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PubMed2000

The evolution of polyandry: multiple mating and female fitness in insects.

Theory suggests that male fitness generally increases steadily with mating rate, while one or a few matings are sufficient for females to maximize their reproductive success. Contrary to these predictions, however, females of the majority of insects mate multiply. We performed a meta-analysis of 122 experimental studies addressing the direct effects of multiple mating on female fitness in insects. Our results clearly show that females gain directly from multiple matings in terms of increased lifetime offspring production. Despite a negative effect of remating on female longevity in species without nuptial feeding, the positive effects (increased egg production rate and fertility) more than outweigh this negative effect for moderate mating rates. The average direct net fitness gain of multiple mating was as high as 30-70%. Therefore, the evolutionary maintenance of polyandry in insects can be understood solely in terms of direct effects. However, our results also strongly support the existence of an intermediate optimal female mating rate, beyond which a further elevated mating rate is deleterious. The existence of such optima implies that sexual conflict over the mating rate should be very common in insects, and that sexually antagonistic coevolution plays a key role in the evolution of mating systems and of many reproductive traits. We discuss the origin and maintenance of nuptial feeing in the light of our findings, and suggest that elaborate and nutritional ejaculates may be the result of sexually antagonistic coevolution. Future research should aim at gaining a quantitative understanding of the evolution of female mating rates. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1996

Host-parasite arms race in mutation modifications: indefinite escalation despite a heavy load?

If constantly changing genotypes are favorable in host and parasite coevolution, an indefinite escalation of mutation rates would result despite heavy mutational loads. We theoretically study this possibility by examining the mutation modifier dynamics of host and parasite that engage in genotype-specific epidemiological interaction. In the first model, we study the evolutionarily stable (ESS) mutation rate or switching rate if two alleles in a single locus are subjected to frequency-dependent selection favoring the rarer of the two. Mutation modifier locus is either tightly linked or unlinked to the selected locus. Sufficiently strong frequency-dependent selection may cause cycles in allele frequencies and a modifier with higher mutation rate enjoys the long-term advantage by randomizing the genotype of their offspring. Through the repeated events of invasion and replacement of mutation modifiers, the mutation rate continues to increase until the allele frequencies are stabilized. If some fraction of mutations are deleterious, there is no longer a pure ESS mutation rate: the evolutionarily stable population then consists of multiple strains concerning mutation modifier, typically one with a very high mutation rate and the other with a very low rate, stably coexisting and fighting off invasion by any other modifiers. These results are almost independent of the linkage between the selected and the modifier loci. In the second model, we consider the joint evolution of host and parasite mutation modifiers, assuming that a specific pair of host and parasite genotype densities change following the Nicholson-Bailey type model. If there is no cost of deleterious mutations, mutation rates of both species are escalated indefinitely by modifier evolution until they completely suppress the fluctuation of genotype densities. However, a small cost of deleterious mutation is enough to collapse this coevolutionary equilibrium of inflated mutations. Typical coevolutionary outcome is that the parasite mutation rate is accelerated to a high level; whereas the host mutation rate is driven to zero. Extension of our results to host-parasite coevolution of recombination modifier evolution is discussed.

Animals↗

PubMed1997

Coevolutionary chase on exploiter-victim systems with polygenic characters.

I study the dynamics of a simple quantitative genetic model describing coevolution of two antagonistic species of the victim-exploiter type. In this model, individuals are different with respect to an additive polygenic character that is under direct stabilizing selection and which also determines the strength of within and between species interactions. The model assumes that between species interactions are most intense when the victim's and exploiter's phenotypes match. I show that a cyclic coevolutionary chase is possible under a broad range of conditions. In most cases, the system cycles if the "victim" has a stronger incentive to win and/or a larger genetic variance, and is under stronger stabilizing selection than the "exploiter". The results presented here provide counter-examples to recent studies that (1) question the applicability of "Red Queen" and "arms race" metaphors for continuously varying traits; (2) argue for the existence of crucial differences between major and minor loci dynamics; and (3) attribute a stabilizing role to coevolution.

Animals↗

PubMed1999

Abundant multilocus polymorphisms caused by genetic interaction between species on trait-for-trait basis.

This paper deals with the problem of polymorphism maintenance in species coevolution mediated by selection for quantitative traits controlled by Mendelian genes. We showed here that the conditions for polymorphism maintenance in interacting species can be deduced from the behavior of the isolated partners in stable and changing environments. This allows also to address such difficult questions as evolution of sex and recombination, that can not be considered properly in non-Mendelian models. An abundance of polymorphic regimes was revealed in the proposed genetic model. The obtained results demonstrate a remarkable property of trait-dependent coevolution concerning the conditions for maintenance of genetic polymorphism: what seems to be more realistic, that is, non-equal gene effects and deviation from purely additive within-locus gene action, promotes polymorphism.

