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PubMed1998

Functional and adaptive significance of primate pads and claws: evidence from New World anthropoids.

This study tests predicted morphoclines in fingertip morphology among four small-bodied (<1 kg) New World monkeys (Saimiri sciureus, Leontopithecus rosalia, Callithrix jacchus, and Saguinus oedipus) in order to test previous functional and adaptive explanations for the evolution of flattened nails, expanded apical pads, and grasping extremities within the Order Primates. Small-bodied platyrrhines which frequently forage among small-diameter substrates are expected to possess 1) relatively expanded apical pads, 2) well-developed epidermal ridges, 3) distally broad terminal phalanges, and 4) reduced flexor and extensor tubercles compared to those species which use large-diameter arboreal supports more frequently for their locomotor and postural behaviors. Results show that as the frequency of small-branch foraging increases among taxa within this sample, relative distal phalanx breadth also increases but distal phalanx length, height, and flexor tubercle size decrease. Moreover, epidermal ridge development becomes more pronounced as the frequency of small-branch foraging increases. Terminal phalanx breadth and epidermal ridge complexity are both positively correlated with apical pad size. The large, flexible apical pad increases stability of the hand and foot on small-diameter arboreal supports because the pad can contact the substrate in several planes which, in turn, enables the pad to resist disruptive forces from different directions by friction and interlocking (Hildebrand, 1995). The observed morphoclines demonstrate that a gradient in form from claw- to nail-like tegulae exists among these taxa. Thus, the distinction between claw- and nail-bearing platyrrhines is essentially arbitrary. These observations corroborate Cartmill's (1972) functional and adaptive model for the loss of claws in primates: namely, expanded apical pads are required for habitual locomotor and postural behaviors on small-diameter supports whereas claws are more useful for positional behaviors on large-diameter substrates. Finally, results from this study support previous suggestions that the keeled tegulae of callitrichines represent a derived postural adaptation rather than a primitive retention from an ancestral eutherian condition.

Adaptation, Physiological↗
PubMed1995

Induction of CO2 and Bicarbonate Transport in the Green Alga Chlorella ellipsoidea (II. Evidence for Induction in Response to External CO2 Concentration).

The critical species and concentrations of dissolved inorganic carbon (DIC) required for the induction of DIC transport during adaptation to low CO2 were determined for the green alga Chlorella ellipsoidea. The concentration of dissolved CO2 needed for the induction of both CO2 and HCO3- transport was independent of pH during adaptation, whereas the total DIC concentration required increased at alkaline pH. At pH 7.5, the minimum equilibrium DIC concentration at which high CO2 characteristics were maintained, i.e. transport was repressed, was 2100 [mu]M, whereas the maximum equilibrium DIC concentration below which DIC transport was fully induced (DICIND) was 500 [mu]M. Intracellular DIC concentration during adaptation to DICIND decreased temporarily after 2 h to 60% of the maximum level but recovered after 3 h of adaptation. After 3 h of adaptation to DICIND, cells exhibited maximum O2 evolution rate at DICIND. When cells partially adapted to DICIND were returned to high CO2, there was an immediate halt to the induction of transport and a gradual decrease in transport capacity over 23 h. The capacity for the induction of transport was unaffected by the absence of light. These results indicate that changes in the internal DIC pool during adaptation to low CO2 do not trigger the induction of DIC transport and that the induction is not light dependent. Induction of DIC transport in C. ellipsoidea appears to occur in response to the continuous exposure of cells to a critical CO2 concentration in the external medium.

Journal Article↗
PubMed2000

Evolution of drug resistance in experimental populations of Candida albicans.

