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Selection Pressures (selection + pressure)
Kinds of Selection Pressures Selected AbstractsCOSTS AND LIMITS OF PHENOTYPIC PLASTICITY IN ISLAND POPULATIONS OF THE COMMON FROG RANA TEMPORARIA UNDER DIVERGENT SELECTION PRESSURESEVOLUTION, Issue 6 2009Martin I. Lind Costs and limits are assumed to be the major constraints on the evolution of phenotypic plasticity. However, despite their expected importance, they have been surprisingly hard to find in natural populations. It has therefore been argued that natural selection might have removed high-cost genotypes in all populations. However, if costs of plasticity are linked to the degree of plasticity expressed, then high costs of plasticity would only be present in populations where increased plasticity is under selection. We tested this hypothesis by investigating costs and limits of adaptive phenotypic plasticity in development time in a common garden study of island populations of the common frog Rana temporaria, which have varying levels of development time and phenotypic plasticity. Costs of plasticity were only found in populations with high-plastic genotypes, whereas the populations with the most canalized genotypes instead had a cost of canalization. Moreover, individuals displaying the most extreme phenotypes also were the most plastic ones, which mean we found no limits of plasticity. This suggests that costs of plasticity increase with increased level of plasticity in the populations, and therefore costs of plasticity might be more commonly found in high-plastic populations. [source] HABITAT-DEPENDENT SONG DIVERGENCE IN THE LITTLE GREENBUL: AN ANALYSIS OF ENVIRONMENTAL SELECTION PRESSURES ON ACOUSTIC SIGNALSEVOLUTION, Issue 9 2002Hans Slabbekoorn Abstract., Bird song is a sexual trait important in mate choice and known to be shaped by environmental selection. Here we investigate the ecological factors shaping song variation across a rainforest gradient in central Africa. We show that the little greenbul (Andropadus virens), previously shown to vary morphologically across the gradient in fitness-related characters, also varies with respect to song characteristics. Acoustic features, including minimum and maximum frequency, and delivery rate of song notes showed significant differences between habitats. In contrast, we found dialectal variation independent of habitat in population-typical songtype sequences. This pattern is consistent with ongoing gene flow across habitats and in line with the view that song variation in the order in which songtypes are produced is not dependent on habitat characteristics in the same way physical song characteristics are. Sound transmission characteristics of the two habitats did not vary significantly, but analyses of ambient noise spectra revealed dramatic and consistent habitat-dependent differences. Matching between low ambient noise levels for low frequencies in the rainforest and lower minimal frequencies in greenbul songs in this habitat suggests that part of the song divergence may be driven by habitat-dependent ambient noise patterns. These results suggest that habitat-dependent selection may act simultaneously on traits of ecological importance and those important in prezygotic isolation, leading to an association between morphological and acoustic divergence. Such an association may promote assortative mating and may be a mechanism driving reproductive divergence across ecological gradients. [source] Morphological variation and floral abnormalities in a trigger plant across a narrow altitudinal gradientAUSTRAL ECOLOGY, Issue 7 2009ARY A. HOFFMANN Abstract Local adaptation in alpine plants has been demonstrated across wide altitudinal gradients, but has rarely been examined across the alpine-to-montane transition that often encompasses only a few hundred metres. Here we characterize morphological variation in leaf and floral characteristics of the trigger plant Stylidium armeria along a narrow altitudinal gradient in the Bogong High Plains in Victoria. Across this gradient, which encompasses the high-elevation limit of this species, linear changes were found for floral scape height, leaf length and flower number. All these traits decreased with increasing altitude, whereas the frequency of abnormal flowers increased. When plants were grown in a common garden environment, an altitudinal pattern for flower abnormalities was no longer detected. However, altitudinal patterns for leaf length and scape height were maintained, albeit weaker than in the field. This indicates heritable variation for these morphological traits; the altitudinal patterns are likely to reflect the effects of selection by environmental factors that vary with altitude. Selection pressures remain to be identified but have generated both cogradient and countergradient patterns of variation. [source] Individual, Population, Community, and Ecosystem Consequences of a Fish Invader in New Zealand StreamsCONSERVATION BIOLOGY, Issue 1 2003Colin R. Townsend But because invaders can have unexpected indirect effects in food webs, invasion ecologists need to integrate processes at the population level and other ecological levels. I describe a series of coordinated studies in New Zealand streams that address the effect of an exotic fish on individual behavior, population, community, and ecosystem patterns. Such case studies are important as an aid to the formulation of policy about invasions that are especially likely to become problematic. At the individual level, grazing invertebrates showed changes in behavior as a result of the introduction of brown trout ( Salmo trutta), a predator that exerts a very different selection pressure than do native fish. At the population level, trout have replaced nonmigratory galaxiid fish in some streams but not others, and have affected the distributions of crayfish and other large invertebrates. At the community level, trout have suppressed grazing pressure from invertebrates and are thus responsible for enhancing algal biomass and changing algal species composition. Finally, at the ecosystem level, essentially all annual production of invertebrates is consumed by trout ( but not by galaxiids), and algal primary productivity is six times higher in a trout stream. This leads, in turn, to an increased flux of nutrients from the water to the benthic community. The trout invasion has led to strong top-down control of community structure and ecosystem functioning via its effects on individual behavior and population distribution and abundance. Particular physiological, behavioral, and demographic traits of invaders can lead to profound ecosystem consequences that managers need to take into account. Resumen: Para desarrollar procedimientos y políticas de manejo efectivos a menudo será necesario conocer la biología de la población de especies invasoras. Sin embargo, debido a que los invasores pueden