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Bacterial colonisation of the intestine has a major role in the post-natal development and maturation of the immune and endocrine systems. These processes are key factors underpinning central nervous system (CNS) signalling. Regulation of the microbiome–gut–brain axis is essential for maintaining homeostasis, including that of the CNS. However, there is a paucity of data pertaining to the influence of microbiome on the serotonergic system. Germ-free (GF) animals represent an effective preclinical tool to investigate such phenomena. Here we show that male GF animals have a significant elevation in the hippocampal concentration of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid, its main metabolite, compared with conventionally colonised control animals. Moreover, this alteration is sex specific in contrast with the immunological and neuroendocrine effects which are evident in both sexes. Concentrations of tryptophan, the precursor of serotonin, are increased in the plasma of male GF animals, suggesting a humoral route through which the microbiota can influence CNS serotonergic neurotransmission. Interestingly, colonisation of the GF animals post weaning is insufficient to reverse the CNS neurochemical consequences in adulthood of an absent microbiota in early life despite the peripheral availability of tryptophan being restored to baseline values. In addition, reduced anxiety in GF animals is also normalised following restoration of the intestinal microbiota. These results demonstrate that CNS neurotransmission can be profoundly disturbed by the absence of a normal gut microbiota and that this aberrant neurochemical, but not behavioural, profile is resistant to restoration of a normal gut flora in later life.

Top predator populations, once intensively hunted, are rebounding in size and geographic distribution. The cessation of sealing along coastal Australia and subsequent recovery of Australian Arctocephalus pusillus doriferus and long-nosed A. forsteri fur seals represents a unique opportunity to investigate trophic linkages at a frontier of predator recolonisation. We characterised the diets of both species across 2 locations of recolonisation, one site an established breeding colony, and the other, a new but permanent haul-out site. Using DNA metabarcoding, high taxonomic resolution data on diets was used to inform ecological trait-based analyses across time and location. Australian and long-nosed fur seals consumed 76 and 73 prey taxa, respectively, a prey diversity greater than previously reported. We found unexpected overlap of prey functional traits in the diets of both seal species at the haul-out site, where we observed strong trophic linkages with coastal ecosystems due to the prevalence of benthic, demersal and reef-associated prey. The diets of both seal species at the breeding colony were consistent with foraging patterns observed in the centre of their geographic range regarding diet partitioning between predator species and seasonal trends typically observed. The unexpected differences between sites in this region and the convergence of both predators’ effective ecological roles at the range-edge haul-out site correlate with known differences in seal population densities and demographics at these and other newly recolonised locations. This study provides a baseline for the diets and trophic interactions for recovering fur seal populations and from which to understand the evolving ecology of predator recolonisation.

1. Habitat suitability models (HSMs) are commonly used in conservation practise to assess the potential of an area to be occupied and colonised. A major limitation of these models, however, is the omission of spatially explicit understanding of human acceptance towards the focal species. As wildlife is more and more subject to human-dominated landscapes, ignoring the sociological component will result in misrepresentation of the observed processes and inappropriate management. 2. We distributed 10 000 questionnaires across Switzerland and identified key socio-demographical factors correlated with human acceptance of the wolf. We then created a spatially explicit acceptance model based on geo-referenced socio-demographical, social and geographical information. Finally, we combined our acceptance model with a HSM to obtain a unified socio-ecological suitability model, which included human and ecological components. 3. We showed that the key factors associated with human acceptance were perception of how harmful the wolf is, interest in wolf-related issues, need for livestock protection, and fear of the wolf. Perceived harmfulness was in turn correlated with direct and indirect experience with the wolf, and level of education. 4. Our acceptance map predicted decreasing acceptance with increasing altitude of residency and proximity to locations of confirmed wolf presence. This resulted in the overall opposition to the wolf for the Alpine region, albeit substantial regional differences. 5. We found little spatial overlap (6% of Switzerland) between areas where the wolf was accepted and areas of suitable habitat. These areas of socio-ecological suitability were concentrated in the Jura Mountains and in the eastern and southern Alps, and were absent in the western and central Alps. Particularly in the Jura region, which is yet to be colonised, management of human acceptance will be a crucial conservation target. 6. Synthesis and applications. We developed an integrative, socio-ecological approach that allowed us to accurately reproduce recent wolf recolonisation. We anticipate our framework to be a powerful tool to reliably evaluate overall suitable habitats and predict short to medium-term range expansion for species whose distribution is also dependent on human attitudes. Because our approach is sensitive to both the ecological and human component, it is ideally suited to identify key regions where proactive and targeted socio-ecological management plans are needed.

