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Selective Advantage (selective + advantage)
Selected AbstractsAutumnal moth , why autumnal?ECOLOGICAL ENTOMOLOGY, Issue 6 2001Toomas 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] Effect of soil hardness on aggression in the solitary wasp Mellinus arvensisECOLOGICAL ENTOMOLOGY, Issue 5 2001Jaboury Ghazoul Summary 1. Two alternative nesting strategies are exhibited by soil-nesting Mellinus arvensis females, digging a new nest (diggers) and searching for an old unoccupied burrow (searchers). Wasps appear unable to distinguish between occupied and unoccupied nests, and aggressive interactions between searchers and nest owners at nest entrances are frequent. 2. In aggressive encounters, there is an advantage in size and residency status. 3. The costs associated with the two nesting strategies vary across geographically separated populations: nest digging incurs costs in terms of time, and these vary according to the hardness of the soil substrate; nest searching is variably costly in terms of risk of injury in aggressive encounters with nest-owning females. 4. Individual female wasps can switch between nesting strategies, and thus soil hardness, by affecting the cost of nest construction, affects the relative frequencies of the two nesting strategies within a population, favouring an increase in the searching strategy. This, in turn, affects the frequency and intensity of aggression between females at a nesting aggregation. 5. Female body size is correlated with soil hardness. As aggressive encounters are more frequent in sites with hard soil substrates, there is increased selective advantage in having large body size at these sites. 6. Body size is determined primarily by the availability of food resources during larval development, which is, to a degree, a function of the size of the adult female. There is a trade-off between provisioning a few cells with many provisions in each, leading to the development of few but large adults, as opposed to many cells with few provisions, leading to many small offspring. The relative advantage of these two provisioning strategies is, at least in part, a function of the hardness of the soil substrate. [source] Contemporary egg size divergence among sympatric grayling demes with common ancestorsECOLOGY OF FRESHWATER FISH, Issue 1 2008F. Gregersen Abstract, This study documents divergence in egg size that has occurred over less than 25 generations among sympatric demes of European grayling (Thymallus thymallus) from Lake Lesjaskogsvatnet in Norway. A cluster analysis identified two clusters of tributaries: one of small, warm tributaries (SW) and the other of large, cold tributaries (LC). Spawning occurs more regularly and up to 4 weeks earlier in SW tributaries compared with that in LC ones. We explored numerous mixed models predicting egg size from year (random effect), basin and tributary (fixed effects), and female length. The most supported model estimated length-adjusted egg size to be larger in SW tributaries compared with that in LC tributaries. Combinations of density-dependent (competition for food/space) and density-independent (temperature) factors along with phenotypic plasticity and maternal effects are discussed as potential differentiation sources. We suggest high temperatures (increased metabolism) to reinforce the selective advantage of large eggs under conditions with highly density-dependent fry interactions. [source] Multiple bacterial symbionts in two species of co-occurring gutless oligochaete worms from Mediterranean sea grass sedimentsENVIRONMENTAL MICROBIOLOGY, Issue 12 2008Caroline Ruehland Summary Gutless oligochaete worms are found worldwide in the pore waters of marine sediments and live in symbiosis with chemoautotrophic sulfur-oxidizing bacteria. In the Mediterranean, two species of gutless oligochaete worms, Olavius algarvensis and O. ilvae, co-occur in sediments around sea grass beds. These sediments have extremely low sulfide concentrations (< 1 ,M), raising the question if O. ilvae, as shown previously for O. algarvensis, also harbours sulfate-reducing symbionts that provide its sulfur-oxidizing symbionts with reduced sulfur compounds. In this study, we used fluorescence in situ hybridization (FISH) and comparative sequence analysis of genes for 16S rRNA, sulfur metabolism (aprA and dsrAB), and autotrophic carbon fixation (cbbL) to examine the microbial community of O. ilvae and re-examine the O. algarvensis symbiosis. In addition to the four previously described symbionts of O. algarvensis, in this study a fifth symbiont belonging to the Spirochaetes was found in these hosts. The symbiotic community of O. ilvae was similar to that of O. algarvensis and also included two gammaproteobacterial sulfur oxidizers and two deltaproteobacterial sulfate reducers, but not a spirochete. The phylogenetic and metabolic similarity of the symbiotic communities in these two co-occurring host species that are not closely related to each other indicates that syntrophic sulfur cycling provides a strong selective advantage to these worms in their sulfide-poor environment. [source] Protection of DNA during early development: adaptations and evolutionary consequencesEVOLUTION AND DEVELOPMENT, Issue 1 2003David Epel SUMMARY The rapidly dividing cleavage stages of embryos do not have the typical responses to cell damage, such as induction of the heat shock response, use of mitotic checkpoints, or use of apoptosis to eliminate severely damaged cells. This could create problems with integrity of DNA, but the solution in these embryos appears to be a "be prepared" approach, in which specific adaptations are