Joachim Hermisson | University of Vienna (original) (raw)
Papers by Joachim Hermisson
Some years ago, Luck proposed a relevance criterion for the effect of aperiodic disorder on the c... more Some years ago, Luck proposed a relevance criterion for the effect of aperiodic disorder on the critical behaviour of ferromagnetic Ising systems. In this article, we show how Luck's criterion can be derived within an exact renormalisation scheme for Ising quantum chains with coupling constants modulated according to substitution rules. Luck's conjectures for this case are confirmed and refined. Among other outcomes, we give an exact formula for the correlation length critical exponent for arbitrary two-letter substitution sequences with marginal fluctuations of the coupling constants.
Both evolution and ecology have long been concerned with the impact of variable environmental con... more Both evolution and ecology have long been concerned with the impact of variable environmental conditions on observed levels of genetic diversity within and between species. We model the evolution of a quantitative trait under selection that fluctuates in space and time, and derive an analytical condition for when these fluctuations promote genetic diversification. As ecological scenario we use a generalized island model with soft selection within patches in which we incorporate generation overlap. We allow for arbitrary fluctuations in the environment including spatio-temporal correlations and any functional form of selection on the trait. Using the concepts of invasion fitness and evolutionary branching, we derive a simple and transparent condition for the adaptive evolution and maintenance of genetic diversity. This condition relates the strength of selection within patches to expectations and variances in the environmental conditions across space and time. Our results unify, clar...
Subcorneal pustular dermatosis (SPD) adalah penyakit inflamasi kulit yang jarang dan kronik-rekur... more Subcorneal pustular dermatosis (SPD) adalah penyakit inflamasi kulit yang jarang dan kronik-rekuren. Penyakit ini umumnya didapatkan pada wanita usia diatas 40 tahun dengan etiologi belum diketahui. Gambaran klinis yang khas berupa pustul atau vesikel yang dengan cepat berubah menjadi pustul di atas dasar kulit eritematosa, menyebar periferal, central healing, dan menyembuh meninggalkan area eritematosa berbentuk polisiklik disertai munculnya lesi baru. Lesi mengenai area intertriginosa, batang tubuh, dan daerah fleksural ekstremitas. Kami melaporkan kasus seorang perempuan usia 47 tahun dengan keluhan lepuh di hampir seluruh tubuh sejak setahun lalu. Lepuh mudah pecah dan meninggalkan erosi. Status dermatologis menunjukkan generalisata makula eritematosa et hiperpigmentasi, multipel, diskret, ukuran lentikular-plakat; vesikel multipel dan pustul diatasnya; dan pustul yang pecah dengan erosi dan krusta. Pada pasien dilakukan anamnesis, pemeriksaan laboratorium, serta biopsi kulit. Pemeriksaan Gram lepuh menunjukkan hanya terdapat leukosit PMN. Laboratorium darah lengkap normal, hitung eosinofil 1,9%, hitung limfosit 24,3%, LED 70 mm/jam, dan IgE total 831.000 IU/mL. Pemeriksaan histopatologik menunjukkan spongiosis, lepuh subkorneal berisi fibrin, neutrofil, sedikit eosinofil di epidermis. Pada dermis tampak superficial perivascular inflammatory infiltration (neutrofil, limfosit, sedikit eosinofil). Pada kasus ini, diagnosis ditegakkan berdasarkan anamnesis, pemeriksaan fisik, dan pemeriksaan histopatologik yang khas untuk SPD.
Physical Review B, 1995
Although I sometimes tend to ignore it, I know very well that there are more important things in ... more Although I sometimes tend to ignore it, I know very well that there are more important things in life than physics. This book is dedicated to my girlfriend Cornelia Buhrke for helping me to keep in touch with the real world during the nearly two years of writing, and for much more... Göttingen, December 1996 Peter Kopietz IV Contents 4. Bosonization of the Hamiltonian and the density-density correlation function .
