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PubMed2003

Peering through the looking glass at a sexual parasite: are Amazon mollies red queens?

The gynogenetic Amazon molly (Poecilia formosa) is a clonal, all-female lineage of livebearing fish that faces an unusual obstacle to evolutionary persistence. Sperm from heterospecific males (either sailfin, P. latipinna, or Atlantic, P. mexicana, mollies) is necessary to trigger embryogenesis. However, none of the male's genes are incorporated into the genome of the gynogenetic offspring. Some investigators have proposed that the evolution of male mate discrimination is a result of this cost, leading to a coevolutionary arms race between male avoidance of P. formosa and P. formosa attractiveness. Given that P. formosa successfully reproduces and has not yet gone extinct, it is clear there are mechanisms by which they attract the sexual attention of males. Although a Red Queen coevolutionary process in typical host/parasite systems has been shown to favor the persistence of sexual species, in this system an arms race has been invoked to explain the reverse. Here I present behavioral data supporting a more parsimonious scenario: that mechanisms of attraction in P. formosa are simply a consequence of its hybrid origin. Poecilia latipinna and P. mexicana males do not discriminate between gynogenetic P. formosa females and first generation sexual hybrid females, and females do not differ in agonistic behaviors associated with competition for mates. Both results contradict predictions from the Red Queen hypothesis. Therefore, coevolution is not necessary to explain the apparent evolutionary persistence of P. formosa.

Animals↗
PubMed2000

Gut bacteria may be involved in interactions between plants, herbivores and their predators: microbial biosynthesis of N-acylglutamine surfactants as elicitors of plant volatiles.

N-Acylamino acids are dominant and widespread constituents of insect oral secretions (regurgitants), serving the insect as biosurfactants in the digestive process. During feeding the conjugates may be introduced into damaged leaves and contribute there to the elicitation of plant defenses such as the induction of volatile biosynthesis. From gut segments of Spodoptera exigua, Mamestra brassicae and Agrotis segetum 23 bacterial strains were isolated, ten of which were able to synthesise typical lepidopteran N-acylamino acids from externally added precursors. Four strains, Providencia rettgeri, Ochrobactrum spec., Myroides odoratus and Acinetobacter sp. genospecies 11 were identified on the basis of their 16 S rDNA. The organisms displayed a very broad substrate tolerance, since fatty acids of different chain length and different degree of saturation were converted into N-acylamino acids. Moreover, most of the proteinogenic amino acids, but not glutamic and aspartic acid, were used as substrates. The dominant occurrence of fatty acids conjugated with glutamine may result from a preferred transport of glutamine from the hemolymph into the gut of the insects. The involvement of bacteria in the biosynthesis of compounds which play a pivotal role in the interaction of plants, herbivores and their predators adds a new trophic level to this complex network of interactions. Due to their short generation cycle and the ease of adaptation endosymbiontic bacteria may have an outstanding importance for the coevolution of plant-insect interactions.

Acylation↗
PubMed2006

Widespread adaptive evolution of Drosophila genes with sex-biased expression.

Many genes in higher eukaryotes show sexually dimorphic expression, and these genes tend to be among the most divergent between species. In most cases, however, it is not known whether this rapid divergence is caused by positive selection or if it is due to a relaxation of selective constraint. To distinguish between these two possibilities, we surveyed DNA sequence polymorphism in 91 Drosophila melanogaster genes with male-, female-, or nonsex-biased expression and determined their divergence from the sister species D. simulans. Using several single- and multilocus statistical tests, we estimated the type and strength of selection influencing the evolution of the proteins encoded by genes of each expression class. Adaptive evolution, as indicated by a relative excess of nonsynonymous divergence between species, was common among the sex-biased genes (both male and female). Male-biased genes, in particular, showed a strong and consistent signal of positive selection, while female-biased genes showed more variation in the type of selection they experience. Genes expressed equally in the two sexes, in contrast, showed no evidence for adaptive evolution between D. melanogaster and D. simulans. This suggests that sexual selection and intersexual coevolution are the major forces driving genetic differentiation between species.