tener efectos indirectos inesperados en las redes alimenticias, ecólogos de invasión necesitan integrar procesos en la población y otros niveles ecológicos. Describo una serie de estudios coordinados en arroyos de Nueva Zelanda que enfocan el impacto de un pez exótico sobre los patrones de comportamiento individual, de la población, la comunidad y el ecosistema. Tales estudios de caso son importantes como un auxiliar para la formulación de políticas sobre invasiones que pueden ser especialmente problemáticas. Al nivel individual, los invertebrados que pastorean mostraron cambios de conducta como resultado de la introducción de la trucha café ( Salmo trutta), un depredador que ejerce una presión de selección muy diferente a la de los peces nativos. En el nivel de población, las truchas han reemplazado a peces galaxídos no migratorios en algunos arroyos pero no en otros y han afectado las distribuciones de cangrejos de río y otros invertebrados mayores. Al nivel de comunidad, las truchas han suprimido la presión de pastoreo por invertebrados y por lo tanto son responsables del incremento de la biomasa de algas y del cambio en la composición de especies de algas. Finalmente, a nivel de ecosistema, la producción anual de invertebrados esencialmente es consumida por las truchas ( pero no por galaxídos), y la productividad primaria de algas es seis veces mayor en arroyos con truchas. A su vez, esto conduce a incrementos en el flujo de nutrientes del agua hacia la comunidad béntica. La invasión de truchas ha conducido a un fuerte control de arriba hacia abajo de la estructura de la comunidad y del funcionamiento del ecosistema por medio de sus efectos sobre la conducta individual y la distribución y abundancia de la población. Las características fisiológicas, de conducta y demográficas particulares de los invasores pueden llevar a consecuencias profundas en los ecosistemas que los administradores necesitan tomar en consideración. [source] Migratory connectivity in a declining bird species: using feather isotopes to inform demographic modellingDIVERSITY AND DISTRIBUTIONS, Issue 4 2010Thomas S. Reichlin Abstract Aim, Conservation programmes for endangered migratory species or populations require locating and evaluating breeding, stopover and wintering areas. We used multiple stable isotopes in two endangered European populations of wrynecks, Jynx torquilla L., to locate wintering regions and assess the degree of migratory connectivity between breeding and wintering populations. Location, Switzerland and Germany. Methods, We analysed stable nitrogen (,15N), carbon (,13C) and hydrogen (,D) isotopes from wing feathers from two populations of wrynecks to infer their wintering origins and to assess the strength of migratory connectivity. We tested whether variation in feather isotopic values within the Swiss population was affected by bird age and collection year and then considered differences in isotopic values between the two breeding populations. We used isotopic values of summer- and winter-grown feathers to estimate seasonal distributions. Finally, we calculated a species-specific ,D discrimination factor between feathers and mean annual ,D values to assign winter-grown feathers to origin. Results, Bird age and collection year caused substantial isotopic variation in winter-grown feathers, which may be because of annually variable weather conditions, movements of birds among wintering sites and/or reflect asynchronous moulting or selection pressure. The large isotopic variance in winter-grown feathers nevertheless suggested low migratory connectivity for each breeding population, with partially overlapping wintering regions for the two populations. Main conclusions, Isotopic variance in winter-grown feathers of two breeding populations of wrynecks and their geographical assignment point to defined, albeit overlapping, wintering areas, suggesting both leapfrog migration and low migratory connectivity. On this basis, integrative demographic models can be built looking at seasonal survival patterns with links to local environmental conditions on both breeding and wintering grounds, which may elucidate causes of declines in migratory bird species. [source] Supplemental feeding reduces natural selection in juvenile red deerECOGRAPHY, Issue 3 2002Karoline T. Schmidt In red deer, variation in winter and spring weather conditions encountered by the mothers during pregnancy and during the first year of life are a main determinant for individual life-history as well as population dynamics. We tested the hypothesis that supplementary feeding which provides constant food supply throughout winter removes the selective pressure of winter harshness on nutrition-mediated phenotypic traits. We analysed cohort variation in body weight in calves in October, before their first winter, and in yearlings in June, after their first winter, in a food-supplemented population in the Eastern Austrian Alps. Over eleven years, cohort body weight varied between years in calves and yearlings. Contrary to studies on non-supplemented red deer populations we found neither short- nor long-term effects of winter weather on body weight. In calves, autumn body weight was negatively related to April,May and June temperatures, suggesting that cool weather during the main growth period retarded plant senescence and thereby prolonged the period of high protein content of summer forage. In yearlings, variation in June body weight, shortly after the end of the feeding period, was lower after a wet April,May, suggesting a negative effect of a prolonged period of supplemental feeding. For both calves and yearlings intra-cohort variation in body weight was higher, inter-cohort variation was lower as compared to non-supplemented red deer, suggesting that in their first year of life supplemented red deer are under reduced natural selection pressure. [source] Fitness drift of an atrazine-degrading population under atrazine selection pressureENVIRONMENTAL MICROBIOLOGY, Issue 3 2008Marion Devers Summary Pseudomonas sp. ADP harbouring the atrazine catabolic plasmid ADP1 was subcultured in liquid medium containing atrazine as sole source of nitrogen. After approximately 320 generations, a new population evolved which replaced the initial population. This newly evolved population grew faster and degraded atrazine more rapidly than the initial population. Plasmid profiles and Southern blot analyses revealed that the evolved strain, unlike the ancestral strain, presented a tandem duplication of the atzB gene encoding the second enzyme of the atrazine catabolic pathway responsible for the transformation of hydroxyatrazine to N-isopropylammelide. This duplication resulted from a homologous recombination that occurred between two direct repeats of 6.2 kb flanking the atzB gene and constituted by the insertion sequences IS1071, ISPps1 and a pdhL homologous sequence. This study highlights the IS-mediated