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PubMed2002

Adaptation for horizontal transfer in a homing endonuclease.

Selfish genes of no function other than self-propagation are susceptible to degeneration if they become fixed in a population, and regular transfer to new species may be the only means for their long-term persistence. To test this idea we surveyed 24 species of yeast for VDE, a nuclear, intein-associated homing endonuclease gene (HEG) originally discovered in Saccharomyces cerevisiae. Phylogenetic analyses show that horizontal transmission has been a regular occurrence in its evolutionary history. Moreover, VDE appears to be specifically adapted for horizontal transmission. Its 31-bp recognition sequence is an unusually well-conserved region in an unusually well-conserved gene. In addition, the nine nucleotide sites most critical for homing are also unusually well conserved. Such adaptation for horizontal transmission presumably arose as a consequence of selection, both among HEGs at different locations in the genome and among variants at the same location. The frequency of horizontal transmission must therefore be a key feature constraining the distribution and abundance of these genes.

Conserved Sequence↗
PubMed2006

Tracking the connection between evolutionary and functional shifts using the fungal lipase/feruloyl esterase A family.

BACKGROUND: There have been many claims of adaptive molecular evolution, but what role does positive selection play in functional divergence? The aim of this study was to test the relationship between evolutionary and functional shifts with special emphasis on the role of the environment. For this purpose, we studied the fungal lipase/feruloyl esterase A family, whose functional diversification makes it a very promising candidate. RESULTS: The results suggested functional shift following a duplication event where neofunctionalisation of feruloyl esterase A had occurred with conservation of the ancestral lipase function. Evolutionary shift was detected using the branch-site model for testing positive selection on individual codons along specific lineages. Positively selected amino acids were detected. Furthermore, biological data obtained from site-directed mutagenesis experiments clearly demonstrated that certain amino acids under positive selection were involved in the functional shift. We reassessed evolutionary history in terms of environmental response, and hypothesized that environmental changes such as colonisation by terrestrial plants might have driven adaptation by functional diversification in Euascomycetes (Aspergilli), thus conferring a selective advantage on this group. CONCLUSION: The results reported here illustrate a rare example of connection between fundamental events in molecular evolution. We demonstrated an unequivocal connection between evolutionary and functional shifts, which led us to conclude that these events were probably linked to environmental change.

Amino Acids↗
PubMed2004

Phosphorylation of MAP kinase-like proteins mediate the response of the halotolerant alga Dunaliella viridis to hypertonic shock.

The microalga Dunaliella viridis has the ability to adapt to a variety of environmental stresses including osmotic and thermal shocks, UV irradiation and nitrogen starvation. Lacking a rigid cell wall, Dunaliella provides an excellent model to study stress signaling in eukaryotic unicellular organisms. When exposed to hyperosmotic stress, UV irradiation or high temperature, a 57-kDa protein is recognized by antibodies specific to mammalian p38, to its yeast homologue Hog1, and to the phospho-p38 MAP kinase motif. This 57-kDa protein appears to be both up-regulated and phosphorylated. Three other proteins (50, 45, 43 kDa) were transiently phosphorylated under stress conditions as detected with an antibody specific to the mammalian phospho c-Jun N-terminal kinase (JNK) motif. Treatment with specific inhibitors of p38 MAP kinase (SB203580) and JNK (SP600125) activities markedly impaired the adaptation of Dunaliella to osmotic stress. From an evolutionary standpoint, these data strongly suggest that MAP kinase signaling pathways, other than ERK, were already operating in the common ancestor of plant and animal kingdoms, probably as early as 1400 million years ago.

Adaptation, Physiological↗
PubMed2006

Animals, energy, and water in extreme environments: perspectives from Ithala 2004.

Animals occupy an impressive range of environments, and many approach the limits of conditions that are compatible with life. Such environments are often characterized by low productivity, and survival depends on abilities to maintain levels of hydration sufficient for biochemical reactions and an adequate level of energy turnover. Specific adaptations for acquiring and conserving water affect the intake and utilization of energy that is available for growth and reproduction. Almost any benign, historically stable environment can become hostile if conditions change, and the severity of challenges to animals depends on temporal as well as spatial factors that are related to the intensity and duration of harsh conditions (e.g., drought). Animals have responded to such changes through avoidance, phenotypically plastic adjustments, and evolutionary changes in genomic structure. Here we present an overview of research findings presented at a session of the Third International Conference of Comparative Physiology and Biochemistry. We hope such a synthesis will stimulate new directions in research that address biological responses to environmental change. In this context, we believe that challenging environments in Africa might provide increasingly useful sites for biological investigations relating to the application of comparative and evolutionary approaches toward a deeper understanding of physiological adaptation.

