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PubMed2000

[Selective pressure in host-parasite systems].

Selective pressures in host-parasite systems are the result of a continuous conflict between the divergent interests of each partner, on the long run. Whereas the fitness (lifetime reproductive success) of parasites is usually increased by a higher frequency of encounters with susceptible hosts and a better survival rate after infection, the fitness of hosts is increased by opposite processes, avoidance of encounters with infective stages and destruction of the parasites. These selective processes, often referred to as coevolution or arms races are in agreement with the Red Queen hypothesis of Van Valen, which assumes indefinite adaptive changes in both partners, in order to set up counter-measures against the weapons of "the other". Arms races in host-parasite systems thus suggest a gradualistic evolution, but this does not contradict the present day ideas on the tempo changes in the course of evolution (punctuated equilibria). Numerous factors, either genetic (evolutionary lag...), environmental (nutritional status...) or cultural (prevention, vaccination, therapy...) influence the severity of infections at an individual scale. The "terrain", which is a component of the individual phenotype, is thus at the cross-roads of genes, environment and culture. Humans must count more on their intelligence than on natural selection to prevent and cure infectious and parasitic diseases.

Adaptation, Physiological↗
PubMed1994

Evolution of the G protein alpha subunit multigene family.

G protein-mediated signal transduction systems have been identified in a diverse group of eukaryotic organisms, including yeast, plants, Dictyostelium and animals. G protein signaling components have been identified in many of these organisms, from the seven transmembrane domain receptors to distinct alpha, beta and gamma subunits of the heterotrimeric G protein and the intracellular effectors which they regulate. Their broad distribution and sequence conservation implies that genes encoding the components of G protein signaling evolved with early eukaryotes. Their subsequent proliferation among eukaryotic organisms provides an opportunity to study the coevolution of these interacting multigene families. We have focused our interests on G protein alpha subunits, which bind and hydrolyze GTP and interact with receptors and effectors. Gene structure and nucleotide sequence comparisons provided a comprehensive picture of G alpha evolution. Sequence comparisons identified three major groups of G alpha genes, termed the GPA, the G alpha-I and G alpha-II Groups. G alpha genes within the three Groups have evolved at different rates. The GPA Group is primarily composed of G alpha genes from fungi, plants, and slime mold. Within the G alpha-I and G alpha-II Groups, four classes of genes have been identified based upon sequence comparisons and functional similarities; Gi, Gq, G12, and GS. Members of all four classes are expressed in invertebrates and vertebrates but not in other eukaryotes, suggesting that this quartet evolved with metazoan progenitors.

Amino Acid Sequence↗
PubMed1989

Coevolution of the major histocompatibility complex and the t-complex in the mouse. II. Modification of response to sharing of histocompatibility antigens.

Selective pressures imposed by high complementarity associations between the major histocompatibility complex (MHC) and the t-complex on a locus that modifies the expression of prezygotic and postzygotic incompatibility are investigated through the analysis of a quantitative model. Sharing of MHC antigens between mates or between mother and offspring elicits weak inhibition of conception or gestation. In the presence of high complementarity associations between the MHC and the t-complex, weak incompatibility depresses the mean fitness of the population. Nevertheless, natural selection favors the enhancement of the expression of incompatibility if the number of antigens associated with the +-haplotype exceeds the number associated with the t-haplotype by a sufficient margin. Under absolute linkage between the modifier locus and the t-complex, the number associated with the +-haplotype need only be greater than the number associated with the t-haplotype. In the absence of linkage, a twofold difference is sufficient to ensure the initial increase of modifier alleles that intensify the expression of incompatibility.

Alleles↗
PubMed2004

Gene flow in the endophyte Neotyphodium and implications for coevolution with Festuca arizonica.