plasticity of atrazine-degrading potential and demonstrates that insertion sequences not only help to disperse the atrazine-degrading gene but also improve the fitness of the atrazine-degrading population. [source] Proteorhodopsin photosystem gene clusters exhibit co-evolutionary trends and shared ancestry among diverse marine microbial phylaENVIRONMENTAL MICROBIOLOGY, Issue 4 2007Jay McCarren Summary Since the recent discovery of retinylidene proteins in marine bacteria (proteorhodopsins), the estimated abundance and diversity of this gene family has expanded rapidly. To explore proteorhodopsin photosystem evolutionary and distributional trends, we identified and compared 16 different proteorhodopsin-containing genome fragments recovered from naturally occurring bacterioplankton populations. In addition to finding several deep-branching proteorhodopsin sequences, proteorhodopsins were found in novel taxonomic contexts, including a betaproteobacterium and a planctomycete. Approximately one-third of the proteorhodopsin-containing genome fragments analysed, as well as a number of recently reported marine bacterial whole genome sequences, contained a linked set of genes required for biosynthesis of the rhodopsin chromophore, retinal. Phylogenetic analyses of the retinal biosynthetic genes suggested their co-evolution and probable coordinated lateral gene transfer into disparate lineages, including Euryarchaeota, Planctomycetales, and three different proteobacterial lineages. The lateral transfer and retention of genes required to assemble a functional proteorhodopsin photosystem appears to be a coordinated and relatively frequent evolutionary event. Strong selection pressure apparently acts to preserve these light-dependent photosystems in diverse marine microbial lineages. [source] The structure of a local population of phytopathogenic Pseudomonas brassicacearum from agricultural soil indicates development under purifying selection pressureENVIRONMENTAL MICROBIOLOGY, Issue 3 2001Johannes Sikorski Among the isolates of a bacterial community from a soil sample taken from an agricultural plot in northern Germany, a population consisting of 119 strains was obtained that was identified by 16S rDNA sequencing and genomic fingerprinting as belonging to the recently described species Pseudomonas brassicacearum. Analysis of the population structure by allozyme electrophoresis (11 loci) and random amplified polymorphic DNA,polymerase chain reaction (RAPD,PCR; four primers) showed higher resolution with the latter method. Both methods indicated the presence of three lineages, one of which dominated strongly. Stochastic tests derived from the neutral theory of evolution (including Slatkin's exact test, Watterson's homozygosity test and the Tajima test) indicated that the population had developed under strong purifying selection pressure. The presence of strains clearly divergent from the majority of the population can be explained by in situ evolution or by influx of strains as a result of migration or both. Phytopathogenicity of a P. brassicacearum strain determined with tomato plants reached the level obtained with the type strain of the known pathogen Pseudomonas corrugata. The results show that a selective sweep was identified in a local population. Previously, a local selective sweep had not been seen in several populations of different bacterial species from a variety of environmental habitats. [source] Bioavailability and microbial adaptation to elevated levels of uranium in an acid, organic topsoil forming on an old mine spoilENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2007Erik Jautris Joner Abstract An old mine spoil at a 19th-century mining site with considerable residues of uranium (400,800 mg U/kg) was investigated with respect to U concentrations in soil and plants and tolerance to U in the soil microbial community in order to describe the bioavailability of U. Measurements of soil fractions representing water-soluble U, easily exchangeable U, and U bound to humified organic matter showed that all fractions contained elevated concentrations of U. Plant U concentrations were only 10 times higher at the mine spoil site compared to the reference site (3 mg U/kg vs 0.3 mg U/kg), while the most easily available soil fractions contained 0.18 to 0.86 mg U/kg soil at the mine spoil. An ecotoxicity bioassay using incorporation of [3H]thymidine into the indigenous microbial communities of the two soils in the presence of increasing U concentrations showed that microorganisms at the mining site were sensitive to U but also that they had acquired a substantial tolerance toward U (EC50, the effective concentration reducing activity by 50% of UO2 -citrate was , 120 ,M as compared to 30 ,M in the reference soil). In the assay, more than 40% of the microbial activity was maintained in the presence of 1 ,M UO2-citrate versus 3% in the reference soil. We conclude that U-enriched mining waste can contain sufficiently elevated concentrations of bioavailable U to affect indigenous microorganisms and that bioavailable U imposes a selection pressure that favors the development of a highly uranium-tolerant microbial community, while plant uptake of U remains low. [source] Highly avid, oligoclonal, early-differentiated antigen-specific CD8+ T cells in chronic HIV-2 infectionEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 7 2010Aleksandra Leligdowicz Abstract HIV-1-specific CD8+ T cells are present in most HIV-1-infected people and play an important role in controlling viral replication, but the characteristics of an effective HIV-specific T-cell response are largely unknown. The majority of HIV-2-infected people behave as long-term non-progressors while those who progress to AIDS do so in a manner indistinguishable from HIV-1. A detailed study of HIV-2 infection may identify protective immune responses. Robust gag p26-specific T-cell responses are elicited during HIV-2 infection and correlate with control of viremia. In this study, we analyzed features of an HLA-B*3501-restricted T-cell response to HIV-2 p26 that may contribute to virus control. In contrast to HIV-1, HIV-2-specific T cells are at an early stage of differentiation (CD27+CD28+), a finding that relates directly to CD4+ T-cell levels and inversely to immune activation. The cells demonstrate IFN-, secretion, oligoclonal T-cell receptor V, gene segment usage, exceptional avidity and secretion of pro-inflammatory cytokines. Despite the potentially strong selection pressure imposed on the virus by these cells, there was no evidence of HIV-2 sequence evolution. We propose that in chronic HIV-2 infection, the maintenance of early-differentiated, highly avid CD8+ T cells could account for the non-progressive course of disease. Such responses may be desirable from an HIV vaccine. [source] HOST GROWTH CONDITIONS INFLUENCE EXPERIMENTAL EVOLUTION OF LIFE HISTORY AND VIRULENCE OF A PARASITE WITH