Adaptation to inhibitory concentrations of the antifungal agent fluconazole was monitored in replicated experimental populations founded from a single, drug-sensitive cell of the yeast Candida albicans and reared over 330 generations. The concentration of fluconazole was maintained at twice the MIC in six populations; no fluconazole was added to another six populations. All six replicate populations grown with fluconazole adapted to the presence of drug as indicated by an increase in MIC; none of the six populations grown without fluconazole showed any change in MIC. In all populations evolved with drug, increased fluconazole resistance was accompanied by increased resistance to ketoconazole and itraconazole; these populations contained ergosterol in their cell membranes and were amphotericin sensitive. The increase in fluconazole MIC in the six populations evolved with drug followed different trajectories, and these populations achieved different levels of resistance, with distinct overexpression patterns of four genes involved in azole resistance: the ATP-binding cassette transporter genes, CDR1 and CDR2; the gene encoding the target enzyme of the azoles in the ergosterol biosynthetic pathway, ERG11; and the major facilitator gene, MDR1. Selective sweeps in these populations were accompanied by additional genomic changes with no known relationship to drug resistance: loss of heterozygosity in two of the five marker genes assayed and alterations in DNA fingerprints and electrophoretic karyotypes. These results show that chance, in the form of mutations that confer an adaptive advantage, is a determinant in the evolution of azole drug resistance in experimental populations of C. albicans.

AIDS-Related Opportunistic Infections↗
PubMed1999

Do parasites live in extreme environments? Constructing hostile niches and living in them.

We develop the hypothesis that parasites do not invade extreme environments, i.e. hostile hosts, but rather 'create' them. We argue that parasites may have driven the evolution of the constitutive and adaptive immune system. This leads to several implications. First, parasites respond to 'genes to kill' by 'genes to survive' and this triggers an indefinite selection of measures and counter-measures. Second, these coevolutionary arms races may lead to local adaptation, in which parasite populations perform better on local hosts. Third, the evolution of the immune system, whose responses are predictable, may allow parasites to specialize, to evade and even to manipulate. Finally we show that the correlations between the increase in the antibody repertoire, the expansion of MHC loci and parasite pressures support our hypothesis that both host complexity and parasite pressures can be invoked to explain the diversity of antibodies, T-receptors and MHC molecules.

Adaptation, Physiological↗
PubMed2002

The evolutionary origins of maternal calcium and bone metabolism during lactation.

Calcium is required for skeletal growth in all vertebrate offspring. In eutherian mammals, calcium is provided by the mother via the placenta during fetal growth and via milk until weaning. Transferring calcium to offspring during pregnancy and lactation significantly stresses maternal calcium homeostasis. During human pregnancy, the extra calcium requirements are met primarily by an increase in absorption of calcium from the diet and by a modest increase in rates of bone resorption. In nursing mothers, the calcium required for milk production is generated by a dramatic increase in rates of bone resorption and a decrease in the rate of renal calcium excretion. To consider the evolution of these maternal adaptations in bone and calcium metabolism, comparisons are made across different species of mammals, and the fundamental problem of maternal transfer of calcium to young is explored in lower vertebrates. These comparisons suggest that maternal adaptations in calcium and bone metabolism during pregnancy and lactation in mammals originate from adaptations in bone and mineral metabolism that supply calcium for egg production in lower vertebrates.

Biological Evolution↗
PubMed2006

Diversification and specialization of HIV protease function during in vitro evolution.

Our goal is to understand how enzymes adapt to utilize novel substrates. We and others have shown that directed evolution tends to generate enzyme variants with broadened substrate specificity. Broad-specificity enzymes are generally deleterious to living cells, so this observed trend might be an artifact of the most commonly employed high throughput screens. Here, we demonstrate a more natural and effective screening strategy for directed evolution. The gene encoding model enzyme HIV protease was randomly mutated, and the resulting library was expressed in Escherichia coli cells to eliminate cytotoxic broad-specificity variants. The surviving variants were screened for clones with activity against a reporter enzyme. The wild-type human immunodeficiency virus type I protease (HIV PR) is cytotoxic and exhibits no detectable activity in reactions with beta-galactosidase (BGAL). In contrast, the selected variants were nontoxic and exhibited greater activity and specificity against BGAL than did the wild-type HIV PR in reactions with any substrate. A single round of whole gene random mutagenesis and conventional high-throughput screening does not usually effect complete inversions of substrate specificity. This suggests that a combination of positive and purifying selection engenders more rapid adaptation than positive selection alone.

