| 1. |
- Geritz, Stefan A. H., et al.
(författare)
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Mutual invadability near evolutionarily singular strategies for multivariate traits, with special reference to the strongly convergence stable case
- 2016
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Ingår i: Journal of Mathematical Biology. - : Springer Science and Business Media LLC. - 0303-6812 .- 1432-1416. ; 72:4, s. 1081-1099
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Tidskriftsartikel (refereegranskat)abstract
- Over the last two decades evolutionary branching has emerged as a possible mathematical paradigm for explaining the origination of phenotypic diversity. Although branching is well understood for one-dimensional trait spaces, a similarly detailed understanding for higher dimensional trait spaces is sadly lacking. This note aims at getting a research program of the ground leading to such an understanding. In particular, we show that, as long as the evolutionary trajectory stays within the reign of the local quadratic approximation of the fitness function, any initial small scale polymorphism around an attracting invadable evolutionarily singular strategy (ess) will evolve towards a dimorphism. That is, provided the trajectory does not pass the boundary of the domain of dimorphic coexistence and falls back to monomorphism (after which it moves again towards the singular strategy and from there on to a small scale polymorphism, etc.). To reach these results we analyze in some detail the behavior of the solutions of the coupled Lande-equations purportedly satisfied by the phenotypic clusters of a quasi-n-morphism, and give a precise characterisation of the local geometry of the set in trait space squared harbouring protected dimorphisms. Intriguingly, in higher dimensional trait spaces an attracting invadable ess needs not connect to . However, for the practically important subset of strongly attracting ess-es (i.e., ess-es that robustly locally attract the monomorphic evolutionary dynamics for all possible non-degenerate mutational or genetic covariance matrices) invadability implies that the ess does connect to , just as in 1-dimensional trait spaces. Another matter is that in principle there exists the possibility that the dimorphic evolutionary trajectory reverts to monomorphism still within the reign of the local quadratic approximation for the invasion fitnesses. Such locally unsustainable branching cannot occur in 1- and 2-dimensional trait spaces, but can do so in higher dimensional ones. For the latter trait spaces we give a condition excluding locally unsustainable branching which is far stricter than the one of strong convergence, yet holds good for a relevant collection of published models. It remains an open problem whether locally unsustainable branching can occur around general strongly attracting invadable ess-es.
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| 2. |
- Lindh, Magnus, 1973-
(författare)
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Evolution of Plants : a mathematical perspective
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Earth harbors around 300 000 plant species. The rich and complex environment provided by plants is considered a key factor for the extraordinary diversity of the terrestrial fauna by, for example, providing food and shelter. This thesis contributes to the understanding of these questions by investigating how the interplay of physiology, demography, and evolution gives rise to variation and diversity in fundamental plant traits. This will help us answer questions such as: How has this amazing diversity of plant species emerged? Which mechanisms maintain diversity? How are plant strategies and plant diversity influenced by variations in the environment?A plant faces multiple problems to survive and reproduce successfully. These problems can be modeled by considering traits, trade-offs and a fitness measure. For example: How to maximize growth rate, while maximizing structural stability? I will investigate four plant models in order to understand the function of plants, and mechanisms promoting diversity. Paper I: We study how annual plants with and without growth constraints should optimize their flowering time when productivity or season length changes. With a dynamic ontogenetic growth model and optimal control theory we prove that a bang-bang reproductive control is optimal under constrained growth and constant mortality rate. We find that growth constraints can flip the direction of optimal phenological response for increasing productivity. The reason is that the growth rate of vegetative mass saturates at high productivity and therefore it is better to flower earlier and take advantage of a longer reproductive period. If season length extends equally both in the beginning and the end of the season, growth constraints control the direction of the optimal response as well. Our theory can help explaining phenological patterns along productivity gradients, and can be linked to empirical observations made on a calendar scale.Paper II: We introduce a new measure of tree crown-rise efficiency based on the loss of biomass of the tree during growth. The more mass the tree looses during growth, the less crown-rise efficient it is. Top-heavy shapes loose more biomass than bottom-heavy shapes. Light-use efficiency is defined as the mean light assimilation of the leaves in the crown times the ratio of leaf mass and total mass. We then study the trade-off between light-use efficiency to crown-rise efficiency for tree crown shapes. We assume that the total tree mass is constant, and a constant vertical light gradient represent the shading from a surrounding forest. We find large differences in crown shapes at intermediate vertical light gradient, when both self-shading and mean-field