Glenn Yannic

Ecotypes offer a window into the earliest stages of adaptive divergence, before reproductive isolation is complete. In eastern Canada, migratory and boreal caribou (Rangifer tarandus caribou) represent a striking example of recent ecological divergence, differing primarily in movement strategy despite ongoing gene flow. We used low- and high-coverage whole-genome sequencing from migratory and boreal populations in Quebec and Labrador to characterize the timing, demographic history, and genomic signatures of this divergence. Demographic modeling supported a secondary contact scenario, with an estimated divergence time roughly 7,000–11,700 years ago, coinciding with the last deglaciation period. Despite weak overall population structure (genome-wide FST = 0.02) and evidence of continued gene flow, we identified distinct genomic peaks of differentiation, nearly half of which coincided with divergent haplotype length (XP-nSL), a pattern consistent with recent, incomplete soft selective sweeps rather than classic hard sweeps. Combining differentiation-, diversity-, and haplotype-based statistics proved essential for detecting this subtle selection signature. Candidate genes under selection point to a polygenic architecture spanning bone and connective tissue development (including antler-related pathways), mitochondrial energy metabolism, and other traits plausibly linked to the ecological differences between ecotypes. Together, our results suggest that caribou ecotypes are not fixed evolutionary endpoints but a dichotomy that can re-emerge from standing genetic variation as opportunity arises.

Species distribution models (SDMs) are widely used to predict habitat suitability but their usefulness and accuracy for inferring population health is still debated. Here, we evaluate whether SDM-derived relative habitat suitability (RHS) predicts genome-wide genetic diversity and connectivity—which are key proxies for population health and the functional integrity of landscapes. We addressed this issue in the Yellow-bellied toad (Bombina variegata), an endangered amphibian species with limited dispersal. We combined hierarchical SDMs, integrating both continental-level bioclimatic data and regional-level landscape variables, with genome-wide SNP data from 404 individuals sampled across 92 sites in southeastern France. We then used a multi-scale modelling framework to test the effect of bioclimatic (BRHS) and landscape (LRHS) habitat suitability on observed heterozygosity and pairwise genetic differentiation, accounting for heterogeneous genetic drift using gravity models. Our results show that both BRHS and LRHS are significant predictors of heterozygosity, with their effects expressed at different spatial scales—11 km and 3 km for BRHS and LRHS, respectively. Connectivity patterns also widely varied depending on scale and were best explained by gravity models integrating LRHS, BRHS, and local heterozygosity, underscoring the combined role of landscape resistance and population size in shaping patterns of genetic differentiation. These findings show that SDMs, when carefully calibrated and interpreted, can provide proxies for genetic diversity and landscape resistance in species with limited dispersal.

Mountain ecosystems are under strong environmental pressure and are considered highly vulnerable to climate change, which is likely to lead to forest expansion and loss of open alpine grasslands, threatening many specialized species. However, for most alpine birds, even basic ecological knowledge, such as their diet, remains limited, restricting our capacity to predict how they will respond to environmental change in the future. In this study, we investigated the diet of the Northern Wheatear Oenanthe oenanthe , a characteristic species of alpine grasslands, in the Italian Alps. We analysed 151 faecal samples collected in 2023 and 2024 using DNA metabarcoding, mainly, but not exclusively, from nestlings. At the same time, we quantified arthropod availability (measured by abundance and biomass) across the breeding season using sweep nets and pitfall traps. The Northern Wheatear's diet consisted of a broad range of arthropods, mainly Diptera, Coleoptera, Lepidoptera and Orthoptera. For most arthropod groups, there was not one peak in availability across the breeding season, but a continuum moving upwards as the season progressed. A compositional selectivity analysis showed that Northern Wheatears exhibited a generalist foraging strategy at the Order level, with no overall preference for specific taxa, although selectivity for Lepidoptera and Orthoptera showed seasonal variation. This suggests that, in the face of global changes, Northern Wheatears can adjust their foraging to temporal and spatial variation in arthropod community composition, provided that overall prey availability remains sufficient. We found no relationship between breeding performance and arthropod availability. Given that nestling starvation has never been recorded in this population, it is likely that the spatio‐temporal dynamism of alpine habitats maintains high food availability throughout the season, preventing food limitation during breeding.

