@unpublished{21968, abstract = {Balancing selection, a form of selection that maintains genetic diversity, is difficult to detect, and the importance of balancing selection for the maintenance of genetic variation may be larger than often assumed. We model the possibility that the diversity-promoting effects of balancing selection extend to other loci that show sign epistasis with a locus under balancing selection. Rather than focusing on overdominance, as was done in previous efforts, we explore the effects of negative frequency dependence and show that this has important effects on the conditions under which the diversity-promoting effect of epistasis can occur in diploids. Our results show that not only recombination rate but also the dominance of sign epistasis are key parameters that determine the maintenance of polymorphism beyond the locus under direct balancing selection. We suggest that the effect we explore may play a significant role, especially when balancing selection acts on major effect loci.}, author = {Khudiakova, Kseniia and Barton, Nicholas H and Arnqvist, Goran}, booktitle = {bioRxiv}, title = {{Sign epistasis extends the effects of balancing selection on genetic diversity}}, doi = {10.1101/2025.04.09.647826}, year = {2026}, } @article{21036, abstract = {Forests under livestock grazing sustain important ecosystem services but face potential trade-offs between production and ecological integrity. While the effects of grazing on individual forest attributes are well documented, their integrated consequences remain poorly understood, particularly in temperate forest ecosystems. We evaluated the combined influence of livestock grazing intensity and canopy cover on individual attributes and ecosystem multifunctionality in native Nothofagus forests of Tierra del Fuego, Argentina. Across eight ranches spanning two agroecological regions (Ecotone and Mountain Range), we quantified forest regeneration, understorey richness and biomass, and soil properties, integrating them into a multifunctionality index. Using generalized linear mixed models, we found strong context-dependence: in the Mountain Range, higher grazing intensity reduced seedling and sapling density, organic matter content, coarse woody debris, and overall multifunctionality. In the Ecotone, these effects of livestock use intensity were attenuated, and canopy cover diminished sapling density and multifunctionality, but moderate cover enhanced understorey. Our results extend multifunctionality research from grazed grasslands to grazed temperate forests and show that ecological responses and trade-offs vary across landscape units. We conclude that the Mountain Range is more vulnerable to grazing, requiring stricter management, whereas the Ecotone retains greater capacity to sustain multifunctionality under controlled livestock use intensity. These findings underscore the importance of region-specific silvopastoral strategies that reconcile food production with forest conservation in southern Patagonia and comparable temperate forest landscapes worldwide.}, author = {Rodríguez, Paula and Cruz Alonso, Verónica and Romano, Silvina and Bustamante, Gimena and Soler Schaller, Rosina Matilde}, issn = {0167-8809}, journal = {Agriculture, Ecosystems and Environment}, publisher = {Elsevier}, title = {{Context-dependent effects of livestock grazing on forest attributes and ecosystem multifunctionality in Nothofagus forests}}, doi = {10.1016/j.agee.2026.110219}, volume = {400}, year = {2026}, } @article{21759, abstract = {Promoters and enhancers are cis-regulatory elements (CREs), DNA sequences that bind transcription factor (TF) proteins to up- or down-regulate target genes. Decades-long efforts yielded TF-DNA interaction models that predict how strongly an individual TF binds arbitrary DNA sequences and how individual binding events on the CRE combine to affect gene expression. These insights can be synthesized into a global, biophysically realistic, and quantitative genotype-phenotype (GP) map for gene regulation, a ‘holy grail’ for the application of evolutionary theory. A global map provides a rare opportunity to simulate the long-term evolution of regulatory sequences and pose several fundamental questions: How long does it take to evolve CREs de novo? How many non-trivial regulatory functions exist in sequence space? How connected are they? For which regulatory architecture is CRE evolution most rapid and evolvable? In this article, the second of a two-part series, we review the application of evolutionary concepts — epistasis, robustness, evolvability, tunability, plasticity, and bet-hedging — to the evolution of gene regulatory sequences. We then evaluate the potential for a unifying theory for the evolution of regulatory sequences and identify key open challenges.