shading are important, suggesting light-use vs crown-rise efficiency as a new trade-off that can explain tree diversity. Our crown-rise efficiency measure could easily be integrated into existing forest models.Paper III: We extend an evolutionary tree crown model, where trees with different heights compete for light, with drought-induced mortality rates depending on ground-water availability and the depth of an optional taproot. The model does not include competition for ground water. Our model explains how ground-water availability can shape plant communities, when taproot and non-taproot strategies can coexist, and when only one of these strategies can persist. We investigate how emerging plant diversity varies with water table depth, soil water gradient and drought-induced mortality rate. The taproot enables plants to reach deep water, thus reducing mortality, but also carries a construction cost, thus inducing a trade-off. We find that taproots maintain plant diversity under increasing drought mortality, and that taproots evolve when groundwater is accessible at low depths. There are no viable strategies at high drought mortality and deep water table. Red Queen evolutionary dynamics appear at intermediate drought mortality in mixed communities with and without taproots, as the community never reaches a final evolutionarily stable composition.Paper IV: We extend a size-structured plant model, with self-shading and two evolving traits, crown top-heaviness and crown width-to-height ratio. The model allows us to identify salient trade-offs for the crown shape. The most important trade-off for top-heaviness is light-use efficiency vs crownrise efficiency, and the most important trade-off for width-to-height ratio is self-shading vs branch costs. We find that when the two traits coevolve; the outcome is a single common evolutionarily stable strategy (ESS), far away from the highest net primary production (NPP). When only sun angle is decreasing with increasing latitude both the crown width-to-height ratio and crown top-heaviness decrease. However, when light response in addition to the sun angle decreases with increasing latitude, the crown width-to-height ratio is nearly invariant of latitude except at low site productivity when the ratio decreases with latitude. Top-heaviness is always decreasing with increasing latitude. Finally, we find that crown top-heaviness increases with the NPP or leaf-area index (LAI) at ESS, but crown width-to-height ratio is maximal at an intermediate NPP or LAI.
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| 3. |
- Martinossi-Allibert, Ivain, 1991-, et al.
(författare)
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Invasion and maintenance of meiotic drivers in populations of ascomycete fungi
- 2021
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Ingår i: Evolution. - : John Wiley & Sons. - 0014-3820 .- 1558-5646. ; 75:5, s. 1150-1169
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Tidskriftsartikel (refereegranskat)abstract
- Meiotic drivers (MDs) are selfish genetic elements that are able to become overrepresented among the products of meiosis. This transmission advantage makes it possible for them to spread in a population even when they impose fitness costs on their host organisms. Whether an MD can invade a population, and subsequently reach fixation or coexist in a stable polymorphism, depends on the one hand on the biology of the host organism, including its life cycle, mating system, and population structure, and on the other hand on the specific fitness effects of the driving allele on the host. Here, we present a population genetic model for spore killing, a type of drive specific to fungi. We show how ploidy level, rate of selfing, and efficiency of spore killing affect the invasion probability of a driving allele and the conditions for its stable coexistence with a nondriving allele. Our model can be adapted to different fungal life cycles, and is applied here to two well-studied genera of filamentous ascomycetes known to harbor spore-killing elements, Neurospora and Podospora. We discuss our results in the light of recent empirical findings for these two systems.
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| 4. |
- Martinossi-Allibert, Ivain, 1991-, et al.
(författare)
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The efficacy of good genes sexual selection under environmental change
- 2019
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 286:1896
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Tidskriftsartikel (refereegranskat)abstract
- Sexual selection can promote adaptation if sexually selected traits are reliable indicators of genetic quality. Moreover, models of good genes sexual selection suggest that, by operating more strongly in males than in females, sexual selection may purge deleterious alleles from the population at a low demographic cost, offering an evolutionary benefit to sexually reproducing populations. Here, we investigate the effect of good genes sexual selection on adaptation following environmental change. We show that the strength of sexual selection is often weakened relative to fecundity selection, reducing the suggested benefit of sexual reproduction. This result is a consequence of incorporating a simple and general mechanistic basis for how sexual selection operates under different mating systems, rendering selection on males frequency-dependent and dynamic with respect to the degree of environmental change. Our model illustrates that incorporating the mechanism of selection is necessary to predict evolutionary outcomes and highlights the need to substantiate previous theoretical claims with further work on how sexual selection operates in changing environments.
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| 5. |
- Ohtsuki, Hisashi, et al.