Adaptation, Biological↗
PubMed1998

Evolution in functional complexity of heart rate dynamics: a measure of cardiac allograft adaptability.

The capacity of self-organized systems to adapt is embodied in the functional organization of intrinsic control mechanisms. Evolution in functional complexity of heart rate variability (HRV) was used as measure of the capacity of the transplanted heart to express newly emergent regulatory order. In a cross-sectional study of 100 patients after (0-10 yr) heart transplantation (HTX), heart rate dynamics were assessed using pointwise correlation dimension (PD2) analysis. A new observation is that, commencing with the acute event of allograft transplantation, the dynamics of rhythm formation proceed through complex phase transitions. At implantation, the donor heart manifested metronome-like chronotropic behavior (PD2 approximately 1.0). At 11-100 days, dimensional complexity of HRV reached a peak (PD2 approximately 2.0) associated with resurgence in the high-frequency component (0.15-0.5 Hz) of the power spectral density. Subsequent dimensional loss to PD2 approximately 1.0 at 20-30 mo after HTX was followed by a progressive near-linear gain in system complexity, reaching PD2 approximately 3.0 7-10 yr after HTX. The "dynamic reorganization" in the allograft rhythm-generating system, seen in the first 100 days, is a manifestation of the adaptive capacity of intrinsic control mechanisms. The loss of HRV 2 yr after HTX implies a withdrawal of intrinsic autonomic control and/or development of an entrained dynamic pattern characteristic of extrinsic sympathetic input. The subsequent long-term progressive rise in dimensional complexity of HRV can be attributed to the restoration of a functional order patterning parasympathetic control. The recognition that the decentralized heart can restitute the multidimensional state space of HR generator dynamics independent of external autonomic signaling may provide a new perspective on principles that constitute homeodynamic regulation.

Adaptation, Physiological↗
PubMed2002

Personal observations on the cultural evolution in academic surgery.

BACKGROUND: The changing environment in academic medical centers has had a major effect on the recruitment and the demographic characteristics of leadership positions in academic surgery. Categorization of "cultures" from the business model has been extrapolated into the academic surgical model. METHODS: The types of cultures in organizations according to Cameron and Quinnn at a school of management can be classified into four: clan culture, adhocracy culture, hierarchy, and market-driven culture. In addition, academic surgical chairmen were surveyed in 1981 and also 20 years later, 2001, by the author. This was done in an effort to determine whether there is a difference in the type of person being attracted to such positions and if there is demographic difference in academic chairmen over the two decades. RESULTS: The organizational profile of academic departments in 1980 is perceived to be more clan and adhocracy in type and less hierarchical and market driven. That has reversed itself dramatically two decades later with much of the energy of a department and structure based on hierarchy and the market. Also, in terms of the chairman, the mean age at the time of appointment in 1981 was 44 years and the mean age at time of appointment in 2001 was 49 years. In 1981 the years in grade was 9.4 years and in 201 it is 7.1 years. The new chairman is now older and will not serve as long as his/her predecessor. CONCLUSIONS: There clearly has been a cultural evolution in academic surgery over the past two decades. The chairman has different priorities than chairmen 20 years ago. The success of an academic department will depend upon the adaptation to this cultural evolution and the understanding of the chairman as to what the job really is.

Academic Medical Centers↗
PubMed2002

Organization and phylogenetic analysis of kappa-bungarotoxin genes from Bungarus multicinctus (Taiwan banded krait).

