Geographical isolation and genetic differentiation: the case of Orestias ascotanensis (Teleostei: Cyprinodontidae), an Andean killifish inhabiting a highland salt pan

Orestias ascotanensis is a killifish endemic to the Ascotán salt pan in the Chilean Altiplano, where it inhabits 12 springs with different degrees of isolation. This species is a suitable model for studying the effect of serial geographical isolations on the differentiation process among populations. The present study examines the genetic variation and structure of the species using mitochondrial DNA control region sequences and eight microsatellite loci, analyzing populations across its distribution range. The evaluation of genetic variation revealed high levels of diversity within the species. The genetic structure analysis showed the existence of four differentiated groups: two groups were formed by the springs located in the northern and southern extremes of the salt pan and two groups were found in the centre of the salt pan. The latter two groups were formed by several springs, most likely as a consequence of the South American summer monsoon that could connect them and allow gene flow. The patterns of genetic differentiation appear to be determined based on the physical isolation of the populations. This isolation may be the result of a combination of factors, including geographical distance, a historical decrease in water levels and altitude differences in the springs of the salt pan. Therefore, this system is a rare example in which hydrological factors can explain genetic differentiation on a very small scale.     

Tibetan and Andean patterns of adaptation to high-altitude hypoxia

Understanding the workings of the evolutionary process in contemporary humans requires linking the evolutionary history of traits with their current genetics and biology. Unusual environments provide natural experimental settings to investigate evolution and adaptation. The example of high-altitude hypoxia illustrates some of the progress and many of the remaining challenges for studies of evolution in contemporary populations. Current studies exemplify the frequently encountered problem of determining whether large, consistent population differences in mean values of a trait reflect genetic differences. In this review I describe 4 quantitative traits that provide evidence that indigenous populations of the Tibetan and Andean plateaus differ in their phenotypic adaptive responses to high-altitude hypoxia. These 4 traits are resting ventilation, hypoxic ventilatory response, oxygen saturation, and hemoglobin concentration. The Tibetan means of the first 2 traits were more than 0.5 standard deviation higher than the Aymara means, whereas the Tibetan means were more than 1 standard deviation lower than the Aymara means for the last 2 traits. Quantitative genetic analyses of within-population variance revealed significant genetic variance in all 4 traits in the Tibetan population but only in hypoxic ventilatory response and hemoglobin concentration in the Aymara population. A major gene for oxygen saturation was detected among the Tibetans. These findings are interpreted as indirect evidence of population genetic differences. It appears that the biological characteristics of sea-level humans did not constrain high-altitude colonists of the 2 plateaus to a single adaptive response. Instead, microevolutionary processes may have operated differently in the geographically separated Tibetan and Andean populations exposed to the same environmental stress. Knowledge of the genetic bases of these traits will be necessary to evaluate these inferences. Future research will likely be directed toward determining whether the population means reflect differences identified at the chromosomal level. Future research will also likely consider the biological pathways and environmental influences linking genotypes to phenotypes, the costs and benefits of the Tibetan and Andean patterns of adaptation, and the question of whether the observed phenotypes are indeed adaptations that enhance Darwinian fitness.     

Andean, Tibetan, and Ethiopian patterns of adaptation to high-altitude hypoxia

Research on humans at high-altitudes contributes to understandingthe processes of human adaptation to the environment and evolution.The unique stress at high altitude is hypobaric hypoxia causedby the fall in barometric pressure with increasing altitudeand the consequently fewer oxygen molecules in a breath of air,as compared with sea level. The natural experiment of humancolonization of high-altitude plateaus on three continents hasresulted in two—perhaps three—quantitatively differentarterial-oxygen-content phenotypes among indigenous Andean,Tibetan and Ethiopian high-altitude populations. This paperillustrates these contrasting phenotypes by presenting evidencefor higher hemoglobin concentration and percent of oxygen saturationof hemoglobin among Andean highlanders as compared with Tibetansat the same altitude and evidence that Ethiopian highlandersdo not differ from sea-level in these two traits. Evolutionaryprocesses may have acted differently on the colonizing populationsto cause the different patterns of adaptation. Hemoglobin concentrationhas significant heritability in Andean and Tibetan samples.Oxygen saturation has no heritability in the Andean sample,but does among Tibetans where an autosomal dominant major genefor higher oxygen saturation has been detected. Women estimatedwith high probability to have high oxygen saturation genotypeshave more surviving children than women estimated with highprobability to have the low oxygen saturation genotype. Thesefindings suggest the hypothesis that ongoing natural selectionis increasing the frequency of the high saturation allele atthis major gene locus.     

