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PubMed2003

Biochemical and immunological adaptation in schistosome parasitism.

The objective of this review is to clarify aspects of immunological and biochemical adaptations of schistosomes to their intermediate and final mammalian hosts. Adaptations to the mammalian hosts are traced in relation to cercarial penetration of mammalian skin, glucose transport and metabolism. The unusual ability of schistosome surface membrane to escape immune recognition and damage are reviewed. Moreover, the behavioural changes induced in the intermediate hosts by schistosomes are considered. The evolutionary adaptation to molluscan hosts aims to increase the probability of transmission of the parasite into its mammalian host. This review inspires more hope for further design of anti-schistosome drugs through disturbing aspects of biochemical and immunological adaptations in schistosome parasitism.

Adaptation, Physiological↗

PubMed1999

Pleiotropic effects of adaptation to a single carbon source for growth on alternative substrates

It is frequently assumed that populations of genetically modified microorganisms will perform their intended function and then disappear from the environment due to inherent fitness disadvantages resulting from their genetic alteration. However, modified organisms used in bioremediation can be expected to adapt evolutionarily to growth on the anthropogenic substrate that they are intended to degrade. If such adaptation results in improved competitiveness for alternative, naturally occurring substrates, then this will increase the likelihood that the modified organisms will persist in the environment. In this study, bacteria capable of degrading the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) were used to test the effects of evolutionary adaptation to one substrate on fitness during growth on an alternative substrate. Twenty lineages of bacteria were allowed to evolve under abundant resource conditions on either 2,4-D or succinate as their sole carbon source. The competitiveness of each evolved line was then measured relative to that of its ancestor for growth on both substrates. Only three derived lines showed a clear drop in fitness on the alternative substrate after demonstrable adaptation to their selective substrate, while five derived lines showed significant simultaneous increases in fitness on both their selective and alternative substrates. These data demonstrate that adaptation to an anthropogenic substrate can pleiotropically increase competitiveness for an alternative natural substrate and therefore increase the likelihood that a genetically modified organism will persist in the environment.

Journal Article↗

PubMed1994

Landscapes: complex optimization problems and biopolymer structures.

The evolution of RNA molecules in replication assays, viroids and RNA viruses can be viewed as an adaptation process on a 'fitness' landscape. The dynamics of evolution is hence tightly linked to the structure of the underlying landscape. Global features of landscapes can be described by statistical measures like number of optima, lengths of walks and correlation functions. The evolution of a quasispecies on such landscapes exhibits three dynamical regimes depending on the replication fidelity: Above the "localization threshold" the population is centered around a (local) optimum. Between localization and "dispersion threshold" the population is still centered around a consensus sequence, which, however, changes in time. For very large mutation rates the population spreads in sequence space like a gas. The critical mutation rates separating the three domains depend strongly on characteristics properties of the fitness landscapes. Statistical characteristics of RNA landscapes are accessible by mathematical analysis and computer calculations on the level of secondary structures: these RNA landscapes belong to the same class as well known optimization problems and simple spin glass models. The notion of a landscape is extended to combinatory maps, thereby allowing for a direct statistical investigation of the sequence structure relationships of RNA at the level of secondary structures. Frequencies of structures are highly non-uniform: we find relatively few common and many rare ones, as expressed by a generalized form of Zipf's law. Using an algorithm for inverse folding we show that sequences sharing the same structure are distributed randomly over sequence space. Together with calculations of structure correlations and a survey of neutral mutations this provides convincing evidence that RNA landscapes are as simple as they could possibly be for evolutionary adaptation: Any desired secondary structure can be found close to an arbitrary initial sequence and at the same time almost all bases can be substituted sequentially without ever changing the shape of the molecule. Consequences of these results for evolutionary optimization, the early stages of life, and molecular biotechnology are discussed.

Adaptation, Biological↗

PubMed1999

Zoite migration during infection: parasite adaptation to host defences.

The apicomplexan parasite Eimeria tenella has evolved a number of strategies for migration into different compartments of the intestinal tissue during its life cycle. These migration events are associated intricately with pathogenesis and are currently of great interest to coccidiologists. Using evidence from in vivo studies and recent work on the dynamics of gut cell turnover, Peter Daszak suggests that E. tenella zoite migration might be viewed as parasite evolutionary adaptation to evade the host innate immune responses (resistance) and deal with the complex, dynamic nature of gut epithelial tissue.

