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PubMed2006

Can random mutation mimic design?: a guided inquiry laboratory for undergraduate students.

Complex biological structures, such as the human eye, have been interpreted as evidence for a creator for over three centuries. This raises the question of whether random mutation can create such adaptations. In this article, we present an inquiry-based laboratory experiment that explores this question using paper airplanes as a model organism. The main task for students in this investigation is to figure out how to simulate paper airplane evolution (including reproduction, inheritance, mutation, and selection). In addition, the lab requires students to practice analytic thinking and to carefully delineate the implications of their results.

Biology↗
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↗
PubMed2005

Food restriction, evolution and ageing.

The food restriction model for life extension is nearing "three-score and 10" years of age and remains in good shape, preserving much of the mystique of its youth. Although originally described for laboratory rodents, recent work shows that food restriction also appears to slow ageing processes in a range of other animal species, raising the question of whether this response represents some generalised evolutionary adaptation, perhaps a strategy to cope with periods of famine. If the food restriction response does have an adaptive basis, this would suggest that specific gene regulatory processes have evolved to shape the organism's physiological response to food restriction. It will then be important to investigate how these are organised and whether the same or different factors are at play in the various species in which food restriction extends life span.

Aging↗
PubMed2001

Patterns of adaptation in a laboratory evolved thermophilic enzyme.

The heat sensitive psychrophilic protease subtilisin S41 was previously subjected to three rounds of mutagenesis/recombination and screening, resulting in variant 3-2G7, whose half-life at 60 degrees C is approx. 500 times that of wild-type. Here we report the results of five additional generations of laboratory evolution starting from 3-2G7. The half-life of 8th generation enzyme 8-4A9 at 60 degrees C is 1200 times that of wild-type, and slightly more than twice that of 3-2G7. This half-life is >20-fold greater than those of homologous mesophilic subtilisins SSII and BPN'. Circular dichroism melting curves indicate that subtilisin 8-4A9 unfolds at temperatures approx. 25 degrees C higher than wild-type. It is also substantially more resistant to proteolysis at 30 degrees C. Nearly half of the 13 amino acid substitutions accumulated in 8-4A9 involve the mutation of serine residues. This mirrors a pattern observed in natural proteins, where serines are statistically less prevalent in thermophilic enzymes compared to mesophilic ones.

Amino Acids↗
PubMed2006

Sexual reproduction and the evolution of microbial pathogens.

Three common systemic human fungal pathogens--Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus--have retained all the machinery to engage in sexual reproduction, and yet their populations are often clonal with limited evidence for recombination. Striking parallels have emerged with four protozoan parasites that infect humans: Toxoplasma gondii, Trypanosoma brucei, Trypanosoma cruzi and Plasmodium falciparum. Limiting sexual reproduction appears to be a common virulence strategy, enabling generation of clonal populations well adapted to host and environmental niches, yet retaining the ability to engage in sexual or parasexual reproduction and respond to selective pressure. Continued investigation of the sexual nature of microbial pathogens should facilitate both laboratory investigation and an understanding of the complex interplay between pathogens, hosts, vectors, and their environments.

Animals↗
PubMed1984

Bacteriological analysis of water by potentiometric measurement of lipoic acid reduction: preliminary assays for selective detection of indicator organisms.

The practical task of adapting an original potentiometric technique to the bacteriological analysis of water is discussed. Various laboratory strains of organisms belonging to the usual aquatic flora were inoculated one by one in a minimal lactose broth supplied with lipoic (thioctic) acid. The time evolution of the redox potential of the cultures was followed during incubation by combined gold versus reference electrodes. When the incubation temperature was regulated at 36 degrees C, most organisms were able to grow and to reduce the coenzyme, generating changes in the redox potential of the culture. However, very few organisms developed significant reductive activity when the temperature was increased to 41 degrees C and when the broth was provided with sodium deoxycholate. Among the fecal coliform organisms, only Escherichia coli and Klebsiella pneumoniae exhibited early but reproducible potential-time responses. Positive potentiometric responses were also recorded with Acinetobacter calcoaceticus. E. coli showed rapid potentiometric signals as compared with K. pneumoniae. The time required for 100-mV shift of potential to be detected was related to the logarithm of the initial concentration of E. coli or K. pneumoniae in the culture broth. Experiments on natural surface water samples showed the the potentiometric method, associated with the selective incubation conditions, mainly detected E. coli among the bacterial flora of the tested environmental water. The calibration curve relating the time required for a 100-mV shift of potential to be detected to the number of fecal coliforms, as determined by control fecal coliform-selective plate counts, was consistent with the composite standard curve of detection times obtained with six different laboratory strains of E. coli.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗
PubMed2004