VERTICAL AND HORIZONTAL TRANSMISSIONEVOLUTION, Issue 7 2010Hélène Magalon In parasites with mixed modes of transmission, ecological conditions may determine the relative importance of vertical and horizontal transmission for parasite fitness. This may lead to differential selection pressure on the efficiency of the two modes of transmission and on parasite virulence. In populations with high birth rates, increased opportunities for vertical transmission may select for higher vertical transmissibility and possibly lower virulence. We tested this idea in experimental populations of the protozoan Paramecium caudatum and its bacterial parasite Holospora undulata. Serial dilution produced constant host population growth and frequent vertical transmission. Consistent with predictions, evolved parasites from this "high-growth" treatment had higher fidelity of vertical transmission and lower virulence than parasites from host populations constantly kept near their carrying capacity ("low-growth treatment"). High-growth parasites also produced fewer, but more infectious horizontal transmission stages, suggesting the compensation of trade-offs between vertical and horizontal transmission components in this treatment. These results illustrate how environmentally driven changes in host demography can promote evolutionary divergence of parasite life history and transmission strategies. [source] An evolutionary concept for altered steroid hormone metabolism in patients with rheumatoid arthritisEXPERIMENTAL DERMATOLOGY, Issue 2 2005Rainer H. Straub The pathogenesis of chronic disabling inflammatory diseases (CDIDs) is partly understood. The presently used concepts focus mainly on abnormalities of the immune system but this view is incomplete. The presented concept is a new framework for the pathogenesis of CDIDs. It integrates evolutionary theories with the classical immunological standpoint, which is further linked with a neuroendocrine immune view of erroneous homeostatic adaptation of the other supersystems (nervous system, endocrine system, reproductive system): 1. In CDIDs, the loss of tolerance against self and harmless foreign antigens leads to continuous immune aggression which is dependent on a multifactorial genetically polymorph background (the initiation). 2. However, advantageous or disadvantageous adaptation to CDIDs were not evolutionary conserved because CDIDs severely impaired reproduction or appeared after the reproductive phase and, thus, imply a strong negative selection pressure. 3. Reactions of all supersystems are evolutionary conserved for transient inflammatory reactions such as the elimination of infectious agents, wound healing, foreign body reaction and many others. 4. The sum of the false reactions of all supersystems , conserved for transient inflammation , provide the pathogenetic background for the chronification of CDIDs because a continuous aggressive situation is created (the chronification). The human disease of rheumatoid arthritis is used as a prototypic CDID to illustrate the integrated view point. The synovial tissue innervation is in the focus of this concept. [source] From ancient genes to modern communities: the cellular stress response and the evolution of plant strategiesFUNCTIONAL ECOLOGY, Issue 5 2005S. PIERCE Summary 1Two major plant strategy theories attempt to explain how phenotype determines community structure. Crucially, CSR plant strategy theory suggests that stress and sporadic resource availability favour conservative phenotypes, whereas the resource-ratio hypothesis views the spatial heterogeneity of resources as selecting for optimal foraging in chronically unproductive habitats. Which view is most realistic? 2The ecophysiology literature demonstrates that stress is comprised of two processes: (1) limitation of resource supply to metabolism; and (2) damage to biomembranes, proteins and genetic material (chronic stress). Thus stress is defined mechanistically as the suboptimal performance of metabolism. 3Adaptations to limitation buffer metabolism against variability in external resource supply; internal storage pools are more consistent. Chronic stress elicits the same ancient cellular stress response in all cellular life: investment in stress metabolites that preserve the integrity and compartmentalization of metabolic components in concert with molecular damage-repair mechanisms. 4The cellular stress response was augmented by morphological innovations during the Silurian,Devonian terrestrial radiation, during which nutrient limitation appears to have been a principal selection pressure (sensu CSR theory). 5The modern stress,tolerator syndrome is conservative and supports metabolism in limiting or fluctuating environmental conditions: standing resource pools with high investment/maintenance costs impose high internal diffusion resistances and limit inherent growth rate (sensu CSR theory). 6The resource-ratio hypothesis cannot account for the cellular stress response or the crucial role of ombrotrophy in primary succession. CSR theory agrees with current understanding of the cellular stress response, terrestrial radiation and modern adaptations recorded in chronically unproductive habitats, and is applicable as CSR classification. [source] Mutational inactivation of TGFBR2 in microsatellite unstable colon cancer arises from the cooperation of genomic instability and the clonal outgrowth of transforming growth factor , resistant cellsGENES, CHROMOSOMES AND CANCER, Issue 2 2008Swati Biswas The mutational inactivation of transforming growth factor , receptor type II (TGFBR2) occurs in ,30% of colon cancers and promotes the formation of colon cancer by inhibiting the tumor suppressor activity of the TGFB signaling pathway. TGFBR2 mutations occur in >90% of microsatellite unstable (MSI) colon cancers and affect a polyadenine tract in exon 3 of TGFBR2, called BAT-RII, which is vulnerable to mutation in the setting of DNA mismatch repair (MMR) system deficiency. In light of the vulnerable nature of the BAT-RII tract in the setting of MMR inactivation and the favorable effects of TGFBR2 inactivation in colon cancer, analysis of TGFBR2 inactivation provides an opportunity to assess the roles of genomic instability vs. clonal selection in cells acquiring TGFBR2 BAT-RII tract mutations in MSI colon cancer formation. The contribution of genomic instability and/or clonal evolution to the mutational inactivation of TGBFR2 in MSI colon cancers has not been studied in a systematic way that would allow a determination of the relative contribution of these two mechanisms in the formation of MSI colon cancer. It has not been demonstrated whether the BAT-RII tract mutations are strictly a consequence of the BAT-RII region being hypermutable in the setting of MMR deficiency or if the mutations are rather a consequence of clonal selection pressure against the TGFB receptor. Through the use of defined cell line