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PubMed2000

On the advantages of information sharing.

During the evolution of life, there have been several transitions in which individuals began to cooperate, forming higher levels of organization, and sometimes losing their independent reproductive identity For example, multicellularity and insect societies evolved independently multiple times. Several factors that confer evolutionary advantages on higher levels of organization have been proposed. In this paper we highlight one additional factor: the sharing of information between individuals. Information sharing is not subject to the intrinsic conservation laws that characterize the sharing of physical resources. A simple model will illustrate how information sharing can result in aggregates in which the individuals both receive more information about their environment and pay less for it. This may have played a role in the evolution of higher levels of organization.

Animal Communication↗
PubMed2003

The adaptive dynamics of altruism in spatially heterogeneous populations.

We study the spatial adaptive dynamics of a continuous trait that measures individual investment in altruism. Our study is based on an ecological model of a spatially heterogeneous population from which we derive an appropriate measure of fitness. The analysis of this fitness measure uncovers three different selective processes controlling the evolution of altruism: the direct physiological cost, the indirect genetic benefits of cooperative interactions, and the indirect genetic costs of competition for space. In our model, habitat structure and a continuous life cycle makes the cost of competing for space with relatives negligible. Our study yields a classification of adaptive patterns of altruism according to the shape of the costs of altruism (with decelerating, linear, or accelerating dependence on the investment in altruism). The invasion of altruism occurs readily in species with accelerating costs, but large mutations are critical for altruism to evolve in selfish species with decelerating costs. Strict selfishness is maintained by natural selection only under very restricted conditions. In species with rapidly accelerating costs, adaptation leads to an evolutionarily stable rate of investment in altruism that decreases smoothly with the level of mobility. A rather different adaptive pattern emerges in species with slowly accelerating costs: high altruism evolves at low mobility, whereas a quasi-selfish state is promoted in more mobile species. The high adaptive level of altruism can be predicted solely from habitat connectedness and physiological parameters that characterize the pattern of cost. We also show that environmental changes that cause increased mobility in those highly altruistic species can beget selection-driven self-extinction, which may contribute to the rarity of social species.

Adaptation, Physiological↗
PubMed1989

Evolution of RNA genomes: does the high mutation rate necessitate high rate of evolution of viral proteins?

RNA genomes have been shown to mutate much more frequently than DNA genomes. It is generally assumed that this results in rapid evolution of RNA viral proteins. Here, an alternative hypothesis is proposed that close cooperation between positive-strand RNA viral proteins and those of the host cells required their coevolution, resulting in similar amino acid substitution rates. Constraints on compatibility with cellular proteins should determine, at any time, the covarion sets in RNA viral proteins. These ideas may be helpful in rationalizing the accumulating data on significant sequence similarities between proteins of positive-strand RNA viruses infecting evolutionarily distant hosts as well as between viral and cellular proteins.

Biological Evolution↗
PubMed2006

A shift to parasitism in the jellyfish symbiont Symbiodinium microadriaticum.

One of the outstanding and poorly understood examples of cooperation between species is found in corals, hydras and jellyfish that form symbioses with algae. These mutualistic algae are mostly acquired infectiously from the seawater and, according to models of virulence evolution, should be selected to parasitize their hosts. We altered algal transmission between jellyfish hosts in the laboratory to examine the potential for virulence evolution in this widespread symbiosis. In one experimental treatment, vertical transmission of algae (parent to offspring) selected for symbiont cooperation, because symbiont fitness was tied to host reproduction. In the other treatment, horizontal transmission (infectious spread) decoupled symbiont fitness from the host, potentially allowing parasitic symbionts to spread. Fitness estimates revealed a striking shift to parasitism in the horizontal treatment. The horizontally transmitted algae proliferated faster within hosts and had higher dispersal rates from hosts compared to the vertical treatment, while reducing host reproduction and growth. However, a trade-off was detected between harm caused to hosts and symbiont fitness. Virulence trade-offs have been modelled for pathogens and may be critical in stabilising 'infectious' symbioses. Our results demonstrate the dynamic nature of this symbiosis and illustrate the potential ease with which beneficial symbionts can evolve into parasites.

Animals↗
PubMed2005

A microbial modified prisoner's dilemma game: how frequency-dependent selection can lead to random phase variation.