The evolution of an annual life cycle in killifish: adaptation to ephemeral aquatic environments through embryonic diapause

An annual life cycle is characterized by growth, maturity, and reproduction condensed into a single, short season favourable to development, with production of embryos (seeds, cysts, or eggs) capable of surviving harsh conditions which juveniles or adults cannot tolerate. More typically associated with plants in desert environments, or temperate‐zone insects exposed to freezing winters, the evolution of an annual life cycle in vertebrates is fairly novel. Killifish, small sexually dimorphic fishes in the Order Cyprinodontiformes, have adapted to seasonally ephemeral water bodies across much of Africa and South America through the independent evolution of an annual life history. These annual killifish produce hardy desiccation‐resistant eggs that undergo diapause (developmental arrest) and remain buried in the soil for long periods when fish have perished due to the drying of their habitat. Killifish are found in aquatic habitats that span a continuum from permanent and stable to seasonal and variable, thus providing a useful system in which to piece together the evolutionary history of this life cycle using natural comparative variation. I first review adaptations for life in ephemeral aquatic environments in killifish, with particular emphasis on the evolution of embryonic diapause. I then bring together available evidence from a variety of approaches and provide a scenario for how this annual life cycle evolved. There are a number of features within Aplocheiloidei killifish including their inhabitation of marginal or edge aquatic habitat, their small size and rapid attainment of maturity, and egg properties that make them particularly well suited to the colonization of ephemeral waters.     

Novel mechanism for high-altitude adaptation in hemoglobin of the Andean frog Telmatobius peruvianus

In contrast to birds and mammals, no information appears to be available on the molecular adaptations for O(2) transport in high-altitude ectothermic vertebrates. We investigated Hb of the aquatic Andean frog Telmatobius peruvianus from 3,800-m altitude as regards isoform differentiation, sensitivity to allosteric cofactors, and primary structures of the alpha- and beta-chains, and we carried out comparative O(2)-binding measurements on Hb of lowland Xenopus laevis. The three T. peruvianus isoHbs show similar functional properties. The high O(2) affinity of the major component results from an almost complete obliteration of chloride sensitivity, which correlates with two alpha-chain modifications: blockage of the NH(2)-terminal residues and replacement by nonpolar Ala of polar residues Ser and Thr found at position alpha131(H14) in human and X. leavis Hbs, respectively. The data indicate adaptive significance of alpha-chain chloride-binding sites in amphibians, in contrast to human Hb where chloride appears mainly to bind in the cavity between the beta-chains. The findings are discussed in relation to other strategies for high-altitude adaptations in amphibians.     

Ancient DNA reveals twenty million years of aquatic life in beavers

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Whole-genome sequencing reveals a complex African population demographic history and signatures of local adaptation

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Proteome analysis reveals adaptation of Pseudomonas aeruginosa to the cystic fibrosis lung environment

Pseudomonas aeruginosa is known for the chronic lung colonization of cystic fibrosis (CF) patients in addition to eye, ear and urinary tract infections. With the underlying disease CF patients are predisposed to P. aeruginosa chronic lung infection, which leads to morbidity and mortality. In this study, we compared the protein expression profile of a CF lung-adapted P. aeruginosa strain C with that of the burn-wound isolate PAO. Differentially expressed proteins from the whole-cell, membrane, periplasmic as well as extracellular fraction were identified. The whole-cell proteome of strain C showed down-regulation of several proteins involved in amino acid metabolism, fatty acid metabolism, energy metabolism and adaptation leading to a highly distinct proteome pattern for strain C in comparison to PAO. Analysis of secreted proteins by strain C compared to PAO revealed differential expression of virulence factors under non-inducing conditions. The membrane proteome of strain C showed modulation of the expression of porins involved in nutrient and antibiotic influx. The proteome of the periplasmic space of strain C showed retention of elastase despite that the equal amounts were secreted by strain C and PAO. Altogether, our results elucidate adaptive strategies of P. aeruginosa towards the nutrient-rich CF lung habitat during the course of chronic colonization.