systems, we show that both genomic instability and clonal selection of TGFB resistant cells contribute to the high frequency of TGFBR2 mutations in MSI colon cancer. © 2007 Wiley-Liss, Inc. [source] A large Norwegian family with inherited malignant melanoma, multiple atypical nevi, and CDK4 mutationGENES, CHROMOSOMES AND CANCER, Issue 1 2005Anders Molven Mutations in two loci encoding cell-cycle-regulatory proteins have been shown to cause familial malignant melanoma. About 20% of melanoma-prone families bear a mutation in the CDKN2A locus, which encodes two unrelated proteins, p16INK4A and p14ARF. Mutations in the other locus, CDK4, are much rarer and have been linked to the disease in only three families worldwide. In the 1960s, a large Norwegian pedigree with multiple atypical nevi and malignant melanomas was identified. Subsequently, six generations and more than 100 family members were traced and 20 cases of melanoma verified. In this article, we report that CDK4 codon 24 is mutated from CGT to CAT (Arg24His) in this unusually large melanoma kindred. Intriguingly, one of the family members had ocular melanoma, but the CDK4 mutation could not be detected in archival tissue samples from this subject. Thus, the case of ocular melanoma in this family was sporadic, suggesting an etiology different from that of the skin tumors. The CDK4 mutation in the Norwegian family was identical to that in melanoma families in France, Australia, and England. Haplotype analysis using microsatellite markers flanking the CDK4 gene and single-nucleotide polymorphisms within the gene did not support the possibility that there was a common founder, but rather indicated at least two independent mutational events. All CDK4 melanoma families known to date have a substitution of amino acid 24. In addition to resulting from selection pressure, this observation may be explained by the CG dinucleotide of codon 24 representing a mutational hot spot in the CDK4 gene. © 2005 Wiley-Liss, Inc. [source] Temperature-induced plasticity at cellular and organismal levels in the lizard Anolis carolinensisINTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 3 2010Rachel M. GOODMAN Abstract Among ectotherms, individuals raised in cooler temperatures often have larger body size and/or larger cell size. The current study tested whether geographic variation in cell size and plasticity for cell size exist in a terrestrial, ectothermic vertebrate, Anolis carolinensis Voigt, 1832. We demonstrated temperature-induced plasticity in erythrocytes and epithelial cells of hatchlings lizards derived from the eggs of females sampled from four populations and incubated at multiple temperatures. Larger cells were produced in hatchlings from cooler treatments; however, hatchling body size was unaffected by temperature. Therefore, temperature-induced plasticity applies at the cellular, but not organismal, level in A. carolinensis. In addition, reaction norms for cell size differed among populations. There was a latitudinal trend in cell size and in plasticity of cell size among our study populations. The two southernmost populations showed plasticity in cell size, whereas the two northernmost ones did not. We suggest that selection pressure for larger cell size in northern, cooler environments has restricted plasticity in A. carolinensis applied at the cellular level in response to variable incubation environments. [source] Genetic redundancy in human cervical carcinoma cells: Identification of cells with "normal" propertiesINTERNATIONAL JOURNAL OF CANCER, Issue 10 2007Anastasia Bachmann Abstract Although it is generally assumed that cancer arises from a singular cell, a tumor must be considered as a dynamic and emergent biological structure, whose organizing principle is determined by genetic and epigenetic modifications, occurring variably in response to microenvironmental selection conditions. As previously shown, HPV-positive cervical carcinoma cells have lost their ability to induce IFN-, upon TNF-, treatment. However, regarding cancer as a non-linear system, which may, even in the absence of an apparent selection pressure, fluctuate between different "metastable" phenotypes, we demonstrate that TNF-, mediated IFN-, induction is not irreversibly disturbed in all cells. Using the IFN-, sensitive Encephalomyocarditis virus (EMCV) as a tool to monitor antiviral activity in long-term established malignant HeLa cells, rare IFN-, expressing clones were rescued from a population of non-responsive and EMCV-sensitive cells. Antiviral activity was mediated by the re-expression of IRF-1 and p48 (IRF-9), both key regulatory molecules normally found to be suppressed in cervical carcinoma cells. Upon inoculating of selected clones into immunocompromised animals, a reduced or even an absence of tumorigenicity of initially highly malignant cells could be discerned. These data indicate that both the absence of interferon signaling and the ability to form tumors were reversed in a minority of cells. We provide a paradigm for the existence of innate genetic redundancy mechanisms, where a particular phenotype persists and can be isolated without application of drugs generally changing the epigenetic context. © 2007 Wiley-Liss, Inc. [source] L1 elements, processed pseudogenes and retrogenes in mammalian genomesIUBMB LIFE, Issue 12 2006Wenyong Ding Abstract Long interspersed nuclear elements 1 (L1 elements or LINE1) are the most active autonomous retrotransposons in mammalian genomes. In addition to L1 elements themselves, other protein-coding mRNAs can also be reverse transcribed and integrated into the genome through the L1-mediated retrotransposition, leading to the formation of processed pseudogenes (PPs) and retrogenes, both of which are characterized by the lack of introns and the presence of a 3' polyA tract and flanking direct repeats. PPs are unable to encode a functional protein and have accumulated frameshift mutations and premature stop codons during evolution. A few of PPs are transcriptionally active. Retrogenes preserve undisrupted coding frames and are capable of encoding a functional protein that is identical or nearly identical to that of the progenitor gene. There is a significant excess of retrogenes that originate from the X chromosome and are retrotransposed into autosomes, and most of these retrogenes are specially expressed in male germ cells, suggesting the inactivation of X-linked genes during male meiosis provides a strong selection pressure on retrogenes originating from the X chromosome. iubmb Life, 58: 677-685, 2006 [source] Diversity in five goat populations of the Lombardy Alps: comparison of estimates obtained from morphometric traits and molecular markersJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2001P. Crepaldi Phenotypic and genetic variability were studied within and between the goat populations of Bionda dell'Adamello, Frisa, Orobica, Verzaschese and Val di