Specificity of genome evolution in experimental populations of evolved at different temperatures.

Isolated populations derived from a common ancestor are expected to diverge genetically and phenotypically as they adapt to different local environments. To examine this process, 30 populations of were evolved for 2,000 generations, with six in each of five different thermal regimes: constant 20 °C, 32 °C, 37 °C, 42 °C, and daily alternations between 32 °C and 42 °C. Here, we sequenced the genomes of one endpoint clone from each population to test whether the history of adaptation in different thermal regimes was evident at the genomic level.

Different tradeoffs result from alternate genetic adaptations to a common environment.

Fitness tradeoffs are often assumed by evolutionary theory, yet little is known about the frequency of fitness tradeoffs during stress adaptation. Even less is known about the genetic factors that confer these tradeoffs and whether alternative adaptive mutations yield contrasting tradeoff dynamics. We addressed these issues using 114 clones of Escherichia coli that were evolved independently for 2,000 generations under thermal stress (42.

The molecular diversity of adaptive convergence.

To estimate the number and diversity of beneficial mutations, we experimentally evolved 115 populations of Escherichia coli to 42.2°C for 2000 generations and sequenced one genome from each population. We identified 1331 total mutations, affecting more than 600 different sites.

Microbial experimental evolution.

Microbes have been widely used in experimental evolutionary studies because they possess a variety of valuable traits that facilitate large-scale experimentation. Many replicated populations can be cultured in the laboratory simultaneously along with appropriate controls. Short generation times and large population sizes make microbes ideal experimental subjects, ensuring that many spontaneous mutations occur every generation and that adaptive variants can spread rapidly through a population.

Bart's familiar quotations: the enduring biological wisdom of George A. Bartholomew.

George A. Bartholomew was one of the most influential organismal biologists of the twentieth century. His insights and research were fundamental to the establishment and growth of physiological ecology and evolutionary physiology.

The energetic advantages of slug specialization in garter snakes (genus Thamnophis).

We tested the hypothesis that dietary specialization by foraging garter snakes is accompanied by increased assimilation efficiency on specialist prey items. Our comparison included two closely related garter snake species considered to be slug specialists (Thamnophis ordinoides and Thamnophis elegans terrestris), one fish specialist (Thamnophis couchii), and one diet generalist (Thamnophis elegans elegans). Our results suggest that slug specialists have an energetic advantage over non-slug-eating snakes when both eat slugs.

Evolutionary adaptation to environmental pH in experimental lineages of Escherichia coli.

This study uses the enteric bacterium Escherichia coli as an experimental system to examine evolutionary responses of bacteria to an environmental acidic-alkaline range between pH 5.3 and 7.8 (15-5000 nM [H(+)]).

An experimental evolutionary study on adaptation to temporally fluctuating pH in Escherichia coli.

In this study, we use the bacterium Escherichia coli to examine evolutionary responses to environmental acidity fluctuating temporally among pH 5.3, 6.3, 7.

An experimental test of evolutionary trade-offs during temperature adaptation.

We used experimental evolution to test directly the important and commonplace evolutionary hypothesis that adaptation, increased fitness within the selective environment, is accompanied by trade-off, a loss of fitness in other nonselective environments. Specifically, we determined whether trade-offs at high temperature generally and necessarily accompany genetic adaptation to low temperature. We measured the relative fitness increment of 24 lineages of the bacterium Escherichia coli evolved for 2,000 generations at 20 degrees C and the relative fitness decrement of these lines at 40 degrees C.

Trade-offs in thermal adaptation: the need for a molecular to ecological integration.

Through functional analyses, integrative physiology is able to link molecular biology with ecology as well as evolutionary biology and is thereby expected to provide access to the evolution of molecular, cellular, and organismic functions; the genetic basis of adaptability; and the shaping of ecological patterns. This paper compiles several exemplary studies of thermal physiology and ecology, carried out at various levels of biological organization from single genes (proteins) to ecosystems. In each of those examples, trade-offs and constraints in thermal adaptation are addressed; these trade-offs and constraints may limit species' distribution and define their level of fitness.

Coadaptation: a unifying principle in evolutionary thermal biology.

Over the last 50 yr, thermal biology has shifted from a largely physiological science to a more integrated science of behavior, physiology, ecology, and evolution. Today, the mechanisms that underlie responses to environmental temperature are being scrutinized at levels ranging from genes to organisms. From these investigations, a theory of thermal adaptation has emerged that describes the evolution of thermoregulation, thermal sensitivity, and thermal acclimation.

Postprandial increase of oleoylethanolamide mobilization in small intestine of the Burmese python (Python molurus).

Oleoylethanolamide (OEA) is an endogenous lipid mediator that inhibits feeding in rats and mice by activating the nuclear receptor peroxisome proliferator-activated receptor-alpha (PPAR-alpha). In rodents, intestinal OEA levels increase about threefold upon refeeding, a response that may contribute to the induction of between-meal satiety. Here, we examined whether feeding-induced OEA mobilization also occurs in Burmese pythons (Python molurus), a species of ambush-hunting snakes that consume huge meals after months of fasting and undergo massive feeding-dependent changes in gastrointestinal hormonal release and gut morphology.

Terrestrial locomotion does not constrain venous return in the American alligator, Alligator mississippiensis.

The effects of treadmill exercise on components of the cardiovascular (heart rate, mean arterial blood pressure, central venous pressure, venous return) and respiratory (minute ventilation, tidal volume, breathing frequency, rate of oxygen consumption, rate of carbon dioxide production) systems and on intra-abdominal pressure were measured in the American alligator, Alligator mississippiensis, at 30 degrees C. Alligators show speed-dependent increases in tidal volume and minute ventilation, demonstrating that the inhibition of ventilation during locomotion that is present in some varanid and iguanid lizards was not present in alligators. Exercise significantly increases intra-abdominal pressure; however, concomitant elevations in central venous pressure acted to increase the transmural pressure of the post caval vein and thus increased venous return.