As wolves recolonise their historical range across Europe, ungulates face predation once more – but in landscapes profoundly altered by human activity. This shift raises crucial questions about their capacity to express adaptive antipredator behaviours. Using a quasi‐experimental camera‐trap design, we examined diel activity responses of ungulates along the ongoing wolf recolonisation in the south‐eastern Alps. Red deer showed higher summer diurnality in sites with a longer history of wolf presence (7% increase over five years, on average) and progressively reduced nocturnality within sites as local wolf establishment advanced (5% decrease per year, on average), also heightening activity overlap with humans. This ‘diel shield effect' disappeared when human hunting occurred. Roe deer and Alpine chamois did not exhibit significant diel activity shifts in relation to wolves, though both species responded to human disturbance, with roe deer adjusting activity to hunting (18% less diurnal, on average) and chamois reducing diurnality in areas of intense outdoor use (up to 38% difference in diurnality between undisturbed and highly disturbed areas). Red deer, too, were less diurnal (up to 27% difference) and more nocturnal (up to 37% difference) in such highly disturbed areas, as well as near human settlements (up to 42% difference in diurnality between remote areas and villages). Our findings show that wolf recovery can induce detectable diel activity shifts in large herbivores over relatively short timescales, yet responses depend on species biology and behavioural plasticity. Importantly, human risk and disturbance can offset or override these behavioural adjustments, potentially altering the ecosystemic effects of returning large carnivores.

Aim Large carnivores worldwide have experienced substantial range contractions due to human activities, though several species are recolonising parts of their historical range. We aimed to assess current and potential European brown bear (Ursus arctos arctos) habitat as well as habitat connectivity on a continental scale. Location The extended biogeographical regions of Europe, spanning from Portugal to central Russia, longitudinally, and from Norway to Türkiye, latitudinally. Excluding inland seas; this area covers 11,151,636 km2. Methods We assessed habitat suitability throughout the study area using an ensemble species distribution model with nine submodels, using data from 10 European bear populations and Türkiye. We used the resulting habitat suitability maps to conduct a least‐cost path connectivity analysis and an omnidirectional circuit connectivity analysis. Main Conclusions Habitat suitability was strongly associated with low percentages of agricultural cover, low percentages of human development, and proximity to forest. Of our entire study area, 37% (4.09 million km2) is occupied or potentially suitable for bears. Connectivity analyses identified corridors that could facilitate movement among southern European bear populations, though agricultural land and human development limit connectivity between northern and southern European bear populations. Previous research estimated bears occupied 0.5 million km2 across the European Union, while our results estimate 1.82 million km2 of this part of our study area is potentially suitable for bears, though connectivity is limited. Our results inform conservation strategies and policy development for the future of brown bears in Europe, emphasising the need for transboundary conservation efforts.

The prevailing paleobiogeographic hypothesis suggests that many steppe and tundra-steppe taxa currently found in Central Asia expanded into Europe during Pleistocene glacial periods, when open habitats dominated. However, previous studies have shown that one such species, the European narrow-headed vole ( Stenocranius anglicus ), diverged from its Asiatic counterparts over 200 thousand years ago, implying its prolonged isolation and survival in European refugia through the Eemian interglacial period. To test whether this was an exception or part of a broader pattern, we analysed the mitochondrial genomes from 33 Late Pleistocene and Holocene small hamster (Cricetinae) remains from Central and Western Europe, the Balkans, and Anatolia, all previously identified morphologically as grey dwarf hamster ( Nothocricetulus migratorius ). Contrary to expectations, 16 Late Pleistocene Central European samples were assigned to the hairy-footed hamster ( Cricetiscus sungorus ), a species currently restricted to northern Kazakhstan and southern Russia, whereas 17 samples from the Balkans and Anatolia belonged to the grey dwarf hamster. In both cases, the Late Pleistocene samples formed clades sister to modern populations; however, with relatively recent divergence times. This suggests population continuity or repeated expansion of hamsters from Asiatic sources rather than long-term isolation in Europe, as previously observed in narrow-headed voles. Our findings indicate that steppe species, despite occupying similar ecological niches, respond to past climate change in a species-specific manner. Therefore, broad generalisations regarding their evolutionary history may be misleading.

1. Human activities have dramatic effects on the distribution and abundance of wildlife. Increased road densities and human presence in wilderness areas have elevated human-caused mortality of grizzly bears and reduced bears' use. Management agencies frequently attempt to reduce human-caused mortality by managing road density and thus human access, but the effectiveness of these actions is rarely assessed. 2. We combined systematic, DNA-based mark-recapture techniques with spatially explicit capture-recapture models to estimate population size of a threatened grizzly bear population (Kettle-Granby), following management actions to recover this population. We tested the effects of habitat and road density on grizzly bear population density. We tested both a linear and threshold-based road density metric and investigated the effect of current access management (closing roads to the public). 3. We documented an c. 50% increase in bear density since 1997 suggesting increased landscape and species conservation from management agencies played a significant role in that increase. However, bear density was lower where road denisities exceeded 0.6 km/km² and higher where motorised vehicle access had been restricted. The highest bear densities were in areas with large tracts of few or no roads and high habitat quality. Access management bolstered bear density in small areas by 27%. 4. Synthesis and applications. Our spatially explicit capture-recapture analysis demonstrates that population recovery is possible in a multi-use landscape when management actions target priority areas. We suggest that road density is a useful surrogate for the negative effects of human land use on grizzly bear populations, but spatial configuration of roads must still be considered. Reducing roads will increase grizzly bear density, but restricting vehicle access can also achieve this goal. We demonstrate that a policy target of reducing human access by managing road density below 0.6 km/km², while ensuring areas of high habitat quality have no roads, is a reasonable compromise between the need for road access and population recovery goals. Targeting closures to areas of highest habitat quality would benefit grizzly bear population recovery the most.

