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Phylogenetic systematic analysis of the Trichostrongylidae (Nematoda), with an initial assessment of coevolution and biogeography.

Phylogenetic analysis of the subfamilies of the Trichostrongylidae based on 22 morphological transformation series produced a single cladogram with a consistency index (CI) = 74.2%. Monophyly for the family was supported by the structure of the female tail and copulatory bursa. Two major clades are recognized: the Cooperiinae clade with the basal Cooperiinae and Libyostrongylinae+Trichostrongylinae, and the Graphidiinae clade with the basal Graphidiinae and Ostertagiinae+Haemonchinae. Dendrograms presented by Durette-Desset (1985) (CI = 56.1%) and Lichtenfels (1987), based on the key to the Trichostrongylidae by Gibbons and Khalil (1982) (CI = 59.0%), were found to be relatively inefficient in describing character evolution and in supporting putative relationships among the subfamilies. Based on the current analysis, the intestine appears to have constituted the ancestral habitat for the trichostrongylids with the stomach/abomasum having been independently colonized in each clade. Assessment of host associations suggests extensive colonization but also a high degree of coevolution with Bovidae and Cervidae for Ostertagiinae+Haemonchinae. Biogeography for this assemblage is complex, but this analysis is compatible with a Palearctic or Eurasian origin for Cooperiinae, Haemonchinae, and Ostertagiinae.

Animals↗

On the evolution of waking and sleeping.

1. The aim of this paper is to present a new hypothesis to explain the evolution of the sleeping and waking states. 2. We propose that the reptilian waking state and the mammalian slow wave sleep are homologous states. 3. We also propose that instead of looking at the polygraphic sleep as a new evolutive acquisition of mammals and birds, it seems more convenient to look at the full waking state; the "advanced wakefulness" as the true new evolutionary acquisition of these animals. 4. These conclusions are reached after examining some available reports of slow wave electroencephalogram in waking reptiles, some other reports showing signs of rapid eye movement sleep in this same group and the coevolution between sleep states and thermoregulation. Finally, a clear parallelism between sleep ontogeny and phylogeny is shown under the light of the proposed hypothesis.

Aging↗

Coevolution, modularity and human disease.

The concepts of coevolution and modularity have been studied separately for decades. Recent advances in genomics have led to the first systematic studies in each of these fields at the molecular level, resulting in several important discoveries. Both coevolution and modularity appear to be pervasive features of genomic data from all species studied to date, and their presence can be detected in many types of datasets, including genome sequences, gene expression data, and protein-protein interaction data. Moreover, the combination of these two ideas might have implications for our understanding of many aspects of biology, ranging from the general architecture of living systems to the causes of various human diseases.

Animals↗

Identification of an ancestral resistance gene cluster involved in the coevolution process between Phaseolus vulgaris and its fungal pathogen Colletotrichum lindemuthianum.

The recent cloning of plant resistance (R) genes and the sequencing of resistance gene clusters have shed light on the molecular evolution of R genes. However, up to now, no attempt has been made to correlate this molecular evolution with the host-pathogen coevolution process at the population level. Cross-inoculations were carried out between 26 strains of the fungal pathogen Colletotrichum lindemuthianum and 48 Phaseolus vulgaris plants collected in the three centers of diversity of the host species. A high level of diversity for resistance against the pathogen was revealed. Most of the resistance specificities were overcome in sympatric situations, indicating an adaptation of the pathogen to the local host. In contrast, plants were generally resistant to allopatric strains, suggesting that R genes that were efficient against exotic strains but had been overcome locally were maintained in the plant genome. These results indicated that coevolution processes between the two protagonists led to a differentiation for resistance in the three centers of diversity of the host. To improve our understanding of the molecular evolution of these different specificities, a recombinant inbred (RI) population derived from two representative genotypes of the Andean (JaloEEP558) and Mesoamerican (BAT93) gene pools was used to map anthracnose specificities. A gene cluster comprising both Andean (Co-y; Co-z) and Mesoamerican (Co-9) host resistance specificities was identified, suggesting that this locus existed prior to the separation of the two major gene pools of P. vulgaris. Molecular analysis revealed a high level of complexity at this locus. It harbors 11 restriction fragment length polymorphisms when R gene analog (RGA) clones are used. The relationship between the coevolution process and diversification of resistance specificities at resistance gene clusters is discussed.