Adaptation, Physiological↗

PubMed2002

Experimental social evolution with Myxococcus xanthus.

Genetically-based social behaviors are subject to evolutionary change in response to natural selection. Numerous microbial systems provide not only the opportunity to understand the genetic mechanisms underlying specific social interactions, but also to observe evolutionary changes in sociality over short time periods. Here we summarize experiments in which behaviors of the social bacterium Myxococcus xanthus changed extensively during evolutionary adaptation to two relatively asocial laboratory environments. M. xanthus moves cooperatively, exhibits cooperative multicellular development upon starvation and also appears to prey cooperatively on other bacteria. Replicate populations of M. xanthus were evolved in both structured (agar plate) and unstructured (liquid) environments that contained abundant resources. The importance of social cooperation for evolutionary fitness in these habitats was limited by the absence of positive selection for starvation-induced spore production or predatory efficiency. Evolved populations showed major losses in all measured categories of social proficiency- motility, predation, fruiting ability, and sporulation. Moreover, several evolved genotypes were observed to exploit the social behavior of their ancestral parent when mixed together during the developmental process. These experiments that resulted in both socially defective and socially exploitative genotypes demonstrate the power of laboratory selection experiments for studying social evolution at the microbial level. Results from additional selection experiments that place positive selection pressure on social phenotypes can be integrated with direct study of natural populations to increase our understanding of principles that underlie the evolution of microbial social behavior.

Biological Evolution↗

PubMed2000

Complete genome sequence of Pseudomonas aeruginosa PAO1, an opportunistic pathogen.

Pseudomonas aeruginosa is a ubiquitous environmental bacterium that is one of the top three causes of opportunistic human infections. A major factor in its prominence as a pathogen is its intrinsic resistance to antibiotics and disinfectants. Here we report the complete sequence of P. aeruginosa strain PAO1. At 6.3 million base pairs, this is the largest bacterial genome sequenced, and the sequence provides insights into the basis of the versatility and intrinsic drug resistance of P. aeruginosa. Consistent with its larger genome size and environmental adaptability, P. aeruginosa contains the highest proportion of regulatory genes observed for a bacterial genome and a large number of genes involved in the catabolism, transport and efflux of organic compounds as well as four potential chemotaxis systems. We propose that the size and complexity of the P. aeruginosa genome reflect an evolutionary adaptation permitting it to thrive in diverse environments and resist the effects of a variety of antimicrobial substances.

Bacterial Proteins↗

PubMedDate not supplied

[From pseudopregnancy to anorexia nervosa].

Translated in the primeval environment where humanization evolved during millions of years (man's environment of evolutionary adaptation, according to Bowlby), the characteristic behaviours of anorectics and bulimics do not look unfavourable but on the contrary adaptive, helping to the survival of the group or kinship (hyperactivity, altruistic feeding, etc.). Analogies, indeed homologies, exist in many animal species, distant or closely related to us (social insects, birds, mammals including primates) observed in nature. It concerns altruistic behaviours described among individuals, for the most part females, referred to as allomothers (aunts) or helpers (co-operative breeding) in ethological terms. From this evolutionary perspective, a biological genetic basis would exist in anorexia and bulimia, as a component of a phylogenetic inheritance of the K-selection strategy of reproduction. At the present time, anorexia would be a pathological extreme of this strategy, whereas pseudocyesis would be, on the contrary, one of the r-selection. Diverse and varying sociocultural and demographic conditions prevailing in modern world would revive either of these phylogenetic programs of reproductive strategies, leading as the case may be, to adaptive or pathological reproductive or helping behaviours.

Altruism↗

PubMed1982

Is obesity an advantageous adaptation?

It is undisputed that modern man is becoming fatter and the extreme expression of increased adiposity 'simple' obesity is becoming more common. Tanner & Whitehouse for example reported that average skinfold thickness in British school children increased by one standard deviation over a 25-year period. What are unclear are the main reasons for this change. In this 'Viewpoint' I will examine--I hope not too contentiously--evidence that this increased level of human adiposity associated with 'Westernisation' reflects an evolutionary adaptation to 'modern' food, particularly the refined carbohydrates, and is not simply a metabolic or behavioural ' disorder' as is commonly assumed. Some 'treatments', including some perhaps based on behavioural assumptions, have been described by Hirsch as equivalent to 'beating the insane to keep them quiet.

