Biology subjects

Caspers, B. A.

Publications and source records attributed to Caspers, B. A..

6 recordsLinked to original sources

bioRxiv2026

Long-term consequences of fostering: Single egg fostering leads to decreased survival in zebra finch females, but not in males

Cross-Fostering, i.e., the exchange of eggs or hatchlings, is a widely used technique, to disentangle genetic from environmental effects or to manipulate the clutch size. In most bird species, this manipulation is easily accepted by the social parents, leading to the conclusion that fostering has no detrimental effect. Using a dataset of four cohorts (N=298) of zebra finches (Taeniopygia castanotis), in which we fostered routinely a single egg into another nest of zebra finches, we explored potential short- and long-time effects of fostering. Noteworthy, these experiments were not designed to test this hypothesis. The objective of the egg fostering experiments was to test for parental recognition (Caspers et al. 2017) and mate choice decisions (Goluke 2018). Consequently, the aim of the present study is purely explorative. Our study confirmed previous findings that fostering has no short-term effects on the morphology and growth rates of the chicks, neither in males nor in females. However, we found that fostering has a sex-specific long-term effect. Females originating from fostered eggs had a significantly reduced lifespan compared to those from non-fostered eggs. Conversely, the lifespan of fostered males was similar to that of non-fostered males. All birds were housed in large groups, experiencing the same conditions after nutritional independence (day 35). Therefore, we can only speculate that fostering might result in early developmental stress, which may affect the individual fitness of females later in life, ultimately leading to shorter lifespans.

animal behavior and cognition↗

bioRxiv2025

From larval stage to adulthood? Habitat type-specific chemical fingerprints of fire salamander larvae might give first indication for adult mate preference

Assortative mating can play a major role in the divergence of a population with gene flow. In a fire salamander population near Bonn, Germany, the larvae differ genetically according to the habitat type they are found in, i.e. ponds or streams. Neither sound nor vision are a source for assortative mating in fire salamanders, but it is known that females can discriminate between sexes and habitat types of the males based on chemical cues. The adults share the same terrestrial habitat which leads to the question whether there is a habitat type-specific chemical fingerprint already existing in the larvae that may be used in the adult stage as the base for assortative mating. We took water samples and captured larvae at two ponds and two streams and used polydimethylsiloxane and TD-GC-MS to collect and analyze samples of the environmental background as well as from the surface of the larvae. We found a significantly different composition of chemical features in the environmental back-ground samples. Additionally, we found the larvae to carry habitat type-specific chemical features. These finding allow to speculate that the features on the larval surface may be used

ecology↗

bioRxiv2024

The gut microbiota-immune-brain axis in a wild vertebrate: dynamic interactions and health impacts

The gut microbiota-immune-brain axis is a feedback network which influences diverse physiological processes and plays a pivotal role in overall health and well-being. Although research in humans and laboratory mice has shed light into the associations and mechanisms governing this communication network, evidence of such interactions in wild, especially in young animals, is lacking. We therefore investigated these interactions during early development in a population of common buzzards (Buteo buteo) and their effects on individual condition. In a longitudinal study, we used a multi-marker approach to establish potential links between the bacterial and eukaryotic gut microbiota, a panel of immune assays and feather corticosterone measurements as a proxy for long-term stress. Using Bayesian structural equation modelling, we found no support for feedback between gut microbial diversity and immune or stress parameters. However, we did find strong relationships in the feedback network. Immunity was negatively correlated with corticosterone levels, and microbial diversity was positively associated with nestling body condition. Furthermore, corticosterone levels and eukaryotic microbiota diversity decreased with age while immune activity increased. The absence of conclusive support for the microbiota-immune-brain axis in common buzzard nestlings, coupled with the evidence for stress mediated immunosuppression, suggests a dominating role of stress-dominated maturation of the immune system during early development. Confounding factors inherent to wild systems and developing animals might override associations known from adult laboratory model subjects. The positive association between microbial diversity and body condition indicates the potential health benefits of possessing a diverse and stable microbiota.

