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Fitness Advantage (fitness + advantage)
Selected AbstractsPlant invasions and the nicheJOURNAL OF ECOLOGY, Issue 4 2009Andrew S. MacDougall Summary 1For plant invaders, being different is often equated with being successful, yet the mechanistic connection remains unclear. 2Classic niche theory predicts that invaders with niches distinct from the native flora should coexist with little interaction with native species, yet such invaders often have substantial impacts. Meanwhile, invaders that overlap in niche space with native species should either be repelled or dominate, yet these invaders often naturalize with little effect. Such discrepancies between theory and observation raise questions about how species differences influence invader establishment and impact. 3Here, we review these issues in light of recent work on coexistence theory, which shows how niche and fitness differences between natives and invaders interact to determine invasion outcomes. We show how successful invader establishment depends on either a fitness advantage or niche difference from resident species, but that only the former allows invaders to become dominant. 4By identifying the role of niche and fitness differences in leading invasion hypotheses, we unify their predictions for invasion success while highlighting new approaches for evaluating the importance of species differences for invasion. 5Synthesis. Situating the invasion process within a recent coexistence framework broadens our understanding of invasion mechanisms and more tightly links problems in invasion ecology with our more general understanding of community dynamics. [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] Coping with third parties in a nursery pollination mutualism: Hadena bicruris avoids oviposition on pathogen-infected, less rewarding Silene latifoliaNEW PHYTOLOGIST, Issue 4 2006Arjen Biere Summary ,,In nursery pollination systems, pollinator offspring usually feed on pollinated fruits or seeds. Costs and benefits of the interaction for plant and pollinator, and hence its local outcome (antagonism,mutualism), can be affected by the presence of ,third-party' species. Infection of Silene latifolia plants by the fungus Microbotryum violaceum halts the development of fruits that provide shelter and food for larvae of the pollinating moth Hadena bicruris. We investigated whether the moth secures its benefit by selective oviposition on uninfected flowers. ,,Oviposition was recorded in eight natural populations as a function of plant infection status, local neighbourhood, plant and flower characteristics. ,,Oviposition was six times lower on flowers from infected than on those from uninfected plants. Oviposition decreased with decreasing flower and ovary size. Moths could use the latter to discriminate against diseased flowers. ,,Although moths show an adaptive oviposition response, they reduce the future potential of healthy hosts because they still visit infected plants for nectar, vectoring the disease, and they reduce any fitness advantage gained by disease-resistant plants through selective predation of those plants. [source] The founding mothers: the genetic structure of newly established Daphnia populationsOIKOS, Issue 5 2007Gerald Louette Colonization dynamics may strongly influence within and among population genetic variation and evolutionary potential of populations. We here analyze the genetic structure during the first three years of 12 cyclical parthenogenetic Daphnia populations in newly created pond habitats. One to three genotypes were observed to colonize the populations, indicating a limited number of founders. Pronounced changes in genetic structure were associated with hatching of sexual dormant eggs after a period of absence of the newly founded populations from the active community. Despite rapid colonization, genetic differentiation among populations was fairly high with limited decay over time, suggesting long-lasting founder effects. After initial colonization, no new alleles were observed in any of the populations, and our analyses suggests that this reflects reduced establishment success of later arrivals. Rare alleles increased in frequency, which likely is the result of inbreeding depression in selfed offspring of initially abundant clones, providing a fitness advantage to the sexual offspring of initially rare clones. [source] Seasonal changes in female size and its relation to reproduction in the parasitoid Asobara tabidaOIKOS, Issue 2 2001Jacintha Ellers The relation between female size and fitness was studied in female Asobara tabida throughout the field season. The size of A. tabida females varied considerably, with average size being smallest in the middle of the season. There was a positive correlation of realized fecundity with size, and the fitness advantage of larger females increased later in the season. A possible explanation for this can be found in the energy expenditure during the season. Regression analysis showed that fat use increases with size of the female, but also with temperature. Temperature was low early and late in the season, but high in the middle. We argue that the high temperatures may constrain fitness advantages of large females because of their increased metabolic needs. Variation in the form of the fitness function within the season may moderate directional selection for larger females. [source] A critique of the grandmother hypotheses: Old and newAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2001Jocelyn Scott Peccei The singularity of reproductive senescence in human females has led many investigators to consider menopause an adaptation permitting increased maternal investment in existing