Adaptive Evolution (adaptive + evolution)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts


EVOLUTION, Issue 8 2008
The importance of contingency versus predictability in evolution has been a long-standing issue, particularly the interaction between genetic background, founder effects, and selection. Here we address experimentally the effects of genetic background and founder events on the repeatability of laboratory adaptation in Drosophila subobscura populations for several functional traits. We found disparate starting points for adaptation among laboratory populations derived from independently sampled wild populations for all traits. With respect to the subsequent evolutionary rate during laboratory adaptation, starvation resistance varied considerably among foundations such that the outcome of laboratory evolution is rather unpredictable for this particular trait, even in direction. In contrast, the laboratory evolution of traits closely related to fitness was less contingent on the circumstances of foundation. These findings suggest that the initial laboratory evolution of weakly selected characters may be unpredictable, even when the key adaptations under evolutionary domestication are predictable with respect to their trajectories. [source]


EVOLUTION, Issue 7 2004
Doris Bachtrog
Abstract We study the population genetics of adaptation in nonequilibrium haploid asexual populations. We find that the accumulation of deleterious mutations, due to the operation of Muller's ratchet, can considerably reduce the rate of fixation of advantageous alleles. Such reduction can be approximated reasonably well by a reduction in the effective population size. In the absence of Muller's ratchet, a beneficial mutation can only become fixed if it creates the best possible genotype; if Muller's ratchet operates, however, mutations initially arising in a nonoptimal genotype can also become fixed in the population, since the loss of the least-loaded class implies that an initially nonoptimal background can become optimal. We show that, while the rate at which adaptive mutations become fixed is reduced, the rate of fixation of deleterious mutations due to the ratchet is not changed by the presence of beneficial mutations as long as the rate of their occurrence is low and the deleterious effects of mutations (sd) are higher than the beneficial effects (sa). When sa>sd, the advantage of a beneficial mutation can outweigh the deleterious effects of associated mutations. Under these conditions, a beneficial allele can drag to fixation deleterious mutations initially associated with it at a higher rate than in the absence of advantageous alleles. We propose analytical approximations for the rates of accumulation of deleterious and beneficial mutations. Furthermore, when allowing for the possible occurrence of interference between beneficial alleles, we find that the presence of deleterious mutations of either very weak or very strong effect can marginally increase the rate of accumulation of beneficial mutations over that observed in the absence of such deleterious mutations. [source]

Autumnal moth , why autumnal?

Toomas Tammaru
Summary 1. As for some other spring-feeding moths, adult flight of Epirrita autumnata (Lepidoptera: Geometridae) occurs in late autumn. Late-season flight is a result of a prolonged pupal period. Potential evolutionary explanations for this phenological pattern are evaluated. 2. In a laboratory rearing, there was a weak correlation between pupation date and the time of adult emergence. A substantial genetic difference in pupal period was found between two geographic populations. Adaptive evolution of eclosion time can thus be expected. 3. Metabolic costs of a prolonged pupal period were found to be moderate but still of some ecological significance. Pupal mortality is likely to form the main cost of the prolonged pupal period. 4. Mortality rates of adults, exposed in the field, showed a declining temporal trend from late summer to normal eclosion time in autumn. Lower predation pressure on adults may constitute the decisive selective advantage of late-season flight. It is suggested that ants, not birds, were the main predators responsible for the temporal trend. 5. Egg mortality was estimated to be low; it is thus unlikely that the late adult period is selected for to reduce the time during which eggs are exposed to predators. 6. In a laboratory experiment, oviposition success was maximal at the time of actual flight peak of E. autumnata, however penalties resulting from sub-optimal timing of oviposition remained limited. [source]


EVOLUTION, Issue 3 2008
Justin Ramsey
Adaptive evolution is often associated with speciation. In plants, however, ecotypic differentiation is common within widespread species, suggesting that climatic and edaphic specialization can outpace cladogenesis and the evolution of postzygotic reproductive isolation. We used cpDNA sequence (5 noncoding regions, 3.5 kb) and amplified fragment length polymorphisms (AFLPs: 4 primer pairs, 1013 loci) to evaluate the history of ecological differentiation in the North American Achillea millefolium, an autopolyploid complex of "ecological races" exhibiting morphological, physiological, and life-history adaptations to diverse environments. Phylogenetic analyses reveal North American A. millefolium to be a monophyletic group distinct from its European and Asian relatives. Based on patterns of sequence divergence, as well as fossil and paleoecological data, colonization of North America appears to have occurred via the Bering Land Bridge during the Pleistocene (1.8 MYA to 11,500 years ago). Population genetic analyses indicate negligible structure within North American A. millefolium associated with varietal identity, geographic distribution, or ploidy level. North American populations, moreover, exhibit the signature of demographic expansion. These results affirm the "ecotype" concept of the North American Achillea advocated by classical research and demonstrate the rapid rate of ecological differentiation that sometimes occurs in plants. [source]