Journal of Physics A: Mathematical and General, 1999
We study thermodynamic properties, specific heat and susceptibility, of XY quantum chains with co... more We study thermodynamic properties, specific heat and susceptibility, of XY quantum chains with coupling constants following arbitrary substitution sequences. Generalizing an exact renormalization group transformation, originally formulated for Ising quantum chains, we obtain exact relevance criteria of Harris-Luck type for this class of models. For two-letter substitution rules, a detailed classification is given of sequences leading to irrelevant, marginal or relevant aperiodic modulations. We find that the relevance of the same aperiodic sequence of couplings in general will be different for XY and Ising quantum chains. By our method, continuously varying critical exponents may be calculated exactly for arbitrary (two-letter) substitution rules with marginal aperiodicity. A number of examples are given, including the period-doubling, three-folding and precious mean chains. We also discuss extensions of the renormalization approach to a special class of long-range correlated random chains, generated by random substitutions.
Journal of Physics A: Mathematical and General, 1997
Evolution, 2006
We investigate the multilinear epistatic model under mutation-limited directional selection. We c... more We investigate the multilinear epistatic model under mutation-limited directional selection. We confirm previous results that only directional epistasis, in which genes on average reinforce or diminish each other's effects, contribute to the initial evolution of mutational effects. Thus, either canalization or decanalization can occur under directional selection, depending on whether positive or negative epistasis is prevalent. We then focus on the evolution of the epistatic coefficients themselves. In the absence of higher-order epistasis, positive pairwise epistasis will tend to weaken relative to additive effects, while negative pairwise epistasis will tend to become strengthened. Positive third-order epistasis will counteract these effects, while negative third-order epistasis will reinforce them. More generally, gene interactions of all orders have an inherent tendency for negative changes under directional selection, which can only be modified by higher-order directional epistasis. We identify three types of nonadditive quasiequilibrium architectures that, although not strictly stable, can be maintained for an extended time: (1) nondirectional epistatic architectures; (2) canalized architectures with strong epistasis; and (3) near-additive architectures in which additive effects keep increasing relative to epistasis.
Genetics, 2012
How much gene flow is needed to inhibit speciation by the accumulation of Dobzhansky–Muller incom... more How much gene flow is needed to inhibit speciation by the accumulation of Dobzhansky–Muller incompatibilities (DMIs) in a structured population? Here, we derive these limits in a classical migration–selection model with two haploid or diploid loci and unidirectional gene flow from a continent to an island. We discuss the dependence of the maximum gene-flow rate on ecological factors (exogeneous selection), genetic factors (epistasis, recombination), and the evolutionary history. Extensive analytical and numerical results show the following: (1) The maximum rate of gene flow is limited by exogeneous selection. In particular, maintenance of neutral DMIs is impossible with gene flow. (2) There are two distinct mechanisms that drive DMI evolution in parapatry, selection against immigrants in a heterogeneous environment and selection against hybrids due to the incompatibility. (3) Depending on the mechanism, opposite predictions result concerning the genetic architecture that maximizes t...
Detecting positive selection in species with heterogeneous habitats and complex demography is not... more Detecting positive selection in species with heterogeneous habitats and complex demography is notoriously difficult and prone to statistical biases. The model plant Arabidopsis thaliana exemplifies this problem: In spite of the large amounts of data, little evidence for classic selective sweeps has been found. Moreover, many aspects of the demography are unclear, whichmakes it hard to judge whether the few signals are indeed signs of selection, or false positives caused by demographic events. Here, we focus on Swedish A. thaliana and we find that the demography can be approximated as a two-population model. Careful analysis of the data shows that such a two island model is characterized by a very old split time that significantly predates the last glacial maximum followed by secondary contact with strong migration. We evaluate selection based on this demography and find that this secondary contact model strongly affects the power to detect sweeps. Moreover, it affects the power diff...
We consider a model of sympatric speciation due to frequency-dependent competition, in which it w... more We consider a model of sympatric speciation due to frequency-dependent competition, in which it was previously assumed that the evolving traits have a very simple genetic architecture. In the present study, we numerically analyze the consequences of relaxing this assumption. First, previous models assumed that assortative mating evolves in infinitesimal steps. Here, we show that the range of parameters for which speciation is possible increases when mutational steps are large. Second, it was assumed that the trait under frequency-dependent selection is determined by a single locus with two alleles and additive effects. As a consequence, the resultant intermediate phenotype is always heterozygous and can never breed true. To relax this assumption, here we add a second locus influencing the trait. We find three new possible evolutionary outcomes: evolution of three reproductively isolated species, a monomorphic equilibrium with only the intermediate phenotype, and a randomly mating population with a steep unimodal distribution of phenotypes. Both extensions of the original model thus increase the likelihood of competitive speciation.