Acclimatization↗
PubMed2001

Evolution and inequality.

Some scientists remain wary of evolutionary theory because of its supposed genetic determinism and insensitivity to the inequalities often associated with gender, race and class. Our aim is to show that such fears are outdated and to foster a role for evolutionary theory in public health. We use complex adaptive systems theory and the concept of a tradeoff between current and future reproduction to argue that when the future is objectively risky and uncertain the optimal reproductive strategy will often be to reproduce at a young age and/or high rate. Because reproducing early and/or often can lead to ill health and shortened lives, and because inequality is a major source of environmental risk and uncertainty, we argue that any attempt to use evolutionary theory to understand human reproduction, health or wellbeing must include considerations of inequality and social capital.

Adolescent↗
PubMed2005

Studying genetics of adaptive variation in model organisms: flowering time variation in Arabidopsis lyrata.

Arabidopsis thaliana has emerged as a model organism for plant developmental genetics, but it is also now being widely used for population genetic studies. Outcrossing relatives of A. thaliana are likely to provide suitable additional or alternative species for studies of evolutionary and population genetics. We have examined patterns of adaptive flowering time variation in the outcrossing, perennial A. lyrata. In addition, we examine the distribution of variation at marker genes in populations form North America and Europe. The probability of flowering in this species differs between southern and northern populations. Northern populations are much less likely to flower in short than in long days. A significant daylength by region interaction shows that the northern and southern populations respond differently to the daylength. The timing of flowering also differs between populations, and is made shorter by long days, and in some populations, by vernalization. North American and European populations show consistent genetic differentiation over microsatellite and isozyme loci and alcohol dehydrogenase sequences. Thus, the patterns of variation are quite different from those in A. thaliana, where flowering time differences show little relationship to latitude of origin and the genealogical trees of accessions vary depending on the genomic region studied. The genetic architecture of adaptation can be compared in these species with different life histories.

Adaptation, Physiological↗
PubMed2006

The unusual adaptive expansion of pancreatic ribonuclease gene in carnivora.

Pancreatic ribonuclease (RNASE1) is a digestive enzyme that has been recognized to be one of the most attractive model systems for molecular evolutionary studies. The contribution of RNASE1 gene duplication to the functional adaptation of digestive physiology in foregut-fermenting herbivores, mostly in ruminants, has been well documented. However, no one has ever done a comprehensive study on the carnivores, which are sister to the artiodactyls. Here, we sequenced this gene from 15 species of the superfamily Caniformia in order Carnivora, which all have a relatively simple digestive system and lack the microbial digestion in rumen or cecum typical of most herbivores. In contrast to our initial expectation that only a single RNASE1 gene is present in these carnivores, we observed a "birth (gene duplication)-and-death (gene deactivation)" process for the evolution of RNASE1 genes in all 3 species of Mustelidae family examined here, adding the growing diversity of RNASE1 gene family evolution. In addition, bursts of positive selection have been shown to contribute the enigmatic diversification of these RNASE1 genes in Mustelidae. The finding of the adaptive expansion of RNASE1 in animals without foregut fermentation provides another opportunity for further studies of the structure, function, and evolution of this gene, raising the possibility that new tissue specificity or other functions of RNASE1 genes might have developed in these species.

Adaptation, Biological↗
PubMed2005

Limits to adaptation in asexual populations.

In asexual populations, the rate of adaptation is basically limited by the frequency and properties of spontaneous beneficial mutations. Hence, knowledge of these mutational properties and how they are affected by particular evolutionary conditions is a precondition for understanding the process of adaptation. Here, we address how the rate of adaptation of asexual populations is limited by its population size and mutation rate, as well as by two factors affecting the fraction of mutations that confer a benefit, i.e. the initial adaptedness of the population and the variability of the environment. These factors both influence which mutations are likely to occur, as well as the probability that they will ultimately contribute to adaptation. We attempt to separate the consequences of these basic population features in terms of their effect on the rate of adaptation by using results from evolution experiments with microorganisms.

Adaptation, Physiological↗
PubMed1994

Ionizing radiation and genetic risks. V. Multifactorial diseases: a review of epidemiological and genetic aspects of congenital abnormalities in man and of models on maintenance of quantitative traits in populations.