(författare)
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The components of directional and disruptive selection in heterogeneous group-structured populations
- 2020
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Ingår i: Journal of Theoretical Biology. - : Academic Press. - 0022-5193 .- 1095-8541. ; 507
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Tidskriftsartikel (refereegranskat)abstract
- We derive how directional and disruptive selection operate on scalar traits in a heterogeneous group-structured population for a general class of models. In particular, we assume that each group in the population can be in one of a finite number of states, where states can affect group size and/or other environmental variables, at a given time. Using up to second-order perturbation expansions of the invasion fitness of a mutant allele, we derive expressions for the directional and disruptive selection coefficients, which are sufficient to classify the singular strategies of adaptive dynamics. These expressions include first- and second-order perturbations of individual fitness (expected number of settled offspring produced by an individual, possibly including self through survival); the first-order perturbation of the stationary distribution of mutants (derived here explicitly for the first time); the first-order perturbation of pairwise relatedness; and reproductive values, pairwise and three-way relatedness, and stationary distribution of mutants, each evaluated under neutrality. We introduce the concept of individual k-fitness (defined as the expected number of settled offspring of an individual for which k - 1 randomly chosen neighbors are lineage members) and show its usefulness for calculating relatedness and its perturbation. We then demonstrate that the directional and disruptive selection coefficients can be expressed in terms individual k-fitnesses with k = 1, 2, 3 only. This representation has two important benefits. First, it allows for a significant reduction in the dimensions of the system of equations describing the mutant dynamics that needs to be solved to evaluate explicitly the two selection coefficients. Second, it leads to a biologically meaningful interpretation of their components. As an application of our methodology, we analyze directional and disruptive selection in a lottery model with either hard or soft selection and show that many previous results about selection in group-structured populations can be reproduced as special cases of our model.
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| 6. |
- Saltini, Marco, et al.
(författare)
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Complex life cycles drive community assembly through immigration and adaptive diversification
- 2023
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Ingår i: Ecology Letters. - : John Wiley & Sons. - 1461-023X .- 1461-0248. ; 26:7, s. 1084-1094
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Tidskriftsartikel (refereegranskat)abstract
- Most animals undergo ontogenetic niche shifts during their life. Yet, standard ecological theory builds on models that ignore this complexity. Here, we study how complex life cycles, where juvenile and adult individuals each feed on different sets of resources, affect community richness. Two different modes of community assembly are considered: gradual adaptive evolution and immigration of new species with randomly selected phenotypes. We find that under gradual evolution complex life cycles can lead to both higher and lower species richness when compared to a model of species with simple life cycles that lack an ontogenetic niche shift. Thus, complex life cycles do not per se increase the scope for gradual adaptive diversification. However, complex life cycles can lead to significantly higher species richness when communities are assembled trough immigration, as immigrants can occupy isolated peaks of the dynamic fitness landscape that are not accessible via gradual evolution.
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| 7. |
- Schmid, Max, et al.
(författare)
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Resource Variation Within and Between Patches : Where Exploitation Competition, Local Adaptation, and Kin Selection Meet
- 2024
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 203:1, s. E19-E34
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Tidskriftsartikel (refereegranskat)abstract
- In patch- or habitat-structured populations, different processes can favor adaptive polymorphism at different scales. While spatial heterogeneity can generate spatially disruptive selection favoring variation between patches, local competition can lead to locally disruptive selection promoting variation within patches. So far, almost all theory has studied these two processes in isolation. Here, we use mathematical modeling to investigate how resource variation within and between habitats influences the evolution of variation in a consumer population where individuals compete in finite patches connected by dispersal. We find that locally and spatially disruptive selection typically act in concert, favoring polymorphism under a wider range of conditions than when in isolation. But when patches are small and dispersal between them is low, kin competition inhibits the emergence of polymorphism, especially when the latter is driven by local competition for resources. We further use our model to clarify what comparisons between trait and neutral genetic differentiation (QST/FST comparisons) can tell about the nature of selection. Overall, our results help us understand the interaction between two major drivers of polymorphism: locally and spatially disruptive selection, and how this interaction is modulated by the unavoidable effects of kin selection under limited dispersal.
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| 8. |
- Siljestam, Mattias, 1989-, et al.
(författare)
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Genetic Polymorphism – A Result of LocalAdaptation or Heterozygote Advantage?