Livo. These are populations reared for most of the year on pastures of the Lombardy Alps, numbering a minimum of 1000 and a maximum of 8000 individuals per breed. The first four are standardized breeds of recent formation; at present they are supported by the European Union measures for the conservation of rare breeds. On the basis of its visible genetic profile the Val di Livo goat may be classified as a primary population. Phenotypic variability was estimated on the basis of six somatic measurements on 60,140 adult goats per breed, whereas genetic variation was measured on the basis of 201 AFLP loci. The partition of the total molecular variation into the within and between breed components indicates that the majority of the molecular variability is conserved within populations, whereas only 8.8% can be attributed to between population variation. Morphometric and molecular marker data produced unrelated distance values and different topology of UPGMA clusters. It may be hypothesized that the morphometric originality of the Val di Livo goat is mostly determined by environmental factors and selection pressure rather than by different origin and genome evolution. Conversely Orobica seems to have diverged from the other breeds at the genome level, which may be explained by an undocumented Southern Italian origin. An objective evaluation of conservation priorities may in the near future be based on the integrated use of molecular markers and of information on quantitative traits and allelic variation with adaptive relevance. Diversité dans cinq populations de chèvres des Alpes lombardes: comparaisons entre estmations obtenues par des mesures somatiques et par des marqueurs moléculaires On a etudié la variabilité phénotypique et génétique entre et parmi les populations de chèvres Bionda dell'Adamello, Frisa, Orobica, Verzaschese et Val di Livo. Il s'agit de populations qui content entre 1000 et 8000 sujets, elevés pour la plus part de l'année sur les pâturages des Alpes de Lombardie. Les quatre premières, actuellement sauvegardées par des mesures communautaires, sont des races à standard recemment constituées. La chèvre de la Val di Livo peut être rangée parmi les races primaires. La diversité phénotypique a été montrée par un dendrogramme obtenus des distances euclidiennes calculées à partir de six mesures somatiques qui avaient été prises sur 60,140 chèvres adultes pour chaque race. La diversité génétique a été montrée par un dendrogramme bâti sur la matrice des distances de Nei obtenues des 201 marqueurs moléculaires AFLP, produits par 7 combinaisons de primers, sur 30 sujets pour chaque race. La décomposition de la variabilité génétique totale estimée par les données moléculaires a montré que la plus part de la variabilité est conservée parmi la population, tandis que seulement l,8,8% peut être imputé aux différences entre populations. Les données moléculaires et somatiques ont donné lieu à des distances qui ne sont pas corrélées et à des cluster avec une topologie nettement différente. La comparaison entre les deux approches permet d'avancer l'hypothèse que l'originalité somatique de la chèvre de la Val di Livo pourrait être due à des facteurs d'environnement et/ou à la pression de sélection plutôt qu'à des facteurs liés à l'évolution du genome. Au contraire ces derniers seraient responsables de l'originalité génétique de la race Orobica et confirmeraient des témoignages orals non documentés. Un choix objectif des ressources génétiques qui méritent d'être conservées pourra probablement se baser sur l'employ conjoint des marqueurs et de renseignements sur les caractères quantitatifs et sur les variantes alléliques des gènes qui ont une valeur adaptative. Diversität in fünf Ziegenpopulationen der lombardischen Alpen: Vergleich von Schätzungen auf der Basis morphologischer Eigenschaften und molekularer Marker Es wurden die phänotypische und genetische Variabilität innerhalb und zwischen Bionda dell'Adamello, Frisa, Orobica, Verzaschese und Val di Livo Ziegenpopulationen untersucht. Diese Populationen, mit Größen zwischen 1000 und 8000 Tieren, werden den größten Teil des Jahres auf Weiden der lombardischen Alpen gehalten. Die vier erstgenannten Populationen sind erst kürzlich standardisierte Rassen; gegenwärtig werden sie mit EU-Mitteln für die Erhaltung seltener Rassen, unterstützt. Auf der Basis des erkennbaren genetischen Profils muß die Rasse Val di Livo als eine Primärpopulation eingeordnet werden. Phänotypische Variabilität wurde auf der Basis von sechs Körpermaßen an 60,140 ausgewachsenen Ziegen je Rasse geschätzt, die genetische Variation wurde auf der Basis von 201 AFLP-Loci gemessen. Die Aufteilung der gesamten molekularen Varianz in Varianzkomponenten innerhalb und zwischen Populationen zeigt, daß der größte Teil der molekularen Variabilität innerhalb der Populationen auftritt, und nur 8,8% der Gesamtvarianz auf die Varianz zwischen den Populationen entfällt. Morphologische und molekulare Marker erzeugten unabhängige Distanzwerte und unterschiedliche upgma-Cluster. Es kann die Hypothese aufgestellt werden, daß die morphologische Einzigartigkeit der Val di Livo Ziege stärker auf Umwelteffekte und Selektionsdruck als auf eine unterschiedliche Herkunft oder genomische Evolution zurückzuführen ist. Dagegen scheint Orobica auf Genomebene von den anderen Rassen abzuweichen, was durch einen nicht dokumentierten süditalienischen Ursprung erklärt werden könnte. Eine objektive Bewertung von Prioritäten für Konservierungsmaßnahmen dürfte in Zukunft auf einen integrierten Gebrauch molekularer Marker, Informationen über quantitative Merkmale sowie der genetischen Variation bezüglich der Adaptationsfähigkeit basieren. [source] Size-dependent predation risk in tree-feeding insects with different colouration strategies: a field experimentJOURNAL OF ANIMAL ECOLOGY, Issue 5 2009Triinu Remmel Summary 1. Body size is positively correlated with fecundity in various animals, but the factors that counterbalance the resulting selection pressure towards large size are difficult to establish. Positively size-dependent predation risk has been proposed as a selective factor potentially capable of balancing the fecundity advantage of large size. 2. To construct optimality models of insect body size, realistic estimates of size-dependent predation rates are necessary. Moreover, prey traits such as colouration should be considered, as they may substantially alter the relationship between body size and mortality risk. 3. To quantify mortality patterns, we conducted field experiments in which we exposed cryptic and conspicuous artificial larvae of different sizes to bird predators, and recorded the incidence of bird attacks. 4. The average daily mortality rate was estimated to vary between 4% and 10%. In both cryptic and conspicuous larvae, predation risk increased with prey size, but the increase tended to be steeper in the conspicuous group. No main effect of colour type was found. All the quantitative relationships were reasonably consistent across replicates. 