Adaptation, Biological↗
PubMed2004

Population variation in the cost and benefit of tolerance and resistance against herbivory in Datura stramonium.

In this study we examine the hypothesis that divergent natural selection produces genetic differentiation among populations in plant defensive strategies (tolerance and resistance) generating adaptive variation in defensive traits against herbivory. Controlled genetic material (paternal half-sib families) from two populations of the annual Datura stramonium genetically differentiated in tolerance and resistance to herbivory were used. This set of paternal half-sib families was planted at both sites of origin and the pattern of genotypic selection acting on tolerance and resistance was determined, as well as the presence and variation in the magnitude of allocational costs of tolerance. Selection analyses support the adaptive differentiation hypothesis. Tolerance was favored at the site with higher average level of tolerance, and resistance was favored at the site with higher average level of resistance. The presence of significant environmentally dependent costs of tolerance was in agreement with site variation in the adaptive value of tolerance. Our results support the expectation that environmentally dependent costs of plant defensive strategies can generate differences among populations in the evolutionary trajectory of defensive traits and promote the existence of a selection mosaic. The pattern of contrasting selection on tolerance suggests that, in some populations of D. stramonium, tolerance may alter the strength of reciprocal coevolution between plant resistance and natural enemies.

Adaptation, Biological↗
PubMed1991

Classification of cell receptors.

This manuscript constitutes a first attempt to categorize the cell receptors. Based on evolutionary and biological characteristics, it is possible to classify ligand-receptor units into original families. Certain dynamic patterns that could not be classified previously lead us towards the ligand-receptor unit. Biological information is transformed at the receptor by cellular transduction and effector pathways. The dynamic code is compared with the genetic code. The dynamic code controls the biological information patterns necessary for the integral function and structure of cells, tissue, organs, and organisms. The genetic code controls the assembly and molecular structure of proteins. The original families can be assigned certain original functions. A coevolution of ligand-receptor and dynamic code is revealed. For the time being the most useful approach to receptor classification would seem to be based on the organization of the molecular and protein structure of receptors. Two classes of receptor can be described: receptors for cyclic hydrophobic compounds and membrane receptors. Until we know of the families of single membrane-spanning receptors, fourfold membrane-spanning receptors, sevenfold membrane-spanning receptors, fourfold membrane-spanning receptors. For the sevenfold membrane-spanning receptor the identity of conformation and dynamics of biological function has been established. Light and peptide ligands are used as examples. A systems theory for information transduction at receptors is introduced which can also describe the processes of sensitivity modulation.

Amino Acid Sequence↗
PubMed1984

Polymorphic sites and the mechanism of evolution in human mitochondrial DNA.

Twelve restriction enzymes were used to screen for the presence or absence of cleavage sites at 441 locations in the mitochondrial DNA of 112 humans from four continents. Cleavage maps were constructed by comparison of DNA fragment sizes with those expected from the published sequence for one human mtDNA. One hundred and sixty-three of the sites were polymorphic, i.e., present in some individuals but absent from others, 278 sites being invariant. These polymorphisms probably result from single base substitutions and occur in all functional regions of the genome.--In 77 cases, it was possible to specify the exact nature and location (within a restriction site) of the mutation responsible for the absence of a restriction site in a known human mtDNA sequence and its presence in another human mtDNA. Fifty-two of these 77 gain mutations occur in genes coding for proteins, 34 being silent and 18 causing amino acid replacements; moreover, nine of the replacements are radical.--Notable also is the anomalous ratio of transitions to transversions required to account for these 77 restriction site differences between the known human mtDNA sequences and other human mtDNAs. This ratio is lower for most groups of restriction sites than has been reported from sequence comparisons of limited parts of the mtDNA genome in closely related mammals, perhaps indicating a special functional role or sensitivity to mutagenesis for palindromic regions containing high levels of guanine and cytosine.--From the genomic distribution of the 163 polymorphic sites, it is inferred that the level of point mutational variability in tRNA and rRNA genes is nearly as high as in protein-coding genes but lower than in noncoding mtDNA. Thus, the functional constraints operating on components of the protein-synthetic apparatus may be lower for mitochondria than for other systems. Furthermore, the mitochondrial genes for tRNAs that recognize four codons are more variable than those recognizing only two codons.--Among the more variable of the human mitochondrial genes coding for proteins is that for subunit 2 of cytochrome oxidase; this polypeptide appears to have been evolving about five times faster in primates than in other mammals. Cytochrome c, a nuclearly encoded protein that interacts directly with the oxidase 2 subunit in electron transport, has also evolved faster in primates than in rodents or ungulates. This example, along with that for the mitochondrial rRNA genes and the nuclear genes coding for mitochondrial ribosomal proteins, provides evidence for coevolution between specific nuclear and mitochondrial genes.