Based upon the torus parametrization which was introduced recently, we present a recipe allowing ... more Based upon the torus parametrization which was introduced recently, we present a recipe allowing for a complete analysis of the symmetry structure of quasiperiodic local isomorphism classes in one and two dimensions. A number of results is provided explicitly, including some widely used planar tiling classes with 8-, 10- and 12-fold rotational symmetry.
Genetic hitchhiking describes evolution at a neutral locus that is linked to a selected locus. If... more Genetic hitchhiking describes evolution at a neutral locus that is linked to a selected locus. If a beneficial allele rises to fixation at the selected locus, a characteristic polymorphism pattern (so-called selective sweep) emerges at the neutral locus. The classical model assumes that fixation of the beneficial allele occurs from a single copy of this allele that arises by mutation. However, recent theory (Pennings and Hermisson, 2006a,b) has shown that recurrent beneficial mutation at biologically realistic rates can lead to markedly different polymorphism patterns, so called soft selective sweeps. We extend an approach that has recently been developed for the classical hitchhiking model (Schweinsberg and Durrett, 2005; Etheridge et al., 2006) to study the recurrent mutation scenario. We show that the genealogy at the neutral locus can be approximated (to leading orders in the selection strength) by a marked Yule process with immigration. Using this formalism, we derive an improv...
Robustness is the invariance of phenotypes in the face of perturbation. The robustness of phenoty... more Robustness is the invariance of phenotypes in the face of perturbation. The robustness of phenotypes appears at various levels of biological organization, including gene expression, protein folding, metabolic flux, physiological homeostasis, development, and even organismal fitness. The mechanisms underlying robustness are diverse, ranging from thermodynamic stability at the RNA and protein level to behavior at the organismal level. Phenotypes can be robust either against heritable perturbations (e.g. mutations) or non-heritable perturbations (e.g. the weather). Here we primarily focus on the first kind of robustness -- genetic robustness -- and survey three growing avenues of research: (1) measuring genetic robustness in nature and in the laboratory, (2) understanding the evolution of genetic robustness, and (3) exploring the implications of genetic robustness for future evolution.
Nature Reviews Genetics
Most adaption processes have a polygenic genetic basis, but even with the recent explosive growth... more Most adaption processes have a polygenic genetic basis, but even with the recent explosive growth of genomic data we are still lacking a unified framework describing the dynamics of selected alleles. Building on recent theoretical and empirical work we introduce the concept of adaptive architecture, which extends the genetic architecture of an adaptive trait by factors influencing its adaptive potential and population genetic principles. Because adaptation can be typically achieved by many different combinations of adaptive alleles (redundancy), we describe how two characteristics — heterogeneity among loci and non-parallelism between replicated populations — are hallmarks for the characterization of polygenic adaptation in evolving populations. We discuss how this unified framework can be applied to natural and experimental populations. Increased capacities for sequencing and genotyping are enabling a more comprehensive understanding of the genetics of adaptation for diverse species. In this Perspective, Barghi, Hermisson and Schlötterer describe how polygenic adaptation can be studied using a framework of ‘adaptive architecture’ that unifies principles from the traditionally disparate fields of quantitative genetics and molecular population genetics.
PLOS ONE
Interspecific hybridization (i.e. mating between species) occurs frequently in animals. Among cyc... more Interspecific hybridization (i.e. mating between species) occurs frequently in animals. Among cyclical parthenogens, hybrids can proliferate and establish through parthenogenetic reproduction, even if their sexual reproduction is impaired. In water fleas of the Daphnia longispina species complex, interspecific hybrids hatch from sexually produced dormant eggs. However, fewer hybrid genotypes contribute to the dormant egg bank and their hatching rate from dormant eggs is reduced, compared to eggs resulting from intraspecific crosses. Therefore, Daphnia hybrids would benefit from adaptations that increase their survival over winter as parthenogenetic lineages, avoiding the need to re-establish populations after winter from sexually produced dormant eggs. Here, we constructed a mathematical model to examine the conditions that could explain the frequently observed establishment of hybrids in the D. longispina species complex. Specifically, we compared the outcome of hybrid and parental taxa competition given a reduced contribution of hybrids to hatchlings from the sexually produced dormant egg bank, but their increased ability to survive winter as parthenogenetic lineages. In addition, different growth rates of parental species and differences in average annual temperatures were evaluated for their influence on hybrid production and establishment. Our model shows that increased overwinter performance as parthenogenetic females can compensate for reduced success in sexual reproduction, across all tested scenarios for varying relative growth rates of parental species. This pattern holds true for lower annual temperatures, but at higher temperatures hybrids were less successful. Consequently, hybrids might become less abundant as temperatures rise due to climate change, resulting in reduced diversity and faster differentiation of the parental species.