Do hosts and parasites coevolve? Empirical support from the Schistosoma system.

Coevolution between host and parasite is, in principle, a powerful determinant of the biology and genetics of infection and disease. However, coevolution is difficult to demonstrate rigorously in practice and therefore has rarely been observed empirically, particularly in animal-parasite systems. Research on host-schistosome interactions has the potential for making an important contribution to the study of coevolution or reciprocal adaptation. This may be particularly pertinent because schistosomes represent an indirectly transmitted macroparasite, so often overlooked among both theoretical and empirical studies. Here we present ideas and experiments on host-schistosome interactions, in part reviewed from published work but focusing in particular on preliminary novel data from our ongoing studies of potential host-schistosome evolution and coevolution in the laboratory. The article is split into three main sections: we first focus on the evidence for evolution in the host, then in the parasite, before combining both to illustrate the gathering evidence of host-parasite coevolution in the snail-schistosome system. In particular, we demonstrate that genetic architecture, variability, and selective pressures are present for the evolution of resistance and susceptibility, virulence, and infectivity to occur, the mechanisms allowing such polymorphisms to be maintained, and that hosts and parasites appear to have reciprocal effects on each other's phenotype and genotype.

Adaptation, Biological↗
PubMed2006

Comprehensive mutation identification in an evolved bacterial cooperator and its cheating ancestor.

Precise characterization of the mutation histories of evolutionary lineages is crucial for understanding the evolutionary process, yet mutation identification has been constrained by traditional techniques. We sought to identify all accumulated mutations in an experimentally evolved lineage of the cooperative bacterium Myxococcus xanthus, which constructs fruiting bodies by a process of social multicellular development in response to starvation. This lineage had undergone two major transitions in social phenotype: from an ancestral cooperator to a socially defective cheater, and from the cheater to a competitively dominant cooperator that re-evolved social and developmental proficiency. The 9.14-Mb genome of the evolved, dominant cooperator (strain "PX") was sequenced to approximately 19-fold coverage by using recent "sequencing-by-synthesis" technology and partially sequenced (approximately 45%) by using capillary technology. The resulting data revealed 15 single-nucleotide mutations relative to the laboratory ancestor of PX after the two phases of experimental evolution but no evidence of duplications, transpositions, or multiple-base deletions. No mutations were identified by capillary sequencing beyond those found by pyrosequencing, resulting in a high probability that all mutations were discovered. Seven errors in the reference strain previously sequenced by the Sanger approach were revealed, as were five mutational differences between two distinct laboratory stocks of the reference strain. A single mutation responsible for the restoration of development in strain PX was identified, whereas 14 mutations occurred during the prior phase of experimental evolution. These results provide insight into the genetic basis of two large adaptive transitions in a social bacterium.

Adaptation, Biological↗
PubMed2026

RND-mediated efflux couples antimicrobial resistance and hypervirulence in contemporary Vibrio cholerae.

