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PubMed2026

Quantifying the evolutionary potential for Delta Smelt persistence in a warming habitat.

Long-term persistence of managed species will depend, in part, on whether the species harbors the physiological or genetic potential to adjust to warming temperatures, and whether relevant genetic variation is modified by management practices. The critically endangered Delta Smelt (Hypomesus transpacificus) is intensively managed, but little is known about the presence of genetic variation for resistance to elevated temperature, which will be important to maintain for their persistence in a rapidly warming future. Using a pedigree and whole genome sequencing data, we characterized the genetic variation and genomic architecture for CTMax (as a metric of upper thermal tolerance) across control and elevated rearing temperatures, alongside covarying traits (body size, degree of hatchery ancestry). Warmer rearing temperatures increased CTMax through acclimation but also resulted in reduced additive genetic variation for the trait, which could constrain adaptation under thermal stress. We found that larger fish had reduced CTMax, although this effect was diminished at elevated temperatures. We observed modest heritability for CTMax at rearing temperatures of 15°C and 18°C (0.26 and 0.16, respectively), but only a limited number of loci were identified that had consistent effects on CTMax across rearing temperatures. Instead, the genomic basis of thermal tolerance was highly dependent on rearing temperature (many loci detected with a GxE effect). The influence of domestication selection was indicated by changes in allele frequency, and divergence in upper thermal tolerance and plasticity, between low and high hatchery ancestry groups. Minimal overlap between loci associated with domestication and CTMax suggests that these traits possess separate genetic underpinnings. Knowledge of genetic variation supporting ecologically relevant physiological variation may be useful for refuge management and may inform supplementation in an ever-warming environment.

conservation physiology↗
PubMedDate not supplied

Cytochrome P-450 in the brain. Potential evolutionary and therapeutic relevance of localization of drug-metabolizing enzymes.

The cytochrome P-4502D6 enzyme is reportedly expressed in the brain. It was hypothesized that brain P-450 may serve to diminish exposure and toxicity from exogenous substances by enhancing their elimination from the central nervous system (CNS). To test this, a physiologic-based kinetic model was developed to simulate drug concentrations in brain and blood in the presence and absence of CNS metabolism. The amount of cytochrome P-450 in the brain was set at 0.25% of hepatic levels to reflect the small amounts of enzyme reportedly present in the CNS. Simulations were performed for low, intermediate, and high clearance drugs, assuming the presence or absence of brain P-450 enzymes. Enzyme localization was simulated by systematically reducing the volume into which the enzyme was expressed. No difference could be detected in drug concentrations in the blood, regardless of whether enzyme was present and/or localized in brain tissue. Marked differences, however, were observed in steady-state tissue drug levels that were highly dependent on the presence or absence of the brain enzyme, its degree of localization, and its efficiency for its substrate. These results suggest that large intersubject variability in CNS response to some drugs could reflect interpatient differences in CNS drug metabolism.

Biological Evolution↗
PubMed2001

Predicting the emergence of resistance to antifungal drugs.

The emergence of antifungal drug resistance is inevitable. Here I discuss antibiotic resistance in the context of the adaptive potential of fungi and I propose an approach to predicting the evolution of antifungal resistance using experimental evolution of DNA sequences and microbial populations. Prediction is based on determination of evolutionary potential at two levels, the gene and the genome. At the level of the gene, evolutionary potential depends on the sequence space of candidate resistance genes defined by the fitness effects of all possible mutations in all possible combinations. At the level of the genome, evolutionary potential depends on the adaptive landscape defined by the fitness effects of all possible interactions among alleles constituting the genotype.

Antifungal Agents↗
PubMed2005

Genetic basis and consequences of niche construction: plasticity-induced genetic constraints on the evolution of seed dispersal in Arabidopsis thaliana.

Because seed dispersal influences the environment experienced by seeds, that environment can change as dispersal evolves. The evolutionary potential of dispersal can in turn change as dispersal evolves, if its expression of genetic variation depends on the postdispersal environment. We examined whether seed dispersion patterns have a detectable genetic basis (and therefore evolutionary potential) and determined whether that genetic basis changed depending on one postdispersal environmental factor: conspecific density. We grew replicates of 12 ecotypes of Arabidopsis thaliana at high and low density and measured seed dispersion patterns and maternal traits associated with dispersal under controlled conditions. We found density-dependent ecotypic variation for maternal traits that influence dispersal. Significant genetic variation for postdispersal sibling density was detected only when plants were grown at high density, suggesting that if dispersal evolves to result in lower postdispersal densities, the expression of genetic variation for dispersal would be reduced. This dynamic could lead to a plasticity-induced constraint on the evolution of dispersal. The ability of organisms to alter the environment they experience and the ability of that environment to evolve can alter evolutionary dynamics by augmenting or reducing evolutionary potential and thereby facilitating or constraining evolutionary responses to selection.