}, author = {Mascolo, Elia and Körei, Reka E and Borst, Noa O. and Barton, Nicholas H and Crocker, Justin and Tkačik, Gašper}, issn = {1879-0380}, journal = {Current Opinion in Genetics and Development}, publisher = {Elsevier}, title = {{Long-term evolution of regulatory DNA sequences. Part 2: Theory and future challenges}}, doi = {10.1016/j.gde.2026.102472}, volume = {98}, year = {2026}, } @article{20848, abstract = {Genetic variation that influences complex disease susceptibility is introduced into the population by mutation and removed by natural selection and genetic drift. This mutation–selection–drift balance (MSDB) shapes the prevalence of a disease and its genetic architecture. To date, however, MSDB has been modeled only for monogenic (Mendelian) diseases. Here, we develop an MSDB model for complex disease susceptibility: we assume that genotype relates to disease risk according to the canonical liability threshold model and that the selection on variants affecting risk stems from the fitness cost of the disease. We focus on diseases that are highly polygenic, entail a substantial fitness cost, and are neither extremely common in the population nor exceedingly rare. The comparison of model predictions with genome-wide association studies and other observations in humans indicates that common genetic variation affecting complex disease susceptibility is little affected by directional selection and instead shaped by pleiotropic stabilizing selection on other traits. In turn, directional selection may exert a more substantial effect on rare, large-effect variants. Our results also suggest that current estimates of disease heritability are likely biased. The model thus provides a better understanding of the evolutionary processes that shape the architecture and prevalence of complex diseases.}, author = {Berg, Jeremy J. and Li, Xinyi and Riall, Kellen and Hayward, Laura and Sella, Guy}, issn = {1943-2631}, journal = {Genetics}, number = {4}, publisher = {Oxford University Press}, title = {{Mutation–selection–drift balance models of complex diseases}}, doi = {10.1093/genetics/iyaf220}, volume = {231}, year = {2025}, } @article{20869, abstract = {Premise: What maintains trait divergence in the face of gene flow? Two varieties of wild snapdragon (Antirrhinum majus) characterized by divergent flower color hybridize in their native range. Selection on flower color genes is indicated by sharp clines, but the selective agents have not been demonstrated. Although previous work has focused on pollinators, pigmentation genes can also contribute to abiotic stress tolerance. We hypothesized that pigmentation in A. majus mediates stress tolerance, which could contribute to hybrid zone maintenance through parental niche divergence or hybrid maladaptation. Specifically, we tested whether morphotype mediates drought tolerance in an experiment comparing magenta-flowered var. pseudomajus, yellow-flowered var. striatum, and their pink-flowered hybrid cross. Methods: We experimentally compared drought tolerance of each morphotype from allopatric crosses within and between varieties using three greenhouse treatments. Control plants were watered as needed, while drought-treated plants were watered half as often, either from the transplant stage (“early” drought), or from flowering onset (“late” drought). Results: Parental morphotypes responded identically to drought in fitness and most phenotypic traits. However, hybrids had lower survival (14%) under late drought stress than parental morphotypes (70%). All hybrids that flowered in the late drought treatment died, compared to ~20% of flowering parental morphotypes. Conclusions: Hybrid maladaptation to abiotic stress could potentially contribute to flower color divergence in the face of gene flow in A. majus. Further research should test the relevance of our results to field conditions and explicitly probe the role of flower color genes in drought tolerance.}, author = {Fuster‐Calvo, Alexandre and Jaworski, Coline C. and Ellis, Thomas and Baskett, Carina}, issn = {1537-2197}, journal = {American Journal of Botany}, number = {12}, publisher = {Wiley}, title = {{Reduced fitness under drought stress in F1 hybrids of Antirrhinum majus varieties with divergent flower colors}}, doi = {10.1002/ajb2.70129}, volume = {112}, year = {2025}, } @article{21322, abstract = {Habitat fragmentation poses a significant risk to population survival, causing both demographic stochasticity and genetic drift within local populations to increase, thereby increasing genetic load. Higher load causes population numbers to decline, which reduces the efficiency of selection and further increases load, resulting in a positive feedback that may drive entire populations to extinction. Here, we investigate this eco-evolutionary feedback in a metapopulation consisting of local demes connected via migration, with individuals subject to deleterious mutation at a large number of loci. We first analyze the determinants of load under soft selection, where population sizes are fixed, and then build on this to understand hard selection, where population sizes and load coevolve. We show