Adaptation, Physiological↗

PubMed2006

Slanted joint axes of the stick insect antenna: an adaptation to tactile acuity.

Like many flightless, obligatory walking insects, the stick insect Carausius morosus makes intensive use of active antennal movements for tactile near range exploration and orientation. The antennal joints of C. morosus have a peculiar oblique and non-orthogonal joint axis arrangement. Moreover, this arrangement is known to differ from that in crickets (Ensifera), locusts (Caelifera) and cockroaches (Blattodea), all of which have an orthogonal joint axis arrangement. Our hypothesis was that the situation found in C. morosus represents an important evolutionary trait of the order of stick and leaf insects (Phasmatodea). If this was true, it should be common to other species of the Phasmatodea. The objective of this comparative study was to resolve this question. We have measured the joint axis orientation of the head-scape and scape-pedicel joints along with other parameters that affect the tactile efficiency of the antenna. The obtained result was a complete kinematic description of the antenna. This was used to determine the size and location of kinematic out-of-reach zones, which are indicators of tactile acuity. We show that the oblique and non-orthogonal arrangement is common to eight species from six sub-families indicating that it is a synapomorphic character of the Euphasmatodea. This character can improve tactile acuity compared to the situation in crickets, locusts and cockroaches. Finally, because molecular data of a recent study indicate that the Phasmatodea may have evolved as flightless, obligatory walkers, we argue that the antennal joint axis arrangement of the Euphasmatodea reflects an evolutionary adaptation to tactile near range exploration during terrestrial locomotion.

Animals↗

PubMed2005

The evolution of flea-borne transmission in Yersinia pestis.

Transmission by fleabite is a recent evolutionary adaptation that distinguishes Yersinia pestis, the agent of plague, from Yersinia pseudotuberculosis and all other enteric bacteria. The very close genetic relationship between Y. pestis and Y. pseudotuberculosis indicates that just a few discrete genetic changes were sufficient to give rise to flea-borne transmission. Y. pestis exhibits a distinct infection phenotype in its flea vector, and a transmissible infection depends on genes that are specifically required in the flea, but not the mammal. Transmission factors identified to date suggest that the rapid evolutionary transition of Y. pestis to flea-borne transmission within the last 1,500 to 20,000 years involved at least three steps: acquisition of the two Y. pestis-specific plasmids by horizontal gene transfer; and recruitment of endogenous chromosomal genes for new functions. Perhaps reflective of the recent adaptation, transmission of Y. pestis by fleas is inefficient, and this likely imposed selective pressure favoring the evolution of increased virulence in this pathogen.

Animals↗

PubMed1988

Natural taxonomy of collagen based on amino acid composition.

Hierarchical cluster analysis and principal components have been used to provide a more detailed separation of the collagens into natural taxonomic groupings than previously obtained. These groups strongly reflect the evolutionary development of collagen. The first component separates land- from sea-based animals, primarily based on the hydroxylation of lysine and proline, indicating that control of hydroxylation, a post-translational event, has exerted a dominant influence during evolutionary adaptation. The power of the technique is illustrated by the ability to partially separate the evolutionarily closely related main homothermic species. Furthermore, the genetically different fibrous collagens, Types I and III, are well separated from basement membrane Type IV collagen and the filamentous collagens. The technique could, therefore, in addition to providing a taxonomic grouping, classify any new collagen and provide clues to its evolutionary development.

Amino Acids↗

PubMed1993

Defence and safety: their function in social behaviour and psychopathology.

This paper suggests that our intuitive use and understanding of the concepts defence and safety can be opened up to more systematic study and theory. This may provide a powerful framework for biopsychosocial approaches in clinical psychology. Defence and safety can be seen as two fundamental, evolutionary adaptive, information-organizing systems. The operation of these two systems has major effects on biological patterns, social behaviour, relationships and the maturation of self-constructs. It is suggested that many forms of psychopathology represent the activation of evolved, defensive strategies. This paper explores the organization and operation of these two systems and attempts to integrate data from neuropsychological work with ideas from evolutionary theory and social psychology on the effects of threat sensitivity and defensiveness, and safety. It is suggested that interpersonal threats are the most common sources of human defensive behaviour and these are often about separation-rejection or power and subordination. In the latter part of the paper discussion will be on the way people try to create safe environments by putting others down, or by submitting to more powerful others.