Phylogenetic approaches in comparative physiology.

Over the past two decades, comparative biological analyses have undergone profound changes with the incorporation of rigorous evolutionary perspectives and phylogenetic information. This change followed in large part from the realization that traditional methods of statistical analysis tacitly assumed independence of all observations, when in fact biological groups such as species are differentially related to each other according to their evolutionary history. New phylogenetically based analytical methods were then rapidly developed, incorporated into ;the comparative method', and applied to many physiological, biochemical, morphological and behavioral investigations.

Differential Patterns of Gene Expression and Gene Complement in Laboratory-Evolved Lines of E. coli.

Laboratory selection experiments play a prominent role in understanding organismal adaptation. Although bacteria are not yet commonly used for such experiments, they are well suited for analyses of both the organismic and the genetic basis of adaptation. Bacteria can be maintained in large populations while occupying limited laboratory space, have short generation times, are well characterized physiologically, biochemically, and genetically, and are readily frozen and revived from the freezer.

Changes in gene expression following high-temperature adaptation in experimentally evolved populations of E. coli.

Transcription profiling (quantitative analysis of RNA abundance) can provide a genome-wide picture of gene expression changes that accompany organismal adaptation to a new environment. Here, we used DNA microarrays to characterize genome-wide changes in transcript abundance in three replicate lines of the bacterium E. coli grown for 2,000 generations at a stressful high temperature (41.

Physiology: postprandial cardiac hypertrophy in pythons.

Oxygen consumption by carnivorous reptiles increases enormously after they have eaten a large meal in order to meet metabolic demands, and this places an extra load on the cardiovascular system. Here we show that there is an extraordinarily rapid 40% increase in ventricular muscle mass in Burmese pythons (Python molurus) a mere 48 hours after feeding, which results from increased gene expression of muscle-contractile proteins. As this fully reversible hypertrophy occurs naturally, it could provide a useful model for investigating the mechanisms that lead to cardiac growth in other animals.

Eat and run: prioritization of oxygen delivery during elevated metabolic states.

The principal function of the cardiopulmonary system is the matching of oxygen and carbon dioxide transport to the metabolic requirements of different tissues. Increased oxygen demands (VO2), for example during physical activity, result in a rapid compensatory increase in cardiac output and redistribution of blood flow to the appropriate skeletal muscles. These cardiovascular changes are matched by suitable ventilatory increments.

Elevated intra-abdominal pressure limits venous return during exercise in Varanus exanthematicus.

The effects of treadmill exercise on components of the cardiovascular (venous return, heart rate, arterial blood pressure) and respiratory systems (minute ventilation, tidal volume, breathing frequency, oxygen consumption, carbon dioxide production) and intra-abdominal pressure were investigated in the Savannah monitor lizard, Varanus exanthematicus B., at 35 degrees C. Compared with resting conditions, treadmill exercise significantly increased lung ventilation, gular pumping, intra-abdominal pressure, mean arterial blood pressure and venous return (blood flow in the post caval vein).

Thermal acclimation effects differ between voluntary, maximum, and critical swimming velocities in two cyprinid fishes.

Temperature acclimation may be a critical component of the locomotor physiology and ecology of ectothermic animals, particularly those living in eurythermal environments. Several studies of fish report striking acclimation of biochemical and kinetic properties in isolated muscle. However, the relatively few studies of whole-animal performance report variable acclimation responses.

Experimental evolution and the Krogh principle: generating biological novelty for functional and genetic analyses.

August Krogh counseled the careful selection of the best subject organism on which to undertake mechanistic physiological research. But what if an organism with the desired properties does not exist? It is now within our power to engineer organisms genetically to achieve novel combinations of traits. I propose that it is a logical extension of the Krogh principle that we use biological methodologies to create novel organisms ideally suited for particular physiological studies.

Evolutionary changes in heat-inducible gene expression in lines of Escherichia coli adapted to high temperature.

The involvement of heat-inducible genes, including the heat-shock genes, in the acute response to temperature stress is well established. However, their importance in genetic adaptation to long-term temperature stress is less clear. Here we use high-density arrays to examine changes in expression for 35 heat-inducible genes in three independent lines of Escherichia coli that evolved at high temperature (41.

Rapid evolution of escape ability in Trinidadian guppies (Poecilia reticulata).

Predators are widely assumed to create selection that shapes the evolution of prey escape abilities. However, this assumption is difficult to test directly due to the challenge of recording both predation and its evolutionary consequences in the wild. We examined these events by studying natural and experimental populations of Trinidadian guppies, Poecilia reticulata, which occur in distinct high-predation and low-predation environments within streams.

EVOLUTIONARY ADAPTATION TO TEMPERATURE. VII. EXTENSION OF THE UPPER THERMAL LIMIT OF ESCHERICHIA COLI.

What factors influence the ability of populations to adapt to extreme environments that lie outside their current tolerance limits? We investigated this question by exposing experimental populations of the bacterium Escherichia coli to lethally high temperatures. We asked: (1) whether we could obtain thermotolerant mutants with an extended upper thermal limit by this selective screen; (2) whether the propensity to obtain thermotolerant mutants depended on the prior selective history of the progenitor genotypes; and (3) how the fitness properties of these mutants compared to those of their progenitors within the ancestral thermal niche. Specifically, we subjected 15 independent populations founded from each of six progenitors to 44°C; all of the progenitors had upper thermal limits between about 40°C and 42°C.