Alpine Populations Research Articles

Assessing the outcome of reintroduction efforts: Trends in population size and drivers of breeding success in alpine bearded vultures

AbstractVulture populations have dramatically declined worldwide over the past few decades. In Europe, various programs have been implemented to reintroduce or restock these birds. In the Alps, the Bearded Vulture (Gypaetus barbatus) was eradicated in the early 20th century, prompting the launch of an international reintroduction program in 1986. Through intensive monitoring of Bearded Vulture breeding territories over 26 years (1995–2021), we observed spatial and temporal changes in population size and assessed environmental and individual factors influencing breeding performance across four countries in the Alpine arc. The number of breeding pairs increased steadily from 1 in 1995 to 65 in 2021, and the number of fledglings from 0 in 1995 to 42 in 2021, although we observed significant differences across areas, with slower growth in the Eastern Alps. The breeding success (proportion of clutches leading to a fledgling) of the entire Alpine population was 68%, higher than that of other European populations. Our analysis, which included individual and environmental variables, revealed that nest elevation positively influenced breeding success, while the proportion of open habitat in the territory had a negative effect. Additionally, breeding success significantly increased with the coverage of not strictly protected areas around the nest. In terms of individual factors, longer pair bonds positively affected breeding success, and pairs composed of wild‐hatched individuals had higher breeding success compared to those including released individuals. Our results confirm the overall positive trend of the reintroduced Alpine population but also highlight the increased vulnerability of the population breeding in the Eastern Alps. Additionally, our findings suggest that an effective network of protected areas can support the establishment of reintroduced populations. We also identified directions for further research to better understand the drivers of Bearded Vulture breeding success in the Alps.

Genetic variability of Linnaea borealis – remnant of Eastern-Southeastern Alpine populations indicates a strong bottleneck and in situ glacial survival

In a rapidly changing environment, habitat loss and fragmentation have primarily led to a decline in the numbers of numerous plant species. We compared the genetic variability of two small, isolated populations of Linnaea borealis L. with three populations from the core distribution area in the boreal region. The results show three main clusters, exemplars from the boreal distribution area being represented in all three clusters. The genetic variability within the two isolated Eastern-Southeastern Alpine populations was found to be very low, while genetic variability between them was very high. In addition, a low proportion of different genotypes was revealed in the Eastern-Southeastern Alpine populations as compared to the northern population. The high genetic variability between the two isolated Eastern-Southeastern Alpine populations indicates that most likely both are glacial relict populations, probably due to consecutive bottlenecks and long-term isolation under specific environmental conditions. Glacial relicts, which tend to be associated with endangered habitats, deserve urgent attention, especially when the recent anthropogenically-driven environmental crisis is considered.

Complex Responses to Climate Warming of Arctic-Alpine Plant Populations From Different Geographic Provenance.

The distribution of 'cold-adapted' plant species is expected to undergo severe range loss in the near future. Species distribution models predicting species' future distribution often do not integrate species ability to respond to environmental factors through genetic traits or phenotypic plasticity. This especially applies to arctic-alpine species whose present-day range is strongly fragmented because of the cyclic vicissitudes they experienced during the Ice Age. We cultivated plants from four European populations of the arctic-alpine species Viscaria alpina from different geographic provenances. Two of the populations were from northern high-latitude regions in Scandinavia; the remaining two populations were from southern mid-latitude mountains. In both areas, one population was from a colder site and the other from a warmer site. We cultivated the plants in controlled thermal conditions with two treatments, one mimicking temperature conditions at the warmest site and the other adding 2 day-temperature peaks mimicking short-term heat waves. At the end of the experiment, we measured growth in length and mortality of all plants along with a set of ecophysiological variables. We also assessed phylogeographic variation in the four populations based on plastid-DNA sequences. The plants from northern provenances grew more than those from the southern provenances. The plants of all populations performed overall well, in terms of growth rate and ecophysiology, under the heat spell, with the plants of the Swedish population exhibiting the highest phenotypic plasticity. Such a pattern was associated with the highest genetic variation in the Swedish population. Mortality of the plants cultivated under warm temperatures was overall low, but mortality strongly increased in the plants exposed to the heat spell. We conclude that plants of V. alpina populations from different geographic provenances are generally able to cope with scenarios resulting from global warming, but drought hampers resilience to heat waves through increased mortality.

Uncovering genetic signatures of the Walser migration in the Alps: Patterns of diversity and differentiation.