Adaptation in extended populations often occurs through multiple independent mutations responding... more Adaptation in extended populations often occurs through multiple independent mutations responding in parallel to a common selection pressure. As the mutations spread concurrently through the population, they leave behind characteristic patterns of polymorphism near selected loci—so-called soft sweeps—which remain visible after adaptation is complete. These patterns are well-understood in two limits of the spreading dynamics of beneficial mutations: the panmictic case with complete absence of spatial structure, and spreading via short-ranged or diffusive dispersal events, which tessellates space into distinct compact regions each descended from a unique mutation. However, spreading behaviour in most natural populations is not exclusively panmictic or diffusive, but incorporates both short-range and long-range dispersal events. Here, we characterize the spatial patterns of soft sweeps driven by dispersal events whose jump distances are broadly distributed, using lattice-based simulati...
1Evolutionary theory has produced two conflicting paradigms for the adaptation of a polygenic tra... more 1Evolutionary theory has produced two conflicting paradigms for the adaptation of a polygenic trait. While population genetics views adaptation as a sequence of selective sweeps at single loci underlying the trait, quantitative genetics posits a collective response, where phenotypic adaptation results from subtle allele frequency shifts at many loci. Yet, a synthesis of these views is largely missing and the population genetic factors that favor each scenario are not well understood. Here, we study the architecture of adaptation of a binary polygenic trait (such as resistance) with negative epistasis among the loci of its basis. The genetic structure of this trait allows for a full range of potential architectures of adaptation, ranging from sweeps to small frequency shifts. By combining computer simulations and a newly devised analytical framework based on Yule branching processes, we gain a detailed understanding of the adaptation dynamics for this trait. Our key analytical result...
Some years ago, Luck proposed a relevance criterion for the effect of aperiodic disorder on the c... more Some years ago, Luck proposed a relevance criterion for the effect of aperiodic disorder on the critical behaviour of ferromagnetic Ising systems. In this article, we show how Luck's criterion can be derived within an exact renormalisation scheme for Ising quantum chains with coupling constants modulated according to substitution rules. Luck's conjectures for this case are confirmed and refined. Among other outcomes, we give an exact formula for the correlation length critical exponent for arbitrary two-letter substitution sequences with marginal fluctuations of the coupling constants.
Both evolution and ecology have long been concerned with the impact of variable environmental con... more Both evolution and ecology have long been concerned with the impact of variable environmental conditions on observed levels of genetic diversity within and between species. We model the evolution of a quantitative trait under selection that fluctuates in space and time, and derive an analytical condition for when these fluctuations promote genetic diversification. As ecological scenario we use a generalized island model with soft selection within patches in which we incorporate generation overlap. We allow for arbitrary fluctuations in the environment including spatio-temporal correlations and any functional form of selection on the trait. Using the concepts of invasion fitness and evolutionary branching, we derive a simple and transparent condition for the adaptive evolution and maintenance of genetic diversity. This condition relates the strength of selection within patches to expectations and variances in the environmental conditions across space and time. Our results unify, clar...