Adaptive evolution of lateral plates in three-spined stickleback Gasterosteus aculeatus: a case study in functional analysis of natural variation

R. D. H. Barrett
The three-spined stickleback Gasterosteus aculeatus is a model species for studying questions in ecology and evolution. The rapid diversification of G. aculeatus in post-glacial freshwater environments, combined with recently developed molecular tools, provides a unique opportunity to study the functional basis of fitness variation in natural populations. In derived freshwater populations, a number of morphological traits have diverged in parallel from the marine ancestral state, including the number of lateral armour plates. Evolution of reduced armour in freshwater populations is due to positive selection from both abiotic and biotic mechanisms. The major effect gene (ectodysplasin-A or Eda), along with several minor effect genetic regions, has recently been shown to control lateral plate variation. Field experiments have further determined the fitness consequences of allelic variation at the major effect locus. This work helps elucidate the mechanisms connecting genetic variation with phenotypic variation and fitness in the wild, a synthesis that should be applicable to many other phenotypic traits and species of fishes. [source]

Adaptive evolution of baker's yeast in a dough-like environment enhances freeze and salinity tolerance

Jaime Aguilera
Summary We used adaptive evolution to improve freeze tolerance of industrial baker's yeast. Our hypothesis was that adaptation to low temperature is accompanied by enhanced resistance of yeast to freezing. Based on this hypothesis, yeast was propagated in a flour-free liquid dough model system, which contained sorbitol and NaCl, by successive batch refreshments maintained constantly at 12░C over at least 200 generations. Relative to the parental population, the maximal growth rate (Ámax) under the restrictive conditions, increased gradually over the time course of the experiment. This increase was accompanied by enhanced freeze tolerance. However, these changes were not the consequence of genetic adaptation to low temperature, a fact that was confirmed by prolonged selection of yeast cells in YPD at 12░C. Instead, the experimental populations showed a progressive increase in NaCl tolerance. This phenotype was likely achieved at the expense of others traits, since evolved cells showed a ploidy reduction, a defect in the glucose derepression mechanism and a loss in their ability to utilize gluconeogenic carbon sources. We discuss the genetic flexibility of S. cerevisiae in terms of adaptation to the multiple constraints of the experimental design applied to drive adaptive evolution and the technologically advantageous phenotype of the evolved population. [source]

Selection of preadapted populations allowed Senecio inaequidens to invade Central Europe

Oliver Bossdorf
ABSTRACT Invasive species often evolve rapidly in response to the novel biotic and abiotic conditions in their introduced range. Such adaptive evolutionary changes might play an important role in the success of some invasive species. Here, we investigated whether introduced European populations of the South African ragwort Senecio inaequidens (Asteraceae) have genetically diverged from native populations. We carried out a greenhouse experiment where 12 South African and 11 European populations were for several months grown at two levels of nutrient availability, as well as in the presence or absence of a generalist insect herbivore. We found that, in contrast to a current hypothesis, plants from introduced populations had a significantly lower reproductive output, but higher allocation to root biomass, and they were more tolerant to insect herbivory. Moreover, introduced populations were less genetically variable, but displayed greater plasticity in response to fertilization. Finally, introduced populations were phenotypically most similar to a subset of native populations from mountainous regions in southern Africa. Taking into account the species' likely history of introduction, our data support the idea that the invasion success of Senecio inaequidens in Central Europe is based on selective introduction of specific preadapted and plastic genotypes rather than on adaptive evolution in the introduced range. [source]


EVOLUTION, Issue 6 2009
Lukas Schńrer
Sex allocation is a crucial life-history parameter in all sexual organisms. Over the last decades a body of evolutionary theory, sex allocation theory, was developed, which has yielded capital insight into the evolution of optimal sex allocation patterns and adaptive evolution in general. Most empirical work, however, has focused on species with separate sexes. Here I review sex allocation theory for simultaneous hermaphrodites and summarize over 50 empirical studies, which have aimed at evaluating this theory in a diversity of simultaneous hermaphrodites spanning nine animal phyla. These studies have yielded considerable qualitative support for several predictions of sex allocation theory, such as a female-biased sex allocation when the number of mates is limited, and a shift toward a more male-biased sex allocation with increasing numbers of mates. In contrast, many fundamental assumptions, such as the trade-off between male and female allocation, and numerous predictions, such as brooding limiting the returns from female allocation, are still poorly supported. Measuring sex allocation in simultaneously hermaphroditic animals remains experimentally demanding, which renders evaluation of more quantitative predictions a challenging task. I identify the main questions that need to be addressed and point to promising avenues for future research. [source]