Arizona fescue (Festuca arizonica) often harbours asymptomatic, asexual endophytic fungi from the genus Neotyphodium. In agronomic grasses, Neotyphodium endophytes are often credited with a wide range of mutualistic benefits to its host many of which are related to fungal production of alkaloids for herbivore deterrence. Neotyphodium in the native grass Arizona fescue, however, usually produces alkaloids at levels too low to deter herbivores, and in general, does not behave mutualistically. This study uses microsatellite markers to examine rates of gene flow among four Arizona populations of Neotyphodium. Haplotypic diversity was generally low; only one population contained more than two haplotypes. Haplotypes carrying multiple loci for some or all of the microsatellite loci were also found, indicating a vegetative hybridization event between Neotyphodium and the grass choke pathogen from the genus Epichloë. Gene flow between Neotyphodium populations is very low, and likely much lower than the pollen mediated gene flow of its host. These differing rates of gene flow are predicted to create trait mismatching between endophyte and host and may explain the low, or lack of, alkaloid production by Neotyphodium in Arizona fescue and other native grass species.

Arizona↗
PubMed1984

Coevolution of functionally constrained characters: prerequisites for adaptive versatility.

One of the major problems of organismic evolution theory is to explain how complex organisms were able to evolve by random mutations in spite of the severe functional constraints that canalize their route of change. The problem is discussed on the basis of a quantitative genetic model. How the degree of genetic variation influences the adaptation speed of functionally coupled but genetically uncorrelated characters is examined. It was found, that if more than three independent characters contribute to the variation of a functionally constrained system, optimal degrees of genetic variation exist. Higher degrees of variation lead to decreasing adaptation rates. Conversely, functional constraints do not limit the degree of adaptely reasonable genetic variability as long as the number of independent characters is not higher than three. The conclusion is drawn that there is no need to develop a genetic correlation between functionally coupled characters as long as not many more than three characters are integrated into a functional system. This explains the fact that there is no genetic coupling between the inherited signal sender and receiver mechanisms in orthopterians, even though there is a strong functional coupling between them.

Adaptation, Biological↗
PubMed2000

Extinctions and taxonomy in a trophic model of coevolution.

We investigate the statistics of extinction sizes and the taxonomy in a trophic model of evolution recently proposed [Phys. Rev. Lett. 82, 652 (1999)]. By further exploring the parameters of this model, we find that the distribution of extinction sizes N(s) shows typically a characteristic maximum before developing the power-law behavior N(s) approximately s(-alpha) with alpha approximately 2, in agreement with empirical observations. Furthermore, the derivation of the alpha=-2 exponent given by Drossel [Phys. Rev. Lett. 81, 5011 (1998)] for this model is completed. The extinction sizes in each trophic level are also analyzed; one finds that at the fourth level and up (l> or =4) the extinction size statistics is a power law with exponent alpha(l) approximately 1.4, and exponential-like at the second level, also in agreement with some empirical data not previously explained by current models. On the other hand, in contrast to the observed power-law distribution of the number of species in genera, numerical simulations yield an exponential law. A modification of the model is presented that provides an approximate potential behavior for taxonomy, and some consequences for future modeling are outlined.

Biological Evolution↗
PubMedDate not supplied

[The coevolution of ixodid ticks and terrestrial vertebrates].

Paleontologic and zoogeographic data speak in favour of Mesozoic origin of ixodid ticks. The absence of strict restrictions for the feeding on unusual species of hosts has caused the domination of polyphagy and oligophagy over monophagy among ixodid ticks. The same peculiarities of ixodid ecology are responsible for a restricted part or absence of phylogenetic parallelism with hosts in their evolution. Primary food relations with reptiles are, apparently, preserved only in the genus Aponomma and in many species of Amblyomma while hosts for most species of other genera are mammals and, to a lesser extent, birds. The number of potential hosts in these species can be much greater than that of real ones. Restrictions in the distribution of some species are connected rather with direct effect of unfavourable environmental factors on their nonparasitic stages of the life cycle than with the absence of suitable hosts. During the evolution of natural landscapes and at a shorter stages under the influence of successions or anthropogenic factors ixodids easily adapt themselves to feeding on new species of hosts. So the differentiation of primary and secondary hosts of these parasites is rather difficult.