Subcorneal pustular dermatosis (SPD) adalah penyakit inflamasi kulit yang jarang dan kronik-rekur... more Subcorneal pustular dermatosis (SPD) adalah penyakit inflamasi kulit yang jarang dan kronik-rekuren. Penyakit ini umumnya didapatkan pada wanita usia diatas 40 tahun dengan etiologi belum diketahui. Gambaran klinis yang khas berupa pustul atau vesikel yang dengan cepat berubah menjadi pustul di atas dasar kulit eritematosa, menyebar periferal, central healing, dan menyembuh meninggalkan area eritematosa berbentuk polisiklik disertai munculnya lesi baru. Lesi mengenai area intertriginosa, batang tubuh, dan daerah fleksural ekstremitas. Kami melaporkan kasus seorang perempuan usia 47 tahun dengan keluhan lepuh di hampir seluruh tubuh sejak setahun lalu. Lepuh mudah pecah dan meninggalkan erosi. Status dermatologis menunjukkan generalisata makula eritematosa et hiperpigmentasi, multipel, diskret, ukuran lentikular-plakat; vesikel multipel dan pustul diatasnya; dan pustul yang pecah dengan erosi dan krusta. Pada pasien dilakukan anamnesis, pemeriksaan laboratorium, serta biopsi kulit. Pemeriksaan Gram lepuh menunjukkan hanya terdapat leukosit PMN. Laboratorium darah lengkap normal, hitung eosinofil 1,9%, hitung limfosit 24,3%, LED 70 mm/jam, dan IgE total 831.000 IU/mL. Pemeriksaan histopatologik menunjukkan spongiosis, lepuh subkorneal berisi fibrin, neutrofil, sedikit eosinofil di epidermis. Pada dermis tampak superficial perivascular inflammatory infiltration (neutrofil, limfosit, sedikit eosinofil). Pada kasus ini, diagnosis ditegakkan berdasarkan anamnesis, pemeriksaan fisik, dan pemeriksaan histopatologik yang khas untuk SPD.
Physical Review B, 1995
Although I sometimes tend to ignore it, I know very well that there are more important things in ... more Although I sometimes tend to ignore it, I know very well that there are more important things in life than physics. This book is dedicated to my girlfriend Cornelia Buhrke for helping me to keep in touch with the real world during the nearly two years of writing, and for much more... Göttingen, December 1996 Peter Kopietz IV Contents 4. Bosonization of the Hamiltonian and the density-density correlation function .
Journal of Physics A: Mathematical and General, 1999
We study thermodynamic properties, specific heat and susceptibility, of XY quantum chains with co... more We study thermodynamic properties, specific heat and susceptibility, of XY quantum chains with coupling constants following arbitrary substitution sequences. Generalizing an exact renormalization group transformation, originally formulated for Ising quantum chains, we obtain exact relevance criteria of Harris-Luck type for this class of models. For two-letter substitution rules, a detailed classification is given of sequences leading to irrelevant, marginal or relevant aperiodic modulations. We find that the relevance of the same aperiodic sequence of couplings in general will be different for XY and Ising quantum chains. By our method, continuously varying critical exponents may be calculated exactly for arbitrary (two-letter) substitution rules with marginal aperiodicity. A number of examples are given, including the period-doubling, three-folding and precious mean chains. We also discuss extensions of the renormalization approach to a special class of long-range correlated random chains, generated by random substitutions.
Journal of Physics A: Mathematical and General, 1997
Evolution, 2006
We investigate the multilinear epistatic model under mutation-limited directional selection. We c... more We investigate the multilinear epistatic model under mutation-limited directional selection. We confirm previous results that only directional epistasis, in which genes on average reinforce or diminish each other's effects, contribute to the initial evolution of mutational effects. Thus, either canalization or decanalization can occur under directional selection, depending on whether positive or negative epistasis is prevalent. We then focus on the evolution of the epistatic coefficients themselves. In the absence of higher-order epistasis, positive pairwise epistasis will tend to weaken relative to additive effects, while negative pairwise epistasis will tend to become strengthened. Positive third-order epistasis will counteract these effects, while negative third-order epistasis will reinforce them. More generally, gene interactions of all orders have an inherent tendency for negative changes under directional selection, which can only be modified by higher-order directional epistasis. We identify three types of nonadditive quasiequilibrium architectures that, although not strictly stable, can be maintained for an extended time: (1) nondirectional epistatic architectures; (2) canalized architectures with strong epistasis; and (3) near-additive architectures in which additive effects keep increasing relative to epistasis.
Genetics, 2012
How much gene flow is needed to inhibit speciation by the accumulation of Dobzhansky–Muller incom... more How much gene flow is needed to inhibit speciation by the accumulation of Dobzhansky–Muller incompatibilities (DMIs) in a structured population? Here, we derive these limits in a classical migration–selection model with two haploid or diploid loci and unidirectional gene flow from a continent to an island. We discuss the dependence of the maximum gene-flow rate on ecological factors (exogeneous selection), genetic factors (epistasis, recombination), and the evolutionary history. Extensive analytical and numerical results show the following: (1) The maximum rate of gene flow is limited by exogeneous selection. In particular, maintenance of neutral DMIs is impossible with gene flow. (2) There are two distinct mechanisms that drive DMI evolution in parapatry, selection against immigrants in a heterogeneous environment and selection against hybrids due to the incompatibility. (3) Depending on the mechanism, opposite predictions result concerning the genetic architecture that maximizes t...
