Physiological problems of biological evolution. "Errors" in the development of physiological functions

During the evolution the physiological functions grow more perfect and complex. However, sometimes a developing function can show some evidence of regress and in certain cases can become the cause of dangerous diseases. The autoimmune diseases are among them. We conventionally call such cases the "error" of the evolution. In this work a negative role of leukocytes in the brain microcirculation is considered. With the help of experimental studies it was shown that leukocytes owing to their large volume (by a factor of 2-2.5 greater than the volume of an erythrocyte) slow down the capillary blood flow. As the result of the increasing tendency to adhesion, under the influence of hypoxia they make leukocyte conglomerates which cause the occlusion of venules and smallest veins of the brain. This is the reason for the known effect "no reflow" and results in an organism death.     

The evolution of resistance through costly acquired immunity

We examine the evolutionary dynamics of resistance to parasites through acquired immunity. Resistance can be achieved through the innate mechanisms of avoidance of infection and reduced pathogenicity once infected, through recovery from infection and through remaining immune to infection: acquired immunity. We assume that each of these mechanisms is costly to the host and find that the evolutionary dynamics of innate immunity in hosts that also have acquired immunity are quantitatively the same as in hosts that possess only innate immunity. However, compared with resistance through avoidance or recovery, there is less likely to be polymorphism in the length of acquired immunity within populations. Long-lived organisms that can recover at intermediate rates faced with fast-transmitting pathogens that cause intermediate pathogenicity (mortality of infected individuals) are most likely to evolve long-lived acquired immunity. Our work emphasizes that because whether or not acquired immunity is beneficial depends on the characteristics of the disease, organisms may be selected to only develop acquired immunity to some of the diseases that they encounter.     

A game theoretical approach to the evolution of structured communication codes

Structured meaning-signal mappings, i.e., mappings that preserve neighborhood relationships by associating similar signals with similar meanings, are advantageous in an environment where signals are corrupted by noise and sub-optimal meaning inferences are rewarded as well. The evolution of these mappings, however, cannot be explained within a traditional language evolutionary game scenario in which individuals meet randomly because the evolutionary dynamics is trapped in local maxima that do not reflect the structure of the meaning and signal spaces. Here we use a simple game theoretical model to show analytically that when individuals adopting the same communication code meet more frequently than individuals using different codes—a result of the spatial organization of the population—then advantageous linguistic innovations can spread and take over the population. In addition, we report results of simulations in which an individual can communicate only with its K nearest neighbors and show that the probability that the lineage of a mutant that uses a more efficient communication code becomes fixed decreases exponentially with increasing K. These findings support the mother tongue hypothesis that human language evolved as a communication system used among kin, especially between mothers and offspring.     

Between cheap and costly signals: the evolution of partially honest communication

Costly signalling theory has become a common explanation for honest communication when interests conflict. In this paper, we provide an alternative explanation for partially honest communication that does not require significant signal costs. We show that this alternative is at least as plausible as traditional costly signalling, and we suggest a number of experiments that might be used to distinguish the two theories.     

Social drive and the evolution of primate hearing

The structure and function of primate communication have attracted much attention, and vocal signals, in particular, have been studied in detail. As a general rule, larger social groups emit more types of vocal signals, including those conveying the presence of specific types of predators. The adaptive advantages of receiving and responding to alarm calls are expected to exert a selective pressure on the auditory system. Yet, the comparative biology of primate hearing is limited to select species, and little attention has been paid to the effects of social and vocal complexity on hearing. Here, we use the auditory brainstem response method to generate the largest number of standardized audiograms available for any primate radiation. We compared the auditory sensitivities of 11 strepsirrhine species with and without independent contrasts and show that social complexity explains a significant amount of variation in two audiometric parameters-overall sensitivity and high-frequency limit. We verified the generality of this latter result by augmenting our analysis with published data from nine species spanning the primate order. To account for these findings, we develop and test a model of social drive. We hypothesize that social complexity has favoured enhanced hearing sensitivities, especially at higher frequencies.     