that under soft selection, very little gene flow (less than one migrant per generation) is enough to prevent fixation of deleterious alleles. By contrast, much higher levels of migration are required to mitigate load and prevent extinction when selection is hard, with critical migration thresholds for metapopulation persistence increasing sharply as the genome-wide deleterious mutation rate becomes comparable to the baseline population growth rate. Moreover, critical migration thresholds are highest if deleterious mutations have intermediate selection coefficients but lower if alleles are predominantly recessive rather than additive (due to more efficient purging of recessive load within local populations). Our analysis is based on a combination of analytical approximations and simulations, allowing for a more comprehensive understanding of the factors influencing load and extinction in fragmented populations.}, author = {Olusanya, Oluwafunmilola O and Khudiakova, Kseniia and Sachdeva, Himani}, issn = {1537-5323}, journal = {The American Naturalist}, number = {6}, pages = {617--636}, publisher = {University of Chicago Press}, title = {{Genetic load, eco-evolutionary feedback, and extinction in metapopulations}}, doi = {10.1086/735562}, volume = {205}, year = {2025}, } @misc{18712, abstract = {This file contains the code associated with the manuscript 'Effect of assortative mating and sexual selection on polygenic barriers to gene flow'. }, author = {Surendranadh, Parvathy and Sachdeva, Himani}, publisher = {Institute of Science and Technology Austria}, title = {{Mathematica notebook and Fortran code for 'Effect of assortative mating and sexual selection on polygenic barriers to gene flow'}}, doi = {10.15479/AT:ISTA:17344}, year = {2025}, } @article{19438, abstract = {Polymorphic short insertions and deletions (INDELs 50 bp) are abundant, although less common than single nucleotide polymorphisms (SNPs). Evidence from model organisms shows INDELs to be more strongly influenced by purifying selection than SNPs. Partly for this reason, INDELs are rarely used as markers for demographic processes or to detect divergent selection. Here, we compared INDELs and SNPs in the intertidal snail Littorina saxatilis, focussing on hybrid zones between ecotypes, in order to test the utility of INDELs in the detection of divergent selection. We computed INDEL and SNP site frequency spectra using capture sequencing data. We assessed the impact of divergent selection by analyzing allele frequency clines across habitat boundaries. We also examined the influence of GC-biased gene conversion because it may be confounded with signatures of selection. We show evidence that short INDELs are affected more by purifying selection than SNPs, but part of the observed site frequency spectra difference can be attributed to GC-biased gene conversion. We did not find a difference in the impact of divergent selection between short INDELs and SNPs. Short INDELs and SNPs were similarly distributed across the genome and so are likely to respond to indirect selection in the same way. A few regions likely affected by divergent selection were revealed by INDELs and not by SNPs. Short INDELs can be useful (additional) genetic markers helping to identify genomic regions important for adaptation and population divergence.}, author = {Perini, Samuel and Johannesson, Kerstin and Butlin, Roger K. and Westram, Anja M}, issn = {1420-9101}, journal = {Journal of Evolutionary Biology}, number = {3}, pages = {367--378}, publisher = {Oxford University Press}, title = {{Short INDELs and SNPs as markers of evolutionary processes in hybrid zones}}, doi = {10.1093/jeb/voaf002}, volume = {38}, year = {2025}, } @article{19442, abstract = {1. Climate change is expected to induce shifts in the composition, structure and functioning of Arctic tundra ecosystems. Increases in the frequency and severity of tundra fires have the potential to catalyse vegetation transitions with far-reaching local, regional and global consequences. 2. We propose that post-fire tundra recovery, coupled with climate change, may not necessarily lead to pre-fire conditions. Our hypothesis, based on surveys and literature, suggests two climate–fire driven trajectories. One trajectory results in increased woody vegetation under low fire frequency; the other results in grass dominance under high frequency. 3. Future research should address uncertainties regarding possible tundra ecosystem shifts linked to fires, using methods that encompass greater temporal and spatial scales than previously addressed. More case studies, especially in underrepresented regions and ecosystem types, are essential to broaden the empirical basis for forecasts and potential fire management strategies. 4. Synthesis. Our review synthesises current knowledge on post-fire vegetation trajectories in Arctic tundra ecosystems, highlighting potential transitions and alternative ecosystem states and their implications. We discuss challenges in defining and predicting these trajectories as well as future directions.