EVOLUTION, Issue 3 2009
Mark E. Sherrard
Environmental stress can alter genetic variation and covariation underlying functional traits, and thus affect adaptive evolution in response to natural selection. However, the genetic basis of functional traits is rarely examined in contrasting resource environments, and consequently, there is no consensus regarding whether environmental stress constrains or facilitates adaptive evolution. We tested whether resource availability affects genetic variation for and covariation among seven physiological traits and seven morphological/performance traits by growing the annual grass Avena barbata in dry and well-watered treatments. We found that differences in the overall genetic variance,covariance (G) matrix between environments were driven by physiological traits rather than morphology and performance traits. More physiological traits were heritable in the dry treatment than the well-watered treatment and many of the genetic correlations among physiological traits were environment dependent. In contrast, genetic variation and covariation among the morphological and performance traits did not differ across treatments. Furthermore, genetic correlations between physiology and performance were stronger in the dry treatment, which contributed to differences in the overall G -matrix. Our results therefore suggest that physiological adaptation would be constrained by low heritable variation in resource-rich environments, but facilitated by higher heritable variation and stronger genetic correlations with performance traits in resource-poor environments. [source]


EVOLUTION, Issue 8 2008
Thomas F. Hansen
Most phylogenetic comparative methods used for testing adaptive hypotheses make evolutionary assumptions that are not compatible with evolution toward an optimal state. As a consequence they do not correct for maladaptation. The "evolutionary regression" that is returned is more shallow than the optimal relationship between the trait and environment. We show how both evolutionary and optimal regressions, as well as phylogenetic inertia, can be estimated jointly by a comparative method built around an Ornstein,Uhlenbeck model of adaptive evolution. The method considers a single trait adapting to an optimum that is influenced by one or more continuous, randomly changing predictor variables. [source]


EVOLUTION, Issue 5 2007
Stephen Wroe
Phenotypic similarities between distantly related marsupials and placentals are commonly presented as examples of convergence and support for the role of adaptive evolution in shaping morphological and ecological diversity. Here we compare skull shape in a wide range of carnivoran placentals (Carnivora) and nonherbivorous marsupials using a three-dimensional (3-D) geometric morphometric approach. Morphological and ecological diversity among extant carnivorans is considerably greater than is evident in the marsupial order Dasyuromorphia with which they have most commonly been compared. To examine convergence across a wider, but broadly comparable range of feeding ecologies, a dataset inclusive of nondasyuromorphian marsupials and extinct taxa representing morphotypes no longer present was assembled. We found support for the adaptive paradigm, with correlations between morphology, feeding behavior, and bite force, although skull shape better predicted feeding ecology in the phylogenetically diverse marsupial sample than in carnivorans. However, we also show that remarkably consistent but differing constraints have influenced the evolution of cranial shape in both groups. These differences between carnivorans and marsupials, which correlate with brain size and bite force, are maintained across the full gamut of morphologies and feeding categories, from small insectivores and omnivores to large meat-specialists. [source]


EVOLUTION, Issue 4 2006
Kevin J. Parsons
Abstract Colonization of a novel environment is expected to result in adaptive divergence from the ancestral population when selection favors a new phenotypic optimum. Local adaptation in the new environment occurs through the accumulation and integration of character states that positively affect fitness. The role played by plastic traits in adaptation to a novel environment has generally been ignored, except for variable environments. We propose that if conditions in a relatively stable but novel environment induce phenotypically plastic responses in many traits, and if genetic variation exists in the form of those responses, then selection may initially favor the accumulation and integration of functionally useful plastic responses. Early divergence between ancestral and colonist forms will then occur with respect to their plastic responses across the gradient bounded by ancestral and novel environmental conditions. To test this, we compared the magnitude, integration, and pattern of plastic character responses in external body form induced by shallow versus open water conditions between two sunfish ecomorphs that coexist in four postglacial lakes. The novel sunfish ecomorph is present in the deeper open water habitat, whereas the ancestral ecomorph inhabits the shallow waters along the lake margin. Plastic responses by open water ecomorphs were more correlated than those of their local shallow water ecomorph in two of the populations, whereas equal levels of correlated plastic character responses occurred between ecomorphs in the other two populations. Small but persistent differences occurred between ecomorph pairs in the pattern of their character responses, suggesting a recent divergence. Open water ecomorphs shared some similarities in the covariance among plastic responses to rearing environment. Replication in the form of correlated plastic responses among populations of open water ecomorphs suggests that plastic character states may evolve under selection. Variation between ecomorphs and among lake populations in the covariance of plastic responses suggests the presence of genetic variation in plastic character responses. In three populations, open water ecomorphs also exhibited larger plastic responses to the environmental gradient than the local shallow water ecomorph. This could account for the greater integration of plastic responses in open water ecomorphs in two of the populations. This suggests that the plastic responses of local sunfish ecomorphs can diverge through changes in the magnitude and coordination of plastic responses. Although these results require further investigation, they suggest that early adaptive evolution in a novel environment can include changes to plastic character states. The genetic assimilation of coordinated plastic responses could result in the further, and possibly rapid, divergence of such populations and could also account for the evolution of genes of major effect that contribute to suites of phenotypic differences between divergent populations. [source]