Arabidopsis↗
PubMed2003

Experimental prediction of the evolution of cefepime resistance from the CMY-2 AmpC beta-lactamase.

Understanding of the evolutionary histories of many genes has not yet allowed us to predict the evolutionary potential of those genes. Intuition suggests that current biochemical activity of gene products should be a good predictor of the potential to evolve related activities; however, we have little evidence to support that intuition. Here we use our in vitro evolution method to evaluate biochemical activity as a predictor of future evolutionary potential. Neither the class C Citrobacter freundii CMY-2 AmpC beta-lactamase nor the class A TEM-1 beta-lactamase confer resistance to the beta-lactam antibiotic cefepime, nor do any of the naturally occurring alleles descended from them. However, the CMY-2 AmpC enzyme and some alleles descended from TEM-1 confer high-level resistance to the structurally similar ceftazidime. On the basis of the comparison of TEM-1 and CMY-2, we asked whether biochemical activity is a good predictor of the evolutionary potential of an enzyme. If it is, then CMY-2 should be more able than the TEMs to evolve the ability to confer higher levels of cefepime resistance. Although we generated CMY-2 evolvants that conferred increased cefepime resistance, we did not recover any CMY-2 evolvants that conferred resistance levels as high as the best cefepime-resistant TEM alleles.

Bacterial Proteins↗
PubMedDate not supplied

Assessing conservation biology priorities through the development of biodiversity indicators.

Biodiversity erosion is now a recognized phenomenon within the scientific community, and it is understood that there is an urgent need for action to relieve this loss. However, no consensus exists on how to go about achieving this goal. This is due to two kinds of problems: namely, that there are many different reasons which can motivate conservation attempts and hence they can lead to different priorities, sometimes in direct contrast with one another; and that of the complexity of the natural world which we have to operate in. Regarding the latter, several authors have lamented a severe lack of theoretical support for many conservation decisions. We briefly review some of the criteria that are commonly adopted in conservation, and indicate some of their problems; we then introduce a new theoretical framework based on the use of a series of biological indicators, many of which have already been proposed in the past but never fully explained and/or adopted. In addition, we propose two indices for one of these potential indicators, i.e. evolutionary potential. We conclude with an appeal for a greater collaboration between conservation scientists and evolutionary biologists, in order to encompass evolutionary evidence in the decision-making process. In doing so, we hope to increase the chances of successful conservation efforts.

Animals↗
PubMed1990

copia expression is variable among natural populations of Drosophila.

A survey of copia (retroviral-like element) expression in flies representing 37 populations worldwide of Drosophila melanogaster, Drosophila simulans and Drosophila mauritiana demonstrates that, although copia elements are present in all three species, copia-encoded transcripts are detectable only in D. melanogaster. Levels of copia transcripts vary nearly 100-fold among flies representing geographically diverse populations of D. melanogaster and this variation is not correlated with variability in copia copy number. Analysis of transcript levels in interpopulation hybrids demonstrates that much of this variability may be attributable to the action of trans-acting controls. The geographic and phylogenetic pattern of copia expression suggests that moderate to high levels of copia expression may be a relatively recent evolutionary acquisition. The potential evolutionary significance of these findings is discussed.

Animals↗
PubMed2007

Differential impact of simultaneous migration on coevolving hosts and parasites.

BACKGROUND: The dynamics of antagonistic host-parasite coevolution are believed to be crucially dependent on the rate of migration between populations. We addressed how the rate of simultaneous migration of host and parasite affected resistance and infectivity evolution of coevolving meta-populations of the bacterium Pseudomonas fluorescens and a viral parasite (bacteriophage). The increase in genetic variation resulting from small amounts of migration is expected to increase rates of adaptation of both host and parasite. However, previous studies suggest phages should benefit more from migration than bacteria; because in the absence of migration, phages are more genetically limited and have a lower evolutionary potential compared to the bacteria. RESULTS: The results supported the hypothesis: migration increased the resistance of bacteria to their local (sympatric) hosts. Moreover, migration benefited phages more than hosts with respect to 'global' (measured with respect to the whole range of migration regimes) patterns of resistance and infectivity, because of the differential evolutionary responses of bacteria and phage to different migration regimes. Specifically, we found bacterial global resistance peaked at intermediate rates of migration, whereas phage global infectivity plateaued when migration rates were greater than zero. CONCLUSION: These results suggest that simultaneous migration of hosts and parasites can dramatically affect the interaction of host and parasite. More specifically, the organism with the lower evolutionary potential may gain the greater evolutionary advantage from migration.

