ABSTRACT
We consider a cell population subject to a parasite infection. Cells divide at a constant rate and, at division, share the parasites they contain between their two daughter cells. The sharing may be asymmetric, and its law may depend on the number of parasites in the mother. Cells die at a rate which may depend on the number of parasites they carry, and are also killed when this number explodes. We study the survival of the cell population as well as the mean number of parasites in the cells, and focus on the role of the parasites partitioning kernel at division.
Subject(s)
Host-Parasite Interactions , Models, Biological , Parasitic Diseases , Animals , Host-Parasite Interactions/physiology , Parasitic Diseases/parasitology , Cell Division , Mathematical Concepts , Humans , Parasites/pathogenicity , Parasites/physiologyABSTRACT
Mate preferences may target traits (a) enhancing offspring adaptation and (b) reducing heterospecific matings. Because similar selective pressures are acting on traits shared by different sympatric species, preference-enhancing offspring adaptation may increase heterospecific mating, in sharp contrast with the classical case of so-called "magic traits." Using a mathematical model, we study which and how many traits will be used during mate choice, when preferences for locally adapted traits increase heterospecific mating. In particular, we study the evolution of preference toward an adaptive versus a neutral trait in sympatric species. We take into account sensory trade-offs, which may limit the emergence of preference for several traits. Our model highlights that the evolution of preference toward adaptive versus neutral traits depends on the selective regimes acting on traits but also on heterospecific interactions. When the costs of heterospecific interactions are high, mate preference is likely to target neutral traits that become a reliable cue limiting heterospecific matings. We show that the evolution of preference toward a neutral trait benefits from a positive feedback loop: The more preference targets the neutral trait, the more it becomes a reliable cue for species recognition. We then reveal the key role of sensory trade-offs and the cost of choosiness favoring the evolution of preferences targeting adaptive traits, rather than traits reducing heterospecific mating. When sensory trade-offs and the cost of choosiness are low, we also show that preferences targeting multiple traits evolve, improving offspring fitness by both transmitting adapted alleles and reducing heterospecific mating. Altogether, our model aims at reconciling "good gene" and reinforcement models to provide general predictions on the evolution of mate preferences within natural communities.
ABSTRACT
AbstractMutualistic interactions between defended species represent a striking case of evolutionary convergence in sympatry, driven by the increased protection against predators brought by mimicry in warning traits. However, such convergence is often limited: sympatric defended species frequently display different or imperfectly similar warning traits. The phylogenetic distance between sympatric species may indeed prevent evolution toward the exact same signal. Moreover, warning traits are also involved in mate recognition, so trait convergence might result in heterospecific courtship and mating. Here, we develop a mathematical model to investigate the strength and direction of the evolution of warning traits in defended species with different ancestral traits. Specifically, we determine the effect of phenotypic distances between ancestral trait states of sympatric defended species and of the costs of heterospecific sexual interactions on imperfect mimicry and trait divergence. Our analytical results confirm that reproductive interference and historical constraints limit the convergence of warning traits, leading to either complete divergence or imperfect mimicry. Our model reveals that imperfect mimicry evolves only when ancestral trait values differ between species because of historical constraints and highlights the importance of female and predator discrimination in the evolution of such imperfect mimicry. Our study thus provides new predictions on how reproductive interference interacts with historical constraints and may promote the emergence of novel warning traits, enhancing mimetic diversity.
Subject(s)
Reproduction , Sympatry , Female , Humans , Phylogeny , Courtship , Phenotype , Biological EvolutionABSTRACT
The emergence and persistence of polymorphism within populations generally requires specific regimes of natural or sexual selection. Here, we develop a unified theoretical framework to explore how polymorphism at targeted loci can be generated and maintained by either disassortative mating choice or balancing selection due to, for example, heterozygote advantage. To this aim, we model the dynamics of alleles at a single locus A in a population of haploid individuals, where reproductive success depends on the combination of alleles carried by the parents at locus A. Our theoretical study of the model confirms that the conditions for the persistence of a given level of allelic polymorphism depend on the relative reproductive advantages among pairs of individuals. Interestingly, equilibria with unbalanced allelic frequencies were shown to emerge from successive introduction of mutants. We then investigate the role of the function linking allelic divergence to reproductive advantage on the evolutionary fate of alleles within the population. Our results highlight the significance of the shape of this function for both the number of alleles maintained and their level of genetic divergence. Large number of alleles are maintained with substantial replacement of alleles, when disassortative advantage slowly increases with allelic differentiation . In contrast, few highly differentiated alleles are predicted to be maintained when genetic differentiation has a strong effect on disassortative advantage. These opposite effects predicted by our model explain how disassortative mate choice may lead to various levels of allelic differentiation and polymorphism, and shed light on the effect of mate preferences on the persistence of balanced and unbalanced polymorphism in natural population.
