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PubMed2001

The influence of a competitor on the geographic mosaic of coevolution between crossbills and lodgepole pine.

The geographic mosaic theory of coevolution posits that the form of selection between interacting species varies across a landscape with coevolution important and active in some locations (i.e., coevolutionary hotspots) but not in others (i.e., coevolutionary coldspots). We tested the hypothesis that the presence of red squirrels (Tamiasciurus hudsonicus) affects the occurrence of coevolution between red crossbills (Loxia curvirostra complex) and Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia) and thereby provides a mechanism giving rise to a geographic mosaic of selection. Red squirrels are the predominant predispersal seed predator and selective agent on lodgepole pine cones. However, in four isolated mountain ranges east and west of the Rocky Mountains, red squirrels are absent and red crossbills are the main predispersal seed predator. These isolated populations of pine have apparently evolved without Tamiasciurus for about 10,000 to 12,000 years. Based on published morphological, genetic, and paleobotanical studies, we infer that cone traits in these isolated populations that show parallel differences from cones in the Rocky Mountains have changed in parallel. We used data on crossbill and conifer cone morphology and feeding preferences and efficiency to detect whether red crossbills and lodgepole pine exhibit reciprocal adaptations, which would imply coevolution. Cone traits that act to deter Tamiasciurus and result in high ratios of cone mass to seed mass were less developed in the isolated populations. Cone traits that act to deter crossbills include larger and thicker scales and perhaps increased overlap between successive scales and were enhanced in the isolated populations. In the larger, isolated mountain ranges crossbills have evolved deeper, shorter, and therefore more decurved bills to exploit these cones. This provides crossbills with higher feeding rates, and the change in bill shape has improved efficiency by reducing the concomitant increases in body mass and daily energy expenditures that would have resulted if only bill size had increased. These parallel adaptations and counter adaptations in red crossbills and lodgepole pine are interpreted as reciprocal adaptations and imply that these crossbills and pine are in coevolutionary arms races where red squirrels are absent (i.e., coevolutionary hotspots) but not where red squirrels are present (i.e., coevolutionary cold-spots).

Animals↗
PubMed2006

Evolution under relaxed sexual conflict in the bulb mite Rhizoglyphus robini.

The experimental evolution under different levels of sexual conflict have been used to demonstrate antagonistic coevolution in muscids, but among other taxa a similar approach has not been employed. Here, we describe the results of 37 generations of evolution under either experimentally enforced monogamy or polygamy in the bulb mite Rhizoglyphus robini. Three replicates were maintained for each treatment. Monogamy makes male and female interests congruent; thus selection is expected to decrease harmfulness of males to their partners. Our results were consistent with this prediction in that females from monogamous lines achieved lower fecundity when housed with males from polygamous lines. Fecundity of polygamous females was not affected by mating system under which their partners evolved, which suggests that they were more resistant to male-induced harm. As predicted by the antagonistic coevolution hypothesis, the decrease in harmfulness of monogamous males was accompanied by a decline in reproductive competitiveness. In contrast, female fecundity and embryonic viability, which were not expected to be correlated with male harmfulness, did not differ between monogamous and polygamous lines. None of the fitness components assayed differed between individuals obtained from crosses between parents from the same line and those obtained from crosses between parents from different lines within the same mating system. This indicates that inbreeding depression did not confound our results. However, interpretation of our results is complicated by the fact that both males and females from monogamous lines evolved smaller body size compared to individuals from polygamous lines. Although a decrease in reproductive performance of males from monogamous lines was still significant when body size was taken into account, we were not able to separate the effects of male body size and mating system in their influence on fecundity of their female partners.

Animals↗
PubMed2006

Evolving physically simulated flying creatures for efficient cruising.

The body-brain coevolution of aerial life forms has not been developed as far as aquatic or terrestrial locomotion in the field of artificial life. We are studying physically simulated 3D flying creatures by evolving both wing shapes and their controllers. A creature's wing is modeled as a number of articulated cylinders, connected by triangular films (patagia). The wing structure and its motor controllers for cruising flight are generated by an evolutionary algorithm within a simulated aerodynamic environment. The most energy-efficient cruising speed and the lift and drag coefficients of each flier are calculated from its morphological characteristics and used in the fitness evaluation. To observe a wide range of creature size, the evolution is run separately for creatures categorized into three species by body weight. The resulting creatures vary in size from pigeons to pterosaurs, with various wing configurations. We discuss the characteristics of shape and motion of the evolved creatures, including flight stability and Strouhal number.