The prevailing view in bacterial pathogenesis is that antimicrobial resistance and virulence are constrained by evolutionary trade-offs, with resistance mechanisms imposing fitness costs that attenuate pathogenic potential. Herein we document that contemporary Vibrio cholerae clinical isolates from the ongoing seventh pandemic have circumvented this paradigm by coupling multidrug resistance with hypervirulence. We examined five geographically diverse Wave 3 isolates collected between 2017 and 2019 and compared them to early pandemic strains. These contemporary isolates exhibited both broad-spectrum antimicrobial resistance and markedly enhanced colonization capacity in the infant mouse model. Phylogenetic analysis of 67 O1 El Tor genomes spanning 1960-2019 confirmed that the isolates cluster within a representative Wave 3 sublineage. We identified the VexB RND efflux pump as a mediator of this coupled phenotype. Elevated vexB expression in the contemporary isolates conferred resistance to multiple antibiotic classes, while vexB inactivation simultaneously impaired resistance and colonization. This dual function was not observed in early pandemic strains, consistent with a recent evolutionary adaptation. VexB-mediated hypervirulence occurred through multiple pathways independent of cholera toxin and toxin-coregulated pilus production levels. VexB deletion impaired bacterial adherence to intestinal epithelial cells, impaired motility, and increased susceptibility to membrane-active antimicrobials. In contrast, laboratory evolution under antibiotic pressure alone generated resistant but avirulent strains, demonstrating that complex selective forces in nature enabled the co-optimization of resistance and virulence. These findings establish VexB as a molecular link between antimicrobial resistance and hypervirulence in pandemic V. cholerae, highlighting efflux pumps as dual-function therapeutic targets whose inhibition could both restore antibiotic activity and attenuate disease.

Animals↗
PubMed2005

[Recombinant analysis of classical swine fever virus].

To study the possible recombinant relationship among differently derived classical swine fever virus, the coding regions of 21 isolates were analyzed to detect recombination and breakpoints through gene trees comparison and quartet analyses. The results show nucleotide area corresponding to E0, E1 and E2 as a possible recombinant tract between ALD ( D49532) and GPE-(D49533) while NS5A-NS5B of the isolate 39 (AF407339) appears to be derived from a virulent Shimen strain (AF092448) sequence. This suggests that intertypic exchanges of genetic materials during mixed infections under natural or laboratorial conditions can lead classical swine fever virus to adapt to the changes of host environment.

Classical Swine Fever Virus↗
PubMed2002

Field and laboratory selection of Frankliniella occidentalis (Pergande) for resistance to insecticides.

Response of western flower thrips, Frankliniella occidentalis (Pergande), to selection for resistance to insecticides commonly used to control this pest in Murcia (south-east Spain) was studied under field and laboratory conditions. In the field, plots within sweet pepper crops in commercial and experimental greenhouses were treated under different selection strategies: insecticide rotation versus formetanate reiteration, formetanate reiteration versus acrinathrin reiteration, and formetanate reiteration versus methiocarb reiteration. Thrips populations were sampled monthly and bioassayed against methiocarb, methamidophos, acrinathrin, endosulfan, deltamethrin and formetanate. In the laboratory, F occidentalis strains were selected against each insecticide for several generations. To evaluate cross-resistance, each selected strain was bioassayed with the other insecticides. Frankliniella occidentalis populations showed a rapid development of acrinathrin resistance, reaching high levels in field and laboratory conditions. Formetanate and methiocarb resistance were also observed, although development was slower and at moderate levels. Cross-resistances between acrinathrin/deltamethrin and acrinathrin/formetanate were detected under field and laboratory conditions. Formetanate/methiocarb cross-resistance was suspected in laboratory selections, but not in field assays. Simultaneous moderate resistance levels to the three specific insecticides against thrips (formetanate, methiocarb and acrinathrin) were shown in laboratory selection strains, indicating a general mechanism of resistance, probably metabolic.

Adaptation, Physiological↗
PubMed2003

Genotype, obesity and cardiovascular disease--has technical and social advancement outstripped evolution?