In bird species with precocial development, i.e. chicks acquire abilities to leave the nest soon after hatching, the nestling period during which parents warm their young in the nest by brooding them is short but critical to breeding success. The duration of the nestling period (DNP) depends on the hatching synchrony of eggs and the speed at which chicks acquire these abilities but may be indirectly affected by parental behaviour and temporal variations in temperature and predation. We assessed the effects of incubation strategy (bi- or uniparental), hatching start time, incubation initiation date and predation risk on the DNP in Arctic-breeding sandpipers. We found that the DNP was longer in biparental species (29.75 ± 8.95 h) compared with uniparental ones (25.82 ± 6.87 h) and was extended in nests where chicks began hatching during the colder ‘night’ hours. No effect of incubation initiation date or predation pressure was found on the DNP. We suggest that parental investment strategies and constraints related to circadian variations in temperature in chicks drive the DNP in Arctic-breeding sandpipers. These results help us better understand how different species may exhibit different behavioural responses during nesting to impending climate change.

Global environmental change is reshaping biodiversity by altering species connectivity, genetic diversity, and long-term viability. A key challenge is to disentangle how historical, environmental, and anthropogenic factors jointly shape contemporary genetic patterns. Here, we combine population genomics with landscape ecology tools to investigate the drivers of levels of genetic diversity and patterns of population genetic structure using more than 20k Single Nucleotide Polymorphisms (SNPs) in the Northern chamois (Rupicapra rupicapra), a wide-ranging Alpine ungulate. Based on 465 individuals sampled across the European and Dinaric Alps as well as the Tatra Mountains, we revealed a pronounced hierarchical genetic structure, with clusters showing marked geographic variation in genetic diversity across the species range. Our results show that current genetic diversity largely reflects the genetic legacy of past climatic conditions, with areas of long-term stability acting as reservoirs of genetic variation. At the same time, large Alpine rivers emerge as strong barriers to gene flow, emphasizing the powerful role of natural landscape features in shaping genetic structure. In contrast, recent anthropogenic infrastructures exerted limited detectable influence, suggesting that contemporary patterns are still predominantly driven by natural processes of population differentiation. By explicitly quantifying the relative contributions of long-term climatic stability and contemporary landscape features to genetic diversity and connectivity, this study demonstrates that historical processes outweigh recent anthropogenic fragmentation in shaping current genetic patterns in this mountain ungulate.

Accurate sex identification of prey remains can provide valuable insights into selective predation, but field studies are often constrained by degraded or digested material. We developed and validated a molecular sexing protocol for the Brown lemming ( Lemmus trimucronatus), a keystone prey species in the Canadian High Arctic. Using tissues from known-sex individuals, we tested candidate primers and established a multiplex PCR combining sex-chromosomal zinc-finger genes (ZFX and ZFY) and sex-determining region Y protein (SRY) markers. This method reliably distinguished males and females, with 98% concordance between genetic and morphological sexing. Validation included dentary bones subjected to artificial digestion, demonstrating consistent success regardless of tissue type or degradation treatment. We then applied the protocol to field-collected lemming remains from snowy owl pellets, ermine caches, and predated lemming winter nests. Despite variable preservation and exposure conditions, 87% of samples yielded viable results, with soft tissues achieving highest success rates and bones and teeth remaining suitable DNA sources even after digestion. Our results confirm that molecular sexing of lemmings from predator-derived remains is feasible, accurate, and robust to sample quality. This protocol can enable researchers in Arctic ecosystems to analyze sex-specific predation patterns even when direct observation or fresh tissue sampling is impractical.

Climate projections predict major changes in alpine environments by the end of the 21st century. To avoid climate-induced maladaptation and extinction, many animal populations will either need to move to more suitable habitats or adapt in situ to novel conditions. Since populations of a species exhibit genetic variation related to local adaptation, it is important to incorporate this variation into predictive models to help assess the ability of the species to survive climate change. Here, we evaluate how the adaptive genetic variation of a mountain ungulate—the Northern chamois (Rupicapra rupicapra)—could be impacted by future global warming. Based on genotype-environment association analyses of 429 chamois using a ddRAD sequencing approach, we identified genetic variation associated with climatic gradients across the European Alps. We then delineated adaptive genetic units and projected the optimal distribution of these adaptive groups in the future. Our results suggest the presence of local adaptation to climate in Northern chamois with similar genetic adaptive responses in geographically distant but climatically similar populations. Furthermore, our results predict that future climatic changes will modify the Northern chamois adaptive landscape considerably, with various degrees of maladaptation risk.