Subject(s)
Genetic Drift , Polymorphism, Genetic , Humans , Alleles , Gene Frequency , HeterozygoteABSTRACT
The striking female-limited mimicry observed in some butterfly species is a text-book example of sexually dimorphic trait submitted to intense natural selection. Two main evolutionary hypotheses, based on natural and sexual selection respectively, have been proposed. Predation pressure favoring mimicry toward defended species could be higher in females because of their slower flight, and thus overcome developmental constraints favoring the ancestral trait that limits the evolution of mimicry in males but not in females. Alternatively, the evolution of mimicry in males could be limited by female preference for non-mimetic males. However, the evolutionary origin of female preference for non-mimetic males remains unclear. Here, we hypothesize that costly sexual interactions between individuals from distinct sympatric species might intensify because of mimicry, therefore promoting female preference for non-mimetic trait. Using a mathematical model, we compare the evolution of female-limited mimicry when assuming either alternative selective hypotheses. We show that the patterns of divergence of male and female trait from the ancestral traits can differ between these selection regimes. We specifically highlight that divergence in female trait is not a signature of the effect of natural selection. Our results also evidence why female-limited mimicry is more frequently observed in Batesian mimics.
Subject(s)
Biological Mimicry , Butterflies , Humans , Animals , Male , Female , Butterflies/genetics , Sex Characteristics , Selection, Genetic , Predatory Behavior , Biological EvolutionABSTRACT
AbstractDisassortative mating is a rare form of mate preference that promotes the persistence of polymorphism. While the evolution of assortative mating and its consequences for trait variation and speciation have been extensively studied, the conditions enabling the evolution of disassortative mating are still poorly understood. Mate preferences increase the risk of missing mating opportunities, a cost that can be compensated by a greater fitness of offspring. Heterozygote advantage should therefore promote the evolution of disassortative mating, which maximizes the number of heterozygous offspring. From the analysis of a two-locus diploid model with one locus controlling the mating cue under viability selection and the other locus coding for the level of disassortative preference, we show that heterozygote advantage and negative frequency-dependent viability selection acting at the cue locus promote the evolution of disassortative preferences. We predict conditions of evolution of disassortative mating coherent with selection regimes acting on traits observed in the wild. We also show that disassortative mating generates sexual selection, which disadvantages heterozygotes at the cue locus, limiting the evolution of disassortative preferences. Altogether, our results partially explain why this behavior is rare in natural populations.
Subject(s)
Mating Preference, Animal , Animals , Phenotype , Polymorphism, Genetic , Reproduction/geneticsABSTRACT
In large clonal populations, several clones generally compete, resulting in complex evolutionary and ecological dynamics: experiments show successive selective sweeps of favorable mutations as well as long-term coexistence of multiple clonal strains. The mechanisms underlying either coexistence or fixation of several competing strains have rarely been studied altogether. Conditions for coexistence have mostly been studied by population and community ecology, while rates of invasion and fixation have mostly been studied by population genetics. To provide a global understanding of the complexity of the dynamics observed in large clonal populations, we develop a stochastic model where three clones compete. Competitive interactions can be intransitive, and we suppose that strains enter the population via mutations or rare immigrations. We first describe all possible final states of the population, including stable coexistence of two or three strains or the fixation of a single strain. Second, we estimate the invasion and fixation times of a favorable mutant (or immigrant) entering the population in a single copy. We show that invasion and fixation can be slower or faster when considering complex competitive interactions. Third, we explore the parameter space assuming prior distributions of reproduction, death, and competition rates, and we estimate the likelihood of the possible dynamics. We show that when mutations can affect competitive interactions even slightly, stable coexistence is likely. We discuss our results in the context of the evolutionary dynamics of large clonal populations.
Subject(s)
Bacterial Physiological Phenomena , Invertebrates/physiology , Plant Physiological Phenomena , Animals , Genotype , Models, Biological , Population Dynamics , Stochastic ProcessesABSTRACT
Size inequality has been considered a key feature of plant population structure with impacts on ecosystem functions. In forest ecosystems, studies examining the relationship between tree size inequality and stand productivity have produced mixed outcomes. These studies found positive, neutral or negative relationships and discussed how this could be influenced by competition for light between trees (e.g. light interception efficiency), but far less attention has been paid to the role played by tree ontogenetic growth. In this article, we present a simple mathematical model that predicts the basal area growth of a two-strata stand as a function of tree basal areas and asymmetric competition. Comparing the growth of this stand to the growth of a spatially homogeneous one-stratum stand and a spatially heterogeneous one-stratum stand, we show that higher growth of the two-strata stand is achieved for concave shape, increasing functions of ontogenetic growth and for low intensities of absolute size-asymmetric competition. We also demonstrate that the difference in growth between the two-strata stand and the one-stratum stands depends on tree size inequality, mean tree basal area and total basal area in the two-strata stand. We finally found that the relationships between tree size inequality and productivity can vary from positive to negative and even non-monotonous. However, we highlight that negative relationships may be more frequent. As a conclusion, our results indicate that ontogenetic growth can have a major impact on the form and the magnitude of the size inequality-productivity relationship.