Amino Acid Sequence↗

Sexually antagonistic coevolution in insects is associated with only limited morphological diversity.

Morphological traits involved in male-female sexual interactions, such as male genitalia, often show rapid divergent evolution. This widespread evolutionary pattern could result from sustained sexually antagonistic coevolution, or from other types of selection such as female choice or selection for species isolation. I reviewed the extensive but under-utilized taxonomic literature on a selected subset of insects, in which male-female conflict has apparently resulted in antagonistic coevolution in males and females. I checked the sexual morphology of groups comprising 500-1000 species in six orders for three evolutionary trends predicted by the sexually antagonistic coevolution hypothesis: males with species-specific differences and elaborate morphology in structures that grasp or perforate females in sexual contexts; corresponding female structures with apparently coevolved species-specific morphology; and potentially defensive designs of female morphology. The expectation was that the predictions were especially likely to be fulfilled in these groups. A largely qualitative overview revealed several surprising patterns: sexually antagonistic coevolution is associated with frequent, relatively weak species-specific differences in males, but male designs are usually relatively simple and conservative (in contrast to the diverse and elaborate designs common in male structures specialized to contact and hold females in other species, and also in weapons such as horns and pincers used in intra-specific battles); coevolutionary divergence of females is not common; and defensive female divergence is very uncommon. No cases were found of female defensive devices that can be facultatively deployed. Coevolutionary morphological races may have occurred between males and females of some bugs with traumatic insemination, but apparently as a result of female attempts to control fertilization, rather than to reduce the physical damage and infections resulting from insertion of the male's hypodermic genitalia. In sum, the sexually antagonistic coevolution that probably occurs in these groups has generally not resulted in rapid, sustained evolutionary divergence in male and female external sexual morphology. Several limitations of this study, and directions for further analyses are discussed.

Animals↗

Relationship between codon usage and sequence-dependent curvature of genomes.

Static DNA curvature distributions of full-sequenced genomes and large DNA contigs from different organisms were calculated. Very distinctive differences among histogram profiles coming from archaebacteria, eubacteria, and eukaryotes were observed. Eubacterial profiles were, on average, more curved than were archaeal and eukaryotic profiles. A comparative analysis between real and randomized DNA sequences revealed that eubacterial genomes presented, overall, higher curvature values than random sequences. An opposite portrait was exhibited by archaeal and eukaryotic genomes. They displayed a lower frequency of curved regions than their corresponding randomized sequences. The contributions of coding and intergenic regions to the curvature profile were also analyzed. Intergenic regions, on average, were found to be more curved than the overall genomic sequences, especially in prokaryotic organisms. Nevertheless, because of their small size with respect to coding regions, the contribution of intergenic sequences to the overall curvature profile tended to be minor. A clear relationship between codon usage and DNA curvature was demonstrated, and a proposal of the possible coevolution of both systems is discussed. Finally, we present a procedure to quantify the deviation of a curvature profile from randomness through a formal statistical analysis.

Archaea↗

Sexual conflict and evolution in Trinidadian guppies.

Recent investigations have highlighted the importance of sexual conflict in the evolution of reproductive isolation. Examination of the Trinidadian guppy (Poecilia reticulata) shows how geographic variation in sexual conflict can mediate the emergence of isolating mechanisms. On the basis of pre-mating behaviour guppy females appear to be winning the battle of the sexes in low risk localities whereas males are apparently ahead in high-predation environments. However, the conclusion that sexual selection (through female choice) is replaced by sexual coercion of females (as a consequence of sneaky mating) in predator rich (and productive) assemblages takes no account of post-copulatory mechanisms. Recent work on sperm competition in guppies suggests coevolution between males and females may also occur in the post-mating, pre-zygotic arena. The potential for the evolution of reproductive isolation at each stage of the mating sequence is assessed.

Animals↗

Ozone exposure triggers the emission of herbivore-induced plant volatiles, but does not disturb tritrophic signalling.