used to minimize DNA damage during cleavage and the use of apoptosis at the mid-blastula transition to remove any cells that were nevertheless damaged. It has been assumed that this approach has evolved because of the advantage of rapid production of a motile larvae. Alternatively, this particular approach may have the selective advantage of increasing mutation rate when there are greater environmental stresses. This could provide more variants on which selective pressures could act and thus accelerate evolution during environmentally stressful periods. [source] Nutritional ecology and diachronic trends in Paleolithic diet and healthEVOLUTIONARY ANTHROPOLOGY, Issue 5 2003Bryan Hockett Modern nutritional studies have found that diverse diets are linked to lower infant mortality rates and longer life expectancies in humans. This is primarily because humans require more than fifty essential nutrients for growth and cell maintenance and repair; most of these essential nutrients must come from outside food sources rather than being manufactured by the body itself; and a diversity of food types is required to consume the full suite of essential nutrients necessary for optimal human health. These principles and their related affects on human adaptations and demography are the hallmarks of a theoretical paradigm defined as nutritional ecology. This essay applies concepts derived from nutritional ecology to the study of human evolution. Principles of nutritional ecology are applied to the study of the Middle-to-Upper Paleolithic transition in order to broadly illustrate the interpretive ramifications of this approach. At any stage in human evolution, those hominid populations that chose to diversify their subsistence base may have had a selective advantage over competitors who restricted their diet principally to one food type, such as terrestrial mammals. [source] Superantigen gene profile diversity among clinical group A streptococcal isolatesFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 2 2008Linda Maripuu Abstract This study examines the diversity of superantigen gene profiles between and within emm -genotypes of 92 clinical group A streptococcal isolates (30 STSS, 24 sepsis, 25 erysipelas, and 12 tonsillitis) collected in Sweden between 1986 and 2001. The emm- genotype and the distribution of smeZ, speG, speJ, speA, speC, speH, speI, speK/L, speL/M, speM, and ssa genes, and the smeZ allelic variant were determined using PCR and DNA sequencing. Forty-five emm1 isolates revealed 10 superantigen gene profiles. One profile dominated and was identified in 22 isolates collected over 14 years. The results indicate that a selective advantage maintained this genotype in circulation. The superantigen content among the emm1 isolates ranged from three to seven, with smeZ-1, speG, and speA present in all but one profile. The 47 isolates of 27 other emm -genotypes exhibited 29 superantigen gene profiles. Thus, the distribution of superantigen genes was highly variable within isolates regardless of emm -genotype. Two novel emm1 subtypes and 14 novel smeZ allelic variants were identified. The 22 smeZ alleles were generally linked to the emm -genotype. The results of the investigation show that superantigen gene profiling is useful for tracking spread of clones in the community. [source] The evolution of floral scent: the influence of olfactory learning by insect pollinators on the honest signalling of floral rewardsFUNCTIONAL ECOLOGY, Issue 5 2009Geraldine A. Wright Summary 1.,The evolution of flowering plants has undoubtedly been influenced by a pollinator's ability to learn to associate floral signals with food. Here, we address the question of ,why' flowers produce scent by examining the ways in which olfactory learning by insect pollinators could influence how floral scent emission evolves in plant populations. 2.,Being provided with a floral scent signal allows pollinators to learn to be specific in their foraging habits, which could, in turn, produce a selective advantage for plants if sexual reproduction is limited by the income of compatible gametes. Learning studies with honeybees predict that pollinator-mediated selection for floral scent production should favour signals which are distinctive and exhibit low variation within species because these signals are learned faster. Social bees quickly learn to associate scent with the presence of nectar, and their ability to do this is generally faster and more reliable than their ability to learn visual cues. 3.,Pollinators rely on floral scent as a means of distinguishing honestly signalling flowers from deceptive ones. Furthermore, a pollinator's sensitivity to differences in nectar rewards can bias the way that it responds to floral scent. This mechanism may select for flowers that provide olfactory signals as an honest indicator of the presence of nectar or which select against the production of a detectable scent signal when no nectar is present. 