Two genomic DNAs were isolated from the liver of Bungarus multicinctus (Taiwan banded krait) encoded kappa1-bungarotoxin and kappa3-bungarotoxin precursors, respectively. They shared virtually identical overall organization with three exons separated by two introns and a high degree of nucleotide-sequence identity with alpha-neurotoxin genes, including similar intron insertions. This suggests that kappa-neurotoxins and alpha-neurotoxins might have originated from a common ancestor. The consensus transcriptional factor binding sites within the promoter regions of these genes indicate that their transcriptions are, at least in part, regulated under the same mechanism. Comparative analyses on kappa-bungarotoxin and alpha-neurotoxin genes revealed that the protein-coding regions of exons were much more diversified than introns except for the signal peptide domain. Phylogenetic analyses on the exon and intron regions of kappa-bungarotoxin and alpha-neurotoxin genes showed that the evolution of exon regions were not in consensus with that of intron regions. The ratio of nonsynonymous to synonymous substitution is higher than 1, reflecting the occurrence of an adaptive selection during the evolution of kappa-bungarotoxins. In contrast to a conserved size of the second intron, segmental insertions and/or deletions within the first intron accelerate the evolutionary divergence of kappa- and alpha-neurotoxin genes.

Amino Acid Sequence↗
PubMed2004

Species interactions and the evolution of sex.

The Red Queen hypothesis posits that sex has evolved in response to the shifting adaptive landscape generated by the evolution of interacting species. Previous studies supporting the Red Queen hypothesis have considered a narrow region of parameter space and only a subset of ecological and genetic interactions. Here, we develop a population genetics model that circumscribes a broad array of ecological and genetic interactions among species and derive the first general analytical conditions for the impact of species interactions on the evolution of sex. Our results show that species interactions typically select against sex. We conclude that, although the Red Queen favors sex under certain circumstances, it alone does not account for the ubiquity of sex.

Alleles↗
PubMed2026

Genome-wide identification of olfactory receptor and odorant-binding protein gene families and their roles in Heliothine chemosensory evolution.

Chemosensory systems play key roles in the survival and reproductive success of insects. Two large and diverse chemosensory gene families, odorant receptors (ORs) and odorant-binding proteins (OBPs), play critical roles in insect chemosensation and mediate odour-guided behaviours. In the process of insect chemosensation, odorants from the environment pass through pores in the antennal sensilla and become soluble in the sensillar lymph, either directly on contact or by binding to an OBP. Solubilized odour molecules diffuse through the lymph until they reach and activate their cognate ORs, sending electrophysiological signals to the insect brain. To better understand the evolutionary roles of OR and OBP gene families among members of the Heliothinae, we systematically characterized these two gene families in Chloridea virescens (Lepidoptera: Noctuidae). A total of 81 ORs and 49 OBPs were identified genome-wide. Based on the number and positions of conserved cysteine residues, the OBPs were classified into three types: 34 Classic OBPs, 8 Minus-C OBPs and 7 Plus-C OBPs. Phylogenetic analyses identified potential gene duplications and losses within OR and OBP gene families among members of the Heliothinae, which may be associated with differences in their volatile sensation and olfactory behaviours. Further motif and structural analyses identified a conserved region that was unique among pheromone receptors and predicted as key residues of the binding pocket, implying its critical role in pheromone detection. Future work should focus on experimentally validating its function. Overall, our findings provide important insights into how chemosensory gene evolution contributes to ecological adaptation and reproductive isolation in the Heliothine moths.

Animals↗
PubMed2000

[Terrestrial adaptation and diversity of the kidney functions in the evolution of vertebrates, Amphibia].

The Amphibia bridge the phyletic gap between the aquatic fishes and the terrestrial vertebrates. This transition has involved many interesting changes of metabolisms. In this short review, we have attempted to summarize the kidney structure and functions on the osmoregulations in the Amphibia. Amphibians excrete the water absorbed through their skin as a dilute urine. Pronephros of tadpoles may start to work in the hatching stages and metanephros is well developed and functions. Glomerular filtration rate is relatively large and glomerular intermittency is important to regulate urine production. The proximal tubule reabsorbs approximately 20-45% of filtered water and sodium. Absorption is driven by the basolateral Na+, K(+)-ATPase common to all tubular cells. The diluting segment, early parts of distal nephron, highly develops basolateral interdigitation and reabsorbs approximately 40% of filtered Na+, K+, and Cl-, but is impermeable to water, thus this part results in the formation of hypo-osmotic tubular fluid. In the late distal tubule, the primary mechanism of reabsorption may be via a luminal NaCl synporter, driven by the ubiquitous Na+, K(+)-ATPase on basolateral membrane. In collecting tubule, there are two types of cells, the principal cells and the intercalated cells. Many hormonal and nervous regulations are involved in the glomerular filtration rate and reabsorptions in the amphibian nephrons.