Base Sequence↗
PubMed1988

Evolution of the secondary structures and compensatory mutations of the ribosomal RNAs of Drosophila melanogaster.

This paper examines the effects of DNA sequence evolution on RNA secondary structures and compensatory mutations. Models of the secondary structures of Drosophila melanogaster 18S ribosomal RNA (rRNA) and of the complex between 2S, 5.8S, and 28S rRNAs have been drawn on the basis of comparative and energetic criteria. The overall AU richness of the D. melanogaster rRNAs allows the resolution of some ambiguities in the structures of both large rRNAs. Comparison of the sequence of expansion segment V2 in D. melanogaster 18S rRNA with the same region in three other Drosophila species and the tsetse fly (Glossina morsitans morsitans) allows us to distinguish between two models for the secondary structure of this region. The secondary structures of the expansion segments of D. melanogaster 28S rRNA conform to a general pattern for all eukaryotes, despite having highly divergent sequences between D. melanogaster and vertebrates. The 70 novel compensatory mutations identified in the 28S rRNA show a strong (70%) bias toward A-U base pairs, suggesting that a process of biased mutation and/or biased fixation of A and T point mutations or AT-rich slippage-generated motifs has occurred during the evolution of D. melanogaster rDNA. This process has not occurred throughout the D. melanogaster genome. The processes by which compensatory pairs of mutations are generated and spread are discussed, and a model is suggested by which a second mutation is more likely to occur in a unit with a first mutation as such a unit begins to spread through the family and concomitantly through the population. Alternatively, mechanisms of proofreading in stem-loop structures at the DNA level, or between RNA and DNA, might be involved. The apparent tolerance of noncompensatory mutations in some stems which are otherwise strongly supported by comparative criteria within D. melanogaster 28S rRNA must be borne in mind when compensatory mutations are used as a criterion in secondary-structure modeling. Noncompensatory mutation may extend to the production of unstable structures where a stem is stabilized by RNA-protein or additional RNA-RNA interactions in the mature ribosome. Of motifs suggested to be involved in rRNA processing, one (CGAAAG) is strongly overrepresented in the 28S rRNA sequence. The data are discussed both in the context of the forces involved with the evolution of multigene families and in the context of molecular coevolution in the rDNA family in particular.

Animals↗
PubMed2004

Interactions among moths, crossbills, squirrels, and lodgepole pine in a geographic selection mosaic.

Repeated patterns among biological communities suggest similar evolutionary and ecological forces are acting on the communities. Conversely, the lack of such patterns suggests that similar forces are absent or additional ones are present. Coevolution between a seed predator, the red crossbill (Loxia curvirostra complex), and lodgepole pine (Pinus contorta var. latifolia) exemplifies the ecological and evolutionary predictions for coevolving systems. In the absence of another seed predator and preemptive competitor (pine squirrels Tamiasciurus hudsonicus), natural selection by crossbills results in the evolution of larger cones with thicker distal scales, while relaxation of selection by squirrels results in the evolution of cones with more seeds and a greater ratio of seed mass to cone mass. However, in one range, the Little Rocky Mountains, distal scale thickness has diverged as expected but cone size has not. In these mountains seed predation by lodgepole pine cone borer moths (Eucosma recissoriana) was about 10 times greater than in other ranges lacking squirrels. We quantified moth predation and cone traits and found that moths select for smaller cones with fewer seeds. Thus, selection by moths in the Little Rocky Mountains counters both selection by crossbills for large cone size and relaxation of selection by squirrels favoring more seeds per cone and accounts for the relatively small and few-seeded cones in these mountains. It is also apparent that selection by crossbills changes seed defenses in a manner that favors seed predation by moths, whereas selection by squirrels likely reduces such predation. These results demonstrate the importance of considering the evolutionary consequences of community context in locally evolved (coevolved) traits and interactions.