Energetically costly behaviour and the evolution of resting metabolic rate in insects

1. A general hypothesis is presented to explain interspecific differences in size-independent resting metabolic rate. This hypothesis is based on a presumed trade-off between a low resting metabolism and adaptations of metabolism during activity.
2. With such a trade-off, selection to reduce resting metabolism is less intense in active species than in species where resting metabolism constitutes a large proportion of the daily metabolic costs. Those animals that spend more energy on activity should therefore have a higher resting metabolic rate than animals that spend less energy on activity.
3. A literature review reveals that flying insects have higher resting metabolic rates than species that use energetically less demanding types of locomotion.
4. Insects producing acoustic advertisement signals can be shown to have higher mass-independent resting metabolic rates than closely related species without this energetically demanding behaviour.
5. Literature data on vertebrate resting metabolic rates are also consistent with the presented hypothesis: the more energy animals spend on activity, the higher the mass-independent resting metabolic rate.     

Modular evolution of phosphorylation-based signalling systems

Phosphorylation sites are formed by protein kinases ('writers'), frequently exert their effects following recognition by phospho-binding proteins ('readers') and are removed by protein phosphatases ('erasers'). This writer-reader-eraser toolkit allows phosphorylation events to control a broad range of regulatory processes, and has been pivotal in the evolution of new functions required for the development of multi-cellular animals. The proteins that comprise this system of protein kinases, phospho-binding targets and phosphatases are typically modular in organization, in the sense that they are composed of multiple globular domains and smaller peptide motifs with binding or catalytic properties. The linkage of these binding and catalytic modules in new ways through genetic recombination, and the selection of particular domain combinations, has promoted the evolution of novel, biologically useful processes. Conversely, the joining of domains in aberrant combinations can subvert cell signalling and be causative in diseases such as cancer. Major inventions such as phosphotyrosine (pTyr)-mediated signalling that flourished in the first multi-cellular animals and their immediate predecessors resulted from stepwise evolutionary progression. This involved changes in the binding properties of interaction domains such as SH2 and their linkage to new domain types, and alterations in the catalytic specificities of kinases and phosphatases. This review will focus on the modular aspects of signalling networks and the mechanism by which they may have evolved.     

Driving change: the evolution of alternative genetic codes

Pioneering studies in the 1960s that elucidated the genetic code suggested that all extant forms of life use the same genetic code. This early presumption has subsequently been challenged by the discovery of deviations of the universal genetic code in prokaryotes, eukaryotic nuclear genomes and mitochondrial genomes. These studies have revealed that the genetic code is still evolving despite strong negative forces working against the fixation of mutations that result in codon reassignment. Recent data from in vitro, in vivo and in silico comparative genomics studies are revealing significant, previously overlooked links between modified nucleosides in tRNAs, genetic code ambiguity, genome base composition, codon usage and codon reassignment.     

Regressive biological evolution due to environmental change

Simulation results are presented which suggest that regressive evolution (i.e., evolution to a less adapted state) often occurs in response to environmental change, by a process analogous to the stress-induced reversal of aging in glassy materials. The key to this process is the stress-induced disappearance of fitness optima that lead to irreversible changes in the location of a population in genotype space. Even though the population may always evolve to higher fitness states, this irreversible process will often act to bring an initially well-adapted system to a less adapted state upon a return to initial conditions.     