EVOLUTION, Issue 3 2004
Peter H. Niewiarowski
Abstract Over the past 15 years, phylogenetic comparative methods (PCMs) have become standard in the study of life-history evolution. To date, most studies have focused on variation among species or higher taxonomic levels, generally revealing the presence of significant phylogenetic effects as well as residual variation potentially attributable to adaptive evolution. Recently, population-level phylogenetic hypotheses have become available for many species, making it possible to apply PCMs directly to the level at which experiments are typically used to test adaptive hypotheses. In this study, we present the results of PCMs applied to life-history variation among populations of the widespread and well-studied lizard Sceloporus undulatus. Using S. undulatus (which may represent four closely related species) as an example, we explore the benefits of using PCMs at the population level, as well as consider the importance of several thorny methodological problems including but not limited to nonindependence of populations, lack of sufficient variation in traits, and the typically small sample sizes dictated by the difficulty of collecting detailed demographic data. We show that phylogenetic effects on life-history variation among populations of S. undulatus appear to be unimportant, and that several classic trade-offs expected by theory and revealed by many interspecific comparisons are absent. Our results suggest that PCMs applied to variation in life-history traits below the species level may be of limited value, but more studies like ours are needed to draw a general conclusion. Finally, we discuss several outstanding problems that face studies seeking to apply PCMs below the species level. [source]


EVOLUTION, Issue 6 2002
Kevin J. Burns
Abstract Despite the importance of Darwin's finches to the development of evolutionary theory, the origin of the group has only recently been examined using a rigorous, phylogenetic methodology that includes many potential outgroups. Knowing the evolutionary relationships of Darwin's finches to other birds is important for understanding the context from which this adaptive radiation arose. Here we show that analysis of mitochondrial DNA sequence data from the cytochrome b gene confirm that Darwin's finches are monophyletic. In addition, many taxa previously proposed as the sister taxon to Darwin's finches can be excluded as their closest living relative. Darwin's finches are part of a well-supported monophyletic group of species, all of which build a domed nest. All but two of the non-Darwin's finches included in this clade occur on Caribbean islands and most are Caribbean endemics. These close relatives of Darwin's finches show a diversity of bill types and feeding behaviors similar to that observed among Darwin's finches themselves. Recent studies have shown that adaptive evolution in Darwin's finches occurred relatively quickly. Our data show that among the relatives of Darwin's finches, the evolution of bill diversity was also rapid and extensive. [source]

Morphological variation over ontogeny and environments in resource polymorphic arctic charr (Salvelinus alpinus)

Kevin J. Parsons
SUMMARY Natural selection requires genetically based phenotypic variation to facilitate its action and cause adaptive evolution. It has become increasingly recognized that morphological development can become canalized likely as a result of selection. However, it is largely unknown how selection may influence canalization over ontogeny and differing environments. Changes in environments or colonization of a novel one is expected to result in adaptive divergence from the ancestral population when selection favors a new phenotypic optimum. In turn, a novel environment may also expose variation previously hidden from natural selection. We tested for changes in phenotypic variation over ontogeny and environments among ecomorphs of Arctic charr (Salvelinus alpinus) from two Icelandic lakes. Populations represented varying degrees of ecological specialization, with one lake population possessing highly specialized ecomorphs exhibiting a large degree of phenotypic divergence, whereas the other displayed more subtle divergence with more ecological overlap. Here we show that ecomorphs hypothesized to be the most specialized in each lake possess significant reductions in shape variation over ontogeny regardless of environmental treatment suggesting canalized development. However, environments did change the amount of shape variation expressed in these ecomorphs, with novel environments slowing the rate at which variation was reduced over ontogeny. Thus, environmental conditions may play an important role in determining the type and amount of genetically based phenotypic variation exposed to natural selection. [source]

Adaptive versus non-adaptive phenotypic plasticity and the potential for contemporary adaptation in new environments

Summary 1The role of phenotypic plasticity in evolution has historically been a contentious issue because of debate over whether plasticity shields genotypes from selection or generates novel opportunities for selection to act. Because plasticity encompasses diverse adaptive and non-adaptive responses to environmental variation, no single conceptual framework adequately predicts the diverse roles of plasticity in evolutionary change. 2Different types of phenotypic plasticity can uniquely contribute to adaptive evolution when populations are faced with new or altered environments. Adaptive plasticity should promote establishment and persistence in a new environment, but depending on how close the plastic response is to the new favoured phenotypic optimum dictates whether directional selection will cause adaptive divergence between populations. Further, non-adaptive plasticity in response to stressful environments can result in a mean phenotypic response being further away from the favoured optimum or alternatively increase the variance around the mean due to the expression of cryptic genetic variation. The expression of cryptic genetic variation can facilitate adaptive evolution if by chance it results in a fitter phenotype. 3We conclude that adaptive plasticity that places populations close enough to a new phenotypic optimum for directional selection to act is the only plasticity that predictably enhances fitness and is most likely to facilitate adaptive evolution on ecological time-scales in new environments. However, this type of plasticity is likely to be the product of past selection on variation that may have been initially non-adaptive. 4We end with suggestions on how future empirical studies can be designed to better test the importance of different kinds of plasticity to adaptive evolution. [source]