Random phase variation (RPV) is a control strategy in which the expression of a cell state or phenotype randomly alternates between discrete 'on' and 'off' states. Though this mode of control is common for bacterial virulence factors like pili and toxins, precise conditions under which RPV confers an advantage have not been well defined. In Part I of this study, we predicted that fluctuating environments select for RPV if transitions between different selective environments cannot be reliably sensed (J. Theor. Biol. (2005)). However, selective forces both inside and outside of human hosts are also likely to be frequency dependent in the sense that the fitnesses of some bacterial states are greatest when rare. Here we show that RPV at slow rates can provide a survival advantage in such a frequency-dependent environment by generating population heterogeneity, essentially mimicking a polymorphism. More surprisingly, RPV at a faster 'optimal' rate can shift the population composition toward an optimal growth rate that exceeds that possible for polymorphic populations, but this optimal strategy is not evolutionarily stable. The population would be most fit if all cells randomly phase varied at the optimal rate, but individual cells have a growth-rate incentive to defect (mutate) to other switching rates or non-phase variable phenotype expression, leading to an overall loss of fitness of the individual and the population. This scenario describes a modified Prisoner's Dilemma game (Evolution and the Theory of Games, Cambridge University Press, Cambridge, New York, 1982, viii, 224pp.; Nature 398 (6726) (1999) 367), with random phase variation at optimal switching rates serving as the cooperation strategy.

Bacteria↗
PubMed1995

Somatic spectrum of cancer-associated single basepair substitutions in the TP53 gene is determined mainly by endogenous mechanisms of mutation and by selection.

The spectrum of somatic TP53 single basepair substitutions detected in 955 cancers was compared with that of 2,224 different germline mutations in 279 different human genes (other than TP53), reported as the cause of inherited disease. This comparison reveals that, disregarding a relatively small subset (12%) of TP53 mutations that probably result from the action of exogenous mutagens, both the relative rates and the nearest-neighbor spectra of single basepair substitutions are similar in the two datasets. This spectral resemblance suggests that a substantial proportion of cancer-associated somatic TP53 mutations result from endogenous cellular mechanisms. The likelihood of clinical observation of a particular mutation type differs, however, between tumors and genetic diseases, when the chemical properties of the resulting amino acid substitutions are considered. Together with a sixfold higher observation likelihood for mutations at evolutionarily conserved residues, this finding argues that selection is a critical factor in determining which TP53 mutations are found to be associated with human cancer.

Base Sequence↗
PubMed1995

Evolutionary origin of expandable G-C-rich triplet repeat DNA sequences.

A model explaining properties exhibited by fragile-X DNA systems arises from observations that time-dependent base substitutions are expressed at G-C sites but not at A-T sites (Biochem. Genet. 32:383, 1994). [CGG]n sequences are classified as most sensitive to evolutionary base substitution processes involving time-dependent populating of G-C sites with enol-imine states having enhanced stability. Increased density of these states in oocyte DNA would introduce a ground-state collapse double-helix of reduced energy that would inhibit strand separation by the replicase. Evolutionarily altered G' in CG'G triplets allows CG'G to be transcribed as CTG, an initiation codon. And this will cause reinitiation of DNA synthesis, thereby adding additional CGG units to the collapsed double helix. This situation would not occur in slower-evolving male haploid DNA that replicates frequently.

Base Composition↗
PubMed1992

The evolution of immune memory and germinal centers.

Antibody responses in homoiothermic and poikilothermic vertebrates are significantly different in their heterogeneity and affinity range, and in the speed of the secondary response following repeated antigenic stimulation. This article presents the hypothesis that the evolutionary development of unique lymphoid structures, the germinal centers, in combination with the development of a distinct B-cell lineage, is a determining feature of these differences.

Animals↗
PubMed1979

Evolution of cardio-pulmonary involvement in Friedreich's ataxia.

The evolution of 15 patients initially evaluated during Phase One of the Quebec Cooperative Study of Friedreich's ataxia has been studied approximately three years later. It is concluded that the deterioration of cardio-pulmonary function in Friedreich's ataxia is multifactorial. The neuromyopathy (or the underlying metabolic or cellular defect) appears to be the main contributing factor to the deterioration of cardio-pulmonary function, which is exacerbated by the scoliosis and varying severity of the cardiomyopathy.

Adolescent↗
PubMed1983

Strong homology in promoter and 3'-untranslated regions of chick and rat alpha-actin genes.

We report here a comparison of the nucleotide sequences of the chick and rat skeletal muscle alpha-actin genes which reveals strongly conserved blocks of sequence in the putative transcriptional promoter and 3'-untranslated regions. This is the first instance of strong sequence conservation in untranslated gene regions between birds and mammals, other than the CAAT and ATA promoter homologies and the putative poly(A) addition signal, AATAAA. The strong conservation of these sequences suggests that they may have a role in the tissue-specific expression of the skeletal muscle alpha-actin gene.

Actins↗
PubMed1997

Potential role for concurrent abnormalities of the cyclin D1, p16CDKN2 and p15CDKN2B genes in certain B cell non-Hodgkin's lymphomas. Functional studies in a cell line (Granta 519).