4.,We expect that an important yet commonly overlooked function of floral scent is an improvement in short-term pollinator specificity which provides an advantage to both pollinator and plant over the use of a visual signal alone. This, in turn, impacts the evolution of plant mating systems via its influence on the species-specific patterns of floral visitation by pollinators. [source] An inherited mitochondrial DNA disruptive mutation shifts to homoplasmy in oncocytic tumor cells,HUMAN MUTATION, Issue 3 2009Giuseppe Gasparre Abstract A disruptive frameshift mtDNA mutation affecting the ND5 subunit of complex I is present in homoplasmy in a nasopharyngeal oncocytic tumor and inherited as a heteroplasmic germline mutation recurring in two of the patient's siblings. Homoplasmic ND5 mutation in the tumor correlates with lack of the ND6 subunit, suggesting complex I disassembly. A few oncocytic areas, expressing ND6 and heteroplasmic for the ND5 mutation, harbor a de novo homoplasmic ND1 mutation. Since shift to homoplasmy of ND1 and ND5 mutations occurs exclusively in tumor cells, we conclude that complex I mutations may have a selective advantage and accompany oncocytic transformation. Hum Mutat 0, 1,6, 2008. © 2008 Wiley-Liss, Inc. [source] Aldehyde oxidase is coamplified with the World's most common Culex mosquito insecticide resistance-associated esterasesINSECT MOLECULAR BIOLOGY, Issue 1 2000J. Hemingway Abstract The evolution and spread of insecticide resistance is an important factor in human disease prevention and crop protection. The mosquito Culex quinquefasciatus is the main vector of the disease filariasis and a member of a species complex which is a common biting nuisance worldwide. The common insecticide resistance mechanism in this species involves germline amplification of the esterases est,21 and est,21. This amplification has arisen once and rapidly spread worldwide. Less common and more variable resistance phenotypes involve coamplification of est,3 and est,1, or individual amplification of a single est,1, different alleles of the same est, and est, gene loci. Est,21 and est,21 are on the same large fragment of amplified DNA (amplicon) 2.7 kb apart. We have now shown that this amplicon contains another full-length gene immediately 5, of est,21 which codes for a molybdenum-containing hydroxylase, with highest homology to aldehyde oxidase (AO) from other organisms. The full-length putative AO gene is not present on the est,3/est,1 or est,1 amplicons, but multiple truncated 5, ends of this gene are present around the presumed est,3/est,1 amplicon breakpoint. Polymerase chain reaction (PCR) analysis of insecticide-susceptible genomic DNA demonstrated that a different allele of the putative AO gene in its non-amplified form is immediately 5, of est,. The ,AO' gene on the est,21/est,21 amplicon is expressed and resistant insects have greater AO activity. This AO activity is sensitive to inhibition by an aldehyde-containing herbicide and pesticide. This enzyme may confer a selective advantage to these insects in the presence of insecticide, as AO in mammals is believed to be important in the detoxification process of several environmental pollutants. [source] Releasing genetically modified organisms: will any harm outweigh any advantage?,JOURNAL OF APPLIED ECOLOGY, Issue 2 2000John E. Beringer Summary 1. ,The public debate about genetically modified organisms has concentrated largely on concerns about food safety and potential risks to the environment. In both cases there appears to be an assumption that existing crops and animals are safe. I discuss the experience we have to date from traditional methods and conclude that most concerns about environmental harm are more relevant to existing crops. 2. ,The flow of genes among species, and even within different genera, is discussed with due attention being paid to the need for inherited genes to confer a selective advantage on hosts. 3. ,A reason why so many people are critical of intensive agriculture and biotechnology is that virtually all changes in agricultural practice have an adverse impact on wildlife, particularly when such change leads to increased intensification. The problem of deciding how to manage agriculture to ensure that we maintain or enhance species diversity of wild plants and animals is discussed against the background that most of the UK environment is the result of human intervention. 4. ,Nature and dense human populations cannot coexist without the former suffering. Our objective should be to develop and exploit our understanding of ecology to provide the information required to enable us to develop a far more enlightened future for agriculture and wildlife. [source] Process in the evolution of bird migration and pattern in avian ecogeographyJOURNAL OF AVIAN BIOLOGY, Issue 2 2000Christopher P. Bell Current ideas about the evolution of bird migration equate its origin with the first appearance of fully migratory populations, and attribute its evolution to a selective advantage generated by increased breeding success, gained through temporary emigration from resident populations to breed in under-exploited seasonal areas. I propose an alternative hypothesis in which migration first appears as a temporary directional shift away from the breeding site outside the reproductive period, in response to seasonal variation in the direction and/or severity of environmental gradients. Fully migratory populations then appear through either extinction of sedentary phenotypes, or colonisation of vacant seasonal areas by migrants. Where colonisation occurs, resident ancestral populations can be driven to extinction by competition from migrants which invade their range outside the breeding season, resulting in fully migratory species. An analogous process drives the evolution of migration between high latitudes and the tropics, since extension of breeding range into higher latitudes may drive low latitude populations to extinction, resulting in an overall shift of breeding range. This process can explain reverse latitudinal gradients in avian diversity in the temperate zone, since the breeding ranges of migratory species concentrate in latitudes where they enjoy the highest breeding success. Near absence of forest-dwelling species among Palaearctic-African migrants is attributable to the lack of forest in northern Africa for much of the Tertiary, which has precluded selection both for southward extension of migration by west Palaearctic forest species, and northward breeding colonisation by African forest species. [source] Increasing Expression of the Retinoic X Receptor-B During Malignant Melanoma ProgressionJOURNAL OF CUTANEOUS PATHOLOGY, Issue 1 2005S.J. McAlhany Retinoic X receptor-b (RXR-b) is a heterodimerization partner for vitamin D receptor (VDR). 