Adaptation, Physiological↗
PubMed2007

A formal test of linguistic and genetic coevolution in native Central and South America.

This paper investigates a mechanism of linguistic and genetic coevolution in Native Central and South America. This mechanism proposes that a process of population fissions, expansions into new territories, and isolation of ancestral and descendant groups will produce congruent language and gene trees. To evaluate this population fissions mechanism, we collected published mtDNA sequences for 1,381 individuals from 17 Native Central and South American populations. We then tested the hypothesis that three well-known language classifications also represented the genetic structure of these populations. We rejected the hypothesis for each language classification. Our tests revealed linguistic and genetic correspondence in several shallow branches common to each classification, but no linguistic and genetic correspondence in the deeper branches contained in two of the language classifications. We discuss the possible causes for the lack of congruence between linguistic and genetic structure in the region, and describe alternative mechanisms of linguistic and genetic correspondence and their predictions.

Cluster Analysis↗
PubMed1995

Molecular coevolution of mammalian ribosomal gene terminator sequences and the transcription termination factor TTF-I.

Both the DNA elements and the nuclear factors that direct termination of ribosomal gene transcription exhibit species-specific differences. Even between mammals--e.g., human and mouse--the termination signals are not identical and the respective transcription termination factors (TTFs) which bind to the terminator sequence are not fully interchangeable. To elucidate the molecular basis for this species-specificity, we have cloned TTF-I from human and mouse cells and compared their structural and functional properties. Recombinant TTF-I exhibits species-specific DNA binding and terminates transcription both in cell-free transcription assays and in transfection experiments. Chimeric constructs of mouse TTF-I and human TTF-I reveal that the major determinant for species-specific DNA binding resides within the C terminus of TTF-I. Replacing 31 C-terminal amino acids of mouse TTF-I with the homologous human sequences relaxes the DNA-binding specificity and, as a consequence, allows the chimeric factor to bind the human terminator sequence and to specifically stop rDNA transcription.

Amino Acid Sequence↗
PubMed2004

The cooperative coevolutionary (1+1) EA.

Coevolutionary algorithms are variants of traditional evolutionary algorithms and are often considered more suitable for certain kinds of complex tasks than noncoevolutionary methods. One example is a general cooperative coevolutionary framework for function optimization. This paper presents a thorough and rigorous introductory analysis of the optimization potential of cooperative coevolution. Using the cooperative coevolutionary framework as a starting point, the CC (1+1) EA is defined and investigated from the perspective of the expected optimization time. The research concentrates on separability, a key property of objective functions. We show that separability alone is not sufficient to yield any advantage of the CC (1+1) EA over its traditional, non-coevolutionary counterpart. Such an advantage is demonstrated to have its basis in the increased explorative possibilities of the cooperative coevolutionary algorithm. For inseparable functions, the cooperative coevolutionary set-up can be harmful. We prove that for some objective functions the CC (1+1) EA fails to locate a global optimum with overwhelming probability, even in infinite time; however, inseparability alone is not sufficient for an objective function to cause difficulties. It is demonstrated that the CC (1+1) EA may perform equal to its traditional counterpart, and may even outperform it on certain inseparable functions.

Algorithms↗
PubMed2002

Coevolution of pathogens and cultural practices: a new look at behavioral heterogeneity in epidemics.

The effect of heterogeneity within populations on the spread of infectious diseases has been a recent focus of research. Such heterogeneity may be, for example, spatial, temporal or behavioral in form. Generally, models that include population subdivision have assumed that individuals are permanently assigned to given behavioral states represented by the subpopulations. We consider a simple epidemic model in which a behavioral trait affects disease transmission, and this trait may be transferred among hosts as a consequence of social interaction. This creates a situation where the frequencies of different behavioral traits and disease states as well as their associations may change over time. We consider the impact of the culturally transmitted trait on the criterion for initial spread of the disease. We also explore the evolution of cultural traits in response to pathogen dynamics and show some conditions under which behavioral traits that reduce transmission evolve. We find that behaviors increasing the risk of infection can also evolve when they are inherently favored or when there is sufficient clustering of contacts between like behaviors.