Algorithms↗
PubMed2001

Coincidence, coevolution, or causation? DNA content, cell size, and the C-value enigma.

Variation in DNA content has been largely ignored as a factor in evolution, particularly following the advent of sequence-based approaches to genomic analysis. The significant genome size diversity among organisms (more than 200000-fold among eukaryotes) bears no relationship to organismal complexity and both the origins and reasons for the clearly non-random distribution of this variation remain unclear. Several theories have been proposed to explain this 'C-value enigma' (heretofore known as the 'C-value paradox'), each of which can be described as either a mutation pressure' or 'optimal DNA' theory. Mutation pressure theories consider the large portion of non-coding DNA in eukaryotic genomes as either 'junk' or 'selfish' DNA and are important primarily in considerations of the origin of secondary DNA. Optimal DNA theories differ from mutation pressure theories by emphasizing the strong link between DNA content and cell and nuclear volumes. While mutation pressure theories generally explain this association with cell size as coincidental, the nucleoskeletal theory proposes a coevolutionary interaction between nuclear and cell volume, with DNA content adjusted adaptively following shifts in cell size. Each of these approaches to the C-value enigma is problematic for a variety of reasons and the preponderance of the available evidence instead favours the nucleotypic theory which postulates a causal link between bulk DNA amount and cell volume. Under this view, variation in DNA content is under direct selection via its impacts on cellular and organismal parameters. Until now, no satisfactory mechanism has been presented to explain this nucleotypic effect. However, recent advances in the study of cell cycle regulation suggest a possible 'gene nucleus interaction model' which may account for it. The present article provides a detailed review of the debate surrounding the C-value enigma, the various theories proposed to explain it, and the evidence in favour of a causal connection between DNA content and cell size. In addition, a new model of nucleotypic influence is developed, along with suggestions for further empirical investigation. Finally, some evolutionary implications of genome size diversity are considered, and a broadening of the traditional 'biological hierarchy' is recommended.

Animals↗
PubMed1999

Coevolution and subsite decomposition for the design of resistance-evading HIV-1 protease inhibitors.

Drug resistance sharply limits the effectiveness of human immunodeficiency virus (HIV) protease inhibitors in acquired immunodeficiency syndrome therapy. In previous work, we presented methods for design of resistance-evading inhibitors using a computational coevolution technique. Here, we report subsite decomposition experiments that examine the relative importance and roles of each subsite in HIV protease, and the constraints on robust inhibitor design that are imposed by possible resistance mutations in each subsite. The results identify several structural features of robust resistance-evading inhibitors for use in drug design, and show their basis in the constraints imposed by the range of allowable mutation in the protease. In particular, the results identify the P3 and P3' sites as being particularly sensitive to protease mutation: inhibitors designed to fill the S3 and S3' sites of the wild-type protease will be susceptible to viral resistance, but inhibitors with side-chains smaller than a phenylalanine residue at P3 and P3', preferably medium-sized amino acids in the range from valine to leucine and isoleucine residues, will be more robust in the face of protease resistance mutation.

Computational Biology↗
PubMed2001

Did dinosaurs invent flowers? Dinosaur-angiosperm coevolution revisited.

Angiosperms first appeared in northern Gondwana during the Early Cretaceous, approximately 135 million years ago. Several authors have hypothesised that the origin of angiosperms, and the tempo and pattern of their subsequent radiation, was mediated by changes in the browsing behaviour of large herbivorous dinosaurs (sauropods and ornithischians). Moreover, the taxonomic and ecological radiation of angiosperms has been associated with the evolution of complex jaw mechanisms among ornithischian dinosaurs. Here, we review critically the evidence for dinosaur-angiosperm interactions during the Cretaceous Period, providing explicit spatiotemporal comparisons between evolutionary and palaeoecological events in both the dinosaur and angiosperm fossil records and an assessment of the direct and indirect evidence for dinosaur diets. We conclude that there are no strong spatiotemporal correlations in support of the hypothesis that dinosaurs were causative agents in the origin of angiosperms; however, dinosaur-angiosperm interactions in the Late Cretaceous may have resulted in some coevolutionary interactions, although direct evidence of such interactions is scanty at present. It is likely that other animal groups (insects, arboreal mammals) had a greater impact on angiosperm diversity during the Cretaceous than herbivorous dinosaurs. Elevated levels of atmospheric CO2 might have played a critical role in the initial stages of the angiosperm radiation.

Animals↗
PubMed1998

Coevolutionary chase in two-species systems with applications to mimicry.