This paper discusses (a) data on the epidemiological and etiological aspects of human congenital abnormalities, (b) the multifactorial threshold model and other models which have been proposed to explain their inheritance patterns and recurrence risks in families and (c) current concepts on mechanisms on the prevalence of heritable variation for quantitative traits in populations. Congenital abnormalities, which afflict an estimated 6% of all live births, are etiologically heterogeneous. The majority of these do not follow Mendelian transmission patterns, but do 'run' in families. The multifactorial threshold model is an extension of genetic principles developed for quantitative traits to all-or-none traits; in its simplest formulation, it assumes the existence in the population of an underlying normally distributed 'liability' (which is due to numerous genetic and environmental factors acting additively, each contributing a small amount of liability) and of a 'threshold' beyond which the individual is affected. For most congenital abnormalities, the nature of these factors remains unknown. Other models assume fewer causal factors although, again, these remain to be identified. The question of how considerable heritable variation for most quantitative/polygenic traits has come to exist is a long-standing one in evolutionary population genetics. Models postulating that its existence is consistent with a balance between recurrent mutation and stabilizing selection or suggesting the possible operation of other mechanisms have been published in the literature. In the absence of knowledge on mechanisms responsible for the stable prevalences of congenital abnormalities or other multifactorial conditions in the population (but which is required to predict the consequences of an increase in mutation rate on their prevalences) it is necessary (a) to adapt and use concepts derived from quantitative and evolutionary population genetics and (b) to examine how sensitive the predictions are to the assumptions used, and how consistent they are with biological realities.

Abnormalities, Radiation-Induced↗
PubMed1994

Adaptation, allometry, and hypertension.

Essential hypertension is a "disease of civilization" but has a clear genetic component. From an evolutionary perspective, persistence in the human genome of elements capable of raising blood pressure presupposes their adaptive significance. Recently, two hypotheses that explicitly appeal to selectionist arguments, the "slavery" and "thrifty gene" theories, have been forwarded. We find neither completely successful, and we advance an alternative explanation of the adaptive importance of genes responsible for hypertension. We propose that blood pressure rises during childhood and adolescence to subserve homeostatic needs of the organism. Specifically, we contend that blood pressure is a flexible element in the repertoire of renal homeostatic mechanisms serving to match renal function to growth. The effect of modern diet and lifestyle on human growth stimulates earlier and more vigorous development, straining biologically necessary relationships between renal and general somatic growth and requiring compensation via homeostatic mechanisms preserved during evolution. Prime among such mechanisms is blood pressure, which rises as a compensation to maintain renal function in the face of greater growth. Since virtually all members of acculturated societies share in the modern lifestyle, the demands imposed by accelerated growth and development result in a populational shift to higher blood pressures, with a consequent increase in the prevalence of hypertension. We propose that hypertension is the product of maladaptation of highly genetically conserved mechanisms subserving important biological homeostatic needs. Elucidation of the mechanisms underlying hypertension will require approaches that examine the developmental processes linking growth to blood pressure.

Adaptation, Physiological↗
PubMed1977

Further studies on the adaptation of fish myofibrillar ATPases to different cell temperatures.

Previous studies on fish Mg2+Ca2+ activated myofibrillar ATPases have been extended to species inhabiting diverse thermal environments. Cold adapted ATPases have considerably higher catalytic centred activities at low temperatures than warm adapted ATPases. Differences in cell temperature have also lead to evolutionary modifications in thermodynamic activation parameters. The free energies (deltaG2+), enthalpies (deltaH2+) and entropies (deltaS2+) of activation of the Mg2+Ca2+ myofibrillar ATPase are positively correlated with adaptation temperature. Myofibrils with CaATP-2 as substrate in the absence of Mg2+ will hydrolyse ATP by a mechanism not associated with fibril shortening. Differences in activation enthalpies (deltaHH) between cold and warm adapted Ca2+-activated myofibrillar ATPases are less pronounced than for the physiological ATPase. Furthermore the Ca2+-activated ATPase showed no relationship between environmental temperature and substrate turnover number or free energy of activation (deltaG2+).

Acclimatization↗
PubMed2005

Selective breeding for high endurance running increases hindlimb symmetry.

Comparative studies provide correlational evidence of morphological adaptations for high locomotor performance, such as the classical indicators of cursoriality in mammals, long limbs and high metatarsal/femur ratios. More recently, enlarged femoral condyles have been suggested as an adaptation for high endurance running in the genus Homo. Asymmetry of locomotor appendages should adversely affect locomotor abilities, but this has not been studied in a rigorous evolutionary context. We used experimental evolution to test for morphological adaptations associated with high voluntary wheel running in selectively bred lines of mice. Surprisingly, the classical indicators of cursoriality had not evolved in concert with high activity levels. Instead, high runners had larger femoral condyles and reduced directional asymmetry of hindlimb bones. We hypothesize that greater limb symmetry and larger femoral heads are general adaptations associated with sustained, high-speed locomotion.

Adaptation, Biological↗