Animals↗

PubMed1982

The evolution of man and the extinction of animals.

Africa has lost only very few big mammals at the end of the pleistocene. Evidence is put forward that the reason for the present richness of the African mammal fauna is a very early coevolution between evolving man and the megafauna of this area. Areas without such an early coevolution suffered severe losses (up to 100%) of their native megafauna, when early hunters invaded them.

Africa↗

PubMed2004

Variation in the relative magnitude of intraspecific and interspecific competitive effects in novel versus familiar environments in two Drosophila species.

Models of competitor coevolution, especially the genetic feedback hypothesis, suggest that a negative correlation between intraspecific and interspecific competitive effects may be important in sustaining competitor coexistence, and can give rise to oscillatory dynamics with repeated reversals of competitive superiority. I reanalyzed previously published census data from an experiment in which populations of Drosophila melanogaster and D. simulans underwent competitive coevolution in one familiar and two novel environments, to specifically look for any evidence of a negative relationship between intraspecific and interspecific competitive effects on population growth rates, and for any indication of short period cycling in the relative magnitude of intraspecific and interspecific competitive effects. While there was considerable variation in the relative magnitude of intraspecific and interspecific competitive effects over generations, among both populations and environments, there was no clear evidence supporting the genetic feedback hypothesis. Intraspecific and interspecific competitive effects on population growth rates were strongly positively correlated in novel environments, and uncorrelated in the familiar environment. Data from the familiar environment indicated that indices of competition of populations of the initially superior competitor, D. melanogaster, might be showing some cyclic behaviour, but I argue that this is likely to be transient, and not suggestive of sustained oscillatory dynamics predicted by the genetic feedback model. I discuss the results in the context of the importance of the genetic architecture of intraspecific and interspecific competitive abilities in determining the coevolutionary trajectory of competitive interactions.

Animals↗

PubMed1997

An analysis of the metabolic theory of the origin of the genetic code.

A computer program was used to test Wong's coevolution theory of the genetic code. The codon correlations between the codons of biosynthetically related amino acids in the universal genetic code and in randomly generated genetic codes were compared. It was determined that many codon correlations are also present within random genetic codes and that among the random codes there are always several which have many more correlations than that found in the universal code. Although the number of correlations depends on the choice of biosynthetically related amino acids, the probability of choosing a random genetic code with the same or greater number of codon correlations as the universal genetic code was found to vary from 0.1% to 34% (with respect to a fairly complete listing of related amino acids). Thus, Wong's theory that the genetic code arose by coevolution with the biosynthetic pathways of amino acids, based on codon correlations between biosynthetically related amino acids, is statistical in nature.

Amino Acids↗

PubMed2001

The level and landscape of optimization in the origin of the genetic code.

We consider a model of the origin of genetic code organization incorporating the biosynthetic relationships between amino acids and their physicochemical properties. We study the behavior of the genetic code in the set of codes subject both to biosynthetic constraints and to the constraint that the biosynthetic classes of amino acids must occupy only their own codon domain, as observed in the genetic code. Therefore, this set contains the smallest number of elements ever analyzed in similar studies. Under these conditions and if, as predicted by physicochemical postulates, the amino acid properties played a fundamental role in genetic code organization, it can be expected that the code must display an extremely high level of optimization. This prediction is not supported by our analysis, which indicates, for instance, a minimization percentage of only 80%. These observations can therefore be more easily explained by the coevolution theory of genetic code origin, which postulates a role that is important but not fundamental for the amino acid properties in the structuring of the code. We have also investigated the shape of the optimization landscape that might have arisen during genetic code origin. Here, too, the results seem to favor the coevolution theory because, for instance, the fact that only a few amino acid exchanges would have been sufficient to transform the genetic code (which is not a local minimum) into a much better optimized code, and that such exchanges did not actually take place, seems to suggest that, for instance, the reduction of translation errors was not the main adaptive theme structuring the genetic code.

Algorithms↗

PubMed2003

Diversifying selection in a parasitoid's symbiotic virus among genes involved in inhibiting host immunity.

During parasitization of their hosts some insect parasitoids deliver resident viruses which encode genes that must be expressed in the host for successful parasitization. Among these viruses the Campoletis sonorensis Ichnovirus has been well studied and encodes a cys-motif gene family implicated in disruption of host immunity and other physiological systems. Members of this gene family encode one or more intercystine-knot structural motifs in which the non-cysteine residues of the motif are variable. We analyzed patterns of synonymous and non-synonymous substitution within the cys-motif to investigate the evolution of this gene family and the likelihood of virus-host gene coevolution. Maximum likelihood techniques suggest positive selection acts on 8 of 51 codons in the aligned cysteine-rich region. Although the detected positive selection was not strong, it likely contributes to the diversification of this gene family. Comparison of selection pressure relative to tertiary structure of the VHv1.1 cys-motif protein suggests that the hypervariable sites are exposed. Furthermore, invariant residues in the motif exhibit a region-specific pattern of codon bias, suggesting there are unusual mechanisms of effecting selection pressure at work in this system, though the mechanism has yet to be studied. The positive selection and duplication of both the gene family and the cys-motif implies either selection is driving the molecular radiation of immune suppressive genes toward novel hosts, or molecular coevolution with host targets.

