Animals breeding in nest‐boxes experience nesting environments in which they did not originally evolve. Despite the central importance of nesting microclimate for offspring fitness, little is known ...about the thermal properties of human‐provided nest sites compared to natural ones. In particular, comparisons with offspring in the nest are lacking. Here, we compare microclimate (temperature and absolute humidity) from the onset of breeding, thus starting with nest‐site choice and ending with the post‐fledging stage, quantified in natural cavities and nest‐boxes used by several species of hollow‐nesting birds in a temperate deciduous forest. We confirm that across all nesting stages, nest‐boxes were thermally unstable when compared to natural cavities, with higher temperature maximums, larger amplitudes and worse insulation from maximum ambient temperatures relative to natural cavities. Surprisingly, as average humidity of natural cavities was previously shown to be higher than in nest‐boxes, in the presence of actively thermoregulating young, nest‐boxes were more humid than natural cavities. When offspring were in the nest, internal microclimatic shifts were mitigated three times more effectively in natural cavities than in nest‐boxes (in terms of mean daily differences from ambient temperature). Artificial cavity microclimate is likely to amplify the adverse effects of projected temperature increases by compromising thermoregulation of developing animals. We stress that conservation efforts should focus on the protection of areas offering natural breeding‐hollows to reduce the potential impacts of climate change on breeding animals.
Reproduction, a basic property of biological life, entails costs for an organism, ultimately detectable as reduction in survival prospects. Telomeres are an excellent candidate biomarker for ...explaining these reproductive costs, because their shortening correlates with increased mortality risk. For similar reasons, telomeres are perceived as biomarkers of individual “quality.” The relationship between reproduction and telomere dynamics is reviewed, emphasizing that cost and quality perspectives, commonly presented in isolation, should be integrated. While a majority of correlative studies have confirmed the relationship between telomere dynamics and various reproductive outputs, only limited experimental support exists showing that reproduction causes telomeres to shorten. A shift of focus to experimental manipulations of reproductive effort/telomere dynamics is crucial. However, the observation of survival reduction in response to these manipulations is essential for establishing telomeres as genuine biomarkers, allowing to unravel trade‐offs related to reproduction.
Several experimental studies show that reproduction causes telomeres to shorten, which may explain reduced survival in breeding animals. Individual quality mediates this cost of reproduction through positive associations between life‐history traits. The relationship between reproduction and telomeres and ways to integrate cost and quality perspectives are reviewed.
Human‐provided nesting shelters such as nest‐boxes mitigate the shortage of natural breeding sites. Since artificial nests are not where animals evolved and optimised their reproductive performance, ...it remains inconclusive if these are adequate substitutes, ensuring equivalent fitness returns while breeding. In particular, most knowledge on the ecology of cavity‐nesting birds comes from nest‐box populations, but no study has directly compared fitness consequences of breeding inside nest‐boxes in relation to natural cavities in cities. We directly compare the reproductive performance, life‐history trait variation and fitness consequences for two small passerines, blue and great tits, breeding in nest‐boxes as opposed to natural cavities in an urban deciduous forest. We use a quasi‐experimental setting to comprehend the conservation potential of these artificial cavities and to support/question generalisations stemming from nest‐box studies. We show that the effects of cavity type vary between species: in blue tits, fitness proxies were negatively affected by nest‐boxes (lower fledging success and fledgling numbers, longer time spent in the nest and later fledging date relative to natural cavities), while in great tits, the fitness proxies were unaffected by cavity type. Importantly, we detected accelerated incubation in both species breeding in nest‐boxes. No differences in pre‐hatching traits (lay date, clutch size, hatching rates) between cavity types suggest that the fitness deterioration occurred because of post‐hatching effects. We highlight the ecological importance of old‐growth tree stands, providing natural cavities for city‐breeding animals and the need for quantifying alterations of reproductive ecology in other taxa using human‐provided nests. Owing to the detected cavity type‐dependent variation in reproductive performance, we support the criticism regarding the unconditional extrapolation of evolutionary and ecological interpretations of nest‐box studies to general populations.
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.