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↗
PubMed1992

Models of plant-pathogen coevolution.

Plant populations are often genetically polymorphic for resistance to pathogens. The effectiveness of this resistance is limited because the pathogens are, in turn, polymorphic for virulence genes that can evade plant resistance. Theoretical models and intriguing preliminary data suggest that these plant-pathogen polymorphisms are maintained by continual cycles of coevolution within populations, combined with occasional immigration of new virulence and resistance genes from distant populations.

Biological Evolution↗
PubMed2004

Sperm competition in mammals.

Although Darwin identified the evolutionary significance of competition between males in the context of reproduction, it is only in the past few decades that we have begun to appreciate the importance of competition at the gametic level. Sperm competition, defined as competition between the sperm of two or more males for fertilization of the same set of ova, is now recognised as a key selective force shaping male reproductive anatomy, physiology and behaviour across diverse animal groups, including mammals. The aim of this article is to provide a brief review of the selective consequences of sperm competition in mammals, with emphasis on recent theoretical advances and empirical controversies. Evidence of female influences on sperm competition outcomes in mammals is also discussed, and it is concluded that understanding the selective pressures driving coevolution between male and female reproductive traits remains a major challenge for researchers in this field.

Animals↗
PubMed2003

Host-dependent genetic structure of parasite populations: differential dispersal of seabird tick host races.

Despite the fact that parasite dispersal is likely to be one of the most important processes influencing the dynamics and coevolution of host-parasite interactions, little information is available on the factors that affect it. In most cases, opportunities for parasite dispersal should be closely linked to host biology. Here we use microsatellite genetic markers to compare the population structure and dispersal of two host races of the seabird tick Ixodes uriae at the scale of the North Atlantic. Interestingly, tick populations showed high within-population genetic variation and relatively low population differentiation. However, gene flow at different spatial scales seemed to depend on the host species exploited. The black-legged kittiwake (Rissa tridactyla) had structured tick populations showing patterns of isolation by distance, whereas tick populations of the Atlantic puffin (Fratercula arctica) were only weakly structured at the largest scale considered. Host-dependent rates of tick dispersal between colonies will alter infestation probabilities and local dynamics and may thus modify the adaptation potential of ticks to local hosts. Moreover, as I. uriae is a vector of the Lyme disease agent Borrelia burgdorferi sensu lato in both hemispheres, the large-scale movements of birds and the subsequent dispersal of ticks will have important consequences for the dynamics and coevolutionary interactions of this microparasite with its different vertebrate and invertebrate hosts.

Alleles↗
PubMed1998

The coevolution of host resistance and parasitoid virulence.

Host-parasitoid interactions are abundant in nature and offer great scope for the study of coevolution. A particularly fertile area is the interaction between internal feeding parasitoids and their hosts. Hosts have evolved a variety of means of combating parasitoids, in particular cellular encapsulation, while parasitoids have evolved a wide range of countermeasures. Studies of the evolution of host resistance and parasitoid virulence are reviewed, with an emphasis on work involving Drosophila and its parasitoids. Genetic variation in both traits has been demonstrated using isofemale line and artificial selection techniques. Recent studies have investigated the fitness costs of maintaining the ability to resist parasitoids, the comparative fitness of flies that have successfully defended themselves against parasitoids, and the degree to which resistance and virulence act against one or more species of host or parasitoid. A number of studies have examined geographical patterns, and sought to look for local adaptation; or have compared the traits across a range of species. Finally, the physiological and genetic basis of change in resistance and virulence is being investigated. While concentrating on Drosophila, the limited amount of work on different systems is reviewed, and other possible areas of coevolution in host-parasitoid interactions are briefly discussed.

Animals↗
PubMed2005

Cadherins in maternal-foetal interactions: red queen with a green beard?