}, author = {Heim, Ramona Julia and Rocha, Adrian V. and Zemlianskii, Vitalii and Barrett, Kirsten and Bültmann, Helga and Breen, Amy and Frost, Gerald Verner and Hollingsworth, Teresa Nettleton and Jandt, Randi and Kozlova, Maria and Kurka, Anastasiya and Jorgenson, Mark Torre and Landhäusser, Simon M. and Loranty, Michael Mark and Miller, Eric A. and Narita, Kenji and Pravdolyubova, Evgeniya and Hölzel, Norbert and Schaepman-Strub, Gabriela}, issn = {1365-2745}, journal = {Journal of Ecology}, number = {5}, pages = {1042--1056}, publisher = {Wiley}, title = {{Arctic tundra ecosystems under fire—Alternative ecosystem states in a changing climate?}}, doi = {10.1111/1365-2745.70022}, volume = {113}, year = {2025}, } @article{19641, abstract = {Mycorrhizal and saprotrophic macromycetes contribute strongly to the carbon and nitrogen cycles of forest ecosystems, often studied by tracing stable isotope composition of carbon and nitrogen. The phenomenon of the saprotrophic-mycorrhizal divide highlights the difference in the stable isotope composition of fruiting bodies of mycorrhizal and saprotrophic fungi. Much less is known about the isotopic composition of the mycelium, which plays an important role in the formation of the soil organic matter and fuels the fungal trophic channel in soil food webs. In this study, we assessed whether the saprotrophic-mycorrhizal divide in the natural δ13С and δ15N values can be traced throughout entire fungal organisms. This hypothesis was tested using 16 species of ectomycorrhizal and six species of saprotrophic basidiomycetous fungi. We showed that not only fruiting bodies, but also the mycelium of ectomycorrhizal and saprotrophic fungi differs in the δ13C and δ15N values. In both ectomycorrhizal and saprotrophic fungi, the δ13C and δ15N values increased from mycelium to hymenophores and correlated positively with the total N content in the corresponding tissues. The differences between ectomycorrhizal and saprotrophic mycelium can be used to reconstruct the fungal-driven belowground carbon and nitrogen allocation, and the contribution of saprotrophic and mycorrhizal fungi to soil food webs.}, author = {Zuev, A. G. and Alexandrova, A. V. and Litvinskiy, V. A. and Pravdolyubova, Evgeniya and Tiunov, A. V.}, issn = {1432-1890}, journal = {Mycorrhiza}, number = {2}, publisher = {Springer Nature}, title = {{Saprotrophic-mycorrhizal divide in stable isotope composition throughout the whole fungus: From mycelium to hymenophore}}, doi = {10.1007/s00572-025-01203-w}, volume = {35}, year = {2025}, } @article{19671, abstract = {Silvopastoral use in native forests could impact population dynamics of key tree species, with contrasting effects at different life cycle stages. Prior studies in South American temperate forests have mainly focused on initial stages, lacking a comprehensive understanding of the entire life cycle within productive systems. We assessed the population dynamics of two key species of mixed forests in northern Patagonia (Austrocedrus chilensis and Nothofagus dombeyi) under two silvopastoral use intensities (high vs. low), using demographic techniques and population projection models. Over 3 years, we quantified vital rates (survival, fertility, growth, reversion and stasis) and used matrix models to calculate deterministic population growth rates (λ). High-intensity silvopastoral use had predominantly negative effects on the elements of the projection matrices of A. chilensis, whereas N. dombeyi exhibited mostly positive or no changes. As a result, projections indicated slight population decreases for A. chilensis (mostly λ < 1) at high silvopastoral use levels compared to low levels, while N. dombeyi showed similar projections (λ ≅ 1) between use levels. Decreased λ for A. chilensis resulted mainly from lower adult tree survival, while early life stages had limited influence on λ for these long-lived species. In summary, silvopastoral use affects population dynamics of key tree species of these mixed forests of northern Patagonia, with implications for sustainable management. Our findings highlight the importance of considering the entire life cycle and suggest targeted practices to enhance A. chilensis populations.}, author = {Arpigiani, Daniela and Aschero, Valeria and Soler Schaller, Rosina Matilde and Amoroso, Mariano M.