5. Our results suggest that the size dependence of mortality risk in insect prey is primarily determined by the probability of being detected by a predator rather than by a size-dependent warning effect associated with conspicuous colouration. Our results therefore imply that warningly coloured insects do not necessarily benefit more than the cryptic species from large body size, as has been previously suggested. [source] Selection for birth date in North Sea haddock and its relation to maternal ageJOURNAL OF ANIMAL ECOLOGY, Issue 2 2005PETER J. WRIGHT Summary 1Birth date can be important to lifetime reproductive success. However, selection for birth date has rarely been addressed in fish, despite the opportunity provided by otolith microstructure. 2This study examined the relationship between maternal age, spawning time and early survivorship in the North Sea haddock stock. Temporal changes in egg production were compared with the birth date distribution of progeny surviving to the demersal phase in 1994, 1996 and 1999, when the age structure of the spawning stock differed. 3Estimates of intra-annual variation in stock egg production indicated that first-time spawning 2-year-olds began spawning much later than older age-classes. 4The form and magnitude of selection on birth date varied between years, indicating that the production of multiple batches of eggs over an extended period has some adaptive significance to progeny survival. 5Survivorship was consistently poor from the late spawning period when age 2 females contributed most to stock egg production. This persistent selection against late hatched offspring could reflect either low parental investment, as age 2 females produce smaller eggs, or the short length of the growing season prior to settlement. 6Variability in birth date selection, particularly with respect to first vs. subsequent years of spawning, implies a strong selection pressure for a long reproductive lifespan. As such, reproductive potential in this and other exploited fish species with a similar reproductive trait may have been affected adversely by the general decline in repeat spawning females in recent years. [source] Determination of baseline susceptibility to Cry1Ab protein for Asian corn borer (Lep., Crambidae)JOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2005K. He Abstract:, Although transgenic Bacillus thuringiensis (Bt) corn can provide a new tool for control of the Asian corn borer (ACB), Ostrinia furnacalis (Guenée), concern has been raised regarding the possibility of the target insect evolving resistance to the Bt protein under intensive selection pressure from Bt corn. Therefore, it is necessary to establish baseline data to enable detection of changes in susceptibility in field populations after prolonged exposure to Bt corn. Susceptibility to purified Cry1Ab protein from Bt was determined for 10 populations of ACB from the major corn-growing regions of China, ranging geographically from Heilongjiang Province in the northeast to Shaanxi Province in the east-central part. Neonate ACB were exposed to semi-artificial diet incorporated with increasing Cry1Ab protein concentrations, and mortality and growth inhibition were evaluated after 7 days. The range of LC50 (50% lethal concentration) among the populations was 0.10 to 0.81 ,g/g (Cry1Ab protein/diet). Differences (P < 0.05) in susceptibility among the populations were significant. LC50s generated from the Huanghuaihai Summer Corn Region were higher than those from the Spring Corn Regions. Bt was one of the significant natural biomortality factors of overwintering generation ACB. There was a significant correlation between percentage of the larvae infected with Bt and their LC50 values to Cry1Ab protein in geographic distinct populations (r = 0.7350*, d.f. = 8, r0.05 = 0.632). Based on the background of Bt formulations used for corn insect pests control in these areas, these differences were not caused by prior exposure to Bt insecticides. Instead, the small differences likely reflect natural Bt selection pressure. Because the variation in susceptibility to Cry1Ab was small (<10-fold), the ACB apparently is susceptible to Cry1Ab across its range within China. [source] Pattern of cross-resistance in pyrethroid-selected populations of Helicoverpa armigera Hübner (Lep., Noctuidae) from IndiaJOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2004T. Ramasubramanian Abstract:, In Helicoverpa armigera, withdrawal of selection pressure resulted in a two- to fourfold increase in susceptibility to synthetic pyrethroids and continuous selection enhanced the resistance level by four- to fivefold to the respective pyrethroids at the end of the 14th generation. Populations selected for resistance to one pyrethroid showed positive cross-resistance to all other pyrethroids, but no cross-resistance to endosulfan and thiodicarb. There was a significant increase in mixed-function oxidase activity with advancing generation suggesting its possible role in the positive cross-resistance among the pyrethroids. The induction of carboxyl esterases in pyrethroid-selected populations may have resulted in the activation of indoxacarb, thereby accounting for the observed negative cross-resistance. [source] Offspring sex ratio skew in the sexually monomorphic house martin Delichon urbicumJOURNAL OF AVIAN BIOLOGY, Issue 5 2010Monika Zieli Sex ratio at conception may be under selection pressure, given that male and female offspring differ in the cost of production or generate different fitness returns under specific conditions. We studied adjustments in the primary, secondary and tertiary sex ratio in house martin Delichon urbicum, which is a sexually monomorphic, socially monogamous, colonial bird. Males of this species engage in extra-pair copulations with heavy males acquiring the highest fertilization success. We analyzed variation in the sex ratio in relation to clutch size and parental characteristics including body condition, wing length, as well as length and pigmentation of the white rump patch during three breeding seasons. The only variable which significantly explained the variation in the sex ratio was wing length of the social father and mother. The proportion of sons among offspring was positively correlated to wing length of the social father and negatively correlated to mother wing length. Social father wing length positively correlated with mean brood body mass at fledging, which may suggest that females that mated with long-winged males produced sons, which acquired the highest total fertilization success. Consequently, our results indicate that house martin females may adaptively adjust offspring sex composition at egg laying in relation to the characteristics of their social mate. [source] Why is mimicry in cuckoo eggs sometimes so poor?JOURNAL OF