Since leaving Africa, human populations have gone through a series of range expansions. While the genomic signatures of these expansions are well detectable on a continental scale, the genomic consequences of small-scale expansions over shorter time spans are more challenging to disentangle. The medieval migration of the Walser people from their homeland in ssouthern Switzerland (Upper Valais) into other regions of the Alps is a good example of such a comparatively recent geographic and demographic expansion in humans. While several studies from the 1980s, based on allozyme markers, assessed levels of isolation and inbreeding in individual Walser communities, they mostly did so by focusing on a single community at a time. Here, we provide a comprehensive overview of genetic diversity and differentiation based on samples from multiple Walser, Walser-homeland, and non-Walser Alpine communities, along with an idealized (simulated) Swiss reference population (Ref-Pop). To explore genetic signals of the Walser migration in the genomes of their descendants, we use a set of forensic autosomal STRs as well as uniparental markers. Estimates of pairwise FST based on autosomal STRs reveal that the Walser-homeland and Walser communities show low to moderate genetic differentiation from the non-Walser Alpine communities and the idealized Ref-Pop. The geographically more remote and likely more isolated Walser-homeland community of Lötschental and the Walser communities of Vals and Gressoney appear genetically more strongly differentiated than other communities. Analyses of mitochondrial DNA revealed the presence of haplogroup W6 among the Walser communities, a haplogroup that is otherwise rare in central Europe. Our study contributes to the understanding of genetic diversity in the Walser-homeland and Walser people, but also highlights the need for a more comprehensive study of the population genetic structure and evolutionary history of European Alpine populations using genome-wide data.

The influence of elevation on genetic structure and variability in a wetland crucifer of the Rocky Mountains.

In mountain ecosystems, environmental conditions (e.g., temperature, ultraviolet radiation) covary with elevation, potentially limiting gene flow over steep gradients. We hypothesized that, (1) due to stark elevational differences in environmental factors, populations from dissimilar elevations (e.g., montane versus alpine) are more strongly differentiated than populations from similar elevations; (2) patterns of migration reflect downslope dispersal more than upslope dispersal; and (3) alpine populations at the cold edge show evidence of expansion, while montane populations at the warm edge have declined. DNA polymorphisms in whole-genome sequences were studied from 6-10 genotypes each in populations of Cardamine cordifolia found at three montane sites (ranging from 2200 to 2800 m a.s.l.) and three alpine sites (ranging from 3000 to 3500 m a.s.l.). Statistical analyses assessed patterns of population structure, genetic diversity, migration, and historical demography since the Pleistocene. Populations maintained very high levels of nucleotide diversity (π range: 0.062-0.071) and were weakly differentiated (pairwise FST = 0.027) on average. Migration among alpine populations was also inferred, with no directionality of migration across elevation bands. Demographic inference suggests that both montane and alpine populations have declined in size since the Pleistocene. Environmental differences across elevation represent diffuse barriers to gene flow. Recent polyploidy and clonal reproduction likely explain excess heterozygosity and high nucleotide diversity within populations. The genetic similarity of populations across elevation suggests highly connected refugia during the Pleistocene; such results may indicate that montane and alpine populations will respond similarly to changing environmental conditions associated with climate change.

Foliar flavonoids across an elevation gradient: Plasticity in response to UV, and links with floral pigmentation patterning

Foliar flavonoids across an elevation gradient: Plasticity in response to UV, and links with floral pigmentation patterning

Metabolite and protein associations with general health in the population-based CHRIS study

Identifying biomarkers able to discriminate individuals on different health trajectories is crucial to understand the molecular basis of age-related morbidity. We investigated multi-omics signatures of general health and organ-specific morbidity, as well as their interconnectivity. We examined cross-sectional metabolome and proteome data from 3,142 adults of the Cooperative Health Research in South Tyrol (CHRIS) study, an Alpine population study designed to investigate how human biology, environment, and lifestyle factors contribute to people’s health over time. We had 174 metabolites and 148 proteins quantified from fasting serum and plasma samples. We used the Cumulative Illness Rating Scale (CIRS) Comorbidity Index (CMI), which considers morbidity in 14 organ systems, to assess health status (any morbidity vs. healthy). Omics-signatures for health status were identified using random forest (RF) classifiers. Linear regression models were fitted to assess directionality of omics markers and health status associations, as well as to identify omics markers related to organ-specific morbidity. Next to age, we identified 21 metabolites and 10 proteins as relevant predictors of health status and results confirmed associations for serotonin and glutamate to be age-independent. Considering organ-specific morbidity, several metabolites and proteins were jointly related to endocrine, cardiovascular, and renal morbidity. To conclude, circulating serotonin was identified as a potential novel predictor for overall morbidity.

