apart from possessing highly distinctive features (perhaps most notably their characteristic “crown of feathers”), they may help us to shed light on the role of beneficial bacteria in the animal kingdom.

Recent discoveries made by researchers at the UGR, published in the Journal of Animal Ecology, reveal that Hoopoes (upupa epops), a colourful bird species found across Afro-Eurasia, coat their eggs with a bacteria which protects them from infections caused by pathogens. This beneficial bacteria, transmitted via a secretion produced in the Hoopoe’s uropygial gland and applied directly by the bird to the egg, increases the likelihood of successful hatching. To date, the Hoopoe is the only known bird species to exhibit this kind of behaviour.

When researchers prevented the birds from covering their eggs with the bacteria, they discovered that the presence of harmful pathogen bacteria inside the eggs which had failed to hatch was significantly greater. This discovery confirmed the original experimental hypothesis that the secretion acts as a protective shield, warding off pathogens.

Upon further analysis, they confirmed that the secretion contains a protein known as bacteriocins (small antimicrobial proteins). In effect, bacteriocins are proteinaceous toxins which deter the growth of closely related bacterial strains. In this case they curb the growth of bacteria which could potentially harm the developing embryo. As the UGR Zoology Professor Manuel Martín-Vivaldi underlines, over the course of the last few years the discipline of evolutionary ecology has acknowledged “the important role played by bacteria, not just as infectious agents capable of producing diseases, but also as allies of animals and other living creatures in their struggle against disease, due to their extraordinary capacity to synthesise compounds with antimicrobial properties”

The research findings highlight that the higher the concentration of a bacterial strain called enterococci, the greater the likelihood that the egg will remain free of pathogens.

The research has also demonstrated that hoopoe eggs have small depressions in their surface structure. These small depressions or hollows appear to act as receptacles designed to retain the bacteria-carrying secretion that covers the egg. “With this experiment we have been able to establish that if the females can apply their secretion, then towards the end of the incubation period those tiny craters are full of a substance saturated with bacteria. If we preclude the use of this secretion, these tiny craters are empty towards the end of the hatching process”, said professors Martín-Vivaldi. These results prove that this particular bird species’ reproductive strategy has “evolved hand in hand with the use of bacteria which may be beneficial for the production of antimicrobial substances, which they cultivate in their gland and then apply upon eggs which are particularly endowed to retain them”

Image 2: Microscopic details of hollow depressions in egg shell structure which retain secretion

These scientists are currently working to determine the specific composition of the bacterial community within the gland, how these symbionts are acquired, and the types of antimicrobial compounds which synthesise these bacteria, capable of protecting the embryos which are undergoing development. Further research along these lines will facilitate a better understanding of the way in which mutual interactions function between animals and beneficial bacteria, and also to detect new antimicrobial substances with a potential use in medicine or for food preservation.

The research project has been jointly pursued by the University of Granada and the Spanish National Research Council, and conducted by the following research groups: Animal Behaviour and Ecology, Microorganism-Produced Antagonistic Substances, both from the UGR, and the Evolutionary Ecology, Behaviour and Conservation groups from the Dry Area Experimental Station (Almería, CSIC)

The research findings have been published in a paper entitled ‘Special structures of hoopoe eggshells enhance the adhesion of symbiont-carrying uropygial secretion that increase the hatching success.’

Bibliography:

'Special structures of hoopoe eggshells enhance the adhesion of symbiont-carrying uropygial secretion that increase hatching'success'

Manuel Martín-Vivaldi, Juan J. Soler, Juan M. Peralta-Sánchez, Laura Arco. Antonio M. Martín-Platero, Manuel Martínez-Bueno, Magdalena Ruiz-Rodríguez and Eva Valdivia.

Journal of Animal Ecology 2014 DOI: 10.1111/1365-2656.12243

Research Group Contact:

Manuel Martín-Vivaldi

Animal Behaviour and Ecology Research Group

Zoology Department, University of Granada

Email: mmv@ugr.es

Phone: 958 249 852

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ARTICLE SOURCE IN SPANISH: UGR News (Canal UGR)