We evaluated the similarities between ozone-induced and mite-induced emission of volatile organic compounds (VOCs) from lima beans, and tested the response of the natural enemies of herbivores to these emissions using trophic system of two-spotted spider mites and predatory mites. The acute ozone-exposure and spider mite-infestation induced the emission of two homoterpenes, (E)-4,8-dimethyl-1,3,7-nonatriene and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, and (Z)-3-hexenyl acetate. Only plants with spider mite-infestation emitted the monoterpene (E)-beta-ocimene. Predatory mites were equally attracted to ozone-exposed and unexposed plants, but discriminated between spider mite-infested and uninfested plants, when both were exposed to ozone. The similarities between ozone and herbivore-induced VOCs suggest that plant defence against phytotoxic ozone and the production of VOCs for attraction of the natural enemies of herbivores may have adaptive coevolution. However, the expected elevated ozone concentrations in future may not disturb tritrophic signalling, unless herbivore-induced VOCs are lost in the process of aerosol formation.

Air Pollutants↗

Rapid evolution of reproductive barriers driven by sexual conflict.

A growing amount of experimental data indicates extremely rapid evolution of traits and proteins related to fertilization in many diverging taxa. These data come from studies of sperm or pollen competition between closely related species, and from molecular studies of fertilization proteins. The positive selection for evolutionary novelty that appears to be acting on fertilization systems seems paradoxical because successful reproduction requires the close matching of female and male traits. It has been suggested that perpetual coevolution between the sexes can result from sexual conflict in mating. Sexual conflict occurs when characteristics that enhance the reproductive success of one sex reduce the fitness of the other sex. Numerous examples of sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating have been discussed in detail. The potential for coevolution due to such conflict has been evaluated experimentally. Here I develop a simple mathematical model describing coevolutionary dynamics of male and female traits involved in reproduction. The model shows that continual change in such traits at a constant speed is expected whenever females (or eggs) experience fitness loss from having too many compatible males (or sperms). The plausibility of runaway coevolution increases with increasing population size. Rapid evolution of reproductive barriers driven by sexual conflict may explain increased speciation rates after colonization of new habitats ('adaptive radiation') and high species richness in resource-rich environments.

Animals↗

Coevolution of genes and languages revisited.

In an earlier paper it was shown that linguistic families of languages spoken by a set of 38 populations associate rather strongly with an evolutionary tree of the same populations derived from genetic data. While the correlation was clearly high, there was no evaluation of statistical significance; no such test was available at the time. This gap has now been filled by adapting to this aim a procedure based on the consistency index, and the level of significance is found to be much stronger than 10(-3). Possible reasons for coevolution of strictly genetic characters and the strictly cultural linguistic system are discussed briefly. Results of this global analysis are compared with those obtained in independent local analysis.

Animals↗

Contributions of domesticated plant studies to our understanding of plant evolution.

BACKGROUND: Plant evolutionary theory has been greatly enriched by studies on crop species. Over the last century, important information has been generated on many aspects of population biology, speciation and polyploid genetics. SCOPE: Searches for quantitative trait loci (QTL) in crop species have uncovered numerous blocks of genes that have dramatic effects on adaptation, particularly during the domestication process. Many of these QTL have epistatic and pleiotropic effects making rapid evolutionary change possible. Most of the pioneering work on the molecular basis of self-incompatibility has been conducted on crop species, along with the sequencing of the phytopathogenic resistance genes (R genes) responsible for the 'gene-to-gene' relations of coevolution observed in host-pathogen relationships. Some of the better examples of co-adaptation and early acting inbreeding depression have also been elucidated in crops. Crop-wild progenitor interactions have provided rich opportunities to study the evolution of novel adaptations subsequent to hybridization. Most crop/wild F1 hybrids have reduced fitness, but in some instances the crop relatives have acquired genes that make them more efficient weeds through crop mimicry. Studies on autopolyploid alfalfa and potato have uncovered the means by which polyploid gametes are formed and have led to hypotheses about how multiallelic interactions are associated with fitness and self-fertility. Research on the cole crops and wheat has discovered that newly formed polyploids can undergo dramatic genome rearrangements that could lead to rapid evolutionary change. CONCLUSIONS: Many more important evolutionary discoveries are on the horizon, now that the whole genome sequence is available of the two major subspecies of rice Oryza sativa ssp. japonica and O. sativa ssp. indica. The rice sequence data can be used to study the origin of genes and gene families, track rates of sequence divergence over time, and provide hints about how genes evolve and generate products with novel biological properties. The rice sequence data has already been mined to show that transposable elements often carry fragments of cellular genes. This type of genome shuffling could play a role in creating novel, reorganized genes with new adaptive properties.

Biological Evolution↗

A model of mass extinction.