Communicable Diseases↗
PubMed1986

Natural selection, fitness entropy, and the dynamics of coevolution.

The coevolutionary dynamics of interacting populations were studied by combining continuous time Lotka-Volterra models of population growth with single-locus genetic models of weak selection. The effects of natural selection on population growth were evaluated using Ginzburg's fitness entropy function as a measure of the deviation of a population's initial allele frequencies from their polymorphic equilibrium values. This entropy measure was used to relate the dynamics of a community composed of evolving populations to the dynamics of a "reference community" whose populations are initially in genetic equilibrium. Specifically, a quantity called the "selective difference area" was defined as the total difference between the population size trajectories of a reference and evolving population. The selective difference area represents the amount of extra life a species would realize if the entire community were at genetic equilibrium. It was shown that this selective difference area is a simple linear function of the initial fitness entropies of each species. This prediction is independent of the strength of selection and holds for any arbitrary set of initial population densities. Numerical examples were presented to illustrate the results. Under the assumption of weak selection, a generalization for arbitrary population growth models was outlined.

Biological Evolution↗
PubMed2002

The coevolution of warning signals.

It has long been recognized that defended prey tend to be conspicuous. Current theories suggest that the association ('aposematism') has arisen because predators more readily learn to avoid attacking defended phenotypes when they are conspicuous. In this paper, I consider why such psychology has evolved. In particular, I argue that aposematism may have evolved not because of an independent and pre-existing receiver bias, but because the conspicuousness of a prey item provides a reliable indicator of its likelihood of being defended. To develop my case I consider how warning signals might coevolve in a system containing a number of predators, whose foraging behaviour is also subject to selection. In these cases, models readily show that the greater the conspicuousness of a novel prey item, the more likely that it has been encountered by other predators and survived. As a consequence, naive predators should be less likely to attack highly conspicuous novel prey on encounter, or at least more inclined to attack them cautiously. This adaptive predator behaviour will greatly facilitate the spread of aposematic phenotypes from extreme rarity, which in turn will enhance selection for forms of predator behaviour under which aposematism will coevolve even more readily.

Animals↗
PubMedDate not supplied

Coevolutionary toxicity as suggested by differential coniferyl alcohol inhibition of ceratocystis species growth.

Coevolution has been shown to lower the toxicity of predator venoms to usual preys, in contrast to higher toxicity to non-prey similar species (Heatwole and Powell, 1998. Resistance of eels (Gymnothorax) to the venom of sea kraits (Laticauda colubrina): a test of coevolution. Toxicon 36, 619-625). In an attempt to examine whether such coevolutionary discrepancies also occur in plant host-parasite interactions, two strains of Ceratocystis grown on artificial medium, C. fimbriata, parasite of the plane tree, and C. bruneociliata, parasite of the Scots pine (Pinus sylvestris), were compared for growth parameters, in controls and in presence of various concentrations of coniferyl alcohol (a phenolic derivative previously found to be released following inoculation of pine trees with C. bruneociliata). Coniferyl alcohol differently inhibited the growth of both fungi. In the case of the conifer-specific fungus, inhibition rate was less marked at low doses (<2.5 mM) but it rose more steeply at higher doses (10 mM) after a sigmoidal transition at around 3.2 mM, indicating a physiological threshold. These results support the hypothesis of a specific action of coniferyl alcohol against C. Bruneociliata, as a coevolutionary adaptative characteristics of the fungus.

Adaptation, Physiological↗
PubMed2006

Evoecotoxicology: environmental changes and life features development during the evolutionary process-the record of the past at developmental stages of living organisms.