1,25-dihydroxyvitamin D3 activation of VDR leads to growth inhibition in numerous cell lines, including some melanoma lines. Evaluation of VDR and RXR-b expression in vivo in melanocytic neoplasms will increase our understanding of this pathways potential role in growth control. Previous studies in our laboratory showed decreased VDR expression in superficially invasive melanoma, and progressive loss of expression in deeply invasive melanomas and metastatic melanomas (MET). We next sought to evaluate RXR-b expression. Twenty-eight melanocytic neoplasms including 8 melanomas in situ (MIS), 9 primary invasive melanomas (PIM), and 11 MET were evaluated for RXR-b expression by immunohistochemistry. Nuclear labeling was assessed as 0 (0%), 1+(<5%), 2+(>5% but <50%), or 3+(>=50%). A significant increase in RXR-b expression from low (0,1+) to high (>1+) was found when comparing MIS to PIM and MET (chi2 p < 0.05). These data suggest: 1) potential loss of 1,25-dihydroxyvitamin D3 induced growth inhibition during melanoma progression may be due to decreased VDR expression without concomitant loss of RXR-b; and 2) increased RXR-b expression during melanoma progression may offer selective advantage through alternative signaling pathways. [source] Infrequent sporophyte production maintains a female-biased sex ratio in the unisexual clonal moss Hylocomium splendensJOURNAL OF ECOLOGY, Issue 5 2010Knut Rydgren Summary 1.,Sex ratios in unisexual bryophytes are most often female biased, whereas male-biased sex ratios predominate in unisexual seed plants. This ,bryophyte paradox', i.e. that sex ratios are biased in favour of the sex associated with the highest reproductive costs, has remained unexplained. 2.,Analysis of sex-ratio patterns via the influence of sex distribution on population growth rates (,) has not previously been carried out for bryophytes. We used this method to model how variation in sex ratio and sporophyte frequency influences , in the clonal bryophyte Hylocomium splendens. We obtained , by matrix modelling of synthetic experimental populations derived from demographic field data, using a linear two-sex model. 3.,In our set of experimental populations , varied between 1.13 and 1.27 in response to variation in sex ratio and sporophyte frequency, with the highest , obtained for the combination of a very low sporophyte frequency and a slightly female-biased sex ratio. 4.,Our results explain the female-biased sex ratio of H. splendens by the slightly lower survival of and production of vegetative offspring by males than by non-sporophytic females. 5.,Synthesis. According to our models, female dominance is the predicted outcome of low to moderate fertilization success and male performance intermediate between that of sporophytic and of non-sporophytic females. Our results therefore explain how a female-biased sex ratio can be maintained despite higher costs of reproduction in females than in males. In dioecious bryophytes, males and females must grow in close contact for fertilization to take place. Better performance of male ramets than of the female ramets they fertilize also explains how male clones can expand into female clones. A similar performance hierarchy of males and females may occur in unisexual clonal seed plants, but more efficient fertilization systems by pollination prevents the selective advantage of unfertilized females from being realized. This explains why vascular plant populations tend to be male biased. We hypothesise difference in fertilization distance range between sperm and pollen as a simple explanation why ramet level sex ratios are in general male dominated in clonal seed plants and female dominated in clonal bryophytes. [source] Moult speed affects structural feather ornaments in the blue titJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2009M. GRIGGIO Abstract Growing evidence suggests that structural feather colours honestly reflect individual quality or body condition but, contrary to pigment-based colours, it is not clear what mechanism links condition to reflectance in structural feather colours. We experimentally accelerated the moult speed of a group of blue tits (Cyanistes caeruleus) by exposing them to a rapidly decreasing photoperiod and compared the spectral characteristics of their structural feather colours with those of control birds. Blue tits were sexually dimorphic on the UV/blue crown and on the white cheek feathers. Moult speed, however, dramatically reduced brightness and the saturation only on the UV/blue crown feathers, whereas structural white on the cheek feathers was basically unaffected by moult speed. Given that the time available for moulting is usually confined to the period between the end of the breeding season and migration or wintering, UV/blue colours, but not structural white, may convey long-term information about an individual's performance during the previous breeding season. The trade-off between fast moulting and structural colour expression may represent a previously unrecognized selective advantage for early-breeding birds. [source] Moult speed constrains the expression of a carotenoid-based sexual ornamentJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2007L. SERRA Abstract We investigated the effect of moult speed on the expression