The neurobiology and evolution of cannabinoid signalling

The plant Cannabis sativa has been used by humans for thousands of years because of its psychoactivity. The major psychoactive ingredient of cannabis is Delta(9)-tetrahydrocannabinol, which exerts effects in the brain by binding to a G-protein-coupled receptor known as the CB1 cannabinoid receptor. The discovery of this receptor indicated that endogenous cannabinoids may occur in the brain, which act as physiological ligands for CB1. Two putative endocannabinoid ligands, arachidonylethanolamide ('anandamide') and 2-arachidonylglycerol, have been identified, giving rise to the concept of a cannabinoid signalling system. Little is known about how or where these compounds are synthesized in the brain and how this relates to CB1 expression. However, detailed neuroanatomical and electrophysiological analysis of mammalian nervous systems has revealed that the CB1 receptor is targeted to the presynaptic terminals of neurons where it acts to inhibit release of 'classical' neurotransmitters. Moreover, an enzyme that inactivates endocannabinoids, fatty acid amide hydrolase, appears to be preferentially targeted to the somatodendritic compartment of neurons that are postsynaptic to CB1-expressing axon terminals. Based on these findings, we present here a model of cannabinoid signalling in which anandamide is synthesized by postsynaptic cells and acts as a retrograde messenger molecule to modulate neurotransmitter release from presynaptic terminals. Using this model as a framework, we discuss the role of cannabinoid signalling in different regions of the nervous system in relation to the characteristic physiological actions of cannabinoids in mammals, which include effects on movement, memory, pain and smooth muscle contractility. The discovery of the cannabinoid signalling system in mammals has prompted investigation of the occurrence of this pathway in non-mammalian animals. Here we review the evidence for the existence of cannabinoid receptors in non-mammalian vertebrates and invertebrates and discuss the evolution of the cannabinoid signalling system. Genes encoding orthologues of the mammalian CB1 receptor have been identified in a fish, an amphibian and a bird, indicating that CB1 receptors may occur throughout the vertebrates. Pharmacological actions of cannabinoids and specific binding sites for cannabinoids have been reported in several invertebrate species, but the molecular basis for these effects is not known. Importantly, however, the genomes of the protostomian invertebrates Drosophila melanogaster and Caenorhabditis elegans do not contain CB1 orthologues, indicating that CB1-like cannabinoid receptors may have evolved after the divergence of deuterostomes (e.g. vertebrates and echinoderms) and protostomes. Phylogenetic analysis of the relationship of vertebrate CB1 receptors with other G-protein-coupled receptors reveals that the paralogues that appear to share the most recent common evolutionary origin with CB1 are lysophospholipid receptors, melanocortin receptors and adenosine receptors. Interestingly, as with CB1, each of these receptor types does not appear to have Drosophila orthologues, indicating that this group of receptors may not occur in protostomian invertebrates. We conclude that the cannabinoid signalling system may be quite restricted in its phylogenetic distribution, probably occurring only in the deuterostomian clade of the animal kingdom and possibly only in vertebrates.     

Copper and the biological evolution

Copper is contained in a number of enzymes and proteins. A remarkable feature is that except for the electron-carrying blue copper proteins (azurin and plastocyanin) and copper-containing cytochrome c oxidase found in some cyanobacteria and some aerobic bacteria, all copper enzymes and proteins are found only in eukaryotes. In the early and middle precambrian period when the stationary oxygen pressure in the atmosphere was quite low, copper existed as either metallic or cuprous sulfides which are very insoluble in aqueous media; thus copper might have been unavailable to organisms. The time when copper became Cu(II) upon rise of the atmospheric oxygen pressure and thus became available to organisms seems to be in the middle of Proteozoic era when first eukaryotic organisms seem to have appeared on earth. Thus copper may be considered to be an indicator element for the atmospheric evolution (switching from anoxygenic to oxygenic) and the evolution of higher organisms (eukaryotes).     

Begging and bleating: the evolution of parent-offspring signalling

The evolution of biological signalling in the face of evolutionary conflicts of interest is an active area of evolutionary ecology, and one to which Maynard Smith has made important contributions. We explore the major theoretical challenges in the field, concentrating largely on how offspring signal to their parents when there is the potential for parent-offspring conflict. Costly offspring solicitation (begging etc.) has been interpreted in terms of a Zahavi Grafen honest handicap signal, but this has been challenged on the grounds of' the costs of signalling. We review this controversy and also explore the issue of pooling versus separating signalling equilibrium. An alternative explanation for costly begging is that it is due to sibling competition, and we discuss the relationship between these ideas and signalling models in families with more than one offspring. Finally we consider signal uncertainty, how signalling models can be made dynamic, and briefly how they may be tested experimentally.     