Biological Evolution↗
PubMed2007

Regulation of male traits by testosterone: implications for the evolution of vertebrate life histories.

The negative co-variation of life-history traits such as fecundity and lifespan across species suggests the existence of ubiquitous trade-offs. Mechanistically, trade-offs result from the need to differentially allocate limited resources to traits like reproduction versus self-maintenance, with selection favoring the evolution of optimal allocation mechanism. Here I discuss the physiological (endocrine) mechanisms that underlie optimal allocation rules and how such rules evolve. The hormone testosterone may mediate life-history trade-offs due to its pleiotropic actions in male vertebrates. Conservation in the actions of testosterone in vertebrates has prompted the 'evolutionary constraint hypothesis,' which assumes that testosterone signaling mechanisms and male traits evolve as a unit. This hypothesis implies that the actions of testosterone are similar across sexes and species, and only the levels of circulating testosterone concentrations change during evolution. In contrast, the 'evolutionary potential hypothesis' proposes that testosterone signaling mechanisms and male traits evolve independently. In the latter scenario, the linkage between hormone and traits itself can be shaped by selection, leading to variation in trade-off functions. I will review recent case studies supporting the evolutionary potential hypothesis and suggest micro-evolutionary experiments to unravel the mechanistic basis of life-history evolution.

Aggression↗
PubMed1979

Symbionticism revisited: a discussion of the evolutionary impact of intracellular symbioses.

Wallin (1927) first published the notion that the fusion of bacteria with host cells was the principal source of genetic novelty for speciation. He suggested that mitochondria are transitional elements in this process. While the significance that he attributed to symbiosis now seem excessive, he was one of the first authors to be aware of the evolutionary potential of symbiotic events and his view of mitochondria may not seem strange to many cell biologist today. The most significant evolutionary development which has been attributed to intracellular symbiosis is the origin of eukaryotic cellular organization. The current status of the 'serial endosymbiosis hypothesis' is briefly review. The case for the symbiotic origin of the chloroplast, based principally on 16 S RNA oligonucleotide cataloguing, is very strong. Mitochondrial origins are more obscure but also appear to be symbiotic due to recent 18 S cataloguing from wheat embryos. The probablility of the multiple origin of some eukaryotic organelles is also examined, the processes in question being the acquisition of distinct stocks of chloroplasts from disparate photosynthetic prokaryotes and the secondary donation of organelles from degenerate eukaryotic endosymbionts to their hosts, with specific reference to the dinoflagellates Peridinium balticum, Kryptoperidinium foliaceum and the ciliate Mesodinium rubrum. It is concluded that the evolutionary potential of intracellular symbiosis ('cytobiosis': a term introduced in this paper) is great, with the best established influence being on the origin of eukaryotic chloroplasts. Together with the potential effects of viral vectors, symbiosis serves as a supplementary speciation mechanism capable of producing directed evolutionary changes. It is likely that these processes will explain some of the apparent anomalies in evolutionary rates and direction which are not readily explicable by the conventional synthetic theory of evolution.

Animals↗
PubMed1997

A structuralist theory of evolution reconsidered.

The structuralist theory of evolution is reconsidered in the light of new discoveries. According to this theory, the evolutionary potentialities are in the genotype (a hierarchically ordered set of interacting elements) and manifest themselves in the course of morphogenesis in association with changes in the environment. It is demonstrated that this theory is in fact the development of a long philosophical tradition, in which Darwin and Neo-Darwinism did not participate. New discoveries in the field of molecular cytogenetics confirm the ideas of evolutionary potentiality and hierarchical genotypic ordering. It is demonstrated that gene regulation can manifest itself in association with instabilities of the morphogenetic field and the attainment of a new equilibrium; this change could be connected with changes in the environment, but has nothing to do with natural selection.

Animals↗
PubMed2004

Phylogenetic effects, the loss of complex characters, and the evolution of development in calyptraeid gastropods.