of a sexually selected, carotenoid-based feather ornament in the rock sparrow (Petronia petronia). We experimentally accelerated the moult speed of a group of birds by exposing them to a rapidly decreasing photoperiod and compared the area and the spectral characteristics of their ornaments with those of control birds. Birds with accelerated moulting rate showed a smaller yellow patch with lower yellow reflectance compared to their slow-moulting counterparts. Considering that the time available for moulting is usually constrained between the end of the breeding season and migration or wintering, carotenoid feather ornaments, whose expression is mediated by moult speed, may convey long term information about an individual's condition, potentially encompassing the previous breeding season. Furthermore, the observed trade-off between moult speed and ornament expression may represent a previously unrecognized selective advantage for early breeding birds. [source] Predation and the persistence of melanic male mosquitofish (Gambusia holbrooki)JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2004L. Horth Abstract The empirical reasons for the persistent rarity of a genotype are typically complex and tedious to identify, particularly in nature. Yet rare morphs occur in a substantial fraction of phenotypic polymorphisms. A colour polymorphism has persisted for decades in the eastern mosquitofish, yet why this is so remains obscure. Here, I report the results of (1) intensive sampling at 45 natural sites to obtain the frequency distribution of the melanic (black) mosquitofish morph in Florida, (2) predation trials, conducted independently in mesocosms, with three different predatory species and (3) two mark-recapture studies, conducted in nature. This work (1) documents the rarity of melanic mosquitofish in nature, (2) demonstrates that melanic males experience a selective advantage over silver males in the presence of predators, (3) indicates no difference in the colour morphs, survival at a natural site essentially devoid of these predators, although suggesting a higher rate of recapture for melanic males at a site rife with predators. Overall, selective predation appears to contribute to the persistence of the melanic morph, despite its rarity in nature. [source] Differential selection of growth rate-related traits in wild barley, Hordeum spontaneum, in contrasting greenhouse nutrient environmentsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2004K. J. F. Verhoeven Abstract Across-species comparisons show that inherent variation in relative growth rate (RGR) and its underlying traits are correlated with habitat productivity. In this study, we test the hypothesis that growth rate-related traits confer differential selective effects in contrasting nutrient environments. We specifically test whether high RGR is targeted by selection in nutrient-rich environments whereas low values of traits that underlie RGR [specific leaf area (SLA), leaf mass fraction and leaf area ratio (LAR)] confer a direct fitness advantage in nutrient-poor environments, resulting in selection of low RGR as a correlated response. We measured RGR, its underlying component traits, and estimated fitness in a range of wild barley (Hordeum spontaneum) accessions grown under high and low nutrient conditions. Selection on component traits differed between the two environments, while total selection of RGR was not significant. Using multiple regression and path analysis to estimate direct fitness effects, a selective advantage of high LAR and SLA was demonstrated only under nutrient-rich conditions. While supporting the view that observed associations between habitat richness and some RGR-component traits reflect adaptation to differing nutrient regimes, our data suggest that direct selection targets component traits rather than RGR itself. [source] UV-B INDUCTION OF UV-B PROTECTION IN ULVA PERTUSA (CHLOROPHYTA),JOURNAL OF PHYCOLOGY, Issue 3 2005Young-Seok Han The green macroalga Ulva pertusa Kjellman produced UV-B absorbing compounds with a prominent absorption maximum at 294 nm in response only to UV-B, and the amounts induced were proportional to the UV-B doses. Under a 12:12-h light:dark regime, the production of UV-absorbing compounds occurred only during the exposure periods with little turnover in the dark. There was significant reduction in growth in parallel with the production of UV-B absorbing compounds. The polychromatic action spectrum for the induction of UV-B absorbing compounds in U. pertusa exhibits a major peak at 292 nm with a smaller peak at 311.5 nm. No significant induction was detected above 354.5 nm, and radiation below 285 nm caused significant reduction in the levels of UV-B absorbing compounds. After UV-B irradiation at 1.0 W·m,2 for 9 h, the optimal photosynthetic quantum yield of the samples with UV-B absorbing compounds slightly increased relative to the initial value, whereas that of thalli lacking the compounds declined to 30%,34% of the initial followed by subsequent recovery in dim light of up to 84%,85% of the initial value. There was a positive and significant relationship between the amount of UV-B absorbing compounds with antioxidant activity as determined by the ,,,-diphenyl-,-picrylhydrazyl scavenging assay. In addition to mat-forming characteristics and light-driven photorepair, the existence and antioxidant capacity of UV-B absorbing compounds may confer U. pertusa a greater selective advantage over other macroalgae, thereby enabling them to thrive in the presence of intense UV-B radiation. [source] Birth size and postnatal growth in cave- and bridge-roosting Brazilian free-tailed batsJOURNAL OF