Predation of Rock Partridge Alectoris graeca saxatilis nests incubated by males and females in the French Alps

ABSTRACT Capsule The predation of incubated nests was investigated in an Alpine population of Rock Partridges, showing a double-nesting behaviour by females that can lay two clutches in succession, one incubated by the mated male and the second by the female. Aims To compare the nest predation rate and hatching success between incubating males and females in relation to the potential effects of year, nest age, and environmental characteristics (presence of nest cameras, visibility of the clutch, and vegetation cover around the nest). Methods The fate of 100 nests incubated by radio-tracked birds was monitored daily over 1738 days using cameras, and with temperature loggers placed in the nest cup. Nest predation rates and daily predation rates were calculated and modelled. Results Egg predation was the main cause of nest loss (87%) followed by predation of the incubating parent during recess periods off the nest (10%). Only mammals were identified as nest predators, and predation events were less frequent during the day than at night. We found no difference in predation rates between nests incubated by males or females. Daily and 25-day predation rates were calculated as 0.02 (95% CI: 0.01–0.03) and 0.39 (95% CI: 0.29–0.49), respectively. Median hatching success was 0.91 (n = 53 nests) and did not differ between sexes. Conclusions The similar level of nest predation between incubating males and females suggested a duplication of the reproductive output of a pair by double-nesting. Consequences of this breeding system were an increase in productivity at the population level. There was no difference in hatching success in nests incubated by either sex and there were no observations of surviving males deserting their nests, suggesting that care during incubation was similar in males and females. Variation in the rate of double-nesting may contribute more than nest predation to the annual variation in reproductive output.

Developmental stage shapes the realized energy landscape for a flight specialist.

The heterogeneity of the physical environment determines the cost of transport for animals, shaping their energy landscape. Animals respond to this energy landscape by adjusting their distribution and movement to maximize gains and reduce costs. Much of our knowledge about energy landscape dynamics focuses on factors external to the animal, particularly the spatio-temporal variations of the environment. However, an animal's internal state can significantly impact its ability to perceive and utilize available energy, creating a distinction between the 'fundamental' and the 'realized' energy landscapes. Here, we show that the realized energy landscape varies along the ontogenetic axis. Locomotor and cognitive capabilities of individuals change over time, especially during the early life stages. We investigate the development of the realized energy landscape in the Central European Alpine population of the golden eagle Aquila chrysaetos, a large predator that requires negotiating the atmospheric environment to achieve energy-efficient soaring flight. We quantified weekly energy landscapes using environmental features for 55 juvenile golden eagles, demonstrating that energetic costs of traversing the landscape decreased with age. Consequently, the potentially flyable area within the Alpine region increased 2170-fold during their first three years of independence. Our work contributes to a predictive understanding of animal movement by presenting ontogeny as a mechanism shaping the realized energy landscape.

Developmental stage shapes the realized energy landscape for a flight specialist

The heterogeneity of the physical environment determines the cost of transport for animals, shaping their energy landscape. Animals respond to this energy landscape by adjusting their distribution and movement to maximize gains and reduce costs. Much of our knowledge about energy landscape dynamics focuses on factors external to the animal, particularly the spatio-temporal variations of the environment. However, an animal’s internal state can significantly impact its ability to perceive and utilize available energy, creating a distinction between the ‘fundamental’ and the ‘realized’ energy landscapes. Here, we show that the realized energy landscape varies along the ontogenetic axis. Locomotor and cognitive capabilities of individuals change over time, especially during the early life stages. We investigate the development of the realized energy landscape in the Central European Alpine population of the golden eagle Aquila chrysaetos, a large predator that requires negotiating the atmospheric environment to achieve energy-efficient soaring flight. We quantified weekly energy landscapes using environmental features for 55 juvenile golden eagles, demonstrating that energetic costs of traversing the landscape decreased with age. Consequently, the potentially flyable area within the Alpine region increased 2170-fold during their first three years of independence. Our work contributes to a predictive understanding of animal movement by presenting ontogeny as a mechanism shaping the realized energy landscape.

Behavioural Thermoregulation of Flowers via Petal Movement.