Behavioural syndromes differ predictably between 12 populations of three-spined stickleback

Summary 1Animals often differ in suites of correlated behaviours, comparable with how humans differ in personality. Constraints on the architecture of behaviour have been invoked to explain why such ,behavioural syndromes' exist. From an adaptationist viewpoint, however, behavioural syndromes should evolve only in those populations where natural selection has favoured such trait covariance, and they should therefore exist only in particular types of population. 2A comparative approach was used to examine this prediction of the adaptive hypothesis. We measured behavioural correlations in 12 different populations of three-spined stickleback (Gasterosteus aculeatus) and assessed whether they indeed varied consistently according to the selective environment, where population was unit of analysis. 3For a sample of fry from each population, we measured five different behaviours within the categories of (i) aggression (towards conspecifics); (ii) general activity; and (iii) exploration,avoidance (of novel foods, novel environments and altered environments). 4We show that behavioural syndromes are not always the same in different types of stickleback population: the often-documented syndrome between aggressiveness, activity and exploratory behaviour existed only in large ponds where piscivorous predators were present. In small ponds where predators were absent, these behaviours were not (or only weakly) associated. 5Our findings imply that population variation in behavioural syndromes does not result from stochastic evolutionary processes, but may result instead from adaptive evolution of behaviour favouring what should prove to be optimal trait combinations. [source]

East meets west: adaptive evolution of an insect introduced for biological control

C. B Phillips
Summary 1A possible explanation for low success rates when introducing natural enemies to new regions for biological control of insect pests is that they fail to adapt to their new conditions. Therefore it has been widely recommended that biological control practitioners increase the probability of local adaptation by maximizing the genetic variation released. An alternative recommendation is to use climate matching to identify native populations that may already possess traits suited to the new region. However, support for these recommendations is weak through lack of empirical evidence that local adaptation is important to biological control. 2This study examined how genetic drift and selection influenced the population frequencies of two asexually reproducing, genetically differentiated parasitoid biotypes that were introduced to New Zealand from South America for biological control. Other than by mutation, the biotypes were genetically fixed due to the absence of recombination both within and between biotypes. This meant that adaptive evolution could occur only if selection acted on any traits that varied between the biotypes introduced from South America. 3The two parasitoid biotypes were released simultaneously at 14 sites and their frequencies were monitored for up to 10 years. Changes in biotype frequency were consistent with strong directional selection favouring one of the South American biotypes, thus generating established parasitoid populations that were better adapted to New Zealand conditions than those that had originally been released. This local adaptation of the control agent contributed to greater mortality of the pest. 4Synthesis and applications. This study provides the first clear demonstration of the importance of releasing natural enemy genetic variation in new regions to foster adaptive evolution and improve success rates in classical biological control. However, the benefit to biological control of maximizing the genetic variation released needs to be balanced against possible risks to non-target species. The results do not support the concept of choosing sampling sites for putative biological control agents based solely on climatic similarities between the source location and the intended region of introduction. [source]

Tornaria of hemichordates and other dipleurula-type larvae: a comparison,

L. P. Nezlin
The evolutionary origin of phylum Chordata is the subject of intensive discussion, with the most conflicting views prevalent. One popular theory advocates the separation of chordates from a dipleurula-like ancestor. Thus the dipleurula-type larvae (tornaria of enteropneusts, auricularia and bipinnaria of echinoderms) are considered to recapitulate the ancestral features and the direct evolutionary path from Echinodermata and Hemichordata to Chordata (i.e. Garstang 1894 Zool. Anzeiger 27, 122,125; Grobben 1908 Verh. Zool.-Bot. Ges. Wien 58, 491,511; Dillon 1965 Evolution 19, 436,446; Jollie 1973 Acta Zool. (Stockholm) 54, 81,100; Ivanova-Kazas and Ivanov 1987 Sov. J. Mar. Biol. 13, 67,80; Crowther and Whittaker 1992 J. Neurophysiol. 23, 280,292; Lacalli 1994 Am. Zool. 34, 533,541; Lacalli et al. 1999 Proc. R. Soc. Biol. Series B 266, 1461,1470; Nielsen 1999 Dev. Genes Evol. 209, 198,205). Comparison of the nervous system in enteropneust tornariae and echinoderm larvae has revealed however, striking differences in distribution of biogenic amines and cholinesterase activity. In tornariae, monoamine-containing cells concentrate in the aboral and oesophageal ganglia. In echinoderms, they are located along the ciliary bands throughout their length. The difference in distribution of cholinesterase activity in each group reasonably suggests that acetylcholine-dependent control of locomotion also differs. Our data do not support the homology of the dipleurula-type larvae. Therefore we believe in the course of adaptive evolution, larvae of certain marine invertebrates acquired a set of common morphological and behavioural characteristics, yet retained different physiological mechanisms of behavioural regulation. Thus, similarities in the dipleurula-type larvae (tornaria, auricularia or bipinnaria, and actinotrocha) may have originated from convergence rather then from a common dipleurula-type predecessor. In consequence we must call into question any attempt to trace the ancestors of Chordata to the dipleurula-type animal. [source]