ZOOLOGY, Issue 1 2010L. C. Allen Abstract As the human population continues to expand, increased encroachment on natural landscapes and wildlife habitats is expected. Organisms able to acclimate to human-altered environments should have a selective advantage over those unable to do so. Over the past two decades, bats have increasingly begun to roost and raise offspring in spaces beneath pre-cast concrete bridges. Few studies have examined the health or fitness of individuals living in these anthropogenic sites. In the present study, we examined birth size and postnatal growth, as surrogates of reproductive success, in Brazilian free-tailed bat pups born at a natural and a human-made roost. Based on putative stress-related conditions (noise from vehicular traffic, chemical pollutants and a modified social environment) present at bridges, we predicted that bats at these sites would have reduced reproductive success. Contrary to our prediction, pups born at a bridge site were on average heavier and larger at birth and grew faster than those born at a cave site. Also, both birth size and growth rates of pups differ between years. We attribute observed differences to a combination of roost-related conditions (i.e. roost temperature and proximity to foraging areas), climate and maternal effects with larger mothers raising larger pups. Thus, some bridge roosts, at least in the short term, are suitable, and in some cases may provide better conditions, for raising young bat pups than cave roosts. [source] Structural and biochemical characterization of gentisate 1,2-dioxygenase from Escherichia coli O157:H7MOLECULAR MICROBIOLOGY, Issue 6 2006Melanie A. Adams Summary Gentisic acid (2,5-dihydroxybenzoic acid) is a key intermediate in aerobic bacterial pathways that are responsible for the metabolism of a large number of aromatic compounds. The critical step of these pathways is the oxygen-dependent reaction catalysed by gentisate 1,2-dioxygenase which opens the aromatic ring of gentisate to form maleylpyruvate. From gentisic acid, the cell derives carbon and energy through the conversion of maleylpyruvate to central metabolites. We have confirmed the annotation of a gentisate 1,2-dioygenase from the pathogenic O157:H7 Escherichia coli strain and present the first structural characterization of this family of enzymes. The identity of the reaction product was revealed using tandem mass spectroscopy. The operon responsible for the degradation of gentisate in this organism exhibits a high degree of conservation with the gentisate-degrading operons of other pathogenic bacteria, including the Shiga toxin-producing E. coli O103:H2, but does not appear to be present in non-pathogenic strains. The acquisition of the gentisate operon may represent a special adaptation to meet carbon source requirements under conditions of environmental stress and may provide a selective advantage for enterohaemorrhagic E. coli relative to their non-pathogenic counterparts. [source] Quorum sensing controls biofilm formation in Vibrio choleraeMOLECULAR MICROBIOLOGY, Issue 1 2003Brian K. Hammer Summary Multiple quorum-sensing circuits function in parallel to control virulence and biofilm formation in Vibrio cholerae. In contrast to other bacterial pathogens that induce virulence factor production and/or biofilm formation at high cell density in the presence of quorum-sensing autoinducers, V. cholerae represses these behaviours at high cell density. Consistent with this, we show here that V. cholerae strains ,locked' in the regulatory state mimicking low cell density are enhanced for biofilm production whereas mutants ,locked' in the regulatory state mimicking high cell density are incapable of producing biofilms. The quorum-sensing cascade we have identified in V. cholerae regulates the transcription of genes involved in exopolysaccharide production (EPS), and variants that produce EPS and form biofilms arise at high frequency from non-EPS, non-biofilm producing strains. Our data show that spontaneous mutation of the transcriptional regulator hapR is responsible for this effect. Several toxigenic strains of V. cholerae possess a naturally occurring frameshift mutation in hapR. Thus, the distinct environments occupied by this aquatic pathogen presumably include niches where cell-cell communication is crucial, as well as ones where loss of quorum sensing via hapR mutation confers a selective advantage. Bacterial biofilms could represent a complex habitat where such differentiation occurs. [source] Spatio-temporal variation in pollen limitation and reproductive success of two scape morphs in Primula farinosaNEW PHYTOLOGIST, Issue 3 2006Didrik Vanhoenacker Summary ,,In plant populations where reproductive output is limited by pollinator visitation, plants with attractive floral displays should have a selective advantage. We examined the effect of inflorescence height on pollination success in Primula farinosa, which is dimorphic for scape length. ,,To test the hypothesis that fruit and seed initiation are more strongly pollen-limited in the short-scaped than in the long-scaped morph, and that this difference is affected by spatio-temporal variation in pollen limitation, we conducted a hand-pollination experiment in four populations over 2 yr. ,,Pollen limitation of fruit initiation varied among populations and years, and was stronger in the short-scaped than in the long-scaped morph. ,,The results suggest that interactions with pollinators will need to be considered for a full understanding of the maintenance of this striking polymorphism. The study also shows that, although pollen limitation is likely to vary in space and time in many plant species, such