Widely documented in animals, behavioural thermoregulation mitigates negative impacts of climate change. Plants experience especially strong thermal variability but evidence for plant behavioural thermoregulation is limited. Along a montane elevation gradient, Argentina anserina flowers warm more in alpine populations than at lower elevation. We linked floral temperature with phenotypes to identify warming mechanisms and documented petal movement and pollinator visitation using time-lapse cameras. High elevation flowers were more cupped, focused light deeper within flowers and were more responsive to air temperature than low; cupping when cold and flattening when warm. At high elevation, a 20° increase in petal angle resulted in a 0.46°C increase in warming. Warming increased pollinator visitation, especially under cooler high elevation temperatures. A plasticity study revealed constitutive elevational differences in petal cupping and stronger temperature-induced floral plasticity in high elevation populations. Thus, plant populations have evolved different behavioural responses to temperature driving differences in thermoregulatory capacity.

Genomic, morphological and physiological data support fast ecotypic differentiation and incipient speciation in an alpine diving beetle.

An intricate interplay between evolutionary and demographic processes has frequently resulted in complex patterns of genetic and phenotypic diversity in alpine lineages, posing serious challenges to species delimitation and biodiversity conservation planning. Here we integrate genomic data, geometric morphometric analyses and thermal tolerance experiments to explore the role of Pleistocene climatic changes and adaptation to alpine environments on patterns of genomic and phenotypic variation in diving beetles from the taxonomically complex Agabus bipustulatus species group. Genetic structure and phylogenomic analyses revealed the presence of three geographically cohesive lineages, two representing trans-Palearctic and Iberian populations of the elevation-generalist A. bipustulatus and another corresponding to the strictly-alpine A. nevadensis, a narrow-range endemic taxon from the Sierra Nevada mountain range in southeastern Iberia. The best-supported model of lineage divergence, along with the existence of pervasive genetic introgression and admixture in secondary contact zones, is consistent with a scenario of population isolation and connectivity linked to Quaternary climatic oscillations. Our results suggest that A. nevadensis is an alpine ecotype of A. bipustulatus, whose genotypic, morphological and physiological differentiation likely resulted from an interplay between population isolation and local altitudinal adaptation. Remarkably, within the Iberian Peninsula, such ecotypic differentiation is unique to Sierra Nevada populations and has not been replicated in other alpine populations of A. bipustulatus. Collectively, our study supports fast ecotypic differentiation and incipient speciation processes within the study complex and points to Pleistocene glaciations and local adaptation along elevational gradients as key drivers of biodiversity generation in alpine environments.

Dispersal of a wolf with complex ancestry from the Dinaric–Alpine region to Germany demonstrates the value of transboundary monitoring networks

AbstractLarge carnivores such as wolves (Canis lupus) at times disperse distances of several hundred kilometers, which may enable gene flow over vast distances. Such long‐distance dispersal events, however, often remain undetected, and documenting long‐distance dispersers and their movements typically depend on strong transboundary collaborations. Here, we report the dispersal of a wolf (MSV0FF) from the Alpine region of northern Slovenia to Bavaria in southern Germany, a straight‐line distance of around 300 km. The disperser originated in a pack with a genetically diverse breeding pair, where the father exhibited ancestry from the Dinaric and Italian Alpine populations. Genetic analysis of the mother indicated that she was an immigrant from a divergent population further south in the Dinaric‐Balkan region. Such a varied ancestry augments the probability of immigrants being genetically misclassified as wolf‐dog hybrids in their area of arrival, which increases the risk of unfavorable management decisions toward individuals that would be genetically highly valuable for the recipient population. Wolf MSV0FF therefore demonstrates the benefits of international collaborative monitoring networks and the value of sharing samples and analytical approaches for the monitoring of wide‐ranging species.

Long‐distance post‐release movements challenge the metapopulation restoration of Bearded Vultures

