Abstract
The common cuckoo (Cuculus canorus) is an avian brood parasite, laying its eggs in the nests of other bird species, where these hosts incubate the parasitic eggs, feed and rear the nestlings. The appearance of a cuckoo egg in a host nest may change the bacterial community in the nest. This may have consequences on the hatchability of host eggs, even when hosts reject the parasitic egg, typically within six days after parasitism. The present study revealed the bacterial community of cuckoo eggshells and those of the great reed warbler (Acrocephalus arundinaceus), one of the main hosts of cuckoos. We compared host eggs from non-parasitized clutches, as well as host and cuckoo eggs from parasitized clutches. As incubation may change bacterial assemblages on eggshells, we compared these egg types in two stages: the egg-laying stage, when incubation has not been started, and the mid-incubation stage (ca. on days 5–7 in incubation), where heat from the incubating female dries eggshells. Our results obtained by the 16S rRNA gene sequencing technique showed that fresh host and cuckoo eggs had partially different bacterial communities, but they became more similar during incubation in parasitized nests. Cluster analysis revealed that fresh cuckoo eggs and incubated host eggs in unparasitized nests (where no cuckoo effect could have happened) were the most dissimilar from the other groups of eggs. Cuckoo eggs did not reduce the hatchability of great reed warbler eggs. Our results on the cuckoo-great reed warbler relationship supported the idea that brood parasites may change bacterial microbiota in the host nest. Further studies should reveal how bacterial communities of cuckoo eggshells may vary by host-specific races (gentes) of cuckoos.
Highlights
Studies on the diversity of microbiota, including bacteria, receive considerable attention by animal ecologists, as bacteria are fundamental components of animal bodies
We revealed that cuckoo parasitism can be regarded as a bacterial vector effect in the nests of their hosts, as we found significant differences in the bacterial community in parasitized host nests when compared with non-parasitized host clutches
We characterised and compared the eggshell cultivable bacteria of these two avian species, and showed that cuckoos changed the hygienic conditions of host nests
Summary
Studies on the diversity of microbiota, including bacteria, receive considerable attention by animal ecologists, as bacteria are fundamental components of animal bodies. They live on skin, scales, feathers, fur and exoskeletons, in digestive, respiratory and reproductive tracts, and in specialized glands for grooming, preening or olfactory communication [1]. Bacteria could be transmitted from nest material to the eggshell, as it was revealed in reed warblers (Acrocephalus scirpaceus) [2] and hoopoes (Upupa epops) [3] Nest visitors, such as brood parasites, may affect the microbiome of the nests and change their bacterial environment [4]. Several behaviours, such as blood-sucking and defecation by ectoparasites [6] or damaging of eggs by brood parasites [7], may affect the microbiome of avian nests by diversifying or partially exchanging their bacterial community
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