Aksel Paalsson

Last Name

Paalsson

First Name

Aksel

ORCID

0009-0002-1199-1156

Organisational unit

03706 - Widmer, Alexander / Widmer, Alexander

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Publications 1 - 5 of 5

Early Life History Divergence Mediates Elevational Adaptation in a Perennial Alpine Plant
Paalsson, Aksel; Walther, Ursina; Fior, Simone; et al. (2024)
Ecology and Evolution
Spatially divergent natural selection can drive adaptation to contrasting environments and thus the evolution of ecotypes. In perennial plants, selection shapes life history traits by acting on subsequent life stages, each contributing to fitness. While evidence of adaptation in perennial plants is common, the expression of life history traits is rarely characterized, limiting our understanding of their role in adaptive evolution. We conducted a multi-year reciprocal transplant experiment with seedlings from low and high elevation populations of the alpine carnation Dianthus carthusianorum to test for adaptation linked to contrasting climates and inferred specific contributions of early life stages to fitness. We assessed genotype by environment interactions in single fitness components, applied matrix population models to achieve an integrated estimate of fitness through population growth rates, and performed trade-off analyses to investigate the advantage of alternate life history traits across environments. We found evidence of genotype by environment interactions consistent with elevational adaptation at multiple stages of the early life cycle. Estimates of population growth rates corroborated a strong advantage of the local genotype. Early reproduction and survival are alternate major contributors to adaptation at low and high elevation, respectively, and are linked by trade-offs that underlie the evolution of divergent life history traits across environments. While these traits have a strong genetic basis, foreign populations express co-gradient plasticity, reflecting the adaptive strategy of the local populations. Our study reveals that selection associated to climate has driven the evolution of divergent life histories and the formation of elevational ecotypes. While the high energy environment and strong competition favor investment in early reproduction at low elevation, limiting resources favor a more conservative strategy relying on self-maintenance at high elevation. The co-gradient plasticity expressed by high-elevation populations may facilitate their persistence under warming climatic conditions.
Genetic and plastic effects on trait variability in two major tree species: Insights from common garden experiments across Europe
Martínez-Sancho, Elisabet; Rellstab, Christian; Fonti, Patrick; et al. (2025)
Forest Ecology and Management
Phenotypic plasticity and genetic adaptation are key mechanisms that enable species to respond to changing environments. Tree traits do not vary independently but rather in coordination. However, our understanding of whether functional traits are governed by the same mechanism is still uncomplete. Thus, we aim at assessing the drivers of trait variability of sessile oak and European beech provenances across their distribution ranges. We estimated growth-related and leaf morphological traits from 9 and 11 provenances of oak (Quercus petraea) and beech (Fagus sylvatica), respectively, grown in four different common gardens distributed across their respective distribution areas. Overall, phenotypic plasticity played a dominant role in explaining individual trait variability. For most oak traits, variation among provenances and genetically based plasticity were correlated with the climate of origin, whereas for beech both provenance-related variation and plasticity showed fewer significant associations with the climate of origin. In oak, climate-transfer distance analyses revealed that some trait measures decreased when provenances were moved away from their local precipitation regime. In beech, significant climate-transfer distances were fewer and primarily related to temperature-related parameters. The pattern of multi-trait phenotypes indicates that resource-use strategies among provenances covary with the temperatures of origin in both species. Although beech shows adaptive potential through genetic differentiation among populations, most trait variation is plastic, which may not suffice long term to cope with extreme climatic events. Oak, by contrast, appears more responsive through adaptive mechanisms. Our study enhances understanding of the interplay between genetic adaptation and phenotypic plasticity in long-lived forest trees.
Unravelling drivers of local adaptation through evolutionary functional-structural plant modelling
de Vries, Jorad; Fior, Simone; Paalsson, Aksel; et al. (2024)
New Phytologist
Local adaptation to contrasting environmental conditions along environmental gradients is a widespread phenomenon in plant populations, yet we lack a mechanistic understanding of how individual agents of selection contribute to this evolutionary process. Here, we developed a novel evolutionary functional–structural plant (E-FSP) model that recreates local adaptation of virtual plants along an environmental gradient. First, we validate the model by testing if it can reproduce two elevational ecotypes of Dianthus carthusianorum occurring in the Swiss Alps. Second, we use the E-FSP model to disentangle the relative contribution of abiotic (temperature) and biotic (competition and pollination) selection pressures to elevational adaptation in D. carthusianorum. Our results suggest that elevational adaptation in D. carthusianorum is predominantly driven by the abiotic environment. The model reproduced the qualitative differences between the elevational ecotypes in two phenological (germination and flowering time) and one morphological trait (stalk height), as well as qualitative differences in four performance variables that emerge from G × E interactions (flowering time, number of stalks, rosette area and seed production). Our approach shows how E-FSP models incorporating physiological, ecological and evolutionary mechanisms can be used in combination with experiments to examine hypotheses about patterns of adaptation observed in the field.
Ancient alleles drive contemporary climate adaptation in an alpine plant
Fior, Simone; Luqman Bin Jalaluddin, Hirzi; Scharmann, Mathias; et al. (2025)
Science