AVIAN BIOLOGY, Issue 3 2002I propose that the existence of imperfect adaptations (e.g. egg mimicry) in brood parasites and their hosts (e.g. discrimination abilities) could reflect age-dependent territory and nest-site selection patterns of the host. Studies of various passerines indicate that (1) older breeders tend to occupy nest sites of higher quality than do young birds (ideal despotic distribution resulting from interference competition), (2) nest-site selection affects the risk of parasitism in various habitats, (3) egg recognition in passerines has a strong learning component (therefore naive breeders tend to accept whereas older birds tend to reject parasitic eggs). Because young naive birds, who tend to accept parasitic eggs, usually breed in low-quality areas where they are frequently parasitised, while old experienced birds, who tend to reject parasitic eggs, breed in high-quality areas where they are rarely parasitised, the distribution of acceptors and rejecters with respect to the risk of parasitism is non-random, i.e. populations of some host species may consist of heavily parasitised acceptors and weakly parasitised rejecters. Therefore, the selection pressure exerted by the host on the parasite should be weaker than if brood parasitism was randomly distributed among naive and experienced breeders and affect adaptations such as egg mimicry. This could explain the existence of imperfect adaptations in some brood parasite-host systems. [source] Evolution of sexual size monomorphism: the influence of passive mate guardingJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 7 2009A. E. DUNHAM Abstract Some species have potential for intense mate competition yet exhibit little or no sexual size dimorphism, despite predictions from sexual selection theory. Using a conceptual model, we show the conditions for which passive mate guarding with copulatory plugs can be an alternative and more successful strategy to active (direct) guarding, reducing selection pressure on large male size. The model predicts that copulatory plugs in mammals should be favoured in species for which females have short sexual receptivity periods. Using data on 62 primate species and a phylogenetic regression approach, we show that, as predicted, copulatory plugs are negatively associated with degree of sexual dimorphism and females' sexual receptivity length. Penile spines are also significantly associated with plug use and short receptivity periods suggesting a possible offensive role in sperm competition. Results highlight that life-history characteristics, such as sexual receptivity lengths, may alter the costs and benefits of alternative male strategies and thus alter the strength of sexual selection. [source] Altitudinal variation in behavioural thermoregulation: local adaptation vs. plasticity in California grasshoppersJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2005J. SAMIETZ Abstract We investigated the adaptive significance of behavioural thermoregulation in univoltine populations of the grasshopper Melanoplus sanguinipes along an altitudinal gradient in California using laboratory tests of animals raised under different temperatures. Trials consisted of continuous body temperature measurements with semi-implanted microprobes in a test arena, and observation and simultaneous recording of behavioural responses. These responses included mobility, basking and orientation of the body axes (aspect angle) towards a radiation source. Mobility and basking are determined by the altitudinal origin of the parental generation and not by the temperature treatments. With increasing altitude, individuals tend increasingly to raise body temperatures via mobility and increased basking. In contrast, body orientation towards the radiation source is influenced by the temperature treatments but not by the altitude of origin. Individuals experiencing higher temperatures during rearing show a lower tendency to lateral flanking. We conclude that body orientation responses are not adapted locally. In contrast other components of the behavioural syndrome that increase body temperature, such as mobility and basking, are adaptive in response to local selection pressure. The thermoregulatory syndrome of these grasshoppers is an important contribution to life-history adaptations that appropriately match season lengths. [source] Polymorphism and signature of selection in the MHC class I genes of the three-spined stickleback Gasterosteus aculeatusJOURNAL OF FISH BIOLOGY, Issue 2006H. Schaschl The role and intensity of positive selection maintaining the polymorphism of major histocompatibility complex (MHC) class I genes in the three-spined stickleback Gasterosteus aculeatus was investigated. The highly polymorphic set of MHC class I genes found was organized in a single linkage group. Between 5 and 14 sequence variants per individual were identified by single-stranded conformation polymorphism (SSCP) analysis. Segregation analysis studied in 10 three-spined stickleback families followed the expected pattern of Mendelian inheritance. The gamete fusion in three-spined stickleback thus seems to be random with respect to the MHC class I genes. The DNA sequence analyses showed that the expressed MHC class I loci are under strong selection pressure, possibly mediated by parasites. Codons that were revealed to be under positive selection are potentially important in antigen binding. MHC class I sequences did not form significant supported clusters within a phylogenetic tree. Analogous to MHC class II genes, it was not possible to assign the class I sequences to a specific locus, suggesting that the class I genes may have been generated by recent gene duplication. [source] Genes, gene flow and adaptation of Diabrotica virgifera virgiferaAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2009Nicholas J. Miller Abstract 1,Diabrotica virgifera virgifera has emerged as a major pest of cultivated maize, due to a combination of its high capacity to inflict economic damage, adaptability to pest management techniques and invasiveness. 2,This review presents a survey of the current state of knowledge about the genetics of D. v. virgifera. In addition, the tools and resources currently available to Diabrotica geneticists are identified, as are areas where knowledge is lacking and research should be prioritized. 3,A substantial amount of information has been published concerning the molecular phylogenetic relationships of D. v. virgifera to other chrysomelids. 4,There is a growing literature focused on the population genetics and evolution of the species. Several adaptations to anthropogenic selection pressure have been studied, with resistance to synthetic insecticides providing some particularly well-characterized examples. 5,A notable deficiency is a lack of studies directed toward the formal genetics of D. v. virgifera. [source] | ||||||||||||||||||||||||||||||||||||||||||||||