Animals↗

PubMed2001

Coevolutionary interactions between a haploid species and a diploid species.

We investigate a general model describing coevolutionary interaction between a haploid population and a diploid population, each with two alleles at a single locus. Both species are allowed to evolve, with the fitness of the genotypes of each species assumed to depend linearly on the frequencies of the genotypes of the other species. We explore the resulting outcomes of these interactions, in particular determining the location of equilibria under various conditions. The coevolution here is much more complex than that between two haploid populations and allows for the possibility of two polymorphic equilibria. To allow for further analysis, we construct a semi-symmetric model. The variety of outcomes possible even in this second model provides support for the geographic mosaic theory of coevolution by suggesting the possibility of small local populations coevolving to very different outcomes, leading to a shifting geographic mosaic as neighboring populations interact with each other through migration.

Alleles↗

PubMed2006

Tall herb herbivory resistance reflects historic exposure to leaf beetles in a boreal archipelago age-gradient.

In this paper, we introduce the coevolution-by-coexistence hypothesis which predicts that the strength of a coevolutionary adaptation will become increasingly apparent as long as the corresponding selection from an interacting counterpart continues. Hence, evolutionary interactions between plants and their herbivores can be studied by comparing discrete plant populations with known history of herbivore colonization. We studied populations of the host plant, Filipendula ulmaria (meadow sweet), on six islands, in a Bothnian archipelago subject to isostatic rebound, that represent a spatio-temporal gradient of coexistence with its two major herbivores, the specialist leaf beetles Galerucella tenella and Altica engstroemi. Regression analyses showed that a number of traits important for insect-plant interactions (leaf concentrations of individual phenolics and condensed tannins, plant height, G. tenella adult feeding and oviposition) were significantly correlated with island age. First, leaf concentrations of condensed tannins and individual phenolics were positively correlated with island age, suggesting that plant resistance increased after herbivore colonization and continued to increase in parallel to increasing time of past coexistence, while plant height showed a reverse negative correlation. Second, a multi-choice experiment with G. tenella showed that both oviposition and leaf consumption of the host plants were negatively correlated with island age. Third, larvae performed poorly on well-defended, older host populations and well on less-defended, younger populations. Thus, no parameter assessed in this study falsifies the coevolution-by-coexistence hypothesis. We conclude that spatio-temporal gradients present in rising archipelagos offer unique opportunities to address evolutionary interactions, but care has to be taken as abiotic (and other biotic) factors may interact in a complicated way.

Animals↗

PubMed1996

Lice and cospeciation: a response to Barker.

"The student who intends working on the Mallophaga should take warning that he will be tried almost beyond endurance by the paradoxes and complexities which beset his subject but he will also find, in the dual and inter-related aspect of insect and bird, an infinite fascination." (Rothschild & Clay, 1952: pp. 156-157). The study of host louse coevolution will benefit greatly from the phylogenetic perspective offered by recent advantages in molecular systematics. However, in order to make best use of phylogenies we need to appreciate the complexities of the possible relations between host and parasite phylogeny. At the same time, the very complexity of louse-host systems has a potentially useful consequence; the presence of multiple lineages of lice on the same hosts allow for replicated tests of coevolutionary hypotheses. For example, if a number of louse clades infest the same host clade but some lice show more cospeciation than others, we might ask whether there are features of louse biology that correlate with this difference in host tracking fidelity. It may further be possible to ascertain the relative importance of these features in ecological time through controlled transfer experiments. By beginning to appreciate "the paradoxes and complexities" of host-louse evolution, lice may offer us not only "infinite fascination" but also a chance to address important questions in coevolution.

Animals↗

PubMed1987

Dynamics and stability in coevolutionary ecological systems. I. Community stability and coevolutionarily stable states.

An extension of J. Roughgarden's [1979, Theor. Pop. Biol. 9, 388; 1979, "An Introduction to Evolutionary Ecology and Population Genetic Theory," Macmillan, New York] formalism for investigating the effects of coevolution on community structure is presented. The extension assumes the result that a coevolved community is asymptotically stable when coevolution takes place at a genetically noninvasible boundary. This is proved for the general case of n interacting species. From this a community persistence function, phi (P), is defined that allows measuring the domain of attraction for the community as well as the resilience time, that is, the time taken for a perturbation to decay to 1-1/e (63%) of its initial value.

Animals↗

PubMed2003

Stability in N-species coevolutionary systems.