Following glacial retreat after the last ice age, brown bears ( Ursus arctos ) recolonised Scandinavia. Previous research based on mitochondrial markers suggests that bears recolonised from both the north and the south, with a contact zone in central Scandinavia. More recently, the Scandinavian brown bear was subjected to a strong population decline with only ca. 130 remaining individuals, due to intense human persecution approximately 100 years ago. Here, we analyse 41 ancient, historical, and modern mitochondrial genomes, to examine the number of female lineages involved in the postglacial recolonisation event and temporal changes in the Scandinavian brown bears’ mitochondrial genetic diversity. Our results support the bi-directional recolonisation hypothesis, indicating multiple mitochondrial lineages from clade 1a possibly followed a southern route, while only a single lineage from clade 3a appears to have followed a northern route. Furthermore, we found that the recent bottleneck had a strong impact on the southern subpopulation, resulting in only one remaining haplotype in the contemporary brown bears. For the northern subpopulation, the impact was moderate, and most haplotypes were retained throughout the bottleneck. By exploring the postglacial recolonisation and recent population pressures, our study enhances understanding of how these factors have influenced the genetic diversity of Scandinavian brown bears.

BackgroundUrban streams are characterised by species-poor and frequently disturbed communities. The recovery of heavily polluted urban streams is challenging but the simple community structure makes recolonisation patterns more transparent. Therefore, they are generally applicable model systems for recolonisation of restored streams. Principal questions of stream restoration concern the drivers and patterns of recolonisation processes. Rarely, recolonisation of restored streams is recorded for a sufficient time to observe patterns of habitat and community development in detail. Over 10 years, we monitored benthic habitat changes and macroinvertebrate communities of eight restored sites in an urban stream network that was formerly used as an open sewer and thus, almost uninhabitable for macroinvertebrates prior to restoration. We analysed changes in environmental variables and communities with a selection of multi-variate analyses and identified indicator species in successional stages.ResultsProportions of stony substrate and conductivity decreased over time since restoration, while the riparian vegetation cover increased along with the amount of sandy substrate. The communities fluctuated strongly after restoration but began to stabilise after around eight years. TITAN analysis identified 9 species, (e.g. the mayfly Cloeon dipterum and the beetle Agabus didymus), whose abundances decreased with time since restoration, and 19 species with an increasing abundance trend (e.g. several Trichopteran species, which colonised once specific habitats developed). Woody riparian vegetation cover and related variables were identified as major driver for changes in species abundance. In the last phase of the observation period, a dry episode resulted in complete dewatering of some sites. These temporarily dried sections were recolonised much more rapidly compared to the recolonisation following restoration.ConclusionsOur results underline that community changes following urban stream restoration are closely linked to the evolving environmental conditions of restored streams, in particular habitat availability initialised by riparian vegetation. It takes about a decade for the development of a rich and stable community. Even in streams that were almost completely lacking benthic invertebrates before restoration, the establishment of a diverse macroinvertebrate community is possible, underlining the potential for habitat restoration in formerly heavily polluted urban areas.

Stream restoration is meant to mitigate increasing anthropogenic pressure and re-establish ecosystem functioning and biodiversity. Extensive research has identified constraints hampering biotic recovery, but successful projects are still scarce. This study documents short-term macroinvertebrate colonisation in a near-natural environment with plentiful potential colonists, which has rarely been studied. Three streams contiguous with near-natural aquatic habitats were monitored over sixteen months after restoration. Sampling sections were categorised and compared to reference sections. Species richness and composition, abundance, functional parameters and similarity to reference were evaluated. Restored streams were colonised rapidly and, in multiple respects, reached reference levels within the study period. Distance from upstream colonisation source and restoration method (newly built and rebuilt channels) had little effect on recovery. However, species composition of upper and lower sections diversified, as they receive colonists from various sources. Repeated sampling revealed dynamic assemblage development with Chironomidae, Baetidae and Nemouridae being among the pioneer colonists. A common successional pattern was observed; gatherers/collectors and small, plurivoltine larvae decreased, whereas predators, grazers/scrapers and medium-sized, univoltine larvae increased. This study demonstrates that restoration of previously channelised streams in near-natural environment is followed by rapid macroinvertebrate colonisation, successfully promoting biodiversity.