Genetic variation is one of the key concepts in evolutionary biology and an important prerequisite of evolutionary change. However, we know very little about processes that modulate its levels in ...wild populations. In particular, we still are to understand why genetic variances often depend on environmental conditions. One of possible environment-sensitive modulators of observed levels of genetic variance are maternal effects. In this study we attempt to experimentally test the hypothesis that maternally transmitted agents (e.g. hormones) may influence the expression of genetic variance in quantitative traits in the offspring. We manipulated the levels of steroid hormones (testosterone and corticosterone) in eggs laid by blue tits in a wild population. Our experimental setup allowed for full crossing of genetic and rearing effects with the experimental manipulation. We observed that birds treated with corticosterone exhibited a significant decrease in broad-sense genetic variance of tarsus length, and an increase in this component in body mass on the 2nd day post-hatching. Our study indicates, that maternally transmitted substances such as hormones may have measurable impact on the levels of genetic variance and hence, on the evolutionary potential of quantitative traits.
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.
The collection of biological material from wild animals plays a fundamental role in many disciplines within ecology and evolution and its storage under optimal conditions ensures its usefulness long after its collection. We report results from an online survey, in which we directly asked scientists to share their experiences in the collection and long‐term storage of blood samples and DNA extracts from wild birds. We show that different storage conditions can generate considerable variation in the quality of stored samples, with consequences for research outcomes.
Relatively few studies have examined the interactive effects of ecological factors on physiological responses in wild animals. Nearly all of them have been short-term investigations that did not ...include experimental manipulations, limiting our ability to understand how climate change will affect natural populations. Using a 10-year brood size manipulation experiment in wild blue tits (Cyanistes caeruleus), we quantified the impact of weather conditions and brood competition on the body mass and structural size (tarsus length) of nestlings just prior to leaving the nest.
We found that variation in nestling body mass on day 14 after hatching was explained by an interactive effect between average ambient temperature experienced during nestling period and brood size treatment. Specifically, in control broods nestling body mass was correlated with temperature in a non-linear manner (concave) with the vertex point (maximum body mass) at ca. 13 °C. In contrast, in enlarged broods nestling body mass permanently increased (also non-linearly) as temperature advanced.
Our results highlight the importance of considering the effects of brood rearing conditions alongside other environmental factors experienced during growth while investigating early-life environmental effects on body condition.
The evolution of brood parasitism has long attracted considerable attention among behavioural ecologists, especially in the common cuckoo system. Common cuckoos (Cuculus canorus) are obligatory brood ...parasites, laying eggs in nests of passerines and specializing on specific host species. Specialized races of cuckoos are genetically distinct. Often in a given area, cuckoos encounter multiple hosts showing substantial variation in egg morphology. Exploiting different hosts should lead to egg-phenotype specialization in cuckoos to match egg phenotypes of the hosts. Here we test this assumption using a wild population of two sympatrically occurring host species: the great reed warbler (Acrocephalus arundinaceus) and reed warbler (A. scirpaceus). Using colour spectrophotometry, egg shell dynamometry and egg size measurements, we studied egg morphologies of cuckoos parasitizing these two hosts. In spite of observing clear differences between host egg phenotypes, we found no clear differences in cuckoo egg morphologies. Interestingly, although chromatically cuckoo eggs were more similar to reed warbler eggs, after taking into account achromatic differences, cuckoo eggs seemed to be equally similar to both host species. We hypothesize that such pattern may represent an initial stage of an averaging strategy of cuckoos, that--instead of specializing for specific hosts or exploiting only one host--adapt to multiple hosts.
Abstract Urbanisation has been increasing worldwide in recent decades, driving environmental change and exerting novel selective pressures on wildlife. Phenotypic differences between urban and rural ...individuals have been widely documented in several taxa. However, the extent to which urbanisation impacts mating strategies is less known. Here, we investigated extra‐pair paternity variation in great tits ( Parus major ) and blue tits ( Cyanistes caeruleus ) breeding in nestboxes set in a gradient of urbanisation in Warsaw, Poland, over three breeding seasons. Urbanisation was quantified as the amount of light pollution, noise pollution, impervious surface area (ISA) and tree cover within a 100‐m radius around each nestbox. We obtained genotypes for 1213 great tits at 7344 SNP markers and for 1299 blue tits at 9366 SNP markers with a genotyping‐by‐sequencing method, and inferred extra‐pair paternity by computing a genomewide relatedness matrix. We report higher extra‐pair paternity in blue tits breeding in more urbanised areas, for example, with higher light pollution and ISA, and lower tree cover. However, no such trend was found in great tits. Late‐stage survival of individual nestlings in both species was not associated with paternity or urbanisation proxies, thus we were not able to detect fitness benefits or drawbacks of being an extra‐pair offspring in relation to urbanisation. Our results contribute to the growing body of knowledge reporting on the effects of urbanisation on avian ecology and behaviour, and confirm species‐specific and population‐specific patterns of extra‐pair paternity variation.
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