AbstractRestoring ecological dynamics is a key objective of conservation translocations. Exemplarily, reconnecting the reintroduced alpine populations with native Pyrenean populations through re‐establishing locally extinct populations in between, in the Causses and the Pre‐Alps, is a major goal for the long‐term conservation of Bearded Vultures in Europe. Understanding Bearded Vultures' post‐release movements and foraging behavior is critical to understanding the settlement of newly restored populations and to supporting conservation measures. The telemetric monitoring of 43 translocated and wild‐born juveniles allowed us to investigate whether differences exist in post‐release movements and foraging behavior during the first year of life between reintroduced and native populations. Medium‐ and long‐distance exploration movements start during the spring following fledging for both translocated and wild‐born individuals. However, birds translocated in the most distant release site (Causses) exhibited greater exploration distances with no clear directional movement pattern, had smaller home ranges, and had a stronger preference for supplementary feeding stations than those from other populations. Although some birds translocated in the Pre‐Alps displayed similar behaviors, the pattern is not as strong as in the Causses, likely because of the proximity to the breeding populations reintroduced in the Alps or differences in the number and management of supplementary feeding stations. Preference for supplementary feeding stations (SFS) mostly occurred in the Pre‐Alps and the native populations, but was lower in the Causses. Seasonal variations in SFS preference were consistent among populations, with a peak in the first spring following fledging. Beyond documenting post‐release movements in Bearded Vultures, we suggest better accounting for the demographic consequences of behaviors to track conservation translocation effectiveness, at both local and regional scales.

Temporal and spatial variation in the direct and indirect effects of climate on reproduction in alpine populations of Ranunculus acris L

Plant reproduction in alpine environments is affected by climate both directly through climate impacts on growth and phenology, and indirectly through impacts on the biotic interactions affecting pollination success. These effects can be highly variable in time and space. In this study we investigated how different abiotic and biotic factors influence reproductive investment and success in populations of Ranunculus acris across an alpine landscape over a two-year period. In an alpine area at Finse, southern Norway, we measured reproductive investment (total seed mass) and reproductive success (seed-set rate) in 38 sites differing in temperature (related to elevation) and length of the growing season (related to time of snowmelt). To assess biotic interactions, we measured floral density and pollinator visits and conducted a supplemental pollen experiment. Reproductive investment and success increased with temperature, but only when floral density and/or number of pollinator visits was high, and only in the warmer year (2016). Reproduction in R. acris was pollen-limited in both years, especially at warmer temperature and in sites with early snowmelt. Pollinator visits increased with temperature and with higher floral density, suggesting a shift in relative importance of the biotic factors (from plants to pollinators) in limiting reproduction with increasing temperature. Our study shows that reproductive investment and success in R. acris is affected by climate through the interactive effects of abiotic and biotic processes. These effects vary between years and across the landscape, suggesting a potential for larger-scale buffering of climate change effects in heterogeneous landscapes.

Genetic identification, morphology and distribution of Natrixhelvetica subspecies in southern and western Switzerland (Reptilia, Squamata, Serpentes).

Most of Switzerland is inhabited by the nominotypical subspecies of the barred grass snake (Natrixhelveticahelvetica), which is characterized by mitochondrial DNA lineage E. Only in the northeast of the country, the common grass snake (N.natrix) occurs and hybridizes with N.h.helvetica in a narrow contact zone. However, we discovered that in southern and western Switzerland barred grass snakes representing another mtDNA lineage (lineage C) are widely distributed. Lineage C is typical for Alpine populations of the southern subspecies N.h.sicula. Our microsatellite analyses of the Swiss samples revealed differences between the two subspecies and also a substructure with two clusters in each subspecies. Furthermore, we discovered a contact and hybrid zone of N.h.helvetica and N.h.sicula along the northern shore of Lake Geneva and also confirm that interbreeding with alien common grass snakes (N.n.moreotica, mtDNA lineage 7) occurs there. This finding is of concern for nature conservation and measures should be taken to prevent further genetic pollution. Using morphometrics, we found no differences between the two subspecies of N.helvetica, while N.natrix was slightly distinct from N.helvetica.

Integrative taxonomy of the groundwater amphipod Niphargus bihorensis Schellenberg, 1940 reveals a species-rich clade

Abstract The genus Niphargus is the most diverse subterranean amphipod genus in the western Palearctic region but, owing to the presence of cryptic species and homoplasy, its taxonomy and biogeographic scenarios are complex, making molecular methods essential to understand its evolution. We conducted a study combining dna-based taxonomy with traditional morphotaxonomy to investigate Niphargus bihorensis Schellenberg, 1940, known from the Western Alps and Carpathians. We redescribed the type material of N. bihorensis from Bihor County, Romania, and revealed the presence of a cryptic species, N. absconditus n. sp., in the same karstic area (Pădurea Craiului Mountains). Additionally, the Alpine populations previously attributed to N. bihorensis turned out to belong to a new, not so closely related species, N. tizianoi n. sp. Phylogenetic analyses based on a concatenated dataset of one mitochondrial and two nuclear markers suggest that the N. bihorensis species complex belongs to a strongly supported clade, together with several species distributed from Switzerland to Iran.