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Stable coexistence of different self-reproducing entities requires negative frequency dependence, such that each type has an advantage when rare. In community ecology, the entities of interest are species or morphs, and negative frequency dependence arises from competition for limiting factors. In this scenario, coexistence is generally interpreted as a result of local adaptation or niche differentiation. In diploid organisms, different alleles in a specific locus can coexist if heterozygote individuals have an advantage over homozygotes. Here, at the allelic level, negative frequency dependence arises because rare alleles tend to occur in a coalition with alleles different from themselves. A classical example are MHC genes where a heterozygote advantage arises if different alleles offer protection against different sets of pathogens. Coexistence of this type can be interpreted as facilitation or division of labour. Here, we study evolution of MHC alleles in a species occurring in two habitats with different pathogen communities. Our aim is to illustrate that both types of frequency-dependent selection can drive the evolution and maintenance of allelic polymorphism, with local adaptation dominating when migration between habitats is rare and MHC alleles have close to additive effects on survival, and facilitation dominating when migration occurs frequently and alleles that offer better protection against a given pathogen community have a more than additive effect on survival.
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| 9. |
- Siljestam, Mattias, 1989-, et al.
(författare)
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Heterozygote Advantage Can Explain the Extraordinary Diversity of Immune Genes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The majority of highly polymorphic genes are related to immune functions and with over 100 alleles within a population, genes of the major histocompatibility complex (MHC) are the most polymorphic loci in vertebrates. How such extraordinary polymorphism arose and is maintained is controversial. One possibility is heterozygote advantage (HA), which can in principle maintain any number of alleles, but biologically explicit models based on this mechanism have so far failed to reliably predict the coexistence of significantly more than ten alleles. We here present an eco-evolutionary model showing that under HA evolution can result in the emergence and maintenance of more than 100 alleles if the following two assumptions are fulfilled: first, pathogens are lethal in the absence of an appropriate immune defence; second, the combined effect of multiple pathogens on host survival exceeds the sum of the effects of each pathogen alone. Thus, our results show that HA can be a more potent force in explaining the extraordinary polymorphism found at MHC loci than currently recognized.
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| 10. |
- Siljestam, Mattias, 1989-
(författare)
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Mathematical Solutions to Divergent Evolution
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diversity is ubiquitous in nature and manifests through various forms of divergent evolution. Using mathematical models that consider the interplay between ecology and evolution, I explore mechanisms driving two types of such divergence: the emergence of genetic diversity in diploid organisms, and the initial sexual dimorphism of anisogamy.Genetic diversity is typically studied as a consequence of competition or local adaptation. However, diploidy introduces an alternative mechanism: heterozygote advantage (HA), where alleles provide complementary functionalities. A classical example is the immune genes of the Major Histocompatibility Complex (MHC), where alleles can protect against complementary sets of pathogens. HA can emerge if individuals encounter multiple pathogens. When pathogens are distributed over habitats, divergence can be driven by local adaptation, or an emerging HA if migration is high. Alternatively, if MHC alleles provide full defence as a single copy (adaptive context-specific dominance), HA can also emerge under low migration. I challenge the view that HA alone cannot explain the high polymorphism observed at MHC loci by demonstrating that over 100 alleles can be maintained based on two critical assumptions: pathogens can be lethal if not properly countered by an immune response, and the combined effect of multiple pathogens can exceed the sum of their individual impacts.For loci under sexually antagonistic selection, divergent evolution can facilitate the coexistence of alleles, each producing a homozygote genotype with an optimal phenotype in one sex while the heterozygote exhibits an intermediate maladapted phenotype. However, I show that sex-specific dominance is expected to evolve, resulting in a marginal HA across the sexes: a heterozygote carrying alleles optimal for each sex exhibits an optimal phenotype in both sexes, whereas the corresponding homozygotes are maladapted in one sex. This leads to further divergence and the coexistence of many alleles, for wide parameter ranges.Additionally, I challenge the traditional view that male-biased competition for mating is an inevitable consequence of anisogamy---the evolutionary differentiation in gamete size between the sexes. I present the first theoretical description of the coevolution of anisogamy and mating competition, demonstrating that anisogamy does not inherently favour male competition. Instead, the specific evolutionary conditions and the nature of the competition trait significantly influence which sex invests more in mating competition.This thesis not only enhances our understanding of the underlying drivers of genetic and phenotypic diversity but also challenges longstanding evolutionary paradigms, shedding light on the complex dynamics that shape life’s vast diversity.
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