Search

The effects of systemic pathogens on gut microbiota of wild animals are poorly understood. Furthermore, coinfections are the norm in nature, yet most studies of pathogen-microbiota interactions focus on effects of single pathogen infections on gut microbiota. We examined the effects of four systemic pathogens (bacteria Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato, apicomplexan protozoa Babesia microti and Puumala orthohantavirus) and coinfections among them on the (bacterial) gut microbiota of wild bank voles Myodes glareolus. We hypothesized that: (1) the effects of coinfection on gut microbiota generally differ from those of a single pathogen infection, (2) systemic pathogens have individual (i.e. distinct) associations with gut microbiota, which are modified by coinfection and (3) the effects of coinfection (compared with those of single infection) are idiosyncratic (i.e. pathogen-specific). The gut microbiota of coinfected bank voles differed from that of single pathogen infected individuals, although, as predicted, the effects of coinfections were unique for each pathogen. After accounting for coinfections, only Puumala orthohantavirus was associated with higher α-diversity; however, all pathogens affected gut microbiota ß-diversity in a pathogen-specific way, affecting both rare and abundant gut bacteria. Our results showed that the effects of systemic pathogens on host's gut microbiota vary depending on the pathogen species, resulting in idiosyncratic signatures of coinfection. Furthermore, our results emphasize that neglecting the impact of coinfections can mask patterns of pathogen-microbiota associations., (© 2022 The Authors. Journal of Animal Ecology © 2022 British Ecological Society.)

Evidence that exposure to environmental pollutants can alter the gut microbiota composition of wildlife includes studies of rodents exposed to radionuclides. Antwis et al. (2021) used amplicon sequencing to characterise the gut microbiota of four species of rodent (Myodes glareolus, Apodemus agrarius, A. flavicollis and A. sylvaticus) inhabiting the Chernobyl Exclusion Zone (CEZ) to examine possible changes in gut bacteria (microbiota) and gut fungi (mycobiota) associated with exposure to radionuclides and whether the sample type (from caecum or faeces) affected the analysis. The conclusions derived from the analyses of gut mycobiota are based on data that represent a mixture of ingested fungi (e.g. edible macrofungi, polypores, lichens and ectomycorrhizae) and gut mycobiota (e.g. microfungi and yeasts), which mask the patterns of inter- and intraspecific variation in the authentic gut mycobiota. Implying that 'faecal samples are not an accurate indicator of gut composition' creates an unnecessary controversy about faecal sampling because the comparison of samples from the caecum and faeces confounds many other possible drivers (including different animals from different locations, sampled in different years) of variation in gut microbiota. It is relevant also that Antwis et al.'s (2021) data lack statistical power to detect an effect of exposure to radionuclides on the gut microbiota because (1) all of their samples of Apodemus mice had experienced a medium or high total absorbed dose rate and (2) they did not collect samples of bank voles (M. glareolus) from replicate contaminated and uncontaminated locations. Discussion of Antwis et al.'s (2021) analysis, especially the claims presented in the Abstract, is important to prevent controversy about the outcome of research on the biological impacts of wildlife inhabiting the CEZ., (© 2022 The Authors. Journal of Animal Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.)

Gut microbiota play an important role in host health. Yet, the drivers and patterns of microbiota imbalance (dysbiosis) in wild animals remain largely unexplored. One hypothesised outcome of stress on animal microbiomes is a destabilised microbial community that is characterised by an increase in inter-individual differences compared with microbiomes of healthy animals, which are expected to be (a) temporally stable and (b) relatively similar among individuals. This set of predictions for response of microbiomes to stressors is known as the Anna Karenina principle (AKP) for animal microbiomes. We examine the AKP in a wild mammal inhabiting disturbed environments by conducting a capture-mark-recapture survey of bank voles Myodes glareolus in areas that contrast in levels of radionuclide contamination (Chernobyl, Ukraine). Counter to key predictions of the AKP, bank voles that are not exposed to radionuclides harbour variable (increased inter-individual differences) and temporally dynamic gut microbiota communities, presumably tracking the natural spatio-temporal variation in resources. Conversely, bank voles exposed to radionuclides host more similar gut microbiota communities that are temporally stable, potentially due to a dysbiosis or selection (on host or bacteria) imposed by chronic radiation exposure. The implication of these data is that environmental stress (radiation exposure) can constrain the natural spatial and temporal variation of wild animal gut microbiota., (© 2020 British Ecological Society.)

The early life environment can have profound, long-lasting effects on an individual's fitness. For example, early life quality might (a) positively associate with fitness (a silver spoon effect), (b) stimulate a predictive adaptive response (by adjusting the phenotype to the quality of the environment to maximize fitness) or (c) be obscured by subsequent plasticity. Potentially, the effects of the early life environment can persist beyond one generation, though the intergenerational plasticity on fitness traits of a subsequent generation is unclear. To study both intra- and intergenerational effects of the early life environment, we exposed a first generation of bank voles to two early life stimuli (variation in food and social environment) in a controlled environment. To assess possible intra-generational effects, the reproductive success of female individuals was investigated by placing them in large outdoor enclosures in two different, ecologically relevant environments (population densities). Resulting offspring were raised in the same population densities where they were conceived and their growth was recorded. When adult, half of the offspring were transferred to opposite population densities to evaluate their winter survival, a crucial fitness trait for bank voles. Our setup allowed us to assess: (a) do early life population density cues elicit an intra-generational adaptive response, that is a higher reproductive success when the density matches the early life cues and (b) can early life stimuli of one generation elicit an intergenerational adaptive response in their offspring, that is a higher growth and winter survival when the density matches the early life cues of their mother. Our results show that the early life environment directly affects the phenotype and reproductive success of the focal generation, but adaptive responses are only evident in the offspring. Growth of the offspring is maintained only when the environment matches their mother's early life environment. Furthermore, winter survival of offspring also tended to be higher in high population densities if their mothers experienced an competitive early life. These results show that the early life environment can contribute to maintain high fitness in challenging environments, but not necessarily in the generation experiencing the early life cues., (© 2019 The Authors. Journal of Animal Ecology © 2019 British Ecological Society.)

