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PubMed2005

Parasite-host fitness trade-offs change with parasite identity: genotype-specific interactions in a plant-pathogen system.

Simultaneous effects of host and parasite in determining quantitative traits of infection have long been neglected in theoretical and experimental investigations of host-parasite coevolution with the notable exception of gene-for-gene resistance studies. A cross-infection experiment, using five lines of the plant Arabidopsis thaliana and two strains of its oomycete pathogen Hyaloperonospora parasitica, revealed that three traits traditionally considered those of the parasite (number of infected leaves, transmission success, and time until 50% transmission), differed among specific combinations of host and parasite lines, being determined by the two protagonists of the infection. However, the two parasite strains did not differ significantly for most measured phenotypic traits of the infection. Globally, transmission increased with increasing virulence among the different host-parasite combinations, as assumed by most models of evolution of virulence. Surprisingly, however, there was no general relationship between parasite and host fitness, estimated respectively as transmission and seed production. Only one of the two strains showed the expected significant negative genetic correlation between these two variables. Our results thus highlight the importance of taking into account both host and parasite genetic variation because their interaction can lead to unexpected evolutionary outcomes.

Arabidopsis↗

PubMed2005

Sex-ratio conflict between queens and workers in eusocial Hymenoptera: mechanisms, costs, and the evolution of split colony sex ratios.

Because workers in the eusocial Hymenoptera are more closely related to sisters than to brothers, theory predicts that natural selection should act on them to bias (change) sex allocation to favor reproductive females over males. However, selection should also act on queens to prevent worker bias. We use a simulation approach to analyze the coevolution of this conflict in colonies with single, once-mated queens. We assume that queens bias the primary (egg) sex ratio and workers bias the secondary (adult) sex ratio, both at some cost to colony productivity. Workers can bias either by eliminating males or by directly increasing female caste determination. Although variation among colonies in kin structure is absent, simulations often result in bimodal (split) colony sex ratios. This occurs because of the evolution of two alternative queen or two alternative worker biasing strategies, one that biases strongly and another that does not bias at all. Alternative strategies evolve because the mechanisms of biasing result in accelerating benefits per unit cost with increasing bias, resulting in greater fitness for strategies that bias more and bias less than the population equilibrium. Strategies biasing more gain from increased biasing efficiency whereas strategies biasing less gain from decreased biasing cost. Our study predicts that whether queens or workers evolve alternative strategies depends upon the mechanisms that workers use to bias the sex ratio, the relative cost of queen and worker biasing, and the rates at which queen and worker strategies evolve. Our study also predicts that population and colony level sex allocation, as well as colony productivity, will differ diagnostically according to whether queens or workers evolve alternative biasing strategies and according to what mechanism workers use to bias sex allocation.

Animals↗

PubMed2006

Cyto-nuclear epistasis: two-locus random genetic drift in hermaphroditic and dioecious species.

We report the findings of our theoretical investigation of the effect of random genetic drift on the covariance of identity-by-descent (ibd) of nuclear and cytoplasmic genes. The covariance in ibd measures of the degree to which cyto-nuclear gene combinations are heritable, that is, transmitted together from parents to offspring. We show how the mating system affects the covariance of ibd, a potentially important aspect of host-pathogen or host-symbiont coevolution. The magnitude of this covariance influences the degree to which the evolution of apparently neutral cytoplasmic genes, often used in molecular phylogenetics, might be influenced by selection acting on unlinked nuclear genes. To the extent that cyto-nuclear gene combinations are inherited together, genomic conflict is mitigated and intergenomic transfer it facilitated, because genes in both organelle and nuclear genomes share the same evolutionary fate. The covariance of ibd also affects the rate at which cyto-nuclear epistatic variance is converted to additive variance necessary for a response to selection. We find that conversion is biased in species with separate sexes, so that the increment of additive variance added to the nuclear genome exceeds that added to the cytoplasmic genome. As a result, the host might have an adaptive advantage in a coevolutionary arms race with vertically (maternally) transmitted pathogens. Similarly, the nuclear genome could be a source of compensatory mutations for its organellar genomes, as occurs in cytoplasmic male sterility in some plant species. We also discuss the possibility that adaptive cytoplasmic elements, such as favorable mitochondrial mutations or endosymbionts (e.g., Wolbachia), have the potential to release heritable nuclear variation as they sweep through a host population, supporting the view that cytoplasmic introgression plays an important role in adaptation and speciation.

Alleles↗

PubMed2006

Damage due to parasites in Mediterranean teleosts.