variation is not necessarily associated with variation in selection on floral characters. [source] Dietary conservatism may facilitate the initial evolution of aposematismOIKOS, Issue 3 2003R. J. Thomas It has generally been assumed that warningly coloured organisms pay a cost associated with their increased visibility, because naïve predators notice and eat them. This cost is offset by their enhanced protection from educated predators who associate the colour pattern with unprofitability. However, some studies have suggested that avoidance of novel prey by avian predators ("dietary conservatism") can actually place novel colour morphs at a selective advantage over familiar ones, even when they are highly conspicuous. To test this idea, we experimentally simulated the appearance of a single novel-coloured mutant in small populations (20 individuals) of palatable artificial prey. The colour morph frequencies in each "generation" were determined by the relative survival of the previous generation under predation by birds. We used wild-caught European robins Erithacus rubecula foraging on pastry "prey" of different colours. The aim was to test whether prey selection by predators prevented or facilitated the novel colour morph persisting in the prey population over successive generations. We found that the novel colour morph quickly increased to fixation in 14/40 prey "populations", and at least once each in 8 of the 10 birds tested. Novel mutants of the classic aposematic colours (red and yellow) reached fixation most frequently, but even the green and blue novel morphs both increased to fixation in 2/40 trials. Novel colours reached fixation significantly faster than could be accounted for by drift, indicating active avoidance by the birds. These results suggest that a novel colour morph arising in a prey population can persist and increase under the selective pressure imposed by predators, even to the local exclusion of the original morph, despite being fully palatable. The consequences of this finding are discussed in relation to receiver psychology, the evolution of aposematism and the existence of polymorphism in Müllerian mimics. [source] Evidence for differential host preference in Microdochium nivale var. majus and Microdochiumnivale var. nivalePLANT PATHOLOGY, Issue 2 2000D.R. Simpson The pathogenicity of Microdochium nivale var. majus and var. nivale was tested on wheat, rye and oat seedlings using both visual disease scoring and quantitative PCR measurements. In an individual inoculation trial at 10°C var. majus and var. nivale were strongly pathogenic towards wheat and rye, with var. nivale causing slightly greater disease in rye. At this temperature only var. nivale caused significant disease of oats. In a further experiment M. nivale was inoculated as a series of mixtures of the two varieties and incubated at 15°C. The ratio of the varieties present in the inoculum and present at harvest was analysed by quantitative PCR and this enabled a coefficient of selection to be calculated for the varieties on each host. M. nivale var. majus showed a weak selective advantage over var. nivale on wheat (0.33 ± 0.08) and oat seedlings (0.35 ± 0.016) and M. nivale var. nivale showed a strong selective advantage over var. majus on rye seedlings (0.92 ± 0.26). The isolates were also compared for sensitivity to benzoxazolinone (BOA), a hydroxamic acid compound derived from rye leaves. M. nivale var majus was found to be significantly more sensitive to BOA than M. nivale var. nivale, indicating a possible mechanism for the selective advantage of var. nivale growing on rye. This is the first substantiated indication of a significant difference in host preference between Microdochium nivale var. majus and var. nivale. [source] Learning to Cooperate: Learning Networks and the Problem of AltruismAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 3 2009John T. Scholz We explore how two populations learn to cooperate with each other in the absence of institutional support. Individuals play iterated prisoner's dilemmas with the other population, but learn about successful strategies from their own population. Our agent-based evolutionary models reconfirm that cooperation can emerge rapidly as long as payoffs provide a selective advantage for nice, retaliatory strategies like tit-for-tat, although attainable levels of cooperation are limited by the persistence of nonretaliatory altruists. Learning processes that adopt the current best response strategy do well only when initial conditions are very favorable to cooperation, while more adaptive learning processes can achieve high levels of cooperation under a wider range of initial conditions. When combined with adaptive learning, populations having larger, better connected learning relationships outperform populations with smaller, less connected ones. Clustered relationships can also enhance cooperation, particularly in these smaller, less connected populations. [source] Protection and selection for gene therapy in the hematopoietic systemTHE JOURNAL OF GENE MEDICINE, Issue 2 2004Michael D. Milsom Abstract Hematopoietic stem cell gene therapy is potentially curative for a number of inherited and acquired disorders. However, poor gene transfer and expression in repopulating hematopoietic stem cells attenuate this potential. Here we review potential means of conferring a selective advantage to hematopoietic stem cells and their progeny, and discuss the issues that surround the use of selective advantages in vivo. Copyright © 2004 John Wiley & Sons, Ltd. [source] Loss of CD59 expression in breast tumours correlates with poor survivalTHE JOURNAL OF PATHOLOGY, Issue 5 2003Z