Defense Mechanisms↗

PubMed2003

Competition and coexistence: exploring mechanisms that restrict and maintain diversity within mutualist guilds.

Mutualistic interactions are diverse and widespread and often involve multispecies guilds of mutualists competing for access to one or more partner species. Despite the ubiquity of these interactions, we know little about the dynamics of competition and coexistence within these guilds or how interactions between mutualists and their shared resource (the partner species) may influence these dynamics. In this article, we review the evidence for interspecific competition for partners within mutualist guilds in both plant-pollinator and ant-myrmecophyte systems. We then review evidence for the operation of different coexistence mechanisms within these guilds and discuss how the dynamics of competition and coexistence may be uniquely shaped by multispecies mutualist interactions. In particular, we note that adaptive and plastic responses by mutualists to variation in partner quality are likely to play an important role in determining these dynamics. We summarize by considering the ecological conditions that are likely to restrict or promote species coexistence within mutualist guilds. We suggest that these guilds may provide powerful model systems for exploring multiple mechanisms of species coexistence, and we discuss how these mechanisms may be modified by evolutionary adaptation.

Adaptation, Biological↗

PubMed1997

Localized frameshift mutation generates selective, high-frequency phase variation of a surface lipoprotein encoded by a mycoplasma ABC transporter operon.

The wall-less mycoplasmas have revealed unusual microbial strategies for adaptive variation of antigenic membrane proteins exposed during their surface colonization of host cells. In particular, high-frequency mutations affecting the expression of selected surface lipoproteins have been increasingly documented for this group of organisms. A novel manifestation of mutational phase variation is shown here to occur in Mycoplasma fermentans, a chronic human infectious agent and possible AIDS-associated pathogen. A putative ABC type transport operon encoding four gene products is identified. The 3' distal gene encoding P78, a known surface-exposed antigen and the proposed substrate-binding lipoprotein of the transporter, is subject to localized hypermutation in a short homopolymeric tract of adenine residues located in the N-terminal coding region of the mature product. High-frequency, reversible insertion/deletion frameshift mutations lead to selective phase variation in P78 expression, whereas the putative nucleotide-binding protein, P63, encoded by the most 5' gene of the operon, is continually expressed. Mutation-based phase variation in specific surface-exposed microbial transporter components may provide an adaptive advantage for immune evasion, while continued expression of other elements of the same transporter may preserve essential metabolic functions and confer alternative substrate specificity. These features could be critical in mycoplasmas, where limitations in both transcriptional regulators and transport systems may prevail. This study also documents that P63 contains an uncharacteristic hydrophobic sequence between predicted nucleotide binding motifs and displays an amphiphilic character in detergent fractionation. Both features are consistent with an evolutionary adaptation favoring integral association of this putative energy-transducing component with the single mycoplasma membrane.

ATP-Binding Cassette Transporters↗

PubMed2000

Risk-taking restraints in a bird with reduced egg-hatching success.

Risk taking, as is any other phenotypic and/or behavioural trait, is determined by proximate constraints related to time or resource availability and by evolutionary adaptive restraints related to the differences in the costs of risk taking and its benefits in terms of fitness. Because risk taking is influenced by many confounding variables related to experimental design, environment, parents and offspring, few field studies have been reported which unambiguously separate the effects of restraints from those of constraints. We compared parental risk taking in blue tits (Parus caeruleus) during brood defence towards a nest predator in broods with experimentally reduced and natural egg-hatching success leaving the original number of eggs in the nest. The experimentally reduced broods had more time or resources available and lower risk-taking benefits compared to the control broods. 'Constraint' would predict more risk taking in broods having experimentally reduced egg-hatching success, whereas 'restraint' would predict the opposite effect with more risk taking in broods with natural egg-hatching success. We report, to our knowledge, the first field study experimentally demonstrating a brood defence restraint in response to reduced egg-hatching success. This demonstration was only possible after controlling for more than 20 potential confounding variables showing once more how complicated it is to separate proximate from evolutionary levels of analyses in natural populations.

Adaptation, Physiological↗

PubMed1992

Evolution of feeding niches in New World monkeys.