Adaptive evolution of baker's yeast in a dough-like environment enhances freeze and salinity tolerance

Jaime Aguilera
Summary We used adaptive evolution to improve freeze tolerance of industrial baker's yeast. Our hypothesis was that adaptation to low temperature is accompanied by enhanced resistance of yeast to freezing. Based on this hypothesis, yeast was propagated in a flour-free liquid dough model system, which contained sorbitol and NaCl, by successive batch refreshments maintained constantly at 12░C over at least 200 generations. Relative to the parental population, the maximal growth rate (Ámax) under the restrictive conditions, increased gradually over the time course of the experiment. This increase was accompanied by enhanced freeze tolerance. However, these changes were not the consequence of genetic adaptation to low temperature, a fact that was confirmed by prolonged selection of yeast cells in YPD at 12░C. Instead, the experimental populations showed a progressive increase in NaCl tolerance. This phenotype was likely achieved at the expense of others traits, since evolved cells showed a ploidy reduction, a defect in the glucose derepression mechanism and a loss in their ability to utilize gluconeogenic carbon sources. We discuss the genetic flexibility of S. cerevisiae in terms of adaptation to the multiple constraints of the experimental design applied to drive adaptive evolution and the technologically advantageous phenotype of the evolved population. [source]

The genetics of adaptation to novel environments: selection on germination timing in Arabidopsis thaliana

When studying selection during adaptation to novel environments, researchers have often paid little attention to an organism's earliest developmental stages. Despite this lack of attention, early life history traits may be under strong selection during colonization, as the expression of adaptive phenotypes at later points is contingent upon early survival. Moreover, the timing of early developmental transitions can constrain the timing of later transitions, with potentially large effects on fitness. In this issue, Huang et al. (2010) underscore the importance of early life history traits in the adaptation of Arabidopsis thaliana to old-field sites in North America. Using a new population of mapped recombinant inbred lines, the authors examined germination timing and total lifetime fitness of A. thaliana while varying site latitude, dispersal season, and maternal photoperiod. Huang et al. (2010) discovered several Quantitative Trait Loci (QTL) with large effects on fitness that colocalized with QTL for field germination timing and seed dormancy,demonstrating that fitness is genetically associated with these early life history traits, and that these loci are likely under strong selection during adaptation to novel environments. In the epistatic interactions of some loci, recombinant genotypes outperformed parental genotypes, supporting the potentially adaptive role of recombination. This study provides elegant evidence that traits expressed early in an organism's development can play an important role during adaptive evolution. [source]

Up against the edge: invasive species as testbeds for basic questions about evolution in heterogeneous environments

Yogi Berra is often credited, with having opined that ,prediction is very difficult, especially about the future'. There is no discipline for which this statement holds with more force than invasion biology, where it has been historically very challenging to predict the fate of introduced species (Williamson 2006). Some species after introduction quickly go extinct. Other relatively similar species may persist, but with little spread from their initial beachheads. Yet others can become aggressive invaders, with devastating consequences for native communities and ecosystems. This lack of predictability may of course sometimes reflect a simple lack of knowledge, both about key features of a species' basic biology, and about the environmental and community milieu in which invasion occurs (Williamson 2006). However, unpredictability may also arise from a fundamental fact about populations of living organisms , they almost always contain genetic variation, and so are not fixed entities responding to an environmental template, but instead labile in how they cope with the environment, over many spatial and temporal scales. Chance vicissitudes in the origination, maintenance and spatial organization of genetic variation could play a large role in generating the observed unpredictability in the fates of introduced species. The degree to which a particular introduced species becomes ,invasive', to the extent of coming to the attention of worried land managers, governmental officials and the public , may reflect in part its capacity for adaptive evolution across a wide range of environmental conditions. [source]

Diversification on an ecologically constrained adaptive landscape

Abstract We used phylogenetic analysis of body-size ecomorphs in a crustacean species complex to gain insight into how spatial complexity of ecological processes generates and maintains biological diversity. Studies of geographically widespread species of Hyalella amphipods show that phenotypic evolution is tightly constrained in a manner consistent with adaptive responses to alternative predation regimes. A molecular phylogeny indicates that evolution of Hyalella ecomorphs is characterized by parallel evolution and by phenotypic stasis despite substantial levels of underlying molecular change. The phylogeny suggests that species diversification sometimes occurs by niche shifts, and sometimes occurs without a change in niche. Moreover, diversification in the Hyalella ecomorphs has involved the repeated evolution of similar phenotypic forms that exist in similar ecological settings, a hallmark of adaptive evolution. The evolutionary stasis observed in clades separated by substantial genetic divergence, but existing in similar habitats, is also suggestive of stabilizing natural selection acting to constrain phenotypic evolution within narrow bounds. We interpret the observed decoupling of genetic and phenotypic diversification in terms of adaptive radiation on an ecologically constrained adaptive landscape, and suggest that ecological constraints, perhaps acting together with genetic and functional constraints, may explain the parallel evolution and evolutionary stasis inferred by the phylogeny. [source]