Madjd Abstract CD59 (protectin), a phosphatidylinositol-anchored glycoprotein, is a member of the cell membrane-bound complement regulatory proteins that inhibits the formation of the terminal membrane attack complex (MAC) of complement. In this study, the expression of CD59 was evaluated in 520 breast carcinomas from patients with a mean follow-up of 87 months. This expression was correlated with clinicopathological features and patient survival. Marked variation in the intensity of CD59 expression, which correlated with histological grade and Nottingham prognostic index (NPI), was found, with higher expression of CD59 found more often in well and moderately differentiated tumours and those of good prognosis (NPI , 3.4). In contrast, high grade and poor prognosis (NPI > 5.4) carcinomas significantly demonstrated lack of CD59 expression (p < 0.001). Moreover, it was found that the percentage of CD59-positive cells correlated significantly with patient survival, ie patients with a high percentage of positive cells (>50%) had a better overall survival (p = 0.006). A correlation was also found between the percentage of CD59-positive cells and tumour type and also the development of distant metastases. No association was found between either the intensity or the percentage of cells expressing CD59 and vascular invasion, lymph node stage, tumour size, patient age or menopausal status. In multivariate analysis, CD59 percentage positivity was of independent prognostic significance with grade and lymph node stage. These findings indicate that loss of CD59 may offer a selective advantage for breast cancers, resulting in more aggressive tumours and conferring a poor prognosis for patients. Copyright © 2003 John Wiley & Sons, Ltd. [source] Sexually transmitted diseases of insects: distribution, evolution, ecology and host behaviourBIOLOGICAL REVIEWS, Issue 3 2004Robert J. Knell ABSTRACT Sexually transmitted diseases (STDs) of insects are known from the mites, nematodes, fungi, protists and viruses. In total 73 species of parasite and pathogen from approximately 182 species of host have been reported. Whereas nearly all vertebrate STDs are viruses or bacteria, the majority of insect STDs are multicellular ectoparasites, protistans or fungi. Insect STDs display a range of transmission modes, with, pure'sexual transmission only described from ectoparasites, all of which are mites, fungi or nematodes, whereas the microparasitic endo-parasites tend to show vertical as well as sexual transmission. The distribution of STDs within taxa of insect hosts appears to be related to the life histories of the hosts. In particular, STDs will not be able to persist if host adult generations do not overlap unless they are also transmitted by some alternative route. This explains the observation that the Coleoptera seem to suffer from more STDs than other insect orders, since they tend to diapause as adults and are therefore more likely to have overlapping generations of adults in temperate regions. STDs of insects are often highly pathogenic, and are frequently responsible for sterilizing their hosts, a feature which is also found in mammalian STDs. This, combined with high prevalences indicates that STDs can be important in the evolution and ecology of their hosts. Although attempts to demonstrate mate choice for unin-fected partners have so far failed it is likely that STDs have other effects on host mating behaviour, and there is evidence from a few systems that they might manipulate their hosts to cause them to mate more frequently. STDs may also play a part in sexual conflict, with males in some systems possibly gaining a selective advantage from transmitting certain STDs to females. STDs may well be important factors in host population dynamics, and some have the potential to be useful biological control agents, but empirical studies on these subjects are lacking. [source] Palms Use a Bluffing Strategy to Avoid Seed Predation by Rats in BrazilBIOTROPICA, Issue 2 2010Constança De Sampaio e Paiva Camilo-Alves ABSTRACT The goal of this study was to ascertain why the production of variable seediness is advantageous for Attalea phalerata palms. Our hypothesis was that variation reduces seed predation by the spiny rats Thrichomys pachyurus and Clyomys laticeps. Although there is a positive correlation between endocarp size and number of seeds, endocarps sometimes contain more or fewer seeds than expected; palms bluff about the number of seed per endocarp. Therefore, rats do not know how many seeds an endocarp contains. To model rats' predating behavior, we applied Charnov's Marginal Value Theorem. The model shows that rats attack endocarps only when the energy gain is higher than the energy available in the habitat. Hence, it is not advantageous to eat all the seeds inside an endocarp. This explains why 45 percent of forest endocarps and 35 percent of savanna endocarps were still viable after predation. We then applied the model to two simulated endocarp populations with less variability in the number of seeds per endocarp size and determined that viable diaspores after predation were reduced to 15 percent. With less variability, palms cannot bluff about the number of seeds inside endocarps and predators can predict accurately how many seeds they should try to eat. Uncertainty about the number of seeds diminished predation but gave selective advantage to multiseeded fruits. Therefore, the bluffing strategy would be evolutionarily stable only if it were counterbalanced by other forces. Otherwise, predators would win the bluffing game. Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp. [source] | |||||||||||||||||||||||||||||||||||||