Evaluation of damages by parasites in teleosts, even if underextimated in the past, is today one of the most used methods to understand the effective impact of a parasite on a certain ichtyc species. The damage caused by a parasite on the host could be classified into direct, with tissue changes, or indirect, with a decrease of the productive performances. Based on this, a preliminary difference could be traced distinguishing parasites that show a coevolution with their host species, characterized by a low damage, and those parasites that can occasionally infect new host species, showing a high degree of damage. In consideration of the damage, parasites can have different actions on the host: subtractive, irritative, mechanical, traumatic, toxic, dismetabolic, antigenic and foretic. Those parasites able to cause tissue changes must be furtherly classified considering the type of inflammation they evoke on tissues: ulcerous, catarral, haemorrhagic, necrotic and granulomatous. Some parasites are encysted in tissues without any host reaction. The fish response against parasite can be inflammatory, the most frequent, but also hyperplastic, metaplastic, neoplastic and immunitary. The paper goes through different tissue changes due to the main parasites of Mediterranean teleosts.

Animals↗

PubMed2006

Experimental evolution of resistance in Paramecium caudatum against the bacterial parasite Holospora undulata.

Host-parasite coevolution is often described as a process of reciprocal adaptation and counter adaptation, driven by frequency-dependent selection. This requires that different parasite genotypes perform differently on different host genotypes. Such genotype-by-genotype interactions arise if adaptation to one host (or parasite) genotype reduces performance on others. These direct costs of adaptation can maintain genetic polymorphism and generate geographic patterns of local host or parasite adaptation. Fixation of all-resistant (or all-infective) genotypes is further prevented if adaptation trades off with other host (or parasite) life-history traits. For the host, such indirect costs of resistance refer to reduced fitness of resistant genotypes in the absence of parasites. We studied (co)evolution in experimental microcosms of several clones of the freshwater protozoan Paramecium caudatum, infected with the bacterial parasite Holospora undulata. After two and a half years of culture, inoculation of evolved and naive (never exposed to the parasite) hosts with evolved and founder parasites revealed an increase in host resistance, but not in parasite infectivity. A cross-infection experiment showed significant host clone-by-parasite isolate interactions, and evolved hosts tended to be more resistant to their own (local) parasites than to parasites from other hosts. Compared to naive clones, evolved host clones had lower division rates in the absence of the parasite. Thus, our study indicates de novo evolution of host resistance, associated with both direct and indirect costs. This illustrates how interactions with parasites can lead to the genetic divergence of initially identical populations.

Animals↗

PubMed2006

Ecological and reproductive character displacement on an environmental gradient.

Character displacement, in which coevolution of similar species alters their phenotypes, can be difficult to identify on the basis of observational data alone. In two-species systems, the most commonly identified (i.e., classic) resulting pattern is greater phenotypic difference between species in sympatry than allopatry. We show that restricting studies to this pattern may exclude many instances of character displacement, particularly in the presence of spatial environmental gradients. We present four spatial models of character displacement in quantitative traits affecting competition and hybridization between the species. Our models highlight the connections between range limits and character displacement in continuous space. We conclude that the classic pattern is less likely to occur for a trait affecting resource acquisition than for a trait affecting mate choice. We also show that interspecific hybridization (when hybrids are inviable), even in very small amounts, has marked effects on the shape and stability of borders between species and the nature of character displacement. A survey of the empirical literature shows that character displacement studies often lack analysis of spatial phenotype and abundance data. We recommend more careful spatial sampling in character displacement studies, and we illustrate how comparison of clines in mean phenotype in sympatry and allopatry can be used to suggest the action of character displacement.

Animals↗

PubMed2006

The role of body size in host specificity: reciprocal transfer experiments with feather lice.

Although most parasites show at least some degree of host specificity, factors governing the evolution of specificity remain poorly understood. Many different groups of host-specific parasites show a striking correlation between parasite and host body size, suggesting that size reinforces specificity. We tested this hypothesis by measuring the relative fitness of host-specific feather lice transferred to pigeons and doves that differ in size by an order of magnitude. To test the general influence of size, we transferred unrelated groups of wing and body lice, which are specialized for different regions of the host. Lice were transferred in both directions, from a large native host species, the rock pigeon (Columba livia), to several progressively smaller hosts, and from a small native host species, the common ground dove (Columbina passerina), to several larger hosts. We measured the relative fitness (population size) of lice transferred to these novel host species after two louse generations. Neither wing lice nor body lice could survive on novel host species that were smaller in size than the native host. However, when host defense (preening behavior) was blocked, both groups survived and reproduced on all novel hosts tested. Thus, host defense interacted with host size to govern the ability of lice to establish on small hosts. Neither wing lice nor body lice could survive on larger hosts, even when preening was blocked. In summary, host size influenced the fitness of both types of feather lice, but through different mechanisms, depending on the direction of the transfer. Our results indicate that host switching is most likely between hosts of similar body size. This finding has important implications for studies of host-parasite coevolution at both the micro- and macroevolutionary scales.

