Biology subjects

Polechova, J.

Publications and source records attributed to Polechova, J..

7 recordsLinked to original sources

bioRxiv2025

Local adaptation in a metapopulation - a multi-habitat perspective

This study extends existing soft selection models of local adaptation in metapopulations from two habitats to a multi-habitat scenario, where each habitat exerts unique selection pressures. Specifically, we examine a three-habitat multilocus model in which each allele is favored in habitat 1, disfavored in habitat 3, and the selection pressure in the intermediate habitat may be different across loci. Employing the diffusion and fixed state approximations under the assumption of linkage equilibrium, we investigate conditions for the persistence of a polymorphism. We derive analytical thresholds for such persistence, which reveal scaling for the model parameters, local deme size (N), migration rate(m), selection pressure (si) and the proportion, (i) of each habitat. We show that under the assumption of infinitely many islands and selective neutrality in the intermediate habitat, the size of the intermediate habitat does not affect the maintenance of polymorphism. With symmetric selection pressure (s1=s3=s) in habitats 1 and 3, the system can be fully characterized by the product Ns, the product Nm, and a parameter {beta}, defined as the ratio of the size of habitat 1 (favoring the allele) to habitat 3 (where the allele is disfavored). We find that the range of polymorphism widens as gene flow between demes decreases and the symmetry of habitats increases ({beta} approaches 1). In the final section, we explore the effect of drift on the critical migration threshold as well as the effect of symmetry between selection. We demonstrate that genetic drift considerably lowers the critical migration threshold required for the maintenance of polymorphism. Furthermore, when each island is small but there are (infinitely) many of them, relatively low levels of gene flow can have a large impact in preventing genetic differentiation in a fragmented population.

evolutionary biology↗

bioRxiv2025

Genome-wide cline analysis identifies new locus contributing to a barrier to gene flow across an Antirrhinum hybrid zone

Identification of the genomic regions that contribute to reproductive isolation and how they interact is a major goal of evolutionary genetics. Much effort has focused on locating candidate genes and potential barrier loci by scanning genomes for regions of excess differentiation (FST). An alternative, and perhaps more robust approach, would be to scan for genomic regions exhibiting steep clines in allele frequency across a hybrid zone. Here we develop this approach and apply it to genomic data from across a hybrid zone between varieties of Antirrhinum majus subspecies majus with different flower colour patterns (A. m. m var. pseudomajus and A. m. m var. striatum). Most steep clines are clustered in seven genomic regions, only four of which were present from FST scans between all pair-wise comparisons. Six of these regions carry previously identified loci that influence flower colour in the hybrid zone. The seventh region harbours a novel locus, RUBIA, modifying magenta intensity. Clines at RUBIA approached towards fixation on magenta side of the hybrid zone, whilst remaining polymorphic on the yellow side. This polymorphism on the yellow side may reflect a smaller phenotypic effect of RUBIA in yellow compared to magenta genetic backgrounds. Our findings illustrate how whole-genome cline scans in hybrid zones can robustly detect genomic regions contributing to phenotypic differences and highlight how different reproductive barrier loci interact across the genome.

evolutionary biology↗

bioRxiv2025

Evolution of species' range and niche in changing environments

What causes species niche and range margins to shift is not only a fundamental theoretical question, but also directly affects how we assess the resilience of natural populations in current and future environments. Yet despite the urgent need for theory that can predict evolutionary and ecological responses in times of accelerated climate change, the assumptions of current eco-evolutionary theory remain restrictive, with predictions neglecting important interactions between ecological and evolutionary forces. In this study, I provide quantitative, testable predictions on limits to adaptation in changing environments, which arise from the feedback between selection, genetic drift, and population dynamics. This eco-evolutionary feedback creates a tipping point beyond which adaptation fails as genetic drift overwhelms selection, and species ranges contract from the margins or fragment abruptly - even under gradual environmental change. This "expansion threshold" is determined by three parameters: two quantifying the effects of spatial and temporal variability on the fitness of the population, and one capturing the impact of genetic drift: the reduction of local genetic diversity across generations in finite populations. Genetic drift is strong in populations with small "neighbourhood size". Increasing dispersal, such as via assisted migration, enlarges neighbourhood size, counteracting the loss of genetic variation due to genetic drift. This increases adaptive potential and can facilitate evolutionary rescue in changing environments. Conversely, beyond the expansion threshold, local genetic variance becomes depleted, increasing extinction probability. The theory provides general predictions for species range and niche dynamics beyond standard ecological niche models, highlighting the fundamental impact of eco-evolutionary interactions. Significance StatementIn a time of accelerating climate change, we need a predictive theory of species range shifts, adaptation, and resilience. Currently, predictions rely on theory that fails to incorporate the effects of interactions between ecological and evolutionary forces. This study demonstrates that eco-evolutionary feedback between selection, genetic drift, and population dynamics can create a tipping point at which genetic variance becomes depleted and species ranges contract or fragment. This tipping point depends on three parameters: two capturing loss of fitness due to spatial and temporal change, and one quantifying genetic drift, increasing as population density and dispersal decrease. By advancing the theoretical foundations of species range dynamics in changing environments, this study can inform the development of strategies in conservation genetics.