For most of evolutionary history, scientific understanding of the environment and life forms is extremely limited. In this commentary I discuss the hypothesis that ontogenetic features of living organisms can be considered biomarkers of coevolution between organisms and physicochemical agents during Earth's history. I provide a new vision of evolution based on correlations between metabolic features and stage-dependent susceptibility of organisms to physicochemical agents with well-known environmental signatures. Thus, developmental features potentially reflect environmental changes during evolution. From this perspective, early multicellular life forms would have flourished in the anoxic Earth more than 2 billion years ago, which is at least 1.2 billion years in advance of available fossil evidence. The remarkable transition to aerobic metabolism in gastrula-stage embryos potentially reflects evolution toward tridermic organisms by 2 billion years ago. Noteworthy changes in embryonic resistance to physicochemical agents at different developmental stages that can be observed in living organisms potentially reflect the influence of environmental stress conditions during different periods of evolutionary history. Evoecotoxicology, as a multidisciplinary and transdisciplinary approach, can enhance our understanding of evolution, including the phylogenetic significance of differences in susceptibility/resistance to physicochemical agents in different organisms.

Animals↗
PubMed2005

The evolutionary origin of signa in female Lepidoptera: natural and sexual selection hypotheses.

Signa are structures of the inner wall of the female corpus bursae (structure where males deposit a spermatophore during copulation) of many Lepidoptera that assist in tearing open spermatophores. In this paper, three hypotheses on the evolutionary origin of signa are proposed. The first hypothesis considers natural selection pressures arising from ecological changes that favor an increase in oviposition rate as the force behind the evolution of signa. The other two hypotheses involve sexual selection. The second hypothesis proposes that sexually antagonistic coevolution is responsible of the evolution of signa: According to this hypothesis, the inverse relation between the length of the female's refractory period and the amount of ejaculate remaining in her corpus bursae, observed in most Lepidoptera studied, selects in males a decreased rate of spermatophore digestion (e.g. a thicker spermatophore envelope or a higher chitin content) that increases the length of the refractory period beyond the female's optimum; in response, females evolved signa as a counteradaptation to restore the female's optimum by increasing the rate of spermatophore digestion. The last hypothesis considers that signa may have evolved as a female device for cryptic choice of males based on the ability of these to influence the length of post-copulatory female refractory period. The different hypotheses make different predictions of the sequence of appearance of specific ecological factors and novel phenotypic traits through evolutionary time. Therefore, testing the relative importance of the hypotheses requires a formal comparative analysis.

Adaptation, Physiological↗
PubMed2005

The effect of migration on local adaptation in a coevolving host-parasite system.

Antagonistic coevolution between hosts and parasites in spatially structured populations can result in local adaptation of parasites; that is, the greater infectivity of local parasites than foreign parasites on local hosts. Such parasite specialization on local hosts has implications for human health and agriculture. By contrast with classic single-species population-genetic models, theory indicates that parasite migration between subpopulations might increase parasite local adaptation, as long as migration does not completely homogenize populations. To test this hypothesis we developed a system-specific mathematical model and then coevolved replicate populations of the bacterium Pseudomonas fluorescens and a parasitic bacteriophage with parasite only, with host only or with no migration. Here we show that patterns of local adaptation have considerable temporal and spatial variation and that, in the absence of migration, parasites tend to be locally maladapted. However, in accord with our model, parasite migration results in parasite local adaptation, but host migration alone has no significant effect.

Adaptation, Physiological↗
PubMed2005

Assessing putative interlocus sexual conflict in Drosophila melanogaster using experimental evolution.

The theoretical foundation of sexually antagonistic coevolution is that females suffer a net fitness cost through their interactions with males. The empirical prediction is that direct costs to female lifetime fecundity will exceed indirect benefits despite a possible increase in the genetic quality of offspring. Although direct costs of males have been repeatedly shown, to date no study has comprehensively tested whether females are compensated for this direct harm through indirect benefits. Here we use experimental evolution to show that a mutation giving Drosophila melanogaster females nearly complete resistance to the direct costs of male courtship and remating, but which also excluded almost all indirect benefits, is strongly favoured by selection. We estimated the selection coefficient favouring the resistance allele to be +20%. These results demonstrate that any indirect benefits that females accrued were not sufficient to counter-balance the direct costs of males, and reinforce a large body of past studies by verifying interlocus sexual conflict in this model system.

Analysis of Variance↗