Animals↗

PubMed1991

Genetic variation and host-parasite relations: Nematospiroides dubius in mice.

Our work deals with aspects of the genetics and immunology of host-parasite relationships as they influence the development of protective immunity and the phenomenon of coevolution. The aim is to understand parasitism through analyses of host specificity. In earlier studies we examined the inheritance of resistances in mice to infections with Nematospiroides dubius (=Heligmosomoides polygyrus) and established the predominant role played by antibodies in protective immunity. Here we report information concerning the selection of lines of N. dubius that differ in their ability to survive antagonistic immunological reactions from mice. Challenge infections with groups of these mice, immunized and protected by previous repeated infections, show that worms selected to survive the immunity that kills other worms do so by inhibiting the effectiveness of the cellular rather than humoral elements of protective immunity.

Animals↗

PubMed1985

Some epidemiological consequences of the evolutionary fit between Leishmaniae and their phlebotomine vectors.

There is a more or less close fit between Leishmania species and their vectors with the proven vector of one parasite often unable to support the full development of another. This fit is presumably a result of coevolution of vector and parasite and it is notable that, if a Leishmania has different invertebrate hosts in different parts of its range, the vectors are often closely related. The epidemiological consequences of this restriction are, firstly, that the spread of the cutaneous leishmaniases of the Old World and, to a lesser degree, that of visceral leishmaniasis is restricted by the distribution of suitable vectors and, secondly, that secondary vectors are of less importance on the epidemiology of the leishmaniases than they are in malaria.

Animals↗

PubMed1979

[Immunological reactivity of the host as an environmental factor and its significance for the development of parasitism].

Concepts--mainly of SPRENT (1959, 1963), DINEEN (1963) and DAMIAN (1964)--concerning the immunological aspects of the phylogeny of host-parasite associations and the function of immune processes in the host-parasite relationship are discussed. In the light of some recent findings an integrating interpretation of the available body of evidence is attempted. The significance of the immuno-selection pressure during the course of host-parasite coevolution is stressed and some of the consequences of this pressure seen in the existing host-parasite systems are pointed out.

Adaptation, Physiological↗

PubMed1985

Phylogenetics and the future of helminth systematics.

Phylogenetic systematics is a relatively new formal technique that increases the precision with which one can make direct estimates of the history of phylogenetic descent. These estimates are made in the form of phylogenetic trees, or cladograms. Cladograms may be converted directly into classifications or they may be used to test various hypotheses about the evolutionary process. More than 20 phylogenetic analyses of helminth groups have been published already, and these have been used to investigate evolutionary questions in developmental biology, biogeography, speciation, coevolution, and evolutionary ecology.

Animals↗

PubMed1994

[Social control, social support and therapy. The tension field of (social-)psychiatric treatment].

As generally in psychiatry the treatment concepts in social psychiatry base to a great extend on disease- and deficit models. These models, however, have their limits and run the risk to promote exactly that, what social psychiatry is fighting against: chronification. The question shall be discussed, if the systemic approach could be helpful to reduce (social) psychiatry's contribution on the process of chronification. Since ever psychiatric institutions have the mandate of social control and exclusion of social disturbing people from society. On the other hand, social support has become a cornerstone of rehabilitation in psychiatry. There the therapist becomes the manager of the disability. The (case-)manager subsequently takes over the responsibility for the future course. So he also gets power over the system to be treated. He decides, how much of social support and control is necessary. But then he gives up the aim of profoundly changing something in the sense that the patient can give up his symptoms and take more self-responsibility for his acting. The consequence is that the patient and psychiatry keep up each other: a coevolution develops. This leads to rigidity and makes changes difficult. By taking over responsibility the therapist becomes part of the system to be treated. So he looses his neutrality and also the possibility of therapeutical influence and change. The whole system quickly moves into a vicious circle of helplessness. Finally it will be reflected how someone, working in an institution, still can do therapy in this field of tension of (social) psychiatry.

Activities of Daily Living↗

PubMed1995

Computer models: killing mosquitoes with information.

This paper looks at the relationship between man and mosquitoes from the perspective of coevolution. From this perspective, the primacy of information processing in vector control programs becomes acutely evident. A composite mosquito control program is developed and illustrated to show the benefits derived from incremental increases in information. The use of computer modeling is seen as the next logical step to be taken by vector control personnel to add the next increment of efficiency and effectiveness. This step could well lead to significant reductions or perhaps the elimination of the need for pesticide use. The author encourages the use of computer modeling in teams as the means to learn across disciplines. The feasibility of this approach has been greatly enhanced by the availability of off-the-shelf modeling programs. The author appeals to university and vector control professionals to support students and staff in learning computer modeling techniques.