evolutionary biology↗

bioRxiv2021

The costs and benefits of dispersal in small populations

AO_SCPLOWBSTRACTC_SCPLOWDispersal has three major effects on adaptation. First, gene flow mixes alleles adapted to different environments, potentially hindering (swamping) adaptation. Second, it brings in other variants and inflates genetic variance: this aids adaptation to spatially (and temporally) varying environments but if selection is hard, it lowers the mean fitness of the population. Third, neighbourhood size, which determines how weak genetic drift is, increases with dispersal - when genetic drift is strong, increase of the neighbourhood size with dispersal aids adaptation. In this note I focus on the role of dispersal in environments which change gradually across space, and when local populations are quite small such that genetic drift has a significant effect. Using individual-based simulations, I show that in small populations, even leptokurtic dispersal benefits adaptation, by reducing the power of genetic drift. This has implications for management of fragmented or marginal populations: the beneficial effect of increased dispersal into small populations is stronger than swamping of adaption under a broad range of conditions, including a mixture of local and long-distance dispersal. However, when environmental gradient is steep, heavily fat-tailed dispersal will swamp continuous adaptation so that only patches of locally adapted subpopulations remain.

evolutionary biology↗

bioRxiv2019

Sympatric ecological divergence with coevolution of niche preference

Reinforcement, the increase of assortative mating driven by selection against unfit hybrids, is conditional on pre-existing divergence. Yet, for ecological divergence to precede the evolution of assortment, strict symmetries between fitnesses in niches must hold, and/or there must be low gene flow between the nascent species. It has thus been argued that conditions favouring sympatric speciation are rarely met in nature. Indeed, we show that under disruptive selection, violating symmetries in niche sizes and increasing strength of the trade-off in selection between the niches quickly leads to loss of genetic variation, instead of evolution of specialists. The region of the parameter space where polymorphism is maintained further narrows with increasing number of loci encoding the diverging trait and the rate of recombination between them. Yet, evolvable assortment and pre-existing assortment both substantially broaden the parameter space within which polymorphism is maintained. Notably, pre-existing niche preference speeds up further increase of assortment, thus facilitating reinforcement in the later phases of speciation. We conclude that in order for sympatric ecological divergence to occur, niche preference must co-evolve throughout the divergence process. Even if populations come into secondary contact, having diverged in isolation, niche preference substantially broadens the conditions for coexistence in sympatry and completion of the speciation process.

evolutionary biology↗

bioRxiv2018

The influence of fluctuating population densities on evolutionary dynamics

The causes and consequences of fluctuating population densities are an important topic in ecological literature. Yet, the effects of such fluctuations on maintenance of variation in spatially structured populations have received little analytic treatment. We analyze what happens when two habitats coupled by migration not only differ in their trade-offs in selection but also in their demographic stability - and show that equilibrium allele frequencies can change significantly due to ecological feedback arising from locally fluctuating population sizes. When an ecological niche exhibits such fluctuations, these drive an asymmetry in the relative impact of gene flow, and therefore, the equilibrium frequency of the locally adapted type decreases. Our results extend the classic conditions on maintenance of diversity under selection and migration by including the effect of fluctuating population densities. We find simple analytic conditions in terms of the strength of selection, immigration, and the extent of fluctuations between generations in a continent-island model. Whereas weak fluctuations hardly affect coexistence, strong recurrent fluctuations lead to extinction of the type better adapted to the fluctuating niche - even if the invader is locally maladapted. There is a disadvantage to specialization to an unstable habitat, as it makes the population vulnerable to swamping from more stable habitats.

evolutionary biology↗

bioRxiv2017

Is the sky the limit? On the expansion threshold of a species’ range

More than a hundred years after Griggs influential analysis of species borders, the causes of limits to species ranges still represent a puzzle that has never been understood with clarity. The topic has become especially important recently as many scientists have become interested in the potential for species ranges to shift in response to climate change - and yet, nearly all of those studies fail to recognise or incorporate evolutionary genetics in a way that relates to theoretical developments. I show that range margins can be understood based on just two measurable parameters: i) the fitness cost of dispersal - a measure of environmental heterogeneity - and ii) the strength of genetic drift, which reduces genetic diversity. Together, these two parameters define an expansion threshold: adaptation fails when genetic drift reduces genetic diversity below that required for adaptation to environmental heterogeneity. When the key parameters drop below this expansion threshold locally, a sharp range margin forms. When they drop below this threshold throughout the species range, adaptation collapses everywhere, resulting in either extinction, or formation of a fragmented meta-population. Because the effects of dispersal differ fundamentally with dimension, the second parameter - the strength of genetic drift - is qualitatively different compared to a linear habitat. In two-dimensional habitats, genetic drift becomes effectively independent of selection. It decreases with neighbourhood size - the number of individuals accessible by dispersal within one generation. Moreover, in contrast to earlier predictions, which neglected evolution of genetic variance and/or stochasticity in two dimensions, dispersal into small marginal populations aids adaptation. This is because the reduction of both genetic and demographic stochasticity has a stronger effect than the cost of dispersal through increased maladaptation. The expansion threshold thus provides a novel, theoretically justified and testable prediction for formation of the range margin and collapse of the species range.\n\nAuthor summaryGene flow across environments has conflicting effects: while it increases the genetic variation necessary for adaptation and counters the loss of genetic diversity due to genetic drift, it may also swamp adaptation to local conditions. This interplay is crucial for the dynamics of a species range expansion, which can thus be understood based on two dimensionless parameters: i) the fitness cost of dispersal - a measure of environmental heterogeneity - and ii) the strength of genetic drift - a measure of reduction of genetic diversity. Together, these two parameters define an expansion threshold: adaptation fails when the number of individuals accessible by dispersal within one generation is so small that genetic drift reduces genetic diversity below the level required for adaptation to environmental heterogeneity. This threshold provides a novel, theoretically justified and testable prediction for formation of a range margin and a collapse of a species range in two-dimensional habitats.

evolutionary biology↗