Despite considerable theoretical and empirical work on the population genetic effects of mode of development in benthic marine invertebrates, it is unclear what factors generate and maintain interspecific variation in mode of development and few studies have examined such variation in a phylogenetic context. Here I combine data on mode of development with a molecular phylogeny of 72 calyptraeid species to test the following hypotheses about the evolution of mode of development: (1) Is the loss of feeding larvae irreversible? (2) Is there a phylogenetic effect on the evolution of mode of development? (3) Do embryos of direct-developing species lose the structures necessary for larval feeding and swimming and, if so, is the degree of embryonic modification correlated with the genetic distance between species? The results of these analyses suggest that mode of development evolves rapidly and with little phylogenetic inertia. There are three cases of the possible regain of feeding larvae, in all cases from direct development with nurse eggs. It appears that species with planktotrophic, lecithotrophic, or direct development with nurse eggs all have equal evolutionary potential and retain the possibility of subsequent evolution of a different mode of development. However, species with direct development from large yolky eggs appear to be subject to phylogenetic constraints and may not be able to subsequently evolve a different mode of development. Finally, species that have more recently evolved direct development have less highly modified embryos than older direct-developing species. Since species with nurse eggs generally have fewer embryonic modifications than those from large yolky eggs, this embryological difference may be the underlying cause of the difference in evolutionary potential.

Animals↗
PubMed2000

Ontogenetic differences in heterostylous plants and implications for development from a herkogamous ancestor.

Alternative ontogenetic pathways among heterostylous species of Rubiaceae may reflect differences in their evolutionary histories. In this study, measurements were taken at different developmental stages on a series of long-styled (LS) and short-styled (SS) buds of the heterostylous taxa Psychotria chiapensis, P. poeppigiana, and Bouvardia ternifolia (all Rubiaceae). Results indicated that modifications in growth rates of stamens relative to corollas in all three species led to differences in anther heights between LS and SS flowers. Distinct style heights for LS and SS flowers of P. chiapensis and P. poeppigiana originate in the earlier stages of bud development and are maintained as styles elongate at equal rates. This contrasts with B. ternifolia, which has differences in style heights resulting from unequal relative growth rates between floral morphs. The "approach herkogamous" floral morphology, defined by having stigmas positioned above anthers, has been proposed as a potential evolutionary precursor for heterostylous taxa. To examine this hypothesis, floral development of two species with approach herkogamous morphologies, Psychotria pittieri and P. brachiata, was compared to that of the three heterostylous taxa. Differences in the relative rates of style elongation for flowers of approach herkogamous versus heterostylous species predict additional steps in the original model for the evolution of heterostyly from an approach herkogamous ancestor. The diversity of heterostylous ontogenies found within Rubiaceae provides insight into potential evolutionary pathways for this sexual system in other angiosperm families.

Biological Evolution↗
PubMed2005

A test of quantitative genetic theory using Drosophila- effects of inbreeding and rate of inbreeding on heritabilities and variance components.

Inbreeding is expected to decrease the heritability within populations. However, results from empirical studies are inconclusive. In this study, we investigated the effects of three breeding treatments (fast and slow rate of inbreeding - inbred to the same absolute level - and a control) on heritability, phenotypic, genetic and environmental variances of sternopleural bristle number in Drosophila melanogaster. Heritability, and phenotypic, genetic and environmental variances were estimated in 10 replicate lines within each of the three treatments. Standard least squares regression models and Bayesian methods were used to analyse the data. Heritability and additive genetic variance within lines were higher in the control compared with both inbreeding treatments. Heritabilities and additive genetic variances within lines were higher in slow compared with fast inbred lines, indicating that slow inbred lines retain more evolutionary potential despite the same expected absolute level of inbreeding. The between line variance was larger with inbreeding and more than twice as large in the fast than in the slow inbred lines. The different pattern of redistribution of genetic variance within and between lines in the two inbred treatments cannot be explained invoking the standard model based on selective neutrality and additive gene action. Environmental variances were higher with inbreeding, and more so with fast inbreeding, indicating that inbreeding and the rate of inbreeding affect environmental sensitivity. The phenotypic variance decreased with inbreeding, but was not affected by the rate of inbreeding. No inbreeding depression for mean sternopleural bristle number was observed in this study. Considerable variance between lines in additive genetic variance within lines was observed, illustrating between line variation in evolutionary potential.

Analysis of Variance↗
PubMed2004

Evolution of triploidy in Apios americana (Leguminosae) revealed by genealogical analysis of the histone H3-D gene.