We study a general dynamical model describing coevolution of two haploid populations with two alleles at a single locus under weak linear symmetric frequency-dependent selection. A novel and more realistic element of our modeling approach is that both species are allowed to evolve. We analyse conditions for "evolutionary chase" between two phenotypically similar species in which one species evolves to decrease its resemblance with the other species while this other species evolves to increase its resemblance with the first species. We apply our results to a series of simple population genetics models describing classical Müllerian and Batesian mimicries as well as intermediate cases. We show that one of the most important factors influencing the plausibility of non-equilibrium dynamics in systems of mimicry is the relationship between the strength of between-species and within-species interactions. This indicates that this relationship should be the focus of both experimental and theoretical work. Our results suggest that systematic studies of frequencies of different mimicry morphs through time may be very useful.

Animals↗
PubMed1998

Host-mediated site segregation of ectoparasites: an individual-based simulation study.

Site segregation of coexisting ectoparasite species may result either from a direct interaction such as resource competition between them or from a host-mediated interaction. Here we present an individual-based model for the coevolution of 1 host and 2 parasite species to study this latter hypothesis. Parasite species are generalists at the start of the simulation and develop site specificities under the following assumptions. Parasite populations are not subject to resource limitations but are limited directly by host defense as predation. Hosts have 2 sites that need different defensive abilities to reduce their parasite burden. Parasites need to exhibit different evasive abilities to survive on different sites. Host grooming selects parasites for an increasing capability for evasion, whereas parasites select hosts for an increasing efficiency of grooming. Two trade-offs are incorporated into the model: one between host defensive abilities on the 2 sites, and another between parasite evasive abilities on the 2 sites. We conclude that, under these assumptions, the optimization of host defense and parasite evasion strategies may select ectoparasites for site segregation and this may stabilize the coexistence of parasite species.

Animals↗
PubMed2005

Discrete hierarchical organization of social group sizes.

The 'social brain hypothesis' for the evolution of large brains in primates has led to evidence for the coevolution of neocortical size and social group sizes, suggesting that there is a cognitive constraint on group size that depends, in some way, on the volume of neural material available for processing and synthesizing information on social relationships. More recently, work on both human and non-human primates has suggested that social groups are often hierarchically structured. We combine data on human grouping patterns in a comprehensive and systematic study. Using fractal analysis, we identify, with high statistical confidence, a discrete hierarchy of group sizes with a preferred scaling ratio close to three: rather than a single or a continuous spectrum of group sizes, humans spontaneously form groups of preferred sizes organized in a geometrical series approximating 3-5, 9-15, 30-45, etc. Such discrete scale invariance could be related to that identified in signatures of herding behaviour in financial markets and might reflect a hierarchical processing of social nearness by human brains.

Anthropology, Cultural↗
PubMed2002

Origin of a complex key innovation in an obligate insect-plant mutualism.

Evolutionary key innovations give organisms access to new ecological resources and cause rapid, sometimes spectacular adaptive radiation. The well known obligate pollination mutualism between yuccas and yucca moths is a major model system for studies of coevolution, and it relies on the key innovation in the moths of complex tentacles used for pollen collecting and active pollination. These structures lack apparent homology in other insects, making them a rare example of a novel limb. We performed anatomical and behavioral studies to determine their origin and found evidence of a remarkably simple mechanism. Morphological analyses of the tentacles and adjacent mouthparts in pollinators and closely related taxa showed that the tentacle appears abruptly in female pollinating yucca moths. Several morphological synapomorphies between the galeae, which constitute the characteristic lepidopteran proboscis, and the tentacle suggest that the tentacle evolved quickly through expression of the genetic template for the galea at an apical growth bud on the first segment of the maxillary palp. Behavioral data indicate that tentacle and proboscis movements are controlled by a shared hydraulic extension mechanism, thus no new mechanism was needed for tentacle function. Known developmental paths from other insects can explain the origin of this sex-specific key innovation in a few steps.

Animals↗
PubMed1989

Genomic organization and sequences of immunoglobulin light chain genes in a primitive vertebrate suggest coevolution of immunoglobulin gene organization.