Stability criteria have recently been developed for coevolutionary Lotka-Volterra systems where individual fitness functions are assumed to be linear in the population state. We extend these criteria as part of a general theory of coevolution (that combines effects of ecology and evolution) based on arbitrary (i.e. nonlinear) fitness functions and a finite number of individual phenotypes. The central role of the stationary density surface where species' densities are at equilibrium is emphasized. In particular, for monomorphic resident systems, it is shown coevolutionary stability is equivalent to ecological stability combined with evolutionary stability on the stationary density surface. Also discussed is how our theory relates to recent treatments of phenotypic coevolution via adaptive dynamics when there is a continuum of individual phenotypes.

Biological Evolution↗

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↗

PubMed2000

Isolation and characterization of cytochrome c from the marine copepod Tigriopus californicus.

Mitochondrial energy production requires complex interactions among proteins encoded in both the nuclear and mitochondrial genomes. The intergenomic coevolution of interacting gene products has been previously suggested based on interspecific comparisons of cytochrome c (encoded by the nuclear CYC gene) and cytochrome c oxidase (partly encoded in the mitochondrial DNA by the COX1, COX2 and COX3 genes). In the intertidal copepod, Tigriopus californicus, non-synonymous substitutions in the COX1 gene have previously been found in interpopulation comparisons. In order to determine if CYC also shows interpopulation variation, this gene was isolated from a cDNA library using a degenerate primer/polymerase chain reaction approach. Characterization of a cDNA sequence and 25 genomic DNA sequences derived from four T. californicus populations yielded the following results: (1) the T. californicus CYC gene is interrupted by an intron that occurs at the same position as the intron found in vertebrate CYC genes; (2) there is extensive sequence variation within both the coding region and intron of this gene and the vast majority of this variation occurs between sequences drawn from geographically distinct populations; (3) the coding sequence variation includes a minimum of five amino acid replacement substitutions; (4) segregation of length variants among offspring in an interpopulation cross revealed genotypic ratios consistent with the proposed allelic nature of the CYC variants. These results demonstrate that the requisite genetic variation required for intergenomic coevolution exists in the CYC-COX system in T. californicus.

Amino Acid Sequence↗

PubMed1999

Do essential genes evolve slowly?

Approximately two thirds of all knockouts of individual mouse genes give rise to viable fertile mice. These genes have thus been termed 'non-essential' in contrast to 'essential' genes, the knockouts of which result in death or infertility. Although non-essential genes are likely to be under selection that favours sequence conservation [1], it is predicted that they are less subject to such stabilising selection than essential genes, and hence evolve faster [2]. We have addressed this issue by analysing the molecular evolution of 108 non-essential and 67 essential genes that have been sequenced in both mouse and rat. On preliminary analysis, the non-essential genes appeared to be faster evolving than the essential ones. We found, however, that the non-essential class contains a disproportionate number of immune-system genes that may be under directional selection (that is, selection favouring change) because of host-parasite coevolution. After correction for this bias, we found that the rate at which genes evolve does not correlate with the severity of the knockout phenotype. This was corroborated by the finding that, whereas neuron-specific genes have significantly lower rates of change than other genes, essential and non-essential neuronal genes have comparable rates of evolution. Our findings most probably reflect strong selection acting against even very subtle deleterious phenotypes, and indicate that the putative involvement of directional selection in host-parasite coevolution and gene expression within the nervous system explains much more of the variance in rates of gene evolution than does the knockout phenotype.

Algorithms↗

PubMed2001

Evolution of the Old World Arenaviridae and their rodent hosts: generalized host-transfer or association by descent?

Ten scenarios optimizing the number of cospeciation events between the phylogenies of the Old World Arenaviridae (OWA) and their murine hosts are tested while attempting to answer the following questions. Does the coevolutionary model explain their respective distribution? What kind of evolutionary events could have most frequently contributed to the horizontal and/or vertical transmission of the OWA? How to define secondary hosts and to interpret their existence in the evolutionary process? Where are the geographical origins of the OWA? All scenarios support the "diffuse coevolution" hypothesis previously proposed for the OWA, in which parallel phylogeny and/or host switches on closely related hosts can be considered as the most common mechanisms of transmission. The scenarios allow defining more precisely the concepts of principal and secondary hosts. Such scenarios also suggest that the diversity of the viruses and their rodent hosts could be higher than currently expected and that cophylogeny could have been underestimated. The "diffuse coevolution" hypothesis permits to interpret the transfer of the viruses to distant hosts as a result of a disturbance in their regular mode of dispersion, which could match with the periods of emergence as human parasites. The comparison of the viral phylogeny with the host cladogram also suggests that the viruses parasitized the Murinae before several lineages became distinct and spread in Africa. This supposes that the origin of the arenaviruses has to be found out of Africa.

Animals↗