Autotriploidy is normally considered to be maladaptive in plants because of its association with high levels of sterility. Nonetheless, triploid individuals are found in many plant species and play important roles in plant evolution, in particular as a first step toward tetraploid formation. However, few studies have addressed the evolutionary potential of triploid lineages, which may principally suffer from the impossibility of combining useful mutations in a single genome due to their low fertility. Therefore, triploids acquire genetic diversity only via recurrent evolution and somaclonal mutation. This study evaluates the potential of multiple origins of polyploidy as a source of genetic diversity in Apios americana, a North American legume that possesses both diploid and triploid populations. Ploidy level determination via flow cytometry shows that triploids are mainly restricted to the portion of eastern North America that was covered by ice during the Wisconsinan glaciation 18,000 years ago. This distribution implies that either selection or postglaciation colonization played a role in shaping this cytogeographic pattern. A haplotype network of the single copy nuclear histone H3-D gene reconstructed using statistical parsimony, together with single-strand conformational polymorphism analysis, shows that autotriploidy evolved at least three times in this species and that heterozygosity is high in triploids. The genetic diversity found in A. americana resulting from recurrent evolution and fixed heterozygosity increases the likelihood of producing successful genotypes and may give the opportunity for triploids to be better fit than diploids in new habitats. This suggests that triploid lineages can exhibit evolutionary potential of their own, and do not serve solely as a first step toward tetraploid formation.

DNA Primers↗
PubMed2004

Phenotypic plasticity can potentiate rapid evolutionary change.

Using a computational model of string-like haploid genotypes, we verify the conjecture (J. Theor. Biol. 188 (1997) 153) that phenotypic plasticity can speed up evolution. The corresponding real-life situation was realized by Waddington in experiments carried out on the fruit fly Drosophila. Waddington found that after selecting for an environmentally induced trait over a number of generations, a new, true-breeding phenotype resulted that was absent in the starting population. The phenomenon, termed 'genetic assimilation', continues to attract interest because of the rapidity of the effect and because of its seemingly Lamarckian implications. By making use of a genetic algorithm-based approach developed previously, we show that conventional Darwinian selection acting on regulatory genes can account for genetic assimilation. The essential assumption in our model is that a structural gene can be in either of three allelic states. These correspond to its being (a) 'on' or 'off' constitutively or (b) in a plastic state in which the probability that it is 'on' or 'off' is influenced by regulatory loci in a dosage-dependent manner.

Animals↗
PubMed2006

The evolution of genetic architecture under frequency-dependent disruptive selection.

We propose a model to analyze a quantitative trait under frequency-dependent disruptive selection. Selection on the trait is a combination of stabilizing selection and intraspecific competition, where competition is maximal between individuals with equal phenotypes. In addition, there is a density-dependent component induced by population regulation. The trait is determined additively by a number of biallelic loci, which can have different effects on the trait value. In contrast to most previous models, we assume that the allelic effects at the loci can evolve due to epistatic interactions with the genetic background. Using a modifier approach, we derive analytical results under the assumption of weak selection and constant population size, and we investigate the full model by numerical simulations. We find that frequency-dependent disruptive selection favors the evolution of a highly asymmetric genetic architecture, where most of the genetic variation is concentrated on a small number of loci. We show that the evolution of genetic architecture can be understood in terms of the ecological niches created by competition. The phenotypic distribution of a population with an adapted genetic architecture closely matches this niche structure. Thus, evolution of the genetic architecture seems to be a plausible way for populations to adapt to regimes of frequency-dependent disruptive selection. As such, it should be seen as a potential evolutionary pathway to discrete polymorphisms and as a potential alternative to other evolutionary responses, such as the evolution of sexual dimorphism or assortative mating.

Alleles↗
PubMed2005

Among- and within-patch components of genetic diversity respond at different rates to habitat fragmentation: an empirical demonstration.

Habitat fragmentation is a ubiquitous by-product of human activities that can alter the genetic structure of natural populations, with potentially deleterious effects on population persistence and evolutionary potential. When habitat fragmentation results in the subdivision of a population, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulation, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulations and greater genetic divergence among them. Theoretical and simulation analyses predict that these two main genetic effects of fragmentation, greater differentiation among resulting subpopulation and reduced genetic diversity within them, will proceed at very different rates. Despite important implications for the interpretation of genetics data from fragmented populations, empirical evidence for this phenomenon has been lacking. In this analysis, we carry out an empirical study in population of an alpine meadow-dwelling butterfly, which have become fragmented increasing forest cover over five decades. We show that genetic differentiation among subpopulations (G(ST)) is most highly correlated with contemporary forest cover, while genetics diversity within subpopulation (expected heterozygosity) is better correlated with the spatial pattern of forest cover 40 years in the past. Thus, where habitat fragmentation has occurred in recent decades, genetic differentiation among subpopulation can be near equilibrium while contemporary measures of within subpopulation diversity may substantially overestimate the equilibrium values that will eventually be attained.

Alberta↗