Adaptation, Biological↗
PubMed1981

Evolution of glycolytic enzymes.

The requirements for glycolysis are examined in relation to other essential metabolic processes in the most primitive organisms. The construction of more complex enzymes from primitive domain building blocks is assessed with respect to glycolytic enzymes. Special attention is given to the evolution of the NAD binding domain in dehydrogenases and the related, frequently observed nucleotide binding domain. An attempt is made to differentiate between convergence and divergence of frequently observed domains. Consideration is given to the structure-function relation of these domains and the development of quaternary structure in later stages of evolution. Some attention is also given to the evolution of the structural adaptation to extreme environments as a means of differentiating between essential functions and specific modifications.

Animals↗
PubMed1998

Adaptive radiation in a heterogeneous environment.

Successive adaptive radiations have played a pivotal role in the evolution of biological diversity. The effects of adaptive radiation are often seen, but the underlying causes are difficult to disentangle and remain unclear. Here we examine directly the role of ecological opportunity and competition in driving genetic diversification. We use the common aerobic bacterium Pseudomonas fluorescens, which evolves rapidly under novel environmental conditions to generate a large repertoire of mutants. When provided with ecological opportunity (afforded by spatial structure), identical populations diversify morphologically, but when ecological opportunity is restricted there is no such divergence. In spatially structured environments, the evolution of variant morphs follows a predictable sequence and we show that competition among the newly evolved niche-specialists maintains this variation. These results demonstrate that the elementary processes of mutation and selection alone are sufficient to promote rapid proliferation of new designs and support the theory that trade-offs in competitive ability drive adaptive radiation.

Adaptation, Physiological↗
PubMedDate not supplied

[Adaptive types of prolamins--specialized proteins from cereal seeds (Poaceae Banrh.)].

Amino acid composition of prolamins and the whole seed in representatives of 52 cereal genera and 22 tribes, as well as amino acid composition of seed protein fractions in representatives of 9 cereal genera are presented. In terms of proposed directed evolution of the seed proteins and adaptive role of prolamins in evolution and distribution of cereals, generalized data on their content in seed protein complex, electrophoretic, immunochemical, and amino acid composition of the seeds, we develop the notion of prolamins biochemical specialization and their polyphyletic origin during evolution of cereal seed protein complex. Seven adaptive types of prolamins are recognized: Sasa, Molinia, Chloris, Zingeria, Poa, Triticum, and Panicum types. Adaptive types of prolamins were formed in response to an ecological request of the environment where taxon ancestors existed and a taxon appeared and in relation to phylogenetic history of a taxon and its assignment to particular tribe and subfamily.

Adaptation, Biological↗
PubMed1996

Long-term experimental evolution in Escherichia coli. IV. Targets of selection and the specificity of adaptation.

This study investigates the physiological manifestation of adaptive evolutionary change in 12 replicate populations of Escherichia coli that were propagated for 2000 generations in a glucose-limited environment. Representative genotypes from each population were assayed for fitness relative to their common ancestor in the experimental glucose environment and in 11 novel single-nutrient environments. After 2000 generations, the 12 derived genotypes had diverged into at least six distinct phenotypic classes. The nutrients were classified into four groups based upon their uptake physiology. All 12 derived genotypes improved in fitness by similar amounts in the glucose environment, and this pattern of parallel fitness gains was also seen in those novel environments where the limiting nutrient shared uptake mechanisms with glucose. Fitness showed little or no consistent improvement, but much greater genetic variation, in novel environments where the limiting nutrient differed from glucose in its uptake mechanisms. This pattern of fitness variation in the novel nutrient environments suggests that the independently derived genotypes adapted to the glucose environment by similar, but not identical, changes in the physiological mechanisms for moving glucose across both the inner and outer membranes.

Adaptation, Physiological↗