In the last few years a number of authors have suggested that evolution may be a so-called self-organized critical phenomenon, and that critical processes might have a significant effect on the dynamics of ecosystems. In particular it has been suggested that mass extinction may arise through a purely biotic mechanism as the result of "coevolutionary avalanches". In this paper we first explore the empirical evidence which has been put forward in favor of this conclusion. The data center principally around the existence of power-law functional forms in the distribution of the sizes of extinction events and other quantities. We then propose a new mathematical model of mass extinction which does not rely on coevolutionary effects and in which extinction is caused entirely by the action of environmental stress on species. In combination with a simple model of species adaption we show that this process can account for all the observed data without the need to invoke coevolution and critical processes. The model also makes some independent predictions, such as the existence of "aftershock" extinctions in the aftermath of large mass extinction events, which should in theory be testable against the fossil record.

Animals↗

Culture in whales and dolphins.

Studies of animal culture have not normally included a consideration of cetaceans. However, with several long-term field studies now maturing, this situation should change. Animal culture is generally studied by either investigating transmission mechanisms experimentally, or observing patterns of behavioural variation in wild populations that cannot be explained by either genetic or environmental factors. Taking this second, ethnographic, approach, there is good evidence for cultural transmission in several cetacean species. However, only the bottlenose dolphin (Tursiops) has been shown experimentally to possess sophisticated social learning abilities, including vocal and motor imitation; other species have not been studied. There is observational evidence for imitation and teaching in killer whales. For cetaceans and other large, wide-ranging animals, excessive reliance on experimental data for evidence of culture is not productive; we favour the ethnographic approach. The complex and stable vocal and behavioural cultures of sympatric groups of killer whales (Orcinus orca) appear to have no parallel outside humans, and represent an independent evolution of cultural faculties. The wide movements of cetaceans, the greater variability of the marine environment over large temporal scales relative to that on land, and the stable matrilineal social groups of some species are potentially important factors in the evolution of cetacean culture. There have been suggestions of gene-culture coevolution in cetaceans, and culture may be implicated in some unusual behavioural and life-history traits of whales and dolphins. We hope to stimulate discussion and research on culture in these animals.

Animals↗

Inter-locus antagonistic coevolution as an engine of speciation: assessment with hemiclonal analysis.

One of Ernst Mayr's legacies is the consensus that the allopatry model is the predominant mode of speciation in most sexually reproducing lineages. In this model, reproductive isolation develops as a pleiotropic byproduct of the genetic divergence that develops among physically isolated populations. Presently, there is no consensus concerning which, if any, evolutionary process is primarily responsible for driving the specific genetic divergence that leads to reproductive isolation. Here, we focus on the hypothesis that inter-locus antagonistic coevolution drives rapid genetic divergence among allopatric populations and thereby acts as an important "engine" of speciation. We assert that only data from studies of experimental evolution, rather than descriptive patterns of molecular evolution, can provide definitive evidence for this hypothesis. We describe and use an experimental approach, called hemiclonal analysis, that can be used in the Drosophila melanogaster laboratory model system to simultaneously screen nearly the entire genome for both standing genetic variation within a population and the net-selection gradient acting on the variation. Hemiclonal analysis has four stages: (i) creation of a laboratory "island population"; (ii) cytogenetic cloning of nearly genome-wide haplotypes to construct hemiclones; (iii) measurement of additive genetic variation among hemiclones; and (iv) measurement of the selection gradient acting on phenotypic variation among hemiclones. We apply hemiclonal analysis to test the hypothesis that there is ongoing antagonistic coevolution between the sexes in the D. melanogaster laboratory model system and then discuss the relevance of this analysis to natural systems.

Animals↗

Evolution of morphological and behavioral ontogenies in females of a highly dimorphic clade of blennioid fishes.