The adaptive radiation of modern New World monkeys unfolded as the major lineages diversified within different dietary-adaptive zones predicated upon a fundamentally frugivorous habit. The broad outlines of this pattern can be seen in the fossil record, beginning in the early Miocene. Cebids are obligate frugivorous predators. The smallest forms (Cebuella, Callithrix) are specialized exudativores, and the largest (cebines) are seasonally flexible omnivores, feeding particularly on insects (Saimiri) or "hard" foods, such as pith and palm nuts (Cebus), when resources are scarce. The smaller-bodied atelids (Callicebus, Aotus) may use insects or leaves opportunistically, but pitheciins (saki-uakaris) specialize on seeds as their major protein source. The larger atelines (Alouatta, Brachyteles) depend on leaves or on ripe fruit (Ateles). Locomotion, body size, and dietary adaptations are linked: claws and small body size opened the canopy-subcanopy niche to callitrichines; climbing and hanging, the fine-branch setting to the atelines; large size and strength, semiprehensile tails, and grasping thumbs, the extractive insectivory of Cebus; deliberate quadrupedalism, the energy-saving transport of folivorous Alouatta. Body size increases and decreases occurred often and in parallel within guilds and lineages. Conventional dietary categories, particularly frugivory, are inadequate for organizing the behavioral and anatomical evidence pertinent to evolutionary adaptation. Related models of morphological evolution based on feeding frequencies tend to obfuscate the selective importance of "critical functions," responses to the biomechanically challenging components of diet that may be determined by a numerically small, or seasonal, dietary fraction. For fossils, body size is an unreliable indicator of diet in the absence of detailed morphological information. More attention needs to be given to developing techniques for identifying and quantifying mechanically significant aspects of dental form, the physical properties of primate foods, their mode of access, and the cycles of availability and nutritional value.

Adaptation, Physiological↗

PubMed2005

Lineage-specific decay of folate biosynthesis genes suggests ongoing host adaptation in phytoplasmas.

Phytoplasmas are nonculturable cell wall-less, obligate intracellular pathogens of plants and insect vectors. In their descent from walled bacterial ancestors, phytoplasmas underwent massive genome reduction, resulting in some of the smallest cellular genomes known in nonsymbiotic bacteria. While requirements for in vitro culture of phytoplasmas remain unknown, two opposing reports have appeared concerning genes encoding the ability of phytoplasmas to synthesize folates de novo. One study found pseudogene homologs of folP and folK, obviating folate synthesis in "Candidatus Phytoplasma asteris"-related strain CPh, whereas, a separate study found intact genes encoding a complete folate biosynthesis pathway in "Ca. Phytoplasma asteris"-related strain OY. To resolve the apparent conflict, we hypothesized that evolutionary adaptation to the availability of folate and/or other metabolites in host cells is an ongoing process in the phytoplasma clade that is reflected in part by differences among phytoplasmas in the status of genes of the folate biosynthesis pathway. By studying folP and folK loci in 11 closely related phytoplasmas, we determined that these essential folate biosynthesis genes are intact in some phytoplasmas but are deteriorating in closely related strains. We suggest that the status of the folate biosynthesis pathway and the course of gene decay are lineage-specific, predicting the eventual, lineage-related loss of recognizable folP and folK homologs in phytoplasma genomes.

Adaptation, Physiological↗

PubMed2001

Hydrogenosomes: convergent adaptations of mitochondria to anaerobic environments.

Hydrogenosomes are membrane-bound organelles that compartmentalise the final steps of energy metabolism in a number of anaerobic eukaryotes. They produce hydrogen and ATP. Here we will review the data, which are relevant for the questions: how did the hydrogenosomes originate, and what was their ancestor? Notably, there is strong evidence that hydrogenosomes evolved several times as adaptations to anaerobic environments. Most likely, hydrogenosomes and mitochondria share a common ancestor, but an unequivocal proof for this hypothesis is difficult because hydrogenosomes lack an organelle genome - with one remarkable exception (Nyctotherus ovalis). In particular, the diversity of extant hydrogenosomes hampers a straightforward analysis of their origins. Nevertheless, it is conceivable to postulate that the common ancestor of mitochondria and hydrogenosomes was a facultative anaerobic organelle that participated in the early radiation of unicellular eukaryotes. Consequently, it is reasonable to assume that both, hydrogenosomes and mitochondria are evolutionary adaptations to anaerobic or aerobic environments, respectively.

Journal Article↗