Recent examples of actuarial senescence in wild insect populations have challenged the long-held assumption that the brevity of wild insect life spans precludes senescence. We investigate age-related patterns in mating behaviour in adults of a short-lived damselfly, Coenagrion puella and the implications of this mating. Using capture histories for 1033 individuals over two field seasons, we conduct both pooled and stratified analyses of variations in breeding activity. Pooled analyses suggest that there is strong age-related variation in the probability of being present at the mating rendezvous. However, no age-related variation was observed in the probability of mating. Stratified approaches confirmed a general pattern of age-related declines in survival probability, but provided only equivocal evidence of an effect of age on transition between temporary breeding states. Mating males and females showed greater survival than non-mating individuals, possibly as a consequence of higher body condition. Older males that were not currently breeding were less likely to commence breeding on the next day, but showed no patterns in breeding cessation. Overall, transitions between both breeding states declined with age, suggesting that males that breed tend to continue breeding while those that do not breed continue to be unsuccessful. Female mating rates were consistently high across all ages with no age-related decline apparent. While previous research has demonstrated actuarial senescence in this population, as does this study, we find little evidence of either age-related declines in reproductive behaviour or breeding-related declines in survival, which might indicate functional senescence or costs of mating, respectively. Indeed, the greater survival in mating individuals of both sexes suggests that variations in individual quality may mediate both reproductive success and longevity. Contrary to recent studies, we found no compelling evidence for reproductive senescence or a cost of mating in an important and well-studied model odonate. The possible link between condition and ageing suggests that individual quality needs to be taken into account when studying senescence. We recommend the use of multistrata models for the future investigation of these phenomena., (© 2015 The Authors. Journal of Animal Ecology published by John Wiley & Sons on behalf of the British Ecological Society.)

1. Age-dependent increases in mortality have been documented in a variety of species of insect under laboratory conditions. However, while strong statistical evidence has been presented for senescence in vertebrate populations in the wild, we know little about the rate and shape of senescence in wild populations of insects. 2. Odonates (damselflies and dragonflies) provide excellent candidate species for evaluating demographic senescence as they are large enough to be marked individually and they are easily re-sighted without recapture. The prevailing opinion - based entirely on qualitative examination of the declines in log numbers alive with time since marking - is that odonates exhibit age-independent daily survivorship. 3. Here, we examine mark-recapture data on the Azure Damselfly Coenagrion puella over two consecutive seasons. For the first time, we evaluate and compare the fit of quantitative models that not only account for weather-dependent daily variation in daily re-sighting rates, but also age-dependent variation in daily survivorship. 4. Models with age-dependent declines in daily survivorship provide a more parsimonious explanation for the data than similar models without these age-dependent effects. In general, models in which mortality increases in an exponential (Gompertz) fashion explain the mark-recapture sequences more efficiently than a range of alternative models, including those in which mortality increases as a power function (Weibull) or reaches a plateau (logistic). These results are indicative of a general senescent decline in physiological functioning, which is particularly marked after 15 days as a mature adult. 5. Weather (temperature, sun and precipitation) and initial mite load influenced the probability of daily re-sighting. Weather and mite load also influenced daily survivorship, but their effects differed between seasons. 6. Overall, fitting models with age as an explicit covariate demonstrates that odonates do indeed senesce. This contradicts previously held assumptions that Odonata do not exhibit age-dependent survivorship in the wild.

1. Effective population sizes (N(e)) and migration rates (m) are critical evolutionary parameters that impact on population survival and determine the relative influence of selection and genetic drift. While the parameter m is well-studied in animal populations, N(e) remains challenging to measure and consequently is only rarely estimated, particularly in insect taxa. 2. We used demographic and genetic methods to estimate N(e) and m in a fragmented population of the endangered damselfly Coenagrion mercuriale to better understand the contrast between genetic and field estimates of these parameters and also to identify the spatial scale over which populations may become locally adapted. 3. We found a contrast between demographic- and genetic-based estimates of these parameters, with the former apparently providing overestimates of N(e), owing to substantial underestimation of the variance in reproductive success, and the latter overestimating m, because spatial genetic structure is weak. 4. The overall N(e) of sites within the population network at Beaulieu Heath, the largest C. mercuriale site in the UK, was estimated to vary between approximately 60 and 2700. 5. While N(e) was not correlated with either the total numbers of adults (N) or the area of habitat, this parameter was always less than N, because of substantial variance in reproductive success. The ratio N(e)/N varied between 0.006 and 0.42 and was generally larger in smaller populations, possibly representing some 'genetic compensation'. 6. From a simple genetic model and these data on N(e) and m, it seems that populations of C. mercuriale have the potential to respond to localized spatial variation in selection and this would need to be considered for future genetic management of this endangered species.