}, issn = {1442-9993}, journal = {Austral Ecology}, number = {4}, publisher = {Wiley}, title = {{A life-cycle approach to understand consequences of silvopastoral use on two native tree species of Northern Patagonia}}, doi = {10.1111/aec.70058}, volume = {50}, year = {2025}, } @article{19876, abstract = {Assortative mating and sexual selection are widespread in nature and can play an important role in speciation by facilitating the buildup and maintenance of reproductive isolation (RI). However, their contribution to genome-wide suppression of gene flow during RI is rarely quantified. Here, we consider a polygenic “magic” trait that is divergently selected across two populations connected by migration, while also serving as the basis of assortative mating, thus generating sexual selection on one or both sexes. We obtain theoretical predictions for divergence at individual trait loci by assuming that the effect of all other loci on any locus can be encapsulated via an effective migration rate, which bears a simple relationship to measurable fitness components of migrants and various early-generation hybrids. Our analysis clarifies how “tipping points” (characterized by an abrupt collapse of adaptive divergence) arise, and when assortative mating can shift the critical level of migration beyond which divergence collapses. We quantify the relative contributions of viability and sexual selection to genome-wide barriers to gene flow and discuss how these depend on existing divergence levels. Our results suggest that effective migration rates provide a useful way of understanding genomic divergence, even in scenarios involving multiple, interacting mechanisms of RI. }, author = {Surendranadh, Parvathy and Sachdeva, Himani}, issn = {1558-5646}, journal = {Evolution}, number = {7}, pages = {1185--1198}, publisher = {Oxford University Press}, title = {{Effect of assortative mating and sexual selection on polygenic barriers to gene flow}}, doi = {10.1093/evolut/qpaf047}, volume = {79}, year = {2025}, } @article{20102, abstract = {Speciation is rarely observable directly. A way forward is to compare pairs of ecotypes that evolved in parallel in similar contexts but have reached different degrees of reproductive isolation. Such comparisons are possible in the marine snail Littorina saxatilis by contrasting barriers to gene flow between parallel ecotypes in Spain and Sweden. In both countries, divergent ecotypes have evolved to withstand either crab predation or wave action. Here, we explore transects spanning contact zones between the Crab and the Wave ecotypes using low-coverage whole-genome sequencing, morphological and behavioural traits. Despite parallel phenotypic divergence, distinct patterns of differentiation between the ecotypes emerged: a continuous cline in Sweden indicating a weak barrier to gene flow, but two highly genetically and phenotypically divergent, and partly spatially overlapping clusters in Spain suggesting a much stronger barrier to gene flow. The absence of Spanish early-generation hybrids supported strong isolation, but a low level of gene flow is evident from molecular data. In both countries, highly differentiated loci were located in both shared and country-specific chromosomal inversions but were also present in collinear regions. Despite being considered the same species and showing similar levels of phenotypic divergence, the Spanish ecotypes are much closer to full reproductive isolation than the Swedish ones. Barriers to gene flow of very different strengths between ecotypes within the same species might be explained by dissimilarities in the spatial arrangement of habitats, the selection gradients or the ages of the systems.}, author = {Raffini, Francesca and De Jode, Aurélien and Johannesson, Kerstin and Faria, Rui and Zagrodzka, Zuzanna B. and Westram, Anja M and Galindo, Juan and Rolán-Alvarez, Emilio and Butlin, Roger K.}, issn = {1365-294X}, journal = {Molecular Ecology}, number = {21}, publisher = {Wiley}, title = {{Phenotypic divergence and genomic architecture between parallel ecotypes at two different points on the speciation continuum in a marine snail}}, doi = {10.1111/mec.70025}, volume = {34}, year = {2025}, } @article{20325, abstract = {Inferring genealogical relationships of wild populations is useful because it gives direct estimates of mating patterns and variance in reproductive success. Inference can be improved by including information about parentage shared between siblings, or by modelling phenotypes or population data related to mating. However, we currently lack a framework to infer parent–offspring relationships, sibships and population parameters in a single analysis. To address this, we here extend a previous method, Fractional Analysis of Paternity and Sibships, to include population data for the case where one parent is known. We illustrate this with the example of pollen dispersal in a natural hybrid zone population of the snapdragon Antirrhinum majus. Pollen dispersal is leptokurtic, with half of mating events occurring within 30 m, but with a long tail of mating events up to 859 m. Using simulations, we find that both sibship and population information substantially improve pedigree reconstruction, and that we can expect to resolve median dispersal distances with high accuracy.