Adapting to winter in wheat: a long-term study follows parallel phenotypic and genetic changes in three experimental wheat populations

Abstract Drawing a direct connection between adaptive evolution at the phenotypic level and underlying genetic factors has long been a major goal of evolutionary biologists, but the genetic characterization of adaptive traits in natural populations is notoriously difficult. The study of evolution in experimental populations offers some help , initial conditions are known and changes can be tracked for extended periods under conditions more controlled than wild populations and more realistic than laboratory or greenhouse experiments. In this issue of Molecular Ecology, researchers studying experimental wheat populations over a 12-year period have demonstrated evolution in a major adaptive trait, flowering time, and parallel changes in underlying genetic variation (RhonÚet al. 2008). Their work suggests that cis -regulatory mutations at a single gene may explain most of the flowering time variation in these populations. [source]

Evidence for the adaptive evolution of the carbon fixation gene rbcL during diversification in temperature tolerance of a clade of hot spring cyanobacteria

S. R. Miller
Abstract Determining the molecular basis of enzyme adaptation is central to understanding the evolution of environmental tolerance but is complicated by the fact that not all amino acid differences between ecologically divergent taxa are adaptive. Analysing patterns of nucleotide sequence evolution can potentially guide the investigation of protein adaptation by identifying candidate codon sites on which diversifying selection has been operating. Here, I test whether there is evidence for molecular adaptation of the carbon fixation gene rbcL for a clade of hot spring cyanobacteria in the genus Synechococcus that has diverged in thermotolerance. Amino acid replacements during Synechococcus radiation have resulted in an increase in the number of hydrophobic residues in the RbcLs of more thermotolerant strains. A similar increase in hydrophobicity has been observed for many thermostable proteins. Maximum likelihood models which allow for heterogeneity among codon sites in the ratio of nonsynonymous to synonymous nucleotide substitutions estimated a class of amino acid sites as a target of positive selection. Depending on the model, a single amino acid site that interacts with a flexible element involved in the opening and closing of the active site was estimated with either low or moderate support to be a member of this class. Site-directed mutagenesis approaches are being explored in order to directly test its adaptive significance. [source]

A bacterial conjugation machinery recruited for pathogenesis

Anja Seubert
Summary Type IV secretion systems (T4SS) are multicomponent transporters of Gram-negative bacteria adapted to functions as diverse as DNA transfer in bacterial conjugation or the delivery of effector proteins into eukaryotic target cells in pathogenesis. The generally modest sequence conservation between T4SS may reflect their evolutionary distance and/or functional divergence. Here, we show that the establishment of intraerythrocytic parasitism by Bartonella tribocorum requires a putative T4SS, which shares an unprecedented level of sequence identity with the Trw conjugation machinery of the broad-host-range antibiotic resistance plasmid R388 (up to 80% amino acid identity for individual T4SS components). The highly conserved T4SS loci are collinear except for the presence of numerous tandem gene duplications in B. tribocorum, which mostly encode variant forms of presumed surface-exposed pilus subunits. Conservation is not only structural, but also functional: R388 mutated in either trwD or trwH encoding essential T4SS components could be trans -complemented for conjugation by the homologues of the B. tribocorum system. Conservation also includes the transcription regulatory circuit: both T4SS loci encode a highly homologous and interchangeable KorA/KorB repressor system that negatively regulates the expression of all T4SS components. This striking example of adaptive evolution reveals the capacity of T4SS to assume dedicated functions in either DNA transfer or pathogenesis over rather short evolutionary distance and implies a novel role for the conjugation systems of widespread broad-host-range plasmids in the evolution of bacterial pathogens. [source]

Chaperone and anti-chaperone: Two-faced synuclein as stimulator of synaptic evolution