Detecting positive selection in species with heterogeneous habitats and complex demography is not... more Detecting positive selection in species with heterogeneous habitats and complex demography is notoriously difficult and prone to statistical biases. The model plant Arabidopsis thaliana exemplifies this problem: In spite of the large amounts of data, little evidence for classic selective sweeps has been found. Moreover, many aspects of the demography are unclear, whichmakes it hard to judge whether the few signals are indeed signs of selection, or false positives caused by demographic events. Here, we focus on Swedish A. thaliana and we find that the demography can be approximated as a two-population model. Careful analysis of the data shows that such a two island model is characterized by a very old split time that significantly predates the last glacial maximum followed by secondary contact with strong migration. We evaluate selection based on this demography and find that this secondary contact model strongly affects the power to detect sweeps. Moreover, it affects the power diff...
We consider a model of sympatric speciation due to frequency-dependent competition, in which it w... more We consider a model of sympatric speciation due to frequency-dependent competition, in which it was previously assumed that the evolving traits have a very simple genetic architecture. In the present study, we numerically analyze the consequences of relaxing this assumption. First, previous models assumed that assortative mating evolves in infinitesimal steps. Here, we show that the range of parameters for which speciation is possible increases when mutational steps are large. Second, it was assumed that the trait under frequency-dependent selection is determined by a single locus with two alleles and additive effects. As a consequence, the resultant intermediate phenotype is always heterozygous and can never breed true. To relax this assumption, here we add a second locus influencing the trait. We find three new possible evolutionary outcomes: evolution of three reproductively isolated species, a monomorphic equilibrium with only the intermediate phenotype, and a randomly mating population with a steep unimodal distribution of phenotypes. Both extensions of the original model thus increase the likelihood of competitive speciation.
Based upon the torus parametrization which was introduced recently, we present a recipe allowing ... more Based upon the torus parametrization which was introduced recently, we present a recipe allowing for a complete analysis of the symmetry structure of quasiperiodic local isomorphism classes in one and two dimensions. A number of results is provided explicitly, including some widely used planar tiling classes with 8-, 10- and 12-fold rotational symmetry.
Genetic hitchhiking describes evolution at a neutral locus that is linked to a selected locus. If... more Genetic hitchhiking describes evolution at a neutral locus that is linked to a selected locus. If a beneficial allele rises to fixation at the selected locus, a characteristic polymorphism pattern (so-called selective sweep) emerges at the neutral locus. The classical model assumes that fixation of the beneficial allele occurs from a single copy of this allele that arises by mutation. However, recent theory (Pennings and Hermisson, 2006a,b) has shown that recurrent beneficial mutation at biologically realistic rates can lead to markedly different polymorphism patterns, so called soft selective sweeps. We extend an approach that has recently been developed for the classical hitchhiking model (Schweinsberg and Durrett, 2005; Etheridge et al., 2006) to study the recurrent mutation scenario. We show that the genealogy at the neutral locus can be approximated (to leading orders in the selection strength) by a marked Yule process with immigration. Using this formalism, we derive an improv...
Robustness is the invariance of phenotypes in the face of perturbation. The robustness of phenoty... more Robustness is the invariance of phenotypes in the face of perturbation. The robustness of phenotypes appears at various levels of biological organization, including gene expression, protein folding, metabolic flux, physiological homeostasis, development, and even organismal fitness. The mechanisms underlying robustness are diverse, ranging from thermodynamic stability at the RNA and protein level to behavior at the organismal level. Phenotypes can be robust either against heritable perturbations (e.g. mutations) or non-heritable perturbations (e.g. the weather). Here we primarily focus on the first kind of robustness -- genetic robustness -- and survey three growing avenues of research: (1) measuring genetic robustness in nature and in the laboratory, (2) understanding the evolution of genetic robustness, and (3) exploring the implications of genetic robustness for future evolution.