An application of information theory to biological evolution

An evolving population of two alleles which generates another new allele is investigated within the framework of information theory. A communication system model of self-reproducing organisms which reproduce the genetic information by the self-reproduction is proposed and the concept of distortion when the genetic information is reproduced is introduced. What genetic information should be transmitted to the next generation? This question may be answered by so called rate distortion theory. The theory is applied to our model and the exact solution is obtained. Numerical results show that in low distortion region, new allele cannot survive, hence no evolution occurs; in intermediate distortion region, all alleles coexist; and in high distortion region, minor allele cannot survive. Moreover, diversity of the progeny takes its maximum value in the intermediate distortion region. This suggests that there may exist an optimal distortion for a population to evolve.     

The evolution of hormonal signalling systems.

1. A comparative analysis was made of chemosignalling systems responsible for the action of hormones, hormone-like substances, pheromones, etc. in vertebrates--multicellular invertebrates--unicellular eukaryotes. Many common features revealed in structural-functional organization of the above systems give evidence of their evolutionary conservatism. 2. It was shown that some molecular components as well as signal transduction mechanisms similar to those of higher eukaryote hormonal signalling systems are present in such early organisms as bacteria. This allowed a suggestion that the roots of chemosignalling systems are likely to be found in prokaryotes. 3. The evolution of hormonal signalling systems is discussed in terms of current theories of the origin of eukaryotic cell, its organelles and components. A hypothesis is put forward about endosymbiotic genesis of these signal transduction systems in eukaryotes. 4. A possible evolutionary scenario of the formation of hormonocompetent systems is proposed with hormone-sensitive adenylate cyclase complex taken as an example.     

On the thermodynamics of biological evolution

A theory is proposed which explains the peculiarities of biological evolution on the basis of classical thermodynamics. Notions are introduced of particular evolutions as components of the general evolution of the biosphere. Thermodynamic criteria of evolutions are formulated allowing experimental proof of the applicability of classical thermodynamics to biological evolution as a whole.     

Rapid evolution of yeast centromeres in the absence of drive

To find the most rapidly evolving regions in the yeast genome we compared most of chromosome III from three closely related lineages of the wild yeast Saccharomyces paradoxus. Unexpectedly, the centromere appears to be the fastest-evolving part of the chromosome, evolving even faster than DNA sequences unlikely to be under selective constraint (i.e., synonymous sites after correcting for codon usage bias and remnant transposable elements). Centromeres on other chromosomes also show an elevated rate of nucleotide substitution. Rapid centromere evolution has also been reported for some plants and animals and has been attributed to selection for inclusion in the egg or the ovule at female meiosis. But Saccharomyces yeasts have symmetrical meioses with all four products surviving, thus providing no opportunity for meiotic drive. In addition, yeast centromeres show the high levels of polymorphism expected under a neutral model of molecular evolution. We suggest that yeast centromeres suffer an elevated rate of mutation relative to other chromosomal regions and they change through a process of "centromere drift," not drive.     

Duplication,concerted evolution and purifying selection drive the evolution of mosquito vitellogenin genes

Background  

Mosquito vitellogenin (Vtg) genes belong to a small multiple gene family that encodes the major yolk protein precursors required for egg production. Multiple Vtg genes have been cloned and characterized from several mosquito species, but their origin and molecular evolution are poorly understood.     

Intralocus sexual conflict can drive the evolution of genomic imprinting

Genomic imprinting is a phenomenon whereby the expression of an allele differs depending upon its parent of origin. There is an increasing number of examples of this form of epigenetic inheritance across a wide range of taxa, and imprinting errors have also been implicated in several human diseases. Various hypotheses have been put forward to explain the evolution of genomic imprinting, but there is not yet a widely accepted general hypothesis for the variety of imprinting patterns observed. Here a new evolutionary hypothesis, based on intralocus sexual conflict, is proposed. This hypothesis provides a potential explanation for much of the currently available empirical data, and it also makes new predictions about patterns of genomic imprinting that are expected to evolve but that have not, as of yet, been looked for in nature. This theory also provides a potential mechanism for the resolution of intralocus sexual conflict in sexually selected traits and a novel pathway for the evolution of sexual dimorphism.