Abnormalities of several cell-cycle regulatory genes including cyclin D1, p16CDKN2 and p15CDKN2B have been described in B cell non-Hodgkin's lymphoma (B-NHL). We describe a new B-NHL cell line (Granta 519), with concurrent abnormalities of the cyclin D1, pl6CDKN2 and pl5CDKN2B genes. An independent clinical case of mantle cell NHL (Mc-NHL) with concomitant overexpression of cyclin D1, and deletion of the p16CDKN2 gene was also identified, suggesting that this combination of oncogenic aberration is a pathophysiologic contribution to a subset of NHL cases. More in-depth functional studies of this concept were facilitated by the availability of the cell line Granta 519 which was derived from a case of high-grade NHL and has a mature B cell immunophenotype. Cytogenetic analysis identified translocation t(11;14)(q13;q32) and complex rearrangements involving chromosomes 9p22, 13p21, 17pl1, and 18q21. Molecular analysis identified overexpression of cyclin D1 mRNA and biallelic deletion of the p16CDKN2 and p15CDKN2B genes. To elucidate the effect of these genetic abnormalities on the G1 control of Granta 519 cells, the level and function of the major components of the cyclinD/retinoblastoma (RB) pathway were investigated. Cyclin D1 was dominant among the D-type cyclins, formed abundant complexes with cyclin-dependent kinase (Cdk) Cdk4 rather than Cdk6, and the immunoprecipitated cyclin D1/Cdk4 holoenzyme was active as a pRB kinase. Electroporation of wild-type pl6CDKN2 arrested the Granta 519 cells in G1, consistent with the p16CDKN2 loss as a biologically relevant event during multistep evolution of the tumor, and with the expression of functional pRB. Direct cooperation of these distinct abnormalities to cell-cycle, deregulation in NHL cells was suggested by G1 acceleration upon inducible overexpression of cyclin D1 in a control breast cancer cell line lacking p16CDKN2, an effect which could be prevented by ectopic expression of p16CDKN2. Taken together, these data suggest that concurrent overexpression of cyclin D1 and functional elimination of p16CDKN2 and p15CDKN2B may characterize certain cases of mantle cell NHL, and that cooperation of the abnormalities is likely to provide a growth advantage of the tumour cells through more efficient inactivation of the RB tumor suppressor. Further clinicopathologic studies of this possibility are warranted.

Aged↗
PubMed1991

Two distinct alpha beta T-cell lineages can be distinguished by the differential usage of T-cell receptor V beta gene segments.

Avian T cells can be divided into three subpopulations based on their expression of distinct T-cell receptors (TCR1, TCR2, and TCR3), ontogeny, and tissue distribution. The TCR1 cells appear to be the equivalent of mammalian gamma delta cells, but the derivation of cells expressing TCR2 and TCR3 has been unclear. Here we report that chickens contain two families of TCR beta variable (V) gene segments, V beta 1 and V beta 2. Furthermore, TCR2 and TCR3 represent subsets of alpha beta cells that are defined by mutually exclusive usage of these two families of V beta gene segments. Sequence comparisons of V beta 1 and V beta 2 with mammalian TCR beta V segments reveal that V beta 1 gene segments encode the conserved amino acids used to define the mammalian V beta consensus subgroup I, while V beta 2 encodes the amino acids used to define the mammalian V beta subgroup II. Although the beta chains of TCR2 and TCR3 cells are encoded by the same diversity (D), joining (J), and constant (C) region segments, V beta 1 gene segments undergo rearrangement before V beta 2 gene segments during T-cell development. This may result from the fact that TCR2 cells undergo V-DJ joining by deletional rearrangement, whereas TCR3 cells undergo V-DJ joining by inversional rearrangement. These data suggest that the TCR alpha beta cells can be divided into two distinct and evolutionarily conserved lineages based on V beta gene segment usage. The clear-cut separation of these lineages in the chicken may help to define their immunologic role.

Aging↗
PubMed1998

Comparative and library epidemiological typing systems: outbreak investigations versus surveillance systems.