The genomic organization and sequence of immunoglobulin light chain genes in Heterodontus francisci (horned shark), a phylogenetically primitive vertebrate, have been characterized. Light chain variable (VL) and joining (JI) segments are separated by 380 nucleotides and together with the single constant region exon (CI), occupy less than 2.7 kb, the closest linkage described thus far for a rearranging gene system. The VL segment is flanked by a characteristic recombination signal sequence possessing a 12 nucleotide spacer; the recombination signal sequence flanking the JL segment is 23 nucleotides. The VL genes, unlike heavy chain genes, possess a typical upstream regulatory octamer as well as conserved enhancer core sequences in the intervening sequence separating JL and CL. Restriction mapping and genomic Southern blotting are consistent with the presence of multiple light chain gene clusters. There appear to be considerably fewer light than heavy chain genes. Heavy and light chain clusters show no evidence of genomic linkage using field inversion gel electrophoresis. The findings of major differences in the organization and functional rearrangement properties of immunoglobulin genes in species representing different levels of vertebrate evolution, but consistent similarity in the organization of heavy and light chain genes within a species, suggests that these systems may be coevolving.

Amino Acid Sequence↗
PubMedDate not supplied

[Specificity of host-parasite relations between arthropods and terrestrial vertebrates].

Specificity of partners in host-parasite system is one of its main characteristics. Unfortunately this term has different senses in scientific literature. In everyday practice one judges an extent of host specificity of a parasite mainly by indices of its occurrence and abundance on different host species. An occurrence of parasites in nature reflects general result of complex eco-physiological interrelationships between partners in hostparasite system. Specificity of parasites in a choice of hosts may depend on a belonging of the latter to certain taxa (phylogenetic specificity), or on biotic and abiotic factors (ecological specificity). In arthropods, the phylogentic specificity and coevolution are characteristic to a greater extent for permanent hosts (lice, Mallophaga, cheyletoid and feather mites). A coevolutionaryphylogenesis is disturbed by transfers of parasites onto new hosts, by different rates of speciation in filial lines or by an extinction of several parasite taxa. In temporary parasites different forms of ecological specificity are prevalent. A host specificity is expressed to the lesser extent in mosquitoes, horseflies and in other blood-sucking Diptera. In temporary parasites with a long-term feeding (ticks) coevolutionary sequences are relatively rare, because this parasites had to adapt not only to a life on host, but also to a lesser stable environment. In some nest-burrow bloodsuckers (fleas, gamasid mites and argasid ticks) the ecological specificity is shown no by their relations with certain host species, but by an associations with habitats occupied by hosts (burrow, nests, caves). In relation with a high dynamics of host-parasite system, a specificity of its partners is comparative and it is kept up only under specific ecological conditions.

Animals↗
PubMed2002

New perspectives on taste and primate evolution: the dichotomy in gustatory coding for perception of beneficent versus noxious substances as supported by correlations among human thresholds.

In various environments where primates are presently observed, as well as in forests and savannas which have been inhabited by australopithecines and early hominids, there are (or there have been presumably) categories of substances eliciting taste signals associated with stereotyped responses. Such is the case for various soluble sugars of fruits and nectars, attracting consumers, and for several plant compounds in which bitter or strongly astringent properties have a repulsive effect. The occurrence of such classes of tasty substances among natural products appears to be related to the evolutionary trends that shaped primate sensory perception (for detecting either beneficent or potentially noxious substances) in the context of a long history of coevolution between animals and plants. Here, we present original psychophysical data on humans (412 individuals aged 17-59 years) as an analogy with which to test recent evidence from electrophysiology in nonhuman primates (Hellekant et al. [1997] J. Neurophysiol. 77:978-993; Danilova et al. [1998] Ann. N.Y. Acad. Sci. 855:160-164) that taste fibers can be grouped into clusters of "best-responding fibers" with two more specific clusters, one for sugars and one for quinine and tannins. The collinearity found between human taste responses (recognition thresholds) for fructose and sucrose, as well as for quinine and tannins, is presented and discussed as another evidence of the two-direction evolutionary trend determining taste sensitivity. Salt perception appears to be totally independent of these trends. Accordingly, the appreciation of a salty taste seems to be a recent culturally learned response, and not a primary taste perception. The very existence of primary tastes is discussed in the context of evolutionary trends, past and present.

Adolescent↗
PubMed1989

Coevolution of the major histocompatibility complex and the t-complex in the mouse. I. Generation and maintenance of high complementarity associations.