Subject(s)
Ecosystem , Forests , Trees/growth & development , EfficiencyABSTRACT
Most emerging human infectious diseases have an animal origin. While zoonotic diseases originate from a reservoir, most theoretical studies have principally focused on single-host processes, either exclusively humans or exclusively animals, without considering the importance of animal to human transmission (i.e. spillover transmission) for understanding the dynamics of emerging infectious diseases. Here we aim to investigate the importance of spillover transmission for explaining the number and the size of outbreaks. We propose a simple continuous time stochastic Susceptible-Infected-Recovered model with a recurrent infection of an incidental host from a reservoir (e.g. humans by a zoonotic species), considering two modes of transmission, (1) animal-to-human and (2) human-to-human. The model assumes that (i) epidemiological processes are faster than other processes such as demographics or pathogen evolution and that (ii) an epidemic occurs until there are no susceptible individuals left. The results show that during an epidemic, even when the pathogens are barely contagious, multiple outbreaks are observed due to spillover transmission. Overall, the findings demonstrate that the only consideration of direct transmission between individuals is not sufficient to explain the dynamics of zoonotic pathogens in an incidental host.
Subject(s)
Communicable Diseases, Emerging , Epidemics , Models, Biological , Zoonoses , Animals , Communicable Diseases, Emerging/epidemiology , Communicable Diseases, Emerging/transmission , Humans , Zoonoses/epidemiology , Zoonoses/transmissionABSTRACT
Divergence between populations for a given trait can be driven by sexual selection, interacting with migration behaviour. Mating preference for different phenotypes may lead to specific migration behaviour, with departures from populations where the preferred trait is rare. Such preferences can then trigger the emergence and persistence of differentiated populations, even without any local adaptation. However the genetic architecture underlying the trait targeted by mating preference may have a profound impact on population divergence. In particular, dominance between alleles encoding for divergent phenotypes can interfere with the differentiation process. Using a diploid model of a trait determining both mating success and migration rate, we explored differentiation between two connected populations, assuming either co-dominance or strict dominance between alleles. The model assumes that individuals prefer mating with partners displaying the same phenotype and therefore tend to move to the other population when their own phenotype is rare. We show that the emergence of differentiated populations in this diploid moded is limited as compared to results obtained with the same model assuming haploidy. When assuming co-dominance, differentiation arises only when migration is limited compared to the strength of the preference. Such differentiation is less dependent on migration when assuming strict dominance between haplotypes. Dominant alleles frequently invade populations because their phenotype is more frequently expressed, resulting in higher local mating success and a rapid decrease in migration. However, depending on the initial distribution of alleles, this advantage associated with dominance (i.e. Haldane's sieve) may lead to fixation of the dominant allele throughout both populations. Depending on the initial distribution of heterozygotes in the two populations, persistence of polymorphisms within populations can also occur because heterozygotes displaying the predominant phenotype benefit from high mating success. Altogether, our results highlight that heterozygotes' behaviour has a strong impact on population differentiation and highlight the need for diploid models of differentiation and speciation driven by sexual selection.
Subject(s)
Animal Migration , Genetics, Population , Mating Preference, Animal , Models, Theoretical , Animals , Diploidy , Female , Genes, Dominant , Heterozygote , Male , PhenotypeABSTRACT
Mechanisms leading to speciation are a major focus in evolutionary biology. In this paper, we present and study a stochastic model of population where individuals, with type a or A, are equivalent from ecological, demographical and spatial points of view, and differ only by their mating preference: two individuals with the same genotype have a higher probability to mate and produce a viable offspring. The population is subdivided in several patches and individuals may migrate between them. We show that mating preferences by themselves, even if they are very small, are enough to entail reproductive isolation between patches, and we provide the time needed for this isolation to occur as a function of the carrying capacity. Our results rely on a fine study of the stochastic process and of its deterministic limit in large population, which is given by a system of coupled nonlinear differential equations. Besides, we propose several generalisations of our model, and prove that our findings are robust for those generalisations.