Comparison of ontogenetic trajectories with those inferred for ancestors provides a powerful but underused tool for the study of the evolution of different types of phenotypic characters. This approach was used to study morphological and behavioral evolution of the highly dimorphic chaenopsid genus Coralliozetus (Teleostei: Blennioidei). All sexually dimorphic synapomorphies of Coralliozetus involved evolution in females only; one character evolved via terminal addition (peramorphosis), whereas six evolved via terminal deletion (paedomorphosis). Evolution of the ontogeny of two behavioral characters (microhabitat use and feeding rate), as inferred by focal animal observations of eight species of tube blennies, was also confined to females and conformed to terminal deletion. Both sexes of outgroups and males of all species of Coralliozetus exhibit an ontogenetic shift from the open as juveniles to shelters as adults. However, females of all species of Coralliozetus retain the juvenile behavior of residing in the open. Blennies residing in the open take significantly more feeding bites than conspecifics residing in shelters, consequently, female Coralliozetus retain the high feeding rate of juveniles. Several of the paedomorphic morphological features of Coralliozetus females are plausibly associated with their paedomorphosis in microhabitat use. These include their reduced conspicuousness and reduced robustness compared to conspecific males. In groups such as chaenopsids, which undergo significant ontogenetic changes in microhabitat, paedomorphosis provides a mechanism for rapid coevolution of behavior and morphology. This study, the first to document the evolution of sexual dimorphism via both behavioral and morphological paedomorphosis, demonstrates the unique insights to be gained from a multidimensional analysis of phenotypic evolution.

Animals↗

The evolution of signal form: effects of learned versus inherited recognition.

Organisms can learn by individual experience to recognize relevant stimuli in the environment or they can genetically inherit this ability from their parents. Here, we ask how these two modes of acquisition affect signal evolution, focusing in particular on the exaggeration and cost of signals. We argue first, that faster learning by individual receivers cannot be a driving force for the evolution of exaggerated and costly signals unless signal senders are related or the same receiver and sender meet repeatedly. We argue instead that biases in receivers' recognition mechanisms can promote the evolution of costly exaggeration in signals. We provide support for this hypothesis by simulating coevolution between senders and receivers, using artificial neural networks as a model of receivers' recognition mechanisms. We analyse the joint effects of receiver biases, signal cost and mode of acquisition, investigating the circumstances under which learned recognition gives rise to more exaggerated signals than inherited recognition. We conclude the paper by discussing the relevance of our results to a number of biological scenarios.

Animals↗

The coevolution of parasites with host-acquired immunity and the evolution of sex.

Here I present a deterministic model of the coevolution of parasites with the acquired immunity of their hosts, a system in which coevolutionary oscillations can be maintained. These dynamics can confer an advantage to sexual reproduction within the parasite population, but the effect is not strong enough to outweigh the twofold cost of sex. The advantage arises primarily because sexual reproduction impedes the response to fluctuating epistasis and not because it facilitates the response to directional selection-in fact, sexual reproduction often slows the response to directional selection. Where the cost of sexual reproduction is small, a polymorphism can be maintained between the sexuals and the asexuals. A polymorphism is maintained in which the advantage gained due to recombination is balanced by the cost of sex. At much higher costs of sex, a polymorphism between the asexual and sexual populations can still be maintained if the asexuals do not have a full complement of genotypes available to them, because the asexuals only outcompete those sexuals with which they share the same selected alleles. However, over time we might expect the asexuals to amass the full array of genotypes, thus permanently eliminating sexuals from the population. The sexuals may avoid this fate if the parasite population is finite. Although the model presented here describes the coevolution of parasites with the acquired immune responses of their hosts, it can be compared with other host-parasite models that have more traditionally been used to investigate Red Queen theories of the evolution of sex.

Animals↗

Phylogenetic insights into the evolution of parasitism in hymenoptera.

The Hymenoptera are one of the four megadiverse orders of insects, with over 100000 described species and several times this number still waiting to be described. A major part of this diverse group is formed of large lineages of parasitoid wasps. Some of these lineages have in turn given rise to subgroups that have gone on to diversify into other lifestyles, such as gall-forming on, and pollination of, plants, as well as a broad array of food-collecting behaviors associated with social living in colonies. Thus, the Hymenoptera demonstrate the large evolutionary potential of parasitism as a lifestyle, in contrast to early assertions that parasitism tends to lead to evolutionary 'dead ends' driven by overspecialization. Phylogenetic approaches have already led to a number of important insights into the evolution of parasitism in Hymenoptera. A series of examples are discussed in this review, including the origin of parasitism in the order, the development of koinobiosis in some groups, coevolution with symbiotic viruses, and the evolution in some groups away from parasitism and into such habits as gall formation, pollination of figs, nest building and sociality. The potential for comparative analysis of hymenopteran habits is large, but progress is still in its early stages due to the paucity of available well-supported phylogenies, and the still limited accumulation of basic biological data for many taxa.

Animals↗