A number of high-resolution molecular typing systems have been developed in recent years. Their availability raises the new issues of selecting the method (s) best suited for a particular purpose and interpreting and communicating typing results. Most of the currently available methods are comparative only: they allow testing of a sample of isolates for delineation of those closely related from those markedly different in genomic backgrounds. This approach is adequate for outbreak investigation, allowing determination of clonal spread in a microenvironment and identification of the source of infection. Comparative methods with sufficient resolution for most pathogens include restriction fragment-length polymorphism (RFLP), pulsed-field gel electrophoresis (PFGE), and arbitrarily primed and randomly amplified polymorphic DNA-polymerase chain reaction (PCR) analysis. For surveillance systems, monitoring clonal spread and prevalence in populations over extended periods of time requires library typing systems. These must be standardized, must have a high throughput, and must use a uniform nomenclature. Promising or validated methods include serotyping, insertion sequence fingerprinting, ribotyping, PFGE, amplified fragment-length polymorphism (AFLP), infrequent-restriction-site amplification PCR, interrepetitive element PCR typing (rep-PCR) and PCR-RFLP of polymorphic loci. PCR methods generating arrays of size-specific amplicons (AFLP, rep-PCR) can be more reproducibly analyzed by using denaturing polyacrylamide gel or capillary electrophoresis with automated laser detection. Binary probe typing systems appear optimal and should be enhanced further through use of DNA chip technology. In these systems, amplification of polymorphic regions is followed by solid-phase hybridization with a reference panel of sequence-variant specific probes. The resulting binary type results allow determination of reproducible, numeric profiles. However, interpretation and nomenclature of typing results for large-scale surveillance purposes still require a better understanding of population structure and microevolution of most microbial pathogens.

Bacterial Infections↗
PubMedDate not supplied

Origin of late lactation protein from beta-lactoglobulin in the tammar wallaby.

Two of the dominant whey proteins of the tammar wallaby, beta-lactoglobulin (BLG) and late lactation protein (LLP), have been positively identified on gradient polyacrylamide gradient gels by N-terminal protein sequencing. The origin of the electrophoretic variation present in these proteins has been found to be principally genetic. The variation was examined in 97 lactating female tammar wallabies, of which 10 were followed throughout lactation to determine if any developmental variation existed. The only distinguishable developmental difference results from the previously described appearance of LLP at the beginning of phase III of lactation (approximately 180 days after birth of the young). Electrophoretic analysis of BLG implies that it exists in monomeric, dimeric, and tetrameric forms. Very strong linkage disequilibrium, indicative of close linkage, was found between alleles at the Blg and Llp loci. Examination of their cDNA sequences suggests that LLP and BLG represent an ancient gene duplication. Both have conserved amino acid residues characteristic of the lipocalins. The results imply that the marsupial mode of lactation, and hence of reproduction, is also very ancient.

Amino Acid Sequence↗
PubMed1999

Free groin flap revisited.

Reported herein are 130 consecutive cases of free groin flap transfer performed by one surgeon over a 19-year period. Transplantation was performed for soft-tissue cover or augmentation of contour defects involving the head and neck (68 cases), trunk (4 cases), upper limb (14 cases), and lower limb (44 cases). Indications for flap coverage/augmentation were classified broadly into tumor, trauma, radiation induced, and miscellaneous. Specific reconstructive problems included augmentation for Romberg's hemifacial atrophy, external ear canal reconstruction after tumor ablation, and coverage of lower limb defects. There were nine failures (total flap loss), seven cases of partial flap loss, and two cases were abandoned intraoperatively. Of 15 cases that were urgently re-explored, 9 flaps were salvaged. The failure rate for the groin flap series (130 cases) was 8.5 percent compared with the failure rate of 4.2 percent for the other 517 cases of microvascular transfer performed over the same period by the same surgeon. Donor-site complications occurred in 24 cases and included hematoma or seroma formation, hypertrophic scars, nerve paresthesiae, infection, and dehiscence. Secondary debulking procedures were performed in 26 cases. The free groin flap, contrary to some reports, is a reliable flap that provides relatively thin pliable soft-tissue cover or augmentation, with minimal donor-site morbidity. The specific indications for its use have undergone an evolution since first described in 1973.

Adolescent↗
PubMed2004

Impulsiveness without discounting: the ecological rationality hypothesis.

Observed animal impulsiveness challenges ideas from foraging theory about the fitness value of food rewards, and may play a role in important behavioural phenomena such as cooperation and addiction. Behavioural ecologists usually invoke temporal discounting to explain the evolution of animal impulsiveness. According to the discounting hypothesis, delay reduces the fitness value of the delayed food. We develop an alternative model for the evolution of impulsiveness that does not require discounting. We show that impulsive or short-sighted rules can maximize long-term rates of food intake. The advantages of impulsive rules come from two sources. First, naturally occurring choices have a foreground-background structure that reduces the long-term cost of impulsiveness. Second, impulsive rules have a discrimination advantage because they tend to compare smaller quantities. Discounting contributes little to this result. Although we find that impulsive rules are optimal in a simple foreground-background choice situation in the absence of discounting, in contrast we do not find comparable impulsiveness in binary choice situations even when there is strong discounting.

Animals↗