}, author = {Ellis, Thomas and Field, David and Barton, Nicholas H}, issn = {1365-294X}, journal = {Molecular Ecology}, number = {15}, publisher = {Wiley}, title = {{Joint estimation of paternity, sibships and pollen dispersal in a snapdragon hybrid zone}}, doi = {10.1111/mec.70051}, volume = {34}, year = {2025}, } @article{20330, abstract = {The evolution of sexual dimorphism (the difference in average trait values between females and males, SD), is often thought to be constrained by shared genetic architecture between the sexes. Indeed, it is commonly expected that SD should negatively correlate with the intersex correlation (the genetic correlation between effects of segregating variants in females and males, r fm), either because (1) traits with ancestrally low r fm are less constrained in their ability to respond to sex-specific selection and thus evolve to be more dimorphic, or because (2) sex-specific selection, driving sexual dimorphism evolution, also acts to reduce r fm. Despite the intuitive appeal and prominence of these ideas, their generality and the conditions in which they hold remain unclear. Here, we develop models incorporating sex-specific stabilizing selection, mutation and genetic drift to examine the relationship between r fm and SD. We show that the two commonly-discussed mechanisms with the potential to generate a negative correlation between SD and r fm could just as easily generate a positive association, since the standard line of reasoning hinges on a hidden assumption that sex-specific adaptation more frequently favors increased dimorphism than reduced dimorphism. Our results provide, to our knowledge, the first mechanistic framework for understanding the conditions under which a correlation between r fm and SD may arise and offer a compelling explanation for inconsistent empirical evidence. We also make the intriguing observation that—even when selection between the two sexes is identical—drift generates nonzero SD. We quantify this effect and discuss its significance.}, author = {Puixeu Sala, Gemma and Hayward, Laura}, issn = {1943-2631}, journal = {Genetics}, number = {3}, publisher = {Oxford University Press}, title = {{The relationship between sexual dimorphism and intersex correlation: Do models support intuition?}}, doi = {10.1093/genetics/iyaf175}, volume = {231}, year = {2025}, } @article{20429, abstract = {Plant–plant interactions are key to understanding ecosystem services and shaping restoration strategies, as they can produce either negative or positive effects, determining species establishment and growth. Recognizing these interactions during early-life stages provides valuable insights for restoration in human-disturbed areas. One promising approach is nucleation planting, which establishes small clusters of native species in strategically selected sites, being particularly useful in sites with large herbivores. In southern Patagonia, livestock production has historically been the main economic activity, severely impacting extensive areas of Nothofagus antarctica forest through grazing and intentional burning to increase forage. In this context, nucleation planting with Berberis microphylla, a non-palatable shrub, could foster forest recovery in degraded sites. To evaluate this, we conducted an experiment testing the response of trees to varying shrub number, while also assessing intraspecific effects in both species. We measured survival, biomass, and functional traits. Results showed that the combination of four shrubs surrounding a single tree maintained tree survival at levels comparable to trees growing alone, while seedlings exhibited conspecific negative plant number dependence. Additionally, B. microphylla increased its below- to above-ground biomass ratio under higher plant number, indicating resource reallocation and niche differentiation through spatial separation of root systems.}, author = {Bustamante, Gimena Noemí and Arena, Miriam Elisabet and Selzer, Luciano and Ruggirello, Matthew and Rodríguez, Paula and Pedrazzani, Samuele and Navarro-Cano, Jose Antonio and Soler Schaller, Rosina Matilde}, issn = {1573-5052}, journal = {Plant Ecology}, pages = {1301--1313}, publisher = {Springer Nature}, title = {{Biotic interactions between trees and colonizing shrubs: Implications for active restoration in southern Patagonian forests}}, doi = {10.1007/s11258-025-01568-0}, volume = {226}, year = {2025}, } @article{20531, abstract = {Genetic drift is potentially an important component of selection for sex, as it is a source of statistical associations between alleles at selected loci. By increasing local drift, population structure may thus amplify the evolutionary advantage of sex. However, most previous models have focused either on haploid populations or on diploid populations without spatial structure. In this article, we use two- and three-locus analytical models and multilocus simulations to explore selection for sex in a diploid population structured according to the island model, in the presence of recurrent deleterious mutations. Our results show that selection generally favors an intermediate rate of sex that decreases as the direct cost of sex increases and increases moderately as the degree of population structure increases. Selection for sex is generated by multiple effects involving genetic associations within and between loci. When selection occurs at many loci, it is generally dominated by interference effects involving deleterious alleles at different loci, captured by our three-locus model. In our multilocus simulations, we observed an irreversible spread of asexual mutants under strong costs of sex, and when deleterious mutations are partially recessive. However, population structure may prevent this spread of asexual mutants when dispersal rates are sufficiently small.