Teleologically, our ancestors were highly adapted hunter-gatherers. In recent history, the environment in which Homo sapiens exists has altered drastically and humans are exposed to environments for which the hunter-gatherer genotype is ill-suited. The adoption of a sedentary Western lifestyle, and the case of obtaining food of a high calorific content imposed upon a thrifty genotype, have resulted in the current global epidemic of obesity, Type 2 diabetes and the Metabolic Syndrome. The ramification of this epidemic is that cardiovascular disease is becoming a global healthcare problem, which will have its greatest impact on the developing nations. A global strategy is required to reduce the impact of the Western lifestyle on the health of developing nations and prevent obesity and Type 2 diabetes. Such an approach needs to be culturally sensitive, integrated, and multidisciplinary and involve a range of interventions that work at the individual and community levels. If lifestyle measures fail, then pharmacological intervention may be necessary. For this, novel agents such as dual PPARalpha/gamma agonists may be the therapy of the future.

Adaptation, Physiological↗
PubMed2025

Ancient climate changes and relaxed selection shape cave colonization in North American cavefishes.

Extreme environments serve as natural laboratories for studying evolutionary processes, with caves offering replicated instances of independent colonizations. The timing, mode and genetic underpinnings underlying cave-obligate organismal evolution remain enigmatic. We integrate phylogenomics, fossils, palaeoclimatic modelling and newly sequenced genomes to elucidate the evolutionary history and adaptive processes of cave colonization in the study group, the North American Amblyopsidae fishes. Amblyopsid fishes present a unique system for investigating cave evolution, encompassing surface, facultative cave-dwelling and cave-obligate (troglomorphic) species. Using 1105 exon markers and total-evidence dating, we reconstructed a robust phylogeny that supports the nested position of eyed, facultative cave-dwelling species within blind cavefishes. We identified three independent cave colonizations, dated to the Early Miocene (18.5 Ma), Late Miocene (10.0 Ma) and Pliocene (3.0 Ma). Evolutionary model testing supported a climate-relict hypothesis, suggesting that global cooling trends since the Early-Middle Eocene may have influenced cave colonization. Comparative genomic analyses of 487 candidate genes revealed both relaxed and intensified selection on troglomorphy-related loci. We found more loci under relaxed selection, supporting neutral mutation as a significant mechanism in cave-obligate evolution. Our findings provide empirical support for climate-driven cave colonization and offer insights into the complex interplay of selective pressures in extreme environments.

Animals↗
PubMed2003

Evolution of genomic diversity and sex at extreme environments: fungal life under hypersaline Dead Sea stress.

We have found that genomic diversity is generally positively correlated with abiotic and biotic stress levels (1-3). However, beyond a high-threshold level of stress, the diversity declines to a few adapted genotypes. The Dead Sea is the harshest planetary hypersaline environment (340 g.liter-1 total dissolved salts, approximately 10 times sea water). Hence, the Dead Sea is an excellent natural laboratory for testing the "rise and fall" pattern of genetic diversity with stress proposed in this article. Here, we examined genomic diversity of the ascomycete fungus Aspergillus versicolor from saline, nonsaline, and hypersaline Dead Sea environments. We screened the coding and noncoding genomes of A. versicolor isolates by using >600 AFLP (amplified fragment length polymorphism) markers (equal to loci). Genomic diversity was positively correlated with stress, culminating in the Dead Sea surface but dropped drastically in 50- to 280-m-deep seawater. The genomic diversity pattern paralleled the pattern of sexual reproduction of fungal species across the same southward gradient of increasing stress in Israel. This parallel may suggest that diversity and sex are intertwined intimately according to the rise and fall pattern and adaptively selected by natural selection in fungal genome evolution. Future large-scale verification in micromycetes will define further the trajectories of diversity and sex in the rise and fall pattern.

Biological Evolution↗
PubMed2000

Evolution of thermotolerance in hot spring cyanobacteria of the genus Synechococcus.