Clinal variation in quantitative traits but not in evolutionary potential along elevational and latitudinal gradients in the widespread Anthyllis vulneraria.

Strong elevational and latitudinal gradients allow the study of genetic differentiation in response to similar environmental changes. However, it is uncertain whether the environmental changes along the two types of gradients result in similar genetically based changes in quantitative traits. Peripheral arctic and alpine populations are thought to have less evolutionary potential than more central populations do. We studied quantitative traits of the widespread Anthyllis vulneraria in a common garden. Plants originated from 20 populations along a 2000-m elevational gradient from the lowlands to the elevational limit of the species in the Alps, and from 20 populations along a 2400-km latitudinal gradient from the center of the distribution of the species in Central Europe to its northern distributional margin. Most traits showed similar clinal variations with elevation and latitude of origin, and the magnitude of all measured traits in relation to mean annual temperature was similar. Higher QST values than FST values in several traits indicated diversifying selection, but for others QST was smaller than FST. Genetic diversity of quantitative traits and neutral molecular markers was not correlated. Plasticity in response to favorable conditions declined with elevation and less strongly with latitude of origin, but the evolvability of traits did not. The clinal variation suggests adaptive differentiation of quantitative traits along the two gradients. The evolutionary potential of peripheral populations is not necessarily reduced, but lower plasticity may threaten their survival under rapidly changing climatic conditions.

Vaccinium dwarf shrubs responses to experimental warming and herbivory resistance treatment are species- and context dependent

Climate change impacts on species and ecosystem functioning may depend on climatic context and study systems. Climate warming and intensified herbivory are two stressors to plants that often appear in combination and are predicted to increase in cold environments. Effects of multiple drivers on plant performance are difficult to predict and warrant studies that use experimental manipulations along climatic gradients to produce more realistic knowledge. Our three study sites by the Sognefjord in Norway, that differed mainly in climatic conditions (ca. 5°C growing season difference), ranged from hemi-boreal lowland (100 masl, Low), via boreal mid-montane (500 masl) to alpine timberline (900 masl, High) bioclimates. At each site, in a randomized block design, we simulated growing-season warming using open-top chambers (OTCs) and experimentally induced herbivory resistance using the plant hormone methyl jasmonate (MeJA). We recorded growth, mortality, flower and fruit numbers, and insect herbivory on tagged ramets in permanent plots across three years (2016-2018) in three open woodland populations of two functionally important plant species with contrasting traits, Vaccinium myrtillus (bilberry) and V. vitis-idaea (lingonberry). Growth of both dwarf shrubs decreased with warming in the warm lowland populations (Low) but increased in the alpine populations (High). Shoot mortality increased most with warming at Low but was reduced at High. Reproduction, both flowering and fruiting, decreased with induced resistance treatment, but the effect was larger when warmed for bilberry and increased with elevation for both species. Leaf herbivory in bilberry increased with warming at Low but decreased at High. The combined warming and resistance treatment had only synergistic negative interaction effects on fruit numbers in bilberry. The clear context- and species-dependent effects of climate warming and increased resistance in this study may predict a potential decline in performance, as well as abundance and distribution, of these functionally important Vaccinium species at our lowest site. Bilberry reproduction appeared to be particularly susceptible to both climate warming and induced resistance in the manipulated populations. Such combined negative effects on plant performance are likely to have considerable knock-on effects via altered species’ interactions and ecosystem functioning.

Detecting directional epistasis and dominance from cross-line analyses in alpine populations of Arabidopsis thaliana.

The contribution of non-additive genetic effects to the genetic architecture of fitness and to the evolutionary potential of populations has been a topic of theoretical and empirical interest for a long time. Yet, the empirical study of these effects in natural populations remains scarce, perhaps because measuring dominance and epistasis relies heavily on experimental line crosses. In this study, we explored the contribution of dominance and epistasis in natural alpine populations of Arabidopsis thaliana for 2 fitness traits, the dry biomass and the estimated number of siliques, measured in a greenhouse. We found that, on average, crosses between inbred lines of A. thaliana led to mid-parent heterosis for dry biomass but outbreeding depression for an estimated number of siliques. While heterosis for dry biomass was due to dominance, we found that outbreeding depression for an estimated number of siliques could be attributed to the breakdown of beneficial epistatic interactions. We simulated and discussed the implication of these results for the adaptive potential of the studied populations, as well as the use of line-cross analyses to detect non-additive genetic effects.