}, author = {Fouqueau, Louise and Roze, Denis}, issn = {1558-5646}, journal = {Evolution}, number = {10}, pages = {2167--2180}, publisher = {Oxford University Press}, title = {{Deleterious mutations and selection for sex in spatially structured, diploid populations}}, doi = {10.1093/evolut/qpaf143}, volume = {79}, year = {2025}, } @phdthesis{20694, abstract = {Understanding the mechanisms underlying speciation is a central aim of evolutionary biology. A persistent challenge in the field is to identify loci that contribute to reproductive isolation, while disentangling signals of selection from demography, linkage and intrinsic genomic features. Traditional population genomic approaches that rely on site-based statistics in arbitrary fixed windows face inherent limitations, as they conflate historical and contemporary processes of divergence and overlook haplotype structure. Recent advances in whole-genome sequencing and methods to infer ancestral recombination graphs (ARGs) now offer the opportunity to study genealogical relationships explicitly, revealing how lineages coalesce and recombine through time. By directly analysing haplotype clustering by species or phenotype and their patterns of coalescence, ARG-based methods show promise for diagnosing sweeps, identifying barrier loci maintained under divergent selection amid gene flow, and tracing their evolutionary history. In this thesis, I explore the utility of genealogical approaches for studying species divergence. In chapter 2, I propose a conceptual framework for defining haplotype blocks through the structure of the ARG, using simulations and empirical data to highlight how genealogical processes generate rich and often overlooked haplotypic patterns. In chapter 3, I examine the genomic basis of a key evolutionary innovation in marine snails Littorina. These snails offer a unique opportunity to study an innovation because they include a very recent transition from egg-laying to live bearing, yet snails with the different reproductive modes are not reciprocally monophyletic. I exploited this by using topology clustering in ARG-derived local genealogical trees to pinpoint narrow genomic regions or haplotype blocks that carry swept alleles, thus revealing that the transition from egg-laying to live-bearing involves multiple, live-bearer-specific sweeps. Chapter 4 establishes a population-scale, phased genomic resource for Antirrhinum majus, using cost-effective haplotagging, then optimizes imputation from low-coverage data against high-accuracy KASP sequencing to maximize sequence completeness with modest accuracy trade-offs against a traditional short-read sequence pipeline. A hybrid phasing strategy combines molecular phasing with statistical phasing to generate phased whole genome sequences of 1084 Antirrhinum individuals at a fraction of long-read sequencing costs. In chapter 5, I analyse hybridising populations from two replicate hybrid zones to find a parallel genetic basis of flower colour, amidst the noise in genomic differentiation landscape driven by variation in demographic history. While outlier genome scans of FST failed to dissect the causes of differentiation, ARG-based topology clustering revealed a reuse of colour associated haplotypes across hybrid zones. In addition to the biological insight, this chapter also presents a comparison of the latest ARG inference tools, showing that signals of Abstract viii topological clustering qualitatively agree between methods, despite differences in the tree sequences. Next, in chapter 6, by leveraging ~1000 individuals in one of the hybrid zones, I integrated genome-wide association studies of floral pigmentation with genealogical inference, to test for additional colour loci, and confirm the effect of previously described loci. This work demonstrates that flower colour variation is driven by a small number of large effect loci, while also hinting at the presence of a new candidate regulatory factor. Finally in chapter 7, in a preliminary analysis, I begin to dissect the genomic island of speciation around Rosea/Eluta to understand its evolutionary origins. My results show that it consists of 5 highly divergent loci, each of which is associated with flower colour. Using patterns of coalescence in genealogical trees, I find evidence of staggered selective sweeps and a persistent localized