Cadherins are homophilic cell surface adhesion proteins, some of which mediate interactions between maternal and foetal tissues during mammalian pregnancy. David Haig suggested that these proteins may exhibit 'green-beard gene' effects, whereby the nature of binding between identical alleles in mother and foetus leads to differential levels of resource transfer. The selfish effects of such self-recognizing alleles should, however, be suppressed over evolutionary time by unlinked genes, which is expected to lead to antagonistic coevolution between placentally expressed cadherins and unlinked modifiers. Such molecular coevolution should leave a signature of positive selection, with high ratios of non-synonymous to synonymous amino acid substitution. We present evidence that three placentally expressed cadherin genes, E-cadherin, P-cadherin and VE-cadherin, have been subject to positive selection. By contrast, a 'control' cadherin that is not expressed in the placenta, H-cadherin, showed no evidence of selection. These results provide support for the hypothesis that the cadherin genes involved in maternal-foetal interactions have been subject to green-beard-effect mutations over the course of evolutionary history, leading to antagonistic coevolution with suppressing elements from the parliament of genes.

Animals↗
PubMed2002

Diversifying coevolution between crossbills and black spruce on Newfoundland.

Coevolution is increasingly recognized as an important process structuring geographic variation in the form of selection for many populations. Here we consider the importance of a geographic mosaic of coevolution to patterns of crossbill (Loxia) diversity in the northern boreal forests of North America. We examine the relationships between geographic variation in cone morphology, bill morphology, and feeding performance to test the hypothesis that, in the absence of red squirrels (Tamiasciurus hudsonicus), black spruce (Picea mariana) has lost seed defenses directed at Tamiasciurus and that red crossbills (L curvirostra) and black spruce have coevolved in an evolutionary arms race. Comparisons of cone morphology and several indirect lines of evidence suggest that black spruce has evolved defenses in response to Tamiasciurus on mainland North America but has lost these defenses on Newfoundland. Cone traits that deter crossbills, including thicker scales that require larger forces to separate, are elevated in black spruce on Newfoundland, and larger billed crossbills have higher feeding performances than smaller billed crossbills on black spruce cones from Newfoundland. These results imply that the large bill of the Newfoundland crossbill (L. c. percna) evolved as an adaptation to the elevated cone defenses on Newfoundland and that crossbills and black spruce coevolved in an evolutionary arms race on Newfoundland during the last 9000 years since glaciers retreated. On the mainland where black spruce is not as well defended against crossbills, the small-billed white-winged crossbill (L leucoptera leucoptera) is more efficient and specializes on seeds in the partially closed cones. Finally, reciprocal adaptations between crossbills and conifers are replicated in black spruce and Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia), with coevolution most pronounced in isolated populations where Tamiasciurus are absent as a competitor. This study further supports the role of Tamiasciurus in determining the selection mosaic for crossbills and suggests that a geographic mosaic of coevolution has been a prominent factor underlying the diversification of North American crossbills.

Animals↗
PubMed2006

Ancient host-pathogen associations maintained by specificity of chemotaxis and antibiosis.

Switching by parasites to novel hosts has profound effects on ecological and evolutionary disease dynamics. Switching requires that parasites are able to establish contact with novel hosts and to overcome host defenses. For most host-parasite associations, it is unclear as to what specific mechanisms prevent infection of novel hosts. Here, we show that parasitic fungal species in the genus Escovopsis, which attack and consume the fungi cultivated by fungus-growing ants, are attracted to their hosts via chemotaxis. This response is host-specific: Escovopsis spp. grow towards their natural host cultivars more rapidly than towards other closely related fungi. Moreover, the cultivated fungi secrete compounds that can suppress Escovopsis growth. These antibiotic defenses are likewise specific: in most interactions, cultivars can inhibit growth of Escovopsis spp. not known to infect them in nature but cannot inhibit isolates of their naturally infecting pathogens. Cases in which cultivars are susceptible to novel Escovopsis are limited to a narrow set of host-parasite strain combinations. Targeted chemotactic and antibiotic responses therefore explain why Escovopsis pathogens do not readily switch to novel hosts, consequently constraining long-term dynamics of host-parasite coevolution within this ancient association.

Animals↗