Masayo Fujita
Previous studies have shown that ,-synuclein (,-syn), the homologue of ,-syn, inhibited ,-syn aggregation and stabilized Akt cell survival signaling molecule, suggesting that ,-syn was protective against ,-syn-related neurodegenerative disorders, such as Parkinson's disease and diffuse Lewy body disease. However, emerging evidence argues that the situation may be not so simple. Two missense mutations of ,-syn were identified in familial and sporadic diffuse Lewy body disease, and wild type ,-syn was induced to form fibril structures in vitro, while, ,-syn was shown to be protective against neurodegeneration caused by deletion of cysteine-string protein-,, the presynaptic cochaperone to Hsc70 in mice. Collectively, ,- and ,-syn are both, but in varying degrees, featured with two opposite properties, namely normal chaperone and anti-chaperone. By reviewing recent progress in syn biology with a particular focus on ,-syn, this manuscript refers to the intriguing possibility that the dual syn proteins might have acquired a driving force for synaptic evolution. Hypothetically, the anti-chaperone syn may provoke stress-induced diverse responses, whereas, the chaperone syn may provide buffering for them, allowing accumulation of nonlethal phenotypic variations in synapses. Consequently, dual syn proteins may cope with forth-coming stresses in the brain by stimulating adaptive evolution. In this context, failure to regulate this process due to various causes, such as gene mutations and environmental risk factors, may result in imperfect adaptability against stresses, leading to neurodegenerative disorders. [source]

Contribution of direct and maternal genetic effects to life-history evolution

Laura F. Galloway
Summary ,,Maternal effects are ubiquitous in nature. In plants, most work has focused on the effects of maternal environments on offspring trait expression. Less is known about the prevalence of genetic maternal effects and how they influence adaptive evolution. Here, we used multivariate genetic models to estimate the contributions of maternal and direct genetic (co)variance, the cross-generation direct-maternal covariance, and M, the matrix of maternal effect coefficients, for life-history traits in Campanulastrum americanum, a monocarpic herb. ,,Following a three-generation breeding design, we grew paternal half-sib families with full-sib relatives of each parent and measured juvenile and adult traits. ,,Seed size was influenced exclusively by maternal environmental effects, whereas maternal genetic effects influenced traits throughout the life cycle, including strong direct and maternal additive genetic correlations within and between generations for phenological and size traits. Examination of M suggested that both juvenile and adult traits in maternal plants influenced the expression of offspring traits. ,,This study reveals substantial potential for genetic maternal effects to contribute to adaptive evolution including cross-generation direct-maternal correlations that may slow selection response, maternal effects on phenology that reinforce genetic correlations, and within- and between-generation genetic correlations that may influence life-history polymorphism. [source]

Interpreting multidimensionality in parasite-induced phenotypic alterations: panselectionism versus parsimony

OIKOS, Issue 8 2010
Frank CÚzilly
The purpose of this note is to provide an alternative to the interpretation of multidimensionality in parasite-induced phenotypic alterations as a set of effectively-independent traits produced by adaptive evolution. We propose here that infection with so-called ,manipulative parasites' typically results in an ,infection syndrome', characterized by several distinctive symptoms corresponding to the alteration of particular phenotypic traits in infected hosts. Based on the available physiological evidence, we argue that symptoms might actually be the consequence of the dysregulation of some key neuromodulator, arising as a byproduct of the subversion of the host's immune system by the parasite. In that respect, it might be inadequate, from a functional point of view, to separate phenotypic effects that appear to increase trophic transmission from those that do not. We suggest that future research should test the validity of the ,infection syndrome' hypothesis through focusing on the mechanisms involved in multidimensionality at the intraspecific level, and through looking for the existence of non-random associations between symptoms at the interspecific level, across host-parasite associations. [source]

Gene function beyond the single trait: natural variation, gene effects, and evolutionary ecology in Arabidopsis thaliana

ABSTRACT The purpose of plant functional genomics is to describe the patterns of gene expression and internal plant function underlying the ecological functions that sustain plant growth and reproduction. Plants function as integrated systems in which metabolic and developmental pathways draw on common resource pools and respond to a relatively small number of signal/response systems. Plants are also integrated with their environment, exchanging energy and matter with their surroundings and are consequently sensitive to changes in energy and resource fluxes. These two levels of integration complicate the description of gene function. Internal integration results in single genes often affecting multiple characteristics (pleiotropy) and interacting with multiple other genes (epistasis). Integration with the external environment leads to gene expression and the genes' phenotypic effects varying across environmental backgrounds (gene,environment interaction). An accurate description of the function of all genes requires an augmentation, already underway, of the study of isolated developmental and metabolic pathways to a more integrated approach involving the study of genetic effects across scales of variation usually regarded as the purview of ecological and evolutionary research. Since the evolution of gene function also depends on this complex of gene effects, progress in evolutionary genetics will also require understanding the nature of gene interactions and pleiotropy and the constraints and patterns they impose on adaptive evolution. Studying gene function in the context of the integrated organism is a major challenge, best met by developing co-ordinated research efforts in model systems. This review highlights natural variation in A. thaliana as a system for understanding integrated gene function in an ecological and evolutionary context. The current state of this research integration in A. thaliana is described by summarizing relevant approaches, current knowledge, and some potentially fruitful future studies. By introducing some of the fundamental questions of ecological and evolutionary research, experimental approaches and systems that can reveal new facets of gene function and gene effect are also described. A glossary is included in the Appendix. [source]