microbiology↗

bioRxiv2023

Stress response of fire salamander larvae differs between habitat types

Different habitats can impose varying selection pressures on individuals of the same species. Larvae of the European fire salamander (Salamandra salamandra) can inhabit two different habitats: streams and ponds. Streams are characterised by lower predation risk and intraspecific density and higher food availability than ponds. Thus, ponds are considered a less suitable habitat. To investigate the differential impacts of the two habitats on larval physiology, we measured the stress response of larvae living in the two different habitats. After successfully validating the measure of water-borne corticosterone (CORT) concentrations in fire salamander larvae, we measured the baseline and stress-induced CORT of 64 larvae from two pond and two stream locations in the field. We found larvae in ponds to be more stressed than larvae in streams. Additionally, we performed a reciprocal transplant experiment and tested whether larvae can adapt their stress response to changing habitat conditions. After two weeks of transfer, we did not find an increase in CORT when comparing stress-induced CORT values with baseline CORT values in larvae transferred into ponds. However, larvae transferred into streams exhibited an increase in the stress-induced CORT response. Moreover, transfer into ponds as well as larvae originating from ponds showed reduced growth rates, indicating that ponds might be the more stressful habitat, as it negatively affected larval physiology. These results show that noninvasive hormone measurements can provide information on habitat quality and potential adaptation and thus emphasis the potential for its use in conservation efforts.

ecology↗

bioRxiv2021

Alterations to the Gut Microbiota of a Wild Juvenile Passerine in an Urban Mosaic

Urbanisation is a major anthropogenic perturbation that progressively alters multiple environmental parameters, thereby presenting novel evolutionary challenges to wild populations. Symbiotic microorganisms residing in the gastrointestinal tracts (gut) of vertebrates have well-established mutual connections with the physiology of their hosts and respond quickly to environmental alterations. However, the impacts of anthropogenic changes and urbanisation on gut microbiota remain poorly understood, especially in early development. To address this knowledge gap, we investigated the gut microbiota in juvenile great tits (Parus major) in an urban mosaic. First, we compared the microbiota of nestlings reared in artificial nest boxes or natural cavities. Next, we analysed microbiota variations employing two distinct urbanisation frameworks, (i) the classical urban/rural dichotomy and (ii) gradual changes in the amount of impervious surface area (ISA) in the urban space and identified the environmental variables that predicted the changes in the microbial communities. Alpha diversity was influenced by cavity type and by the amount of impervious surface surrounding the breeding location. Alpha diversity was also positively correlated with the tree cover density. Beta diversity differed between urban and rural sites, and these alterations covaried with sound pollution, the distance to the city centre and the distance to the closest road. 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 used to define the urban space can influence the outcomes of studies investigating animal-microbe symbiosis. Our results open new perspectives from which the potential function of microbial symbionts in the adaptation of their hosts to anthropogenic stress can be investigated.

ecology↗

bioRxiv2020

Behavioural responses to chemical cues of predators differ between fire salamander larvae from two different habitats

Predation is one of the strongest selection pressures, forcing prey organisms to detect predators and to display various antipredator behaviours, such as refuge-use or decreased activity. To recognise predators, chemosensory cues play a pivotal role, particularly in aquatic ecosystems. However, it is less known whether the ability to use these cues to respond with adequate antipredator behaviour varies between individuals occupying different habitats that are dissimilar in predation risk. Using field experiments, we examined antipredator behaviour of larval fire salamanders (Salamandra salamandra) from two different habitats, ponds and streams. Among other differences, ponds and streams are inhabited by habitat-specific predators, such as alpine newts (Ichthyosaura alpestris) occurring in ponds. We exposed larvae from both habitats to either chemical cues from alpine newts or a blank control (tap water) and investigated potential differences in their behavioural responses in two experiments. Pond larvae, but not stream larvae, became significantly less active when faced with chemical cues from newts compared to those faced with a control stimulus. Moreover, larvae from both habitats tested in water containing chemical cues spent significantly less time outside a shelter than those in control water. Our results demonstrate that larval fire salamanders recognise predatory newts through kairomones and alter their behaviour accordingly. However, experience with predatory newts may not be necessary to differentiate kairomones from control water, but may be beneficial for larvae to further develop their antipredator behaviour, thus representing conformance to a niche.

animal behavior and cognition↗