The extension of ecological tolerance limits may be an important mechanism by which microorganisms adapt to novel environments, but it may come at the evolutionary cost of reduced performance under ancestral conditions. We combined a comparative physiological approach with phylogenetic analyses to study the evolution of thermotolerance in hot spring cyanobacteria of the genus Synechococcus. Among the 20 laboratory clones of Synechococcus isolated from collections made along an Oregon hot spring thermal gradient, four different 16S rRNA gene sequences were identified. Phylogenies constructed by using the sequence data indicated that the clones were polyphyletic but that three of the four sequence groups formed a clade. Differences in thermotolerance were observed for clones with different 16S rRNA gene sequences, and comparison of these physiological differences within a phylogenetic framework provided evidence that more thermotolerant lineages of Synechococcus evolved from less thermotolerant ancestors. The extension of the thermal limit in these bacteria was correlated with a reduction in the breadth of the temperature range for growth, which provides evidence that enhanced thermotolerance has come at the evolutionary cost of increased thermal specialization. This study illustrates the utility of using phylogenetic comparative methods to investigate how evolutionary processes have shaped historical patterns of ecological diversification in microorganisms.

Biological Evolution↗
PubMed1981

Ergonomic aspects of sport and recreation.

Human factors engineering or ergonomics originated in military technology from the team-work of engineers and specialists in the human sciences. The central focus is on the human operator upon whom the task and environment impose specific loadings. Intransigence of task demands in sport tends to shift emphasis to training and selection. Heredity seems to play the more important role in the evolution of the champion athlete. An integrated interdisciplinary approach is advocated in assessing task demands and individual capacity to meet them. Improving equipment and facility design promotes safety and performance efficiency. Environmental stresses may be simulated in laboratory conditions to provide opportunity for prior adaptation. Stresses associated with urbanized civilization present novel risks to social health. Quality of life can be enhanced from an ergonomics input into the design of sports facilities and exercise programmes and their subsequent monitoring.

Aerobiosis↗
PubMed2002

Distribution and evolution of the Anopheles punctulatus group (Diptera: Culicidae) in Australia and Papua New Guinea.

The members of the Anopheles punctulatus group are major vectors of malaria and Bancroftian filariasis in the southwest Pacific region. The group is comprised of 12 cryptic species that require DNA-based tools for species identification. From 1984 to 1998 surveys were carried out in northern Australia, Papua New Guinea and on islands in the southwest Pacific to determine the distribution of the A. punctulatus group. The results of these surveys have now been completed and have generated distribution data from more than 1500 localities through this region. Within this region several climatic and geographical barriers were identified that restricted species distribution and gene flow between geographic populations. This information was further assessed in light of a molecular phylogeny derived from the ssrDNA (18S). Subsequently, hypotheses have been generated on the evolution and distribution of the group so that future field and laboratory studies may be approached more systematically. This study suggested that the ability for widespread dispersal was found to have appeared independently in species that show niche-specific habitat preference (Anopheles farauti s.s. and A. punctulatus) and conversely in species that showed diversity in their larval habitat (Anopheles farauti 2). Adaptation to the monsoonal climate of northern Australia and southwest Papua New Guinea was found to have appeared independently in A. farauti s.s., A. farauti 2 and Anopheles farauti 3. Shared or synapomorphic characters were identified as saltwater tolerance (A. farauti s.s. and Anopheles farauti 7) and elevational affinities above 1500 m (Anopheles farauti 5, Anopheles farauti 6 and A. farauti 2).

Animals↗
PubMed2006

Evolution of natural algal populations at elevated CO2.

Over the next century, it is expected that the concentration of CO(2) in the atmosphere will roughly double (Watson et al., 2001, Climate Change 2001: the Scientific Basis, Intergovernmental Panel on Climate Change, Geneva). Microbial populations, which have large population sizes and short generation times, may respond to CO(2) enrichment through genetic change. Here we describe microalgae isolated from the soil of natural CO(2) springs and compare these strains with lines of Chlamydomonas that were selected at elevated CO(2) in the laboratory. Both the laboratory and natural populations failed to evolve specific adaptations to elevated CO(2), and contain populations that grow poorly at ambient levels of CO(2). Laboratory and CO(2) spring populations also include lines whose growth rates are insensitive to CO(2). This demonstrates that, although laboratory selection experiments use simplified environments, the evolutionary responses that are seen following long-term CO(2) enrichment correspond to those found in natural populations that have experienced similar conditions.

Atmosphere↗