Animals↗

PubMedDate not supplied

[The ecological concept of parasitism].

Analysis of morpho-ecological adaptations of parasites showed that their necessary and sufficient characteristic is their inhabiting the host environment. Integration with the environment is achieved 1) by adaptations towards a particular habitat (first order environment) at certain phases of ontogenesis, and 2) by adaptations to the aggregate of hosts, their ecology and factors regulating the numbers of parasites (second order environment) at the level of their entire life cycle. The evolutionary progress of parasites is sustained by the increase in their independence from extrinsic factors not by means of general organization complication and integration (as in free-living animals), but by elimination of free-living developmental stages and by increase of integration with the host environment. The basis of the latter is formed by ecological adjusting of parasites to the environment. It is achieved by syncytial transformation of the covers and the use of communication means analogous to those of host cells. The consequence of host-parasite integration is the transition of parasites from resource consumption to the "management" of the environment. It is manifested by their influence on defensive reactions and other functions of the organism, as well as on its behavior and ecology. Parasitism may turn into other forms of coexistence (commensalism, mutualism) in the course of coevolution, as a result of dialectical overcoming of antagonistic interactions of the two partners.

Animals↗

PubMed1995

Agonist selectivity for three species of natriuretic peptide receptor-A.

We determined the nucleotide sequence of mouse natriuretic peptide receptor-A (NPR-A) cDNA and compared the revised deduced amino acid sequence with those of rat and human NPR-A. The ligand selectivity of these three receptor/guanylyl cyclases was examined by whole-cell stimulation of cGMP production. The 28-amino acid atrial natriuretic peptide (ANP) has only one difference among these three species, i.e., human Met-12 versus rat and mouse Ile-12. However, despite the nearly invariant ANP sequence among these species, ANP analogs have marked differences in ED50 values and maximal cGMP responses among the three receptors. With the natriuretic peptide analogs we tested, human NPR-A is less sensitive than rat or mouse NPR-A to changes in the 17-amino acid, disulfide-bonded ring of ANP and to the species differences in brain natriuretic peptide (BNP) but is more sensitive to deletions in the carboxyl tail of ANP. The ANP determinants of agonist potency have therefore changed for different species of NPR-A. This is reflected in the amino acid sequence divergence in the receptor extracellular domains and in the divergence and specificity of BNP among species. Our results suggest that the coevolution of NPR-A and BNP has thus been constrained within the context of the conserved ANP sequence.

Amino Acid Sequence↗

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↗

PubMed1993

Endocrine and neuroendocrine host-parasite relationships.

The relationships between parasites and hosts are complex, with many of these interactions involving an amazing degree of biochemical coevolution and communication. Hormones, neurohormones, and growth factors figure prominently in these relationships. In vertebrate hosts, many parasites secrete hormones, neuropeptides, or cytokine-like molecules that influence the host's physiological and immunological responses. Alternatively, the parasites secrete factors that alter the host's hormone levels. Simultaneously, molecules emanating from the host strongly influence the parasites' success. In some cases the host's hormones directly influence the parasites; in others, effects are mediated indirectly via the host's immune system. In invertebrates, the presence of parasites likewise has a major influence on the host's endocrine status and the normal suite of processes governed by hormones, including host development, metamorphosis, and reproduction. In insects, interactions involving juvenile hormone and ecdysteroids are especially well-documented, and recent evidence suggests that neuropeptides may also be affected by parasitism. Moreover, recent data suggest that in some species, such as snails, the host's nervous, neuroendocrine, and immune systems are functionally linked, similar to the complex interactions seen in vertebrates.

Animals↗

PubMed1994

[Dynamics of evolutionary rates of proteins from small ribosomal subunits].

Phylogenetic analysis of small ribosomal subunit proteins was performed. Plausible taxon-specific acceleration of evolutionary rates ("leading") of base substitution of some ribosomal proteins and 16S rRNA sites in different phyletic lines were revealed. The limited number of synchronously changing proteins is discussed in terms of relay-race model of coevolution of ribosome. The analogy with dilemma of Haldane is drawn. Plausible differences in the evolutionary rates of regions with different secondary structure were revealed. Changes in correlation of evolutionary rates of regions with different secondary structure during leading were determined. It is anticipated that S14 with S19 ribosomal proteins and S7 with corresponding site on 16S rRNA change co-evolutionary.

Animals↗