A quantitative model is developed to explore the effects of prezygotic and postzygotic incompatibility on the origin and maintenance of associations between the major histocompatibility complex (MHC) and the t-complex in the mouse. Incompatibility is represented by a reduction in the rate of conception or gestation of offspring derived from sperm bearing MHC antigens in common with the mother. Incompatibility encourages the evolution of associations from a state of complete independence between the two complexes by promoting the invasion of all novel antigens, including those that exhibit associations with the t-complex. Incompatibility can modify the relative numbers of antigens associated with each haplotype by actively promoting the exclusion or invasion of recombinants that bear formerly +-specific or t-specific antigens on the alternative haplotype. The results of the analysis indicate that the state of complete independence between the MHC and the t-complex is not preserved over evolutionary time in the presence of incompatibility. Further, the expression of incompatibility maintains fully associated states that include a single antigen associated with the t-haplotype and up to three to five antigens associated with the +-haplotype within a single population.

Animals↗
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↗
PubMed2006

Rapidly evolving zona pellucida domain proteins are a major component of the vitelline envelope of abalone eggs.

Proteins harboring a zona pellucida (ZP) domain are prominent components of vertebrate egg coats. Although less well characterized, the egg coat of the non-vertebrate marine gastropod abalone (Haliotis spp.) is also known to contain a ZP domain protein, raising the possibility of a common molecular basis of metazoan egg coat structures. Egg coat proteins from vertebrate as well as non-vertebrate taxa have been shown to evolve under positive selection. Studied most extensively in the abalone system, coevolution between adaptively diverging egg coat and sperm proteins may contribute to the rapid development of reproductive isolation. Thus, identifying the pattern of evolution among egg coat proteins is important in understanding the role these genes may play in the speciation process. The purpose of the present study is to characterize the constituent proteins of the egg coat [vitelline envelope (VE)] of abalone eggs and to provide preliminary evidence regarding how selection has acted on VE proteins during abalone evolution. A proteomic approach is used to match tandem mass spectra of peptides from purified VE proteins with abalone ovary EST sequences, identifying 9 of 10 ZP domain proteins as components of the VE. Maximum likelihood models of codon evolution suggest positive selection has acted among a subset of amino acids for 6 of these genes. This work provides further evidence of the prominence of ZP proteins as constituents of the egg coat, as well as the prominent role of positive selection in diversification of these reproductive proteins.

Adaptation, Biological↗
PubMed1995

Evidence of the coevolution of a snake toxin and its endogenous antitoxin cloning, sequence and expression of a serum albumin cDNA of the Chinese cobra.

A full-length cDNA of the serum albumin (CSA) of the cobra (Naja naja kaouthia) was cloned from a lambda gt 11 library. It encodes a mature protein of 614 amino-acid residues homologous to the precursor of mammalian serum albumins. The 1 degree and 2 degrees structures of the CSA resemble those of the human variety. The putative toxin binding sites are mainly located in the subdomains IIA and IIIA. The relation between structural homology and function of the serum albumins (SA) is discussed. An analysis of their evolutionary tree revealed that anti-toxicity arose by < 90 amino-acid exchanges. The rate of substitution is much higher in the SA than in cytochrome C, which probably reflects the difference in evolutionary driving forces. The evolutionary period of the SA (6.7 +/- 0.1 M.Y.) significantly exceeds that of hemoglobin (5.8 M.Y.). Eight tripeptides in the nicotinic acetylcholine receptor (ACR), all flanking the putative toxin binding site, are also found in the CSA where they join to form 1 octa-, 1 penta- and 4 tripeptides, thus indicating the concerted evolution of two functionally linked proteins: toxin and antitoxin (CSA).

Amino Acid Sequence↗
PubMedDate not supplied

Coevolution in bicoid-dependent promoters and the inception of regulatory incompatibilities among species of higher Diptera.

To what extent and in what way do gene promoters and their transacting regulatory proteins coevolve? In this and in earlier publications we show that the Bicoid-dependent promoters of the segmentation genes hunchback and tailless in species of higher Diptera (Drosophila, Musca, Calliphora, and Lucilia) are different with respect to the copy number, spacing, sequence, and orientation of Bicoid binding sites. At the same time there are significant amino acid differences in the Bicoid homeodomain. To test these interspecific differences, we used a series of functional assays, starting with the analysis of Bicoid binding affinities of individual sites, through to transgene rescue experiments, to compare within-species with between-species mixtures of Bicoid homeodomains and hunchback or tailless promoters. We observed that components taken from different species interact with less efficiency compared with those taken from within the same species. Our interpretation is that such interspecific incompatibilities are a consequence of interactive genetic elements coevolving one with another, hence maintaining functional compatibility within each species. At the same time such a process allows differences to accumulate between species regarding the precise molecular basis whereby the common function is effected.

Animals↗