barrier to gene flow within an otherwise permeable genome. Together, these chapters add to the increasing pool of studies using genealogical approaches to complement and extend site-based statistics to use haplotype structures in speciation research. By tracking haplotypes directly and connecting genealogical clustering to population processes, ARG-based inference promises to provide new insights into how local selective pressures, demographic history, and long-term barriers interact to shape the genomic architecture of divergence. By underscoring the value of ARGs in revealing the finescale origins and maintenance of biodiversity, this thesis presents cautious optimism about the benefits of using genealogical inference to learn more than what site-based statistics could tell us.}, author = {Pal, Arka}, issn = {2663-337X}, pages = {268}, publisher = {Institute of Science and Technology Austria}, title = {{Using genealogies to study the genomic basis of species divergence}}, doi = {10.15479/AT-ISTA-20694}, year = {2025}, } @article{20190, abstract = {A major goal of speciation research is identifying loci that underpin barriers to gene flow. Population genomics takes a ‘bottom-up’ approach, scanning the genome for molecular signatures of processes that drive or maintain divergence. However, interpreting the ‘genomic landscape’ of speciation is complicated, because genome scans conflate multiple processes, most of which are not informative about gene flow. However, studying replicated population contrasts, including multiple incidences of secondary contact, can strengthen inferences. In this paper, we use linked-read sequencing (haplotagging), FST scans and genealogical methods to characterise the genomic landscape associated with replicate hybrid zone formation. We studied two flower colour varieties of the common snapdragon, Antirrhinum majus subspecies majus, that form secondary hybrid zones in multiple independent valleys in the Pyrenees. Consistent with past work, we found very low differentiation at one well-studied zone (Planoles). However, at a second zone (Avellanet), we found stronger differentiation and greater heterogeneity, which we argue is due to differences in the amount of introgression following secondary contact. Topology weighting of genealogical trees identified loci where haplotype diversity was associated with the two snapdragon varieties. Two of the strongest associations were at previously identified flower colour loci: Flavia, that affects yellow pigmentation, and Rosea/Eluta, two linked loci that affect magenta pigmentation. Preliminary analysis of coalescence times provides additional evidence for selective sweeps at these loci and barriers to gene flow. Our study highlights the impact of demographic history on the differentiation landscape, emphasising the need to distinguish between historical divergence and recent introgression.}, author = {Pal, Arka and Shipilina, Daria and Le Moan, Alan and Mcnairn, Adrian J. and Grenier, Jennifer K. and Kucka, Marek and Coop, Graham and Chan, Yingguang Frank and Barton, Nicholas H and Field, David and Stankowski, Sean}, issn = {1365-294X}, journal = {Molecular Ecology}, number = {22}, publisher = {Wiley}, title = {{Genealogical analysis of replicate flower colour hybrid zones in Antirrhinum}}, doi = {10.1111/mec.70067}, volume = {34}, year = {2025}, } @unpublished{21967, abstract = {Selection against deleterious mutations, called purifying selection, plays a central role in evolution and acts in all populations. It is known that the genetic patterns observed in genomic regions undergoing purifying selection differ from those resulting from neutral evolution. However, a comprehensive understanding of the underlying mechanisms shaping those patterns is still lacking. In the present work, we use simulations combined with a genealogical approach to identify the effect of purifying selection on the ancestry and thus on the genetic diversity. Our analysis relies on the postulate that the genealogy belongs to the universality class of Beta-coalescents. Under this assumption, we derive statistics measuring the distortion of the genealogy. This approach allows us to consider a wide range of regimes (i.e. arbitrary selection and mutation strengths) and uncover a rich phase diagram. We find that, for strong selection, the limiting genealogy is given by Kingman’s coalescent on a polynomial timescale. As selection gets weaker, Muller’s ratchet starts operating, setting off the emergence of multiple mergers in the genealogical structures. Our results show that while multiple-merger coalescents are often interpreted as the signature of selective sweeps in rapidly adapting populations, these structures can also appear in the context of Muller’s ratchet.}, author = {Khudiakova, Kseniia and Boenkost, Florin and Tourniaire, Julie N}, booktitle = {bioRxiv}, title = {{Genealogies under purifying selection}}, doi = {10.1101/2024.10.15.618444}, year = {2024}, }