Extra-pair paternity, breeding density, and synchrony in natural cavities versus nestboxes in two passerine birds.

Most of what is known about extra-pair paternity in hole-nesting birds derives from studies using artificial nesting sites, such as nestboxes. However, it has rarely been investigated whether inference drawn from breeding events taking place in nestboxes matches what would be observed under natural conditions, that is, in natural cavities. We here report on a variation in promiscuity in blue tits and great tits nesting in natural cavities and nestboxes in an urban forest in Warsaw, Poland. Specifically, we tested whether local breeding density, local breeding synchrony, and extra-pair paternity (inferred from SNP data generated with a high-throughput genotyping by sequencing method) differed between birds nesting in natural cavities and nestboxes. In both blue tits and great tits, the frequency of extra-pair paternity was similar between the two cavity types. In blue tits, we observed shorter nearest neighbor distance, higher neighbor density, and higher synchronous neighbor density (i.e., density of fertile females) in nestboxes relative to natural cavities. No such pattern was found in great tits. Moreover, we detected a positive relationship between the proportion of extra-pair offspring in the nest and neighbor density around the nest in blue tits. Our results revealed that the provisioning of nestboxes did not change rates of extra-pair paternity, suggesting that conclusions drawn from nestbox studies might adequately represent the natural variation in extra-pair matings in some species or sites. However, the observed differences in spatiotemporal components of breeding dynamics highlight the fact that these parameters should be carefully considered when comparing mating behavior across studies and/or sites.

Preserving avian blood and DNA sampled in the wild: A survey of personal experiences.

Collecting and storing biological material from wild animals in a way that does not deteriorate DNA quality for subsequent analyses is instrumental for research in ecology and evolution. Our aims were to gather reports on the effectiveness of methods commonly used by researchers for the field collection and long-term storage of blood samples and DNA extracts from wild birds. Personal experiences were collected with an online survey targeted specifically at researchers sampling wild birds. Many researchers experienced problems with blood sample storage but not with DNA extract storage. Storage issues generated problems with obtaining adequate DNA quality and sufficient DNA quantity for the targeted molecular analyses but were not related to season of blood sampling, access to equipment, transporting samples, temperature, and method of blood storage. Final DNA quality and quantity were also not affected by storage time before DNA extraction or the methods used to extract DNA. We discuss practical aspects of field collection and storage and provide some general recommendations, with a list of pros and cons of different preservation methods of avian blood samples and DNA extracts.

Changes to the gut microbiota of a wild juvenile passerine in a multidimensional urban mosaic.

Urbanisation is a major anthropogenic perturbation presenting novel ecological and evolutionary challenges to wild populations. Symbiotic microorganisms residing in the gastrointestinal tracts (gut) of vertebrates have mutual connections with host physiology and respond quickly to environmental alterations. However, the impact of anthropogenic changes and urbanisation on the gut microbiota remains poorly understood, especially in early development. To address this knowledge gap, we characterised the gut microbiota of juvenile great tits (Parus major) reared in artificial nestboxes and in natural cavities in an urban mosaic, employing two distinct frameworks characterising the urban space. Microbial diversity was influenced by cavity type. Alpha diversity was affected by the amount of impervious surface surrounding the breeding location, and positively correlated with tree cover density. Community composition differed between urban and rural sites: these alterations covaried with sound pollution and distance to the city centre. Overall, the microbial communities reflect and are possibly influenced by the heterogeneous environmental modifications that are typical of the urban space. Strikingly, the choice of framework and environmental variables characterising the urban space can influence the outcomes of such ecological studies. Our results open new perspectives to investigate the impact of microbial symbionts on the adaptive capacity of their hosts.

Growing in the city: Urban evolutionary ecology of avian growth rates.

INTRODUCTION: Rapid environmental change driven by urbanization offers a unique insight into the adaptive potential of urban-dwelling organisms. Urban-driven phenotypic differentiation is increasingly often demonstrated, but the impact of urbanization (here modelled as the percentage of impervious surface (ISA) around each nestbox) on offspring developmental rates and subsequent survival remains poorly understood. Furthermore, the role of selection on urban-driven phenotypic divergence was rarely investigated to date. METHODS AND RESULTS: Data on nestling development and body mass were analysed in a gradient of urbanization set in Warsaw, Poland, in two passerine species: great tits (Parus major) and blue tits (Cyanistes caeruleus). Increasing levels of impervious surface area (ISA) delayed the age of fastest growth in blue tits. Nestling body mass was also negatively affected by increasing ISA 5 and 10 days after hatching in great tits, and 10 and 15 days in blue tits, respectively. High levels of ISA also increased nestling mortality 5 and 10 days after hatching in both species. An analysis of selection differentials performed for two levels of urbanization (low and high ISA) revealed a positive association between mass at day 2 and survival at fledging. DISCUSSION: This study confirms the considerable negative impact of imperviousness-a proxy for urbanization level-on offspring development, body mass and survival, and highlights increased selection on avian mass at hatching in a high ISA environment.

Patterns of Midichloria infection in avian-borne African ticks and their trans-Saharan migratory hosts.

BACKGROUND: Ticks are obligate haematophagous ectoparasites of vertebrates and frequently parasitize avian species that can carry them across continents during their long-distance migrations. Ticks may have detrimental effects on the health state of their avian hosts, which can be either directly caused by blood-draining or mediated by microbial pathogens transmitted during the blood meal. Indeed, ticks host complex microbial communities, including bacterial pathogens and symbionts. Midichloria bacteria (Rickettsiales) are widespread tick endosymbionts that can be transmitted to vertebrate hosts during the tick bite, inducing an antibody response. Their actual role as infectious/pathogenic agents is, however, unclear. METHODS: We screened for Midichloria DNA African ticks and blood samples collected from trans-Saharan migratory songbirds at their arrival in Europe during spring migration. RESULTS: Tick infestation rate was 5.7%, with most ticks belonging to the Hyalomma marginatum species complex. Over 90% of Hyalomma ticks harboured DNA of Midichloria bacteria belonging to the monophylum associated with ticks. Midichloria DNA was detected in 43% of blood samples of avian hosts. Tick-infested adult birds were significantly more likely to test positive to the presence of Midichloria DNA than non-infested adults and second-year individuals, suggesting a long-term persistence of these bacteria within avian hosts. Tick parasitism was associated with a significantly delayed timing of spring migration of avian hosts but had no significant effects on body condition, whereas blood Midichloria DNA presence negatively affected fat deposits of tick-infested avian hosts. CONCLUSIONS: Our results show that ticks effectively transfer Midichloria bacteria to avian hosts, supporting the hypothesis that they are infectious to vertebrates. Bird infection likely enhances the horizontal spread of these bacteria across haematophagous ectoparasite populations. Moreover, we showed that Midichloria and tick parasitism have detrimental non-independent effects on avian host health during migration, highlighting the complexity of interactions involving ticks, their vertebrate hosts, and tick-borne bacteria.