Nature Reviews Genetics
Most adaption processes have a polygenic genetic basis, but even with the recent explosive growth... more Most adaption processes have a polygenic genetic basis, but even with the recent explosive growth of genomic data we are still lacking a unified framework describing the dynamics of selected alleles. Building on recent theoretical and empirical work we introduce the concept of adaptive architecture, which extends the genetic architecture of an adaptive trait by factors influencing its adaptive potential and population genetic principles. Because adaptation can be typically achieved by many different combinations of adaptive alleles (redundancy), we describe how two characteristics — heterogeneity among loci and non-parallelism between replicated populations — are hallmarks for the characterization of polygenic adaptation in evolving populations. We discuss how this unified framework can be applied to natural and experimental populations. Increased capacities for sequencing and genotyping are enabling a more comprehensive understanding of the genetics of adaptation for diverse species. In this Perspective, Barghi, Hermisson and Schlötterer describe how polygenic adaptation can be studied using a framework of ‘adaptive architecture’ that unifies principles from the traditionally disparate fields of quantitative genetics and molecular population genetics.
PLOS ONE
Interspecific hybridization (i.e. mating between species) occurs frequently in animals. Among cyc... more Interspecific hybridization (i.e. mating between species) occurs frequently in animals. Among cyclical parthenogens, hybrids can proliferate and establish through parthenogenetic reproduction, even if their sexual reproduction is impaired. In water fleas of the Daphnia longispina species complex, interspecific hybrids hatch from sexually produced dormant eggs. However, fewer hybrid genotypes contribute to the dormant egg bank and their hatching rate from dormant eggs is reduced, compared to eggs resulting from intraspecific crosses. Therefore, Daphnia hybrids would benefit from adaptations that increase their survival over winter as parthenogenetic lineages, avoiding the need to re-establish populations after winter from sexually produced dormant eggs. Here, we constructed a mathematical model to examine the conditions that could explain the frequently observed establishment of hybrids in the D. longispina species complex. Specifically, we compared the outcome of hybrid and parental taxa competition given a reduced contribution of hybrids to hatchlings from the sexually produced dormant egg bank, but their increased ability to survive winter as parthenogenetic lineages. In addition, different growth rates of parental species and differences in average annual temperatures were evaluated for their influence on hybrid production and establishment. Our model shows that increased overwinter performance as parthenogenetic females can compensate for reduced success in sexual reproduction, across all tested scenarios for varying relative growth rates of parental species. This pattern holds true for lower annual temperatures, but at higher temperatures hybrids were less successful. Consequently, hybrids might become less abundant as temperatures rise due to climate change, resulting in reduced diversity and faster differentiation of the parental species.
Adaptation in extended populations often occurs through multiple independent mutations responding... more Adaptation in extended populations often occurs through multiple independent mutations responding in parallel to a common selection pressure. As the mutations spread concurrently through the population, they leave behind characteristic patterns of polymorphism near selected loci—so-called soft sweeps—which remain visible after adaptation is complete. These patterns are well-understood in two limits of the spreading dynamics of beneficial mutations: the panmictic case with complete absence of spatial structure, and spreading via short-ranged or diffusive dispersal events, which tessellates space into distinct compact regions each descended from a unique mutation. However, spreading behaviour in most natural populations is not exclusively panmictic or diffusive, but incorporates both short-range and long-range dispersal events. Here, we characterize the spatial patterns of soft sweeps driven by dispersal events whose jump distances are broadly distributed, using lattice-based simulati...
1Evolutionary theory has produced two conflicting paradigms for the adaptation of a polygenic tra... more 1Evolutionary theory has produced two conflicting paradigms for the adaptation of a polygenic trait. While population genetics views adaptation as a sequence of selective sweeps at single loci underlying the trait, quantitative genetics posits a collective response, where phenotypic adaptation results from subtle allele frequency shifts at many loci. Yet, a synthesis of these views is largely missing and the population genetic factors that favor each scenario are not well understood. Here, we study the architecture of adaptation of a binary polygenic trait (such as resistance) with negative epistasis among the loci of its basis. The genetic structure of this trait allows for a full range of potential architectures of adaptation, ranging from sweeps to small frequency shifts. By combining computer simulations and a newly devised analytical framework based on Yule branching processes, we gain a detailed understanding of the adaptation dynamics for this trait. Our key analytical result...