Adaptive evolution is key for species to persist in a warming climate. However, how adaptive genetic variants arise and shape both past and future evolutionary trajectories remains largely unknown. In this work, we integrate genomics with functional and ecological assays to unravel the evolutionary history and adaptive potential of alleles governing adaptation to climate through flowering time in an Alpine carnation. We reveal that “warm” and “cold” alleles of the flowering inhibitor CENTRORADIALIS (DsCEN/2) originated through recombination of highly divergent haplotypes during the carnation radiation, implicating ancestral variation in seeding climate-adaptive alleles. these alleles survived in glacial refugia before mediating the species’ range expansion in response to postglacial warming. We predict that, by recapitulating past evolution, warm alleles will continue to facilitate adaptation under future climate change.
Uncovering the evolution of elevational ecotypes in Alpine carnations
Paalsson, Aksel (2023)
Divergent selection pressures imposed by contrasting environmental conditions at opposite ends of environmental gradients can drive the evolution of populations that are adapted to local conditions. Elevational gradients in the Alps coincide with steep climatic gradients where plant populations experience divergent selection within a limited geographic scale. This feature makes alpine plants with a broad elevational range ideal for the study of evolution of local adaptation. In this thesis, we aimed to unravel the evolution of distinct locally adapted ecotypes of alpine carnations (Dianthus spp., Caryophyllaceae) in response to climate driven selection imposed by contrasting elevational habitats. As a study system, we used two perennial systems with an elevational distribution ranging from the colline to alpine belts in central Europe, D. carthusianorum and D. sylvestris. We used populations from low and high elevation growing in long-term reciprocal transplant experiments to study the evolutionary processes underlying ecotype formation by investigating performance across multiple fitness components and life stages of the perennial life cycle. Experiments for D. sylvestris were further combined with phenotypic selection analyses and a genome-wide association study based on a transplant of recombinant F2 crosses, which were used to examine the both contribution of divergent traits to adaptation and the fitness effect of alleles underlying these traits. In chapter I, we first tested for local adaptation in D. carthusianorum by using data on performance in individual fitness components measured over a period of three years in the reciprocal transplant experiment. We found evidence of genotype by environment (GxE) interactions and fitness advantages of the local ecotype, though with extensive variation at different stages of the life cycle. We thus performed a complementary seedling recruitment experiment and integrated fitness over the course of the experiment through matrix population models. Population growth rates showed a strong signal of local adaptation in both elevational environments and further provided evidence of alternate life-history traits as determinants of plant fitness. The low elevation environment caused the local plants to express a faster life cycle characterized by high investment in early reproduction. Contrarily, fitness of the local plants in the high elevation ecotype was driven primarily by survival. The high elevation plants also reproduced more in the foreign environment, which caused them to exceed their physiological limit of resource allocation to reproduction and suffer a cost in terms of reduced post reproductive survival. Chapter I shows how selection imposed at the extremes of an elevational gradient drove ecotype formation in a perennial plant, highlighting the influence of trade-offs and phenotypic plasticity of life history traits as determinants of population performance under different environmental conditions. In chapter II, we explored how selection acting through different fitness components of the perennial life cycle has driven ecotype formation in D. sylvestris, and we dissected the contribution of divergent traits to this process. Populations of D. sylvestris persisted in high elevation refugia during the Last Glacial Maximum and have subsequently colonized low elevation habitats. We combined phenotypic and fitness data collected in a reciprocal transplant experiment over five years with phenotypic selection analyses on F2 crosses to unravel the contributions of adaptive traits to the responses to the contrasting environmental conditions and associated selection regimes. Our results revealed a strong genetic basis for plant size, plant height and flowering time, associated with elevational adaptation. The high elevation environment favored a conservative life history strategy characterized by a long life span and limited investment in reproduction. Consistently, selection acted towards early flowering to ensure completion of the reproductive cycle in the short alpine summer season. In contrast, the warmer low elevation environment favored a life history strategy characterized by high investment in early reproduction at the expense of a shorter life cycle, and thus plants achieving large size and maximized fecundity. Our results show that colonization of the warmer low elevation habitats proceeded through a shift in both phenotypic and life history traits linked to resource allocation in a high-energy environment with a longer reproductive season. In chapter III, we leveraged results from chapter II to uncover the fitness effect of alleles underlying the traits that contributed to the adaptive divergence between the low and high elevation populations of D. sylvestris. We performed genome-wide association analyses and identified a polygenic genetic architecture underlying the studied adaptive traits. We found examples of both antagonistic pleiotropy and conditional neutrality describing the fitness effects of allelic variation at these loci. By dissecting separate fitness components, we revealed that alleles underlying successful reproduction at high elevation had a negative effect on fecundity, while this relationship turned positive at low elevation. These results suggest that the trade-off in resource allocation indicated in chapter II is accompanied by congruent signals at the level of the underlying genetic variants.

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Aksel Paalsson

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