progeny. Much of the focus has been on the grandmother hypothesis,the notion that aging women gain an inclusive fitness advantage from investing in their grandchildren. This hypothesis has evolved from an explanation for menopause into an explanation for the exceptionally long postreproductive lifespan in human females. In the old grandmother hypothesis, menopause is an adaptation facilitating grandmothering; it is about stopping early in order to create a postreproductive lifespan. In the new grandmother hypothesis, grandmothering is an adaptation facilitating increased longevity, and menopause is a byproduct. This paper reviews and critically evaluates the evidence for and against both hypotheses, focusing on key predictions of each. If menopause is the result of selection for increased maternal investment, this involved mainly mothers, not grandmothers. Am. J. Hum. Biol. 13:434,452, 2001. © 2001 Wiley-Liss, Inc. [source] Discovery of male sterile plants and their contrasting occurrence between self-compatible and self-incompatible populations of the hermaphroditic perennial Trillium camschatcensePLANT SPECIES BIOLOGY, Issue 3 2009SHOSEI KUBOTA Abstract The sex type of Trillium camschatcense has been considered to be strictly monomorphic, composed of only hermaphroditic individuals. However, field observations have detected anther-degenerated (AD) plants coexisting with hermaphrodites. The present study aimed to elucidate whether AD plants could be regarded as females and, if so, how their loss of male function is compensated. Because T. camschatcense retains both self-compatible (SC) and self-incompatible (SI) populations, the frequencies of AD plants in multiple populations (22 SC and eight SI) were examined to predict the fate of these individuals under contrasting breeding systems. Morphological and genetic analyses in a SC population demonstrated that AD plants were completely male sterile, but female fertile. Although the quantity of seed produced was similar, hermaphrodites produced seeds predominantly via selfing, whereas seeds of AD plants were entirely outcrossed. Because inbreeding depression was severe, AD plants achieved a fitness advantage through inbreeding avoidance. However, the frequency of AD plants varied among SC populations (0,42%), suggesting that environmental variance can modify the relative fitness. Conversely, the frequency was suppressed among SI populations (0,2%). Because SI hermaphrodites are free from inbreeding, AD plants would not benefit from inbreeding avoidance and would find it difficult to invade a SI population. [source] Phytochrome-mediated agravitropism in Arabidopsis hypocotyls requires GIL1 and confers a fitness advantageTHE PLANT JOURNAL, Issue 4 2006Trudie Allen Summary Plants use specialized photoreceptors to detect the amount, quality, periodicity and direction of light and to modulate their growth and development accordingly. These regulatory light signals often interact with other environmental cues. Exposure of etiolated Arabidopsis seedlings to red (R) or far-red (FR) light causes hypocotyls to grow in random orientations with respect to the gravitational vector, thus overcoming the signal from gravity to grow upwards. This light response, mediated by either phytochrome A or phytochrome B, represents a prime example of cross-talk between environmental signalling systems. Here, we report the isolation the mutant gil1 (for gravitropic in the light) in which hypocotyls continue to grow upwards after exposure of seedlings to R or FR light. The gil1 mutant displays no other phenotypic alterations in response to gravity or light. Cloning of GIL1 has identified a novel gene that is necessary for light-dependent randomization of hypocotyl growth orientation. Using gil1, we have demonstrated that phytochrome-mediated randomization of Arabidopsis hypocotyl orientation provides a fitness advantage to seedlings developing in patchy, low-light environments. [source] The fitness advantage of a high-performance weaponBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009JERRY F. HUSAK Weapons used in combat between males are usually attributed to sexual selection, which operates via a fitness advantage for males with weapons of better ,quality'. Because the performance capacity of morphological traits is typically considered the direct target of selection, Darwin's intrasexual selection hypothesis can be modified to predict that variation in reproductive success should be explained by variation in performance traits relevant to combat. Despite such a straightforward prediction, tests of this hypothesis are conspicuously lacking. We show that territorial male collared lizards with greater bite-force capacity sire more offspring than weaker biting rivals but exhibit no survival advantage. We did not detect stabilizing or disruptive selection on bite-force capacity. Taken together, these results support the hypothesis that superior weapon performance provides a fitness advantage through increased success in male contests. Sexual selection on weapon performance therefore appears to be a force driving the evolution and maintenance of sexual dimorphism in head shape. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 840,845. [source] Evolutionary ecology of insect adaptation to Bt cropsEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 5-6 2010Yves Carrière Abstract Transgenic crops producing Bacillus thuringiensis (Bt) toxins are used worldwide to control major pests of corn and cotton. Development of strategies to delay the evolution of pest resistance to Bt crops requires an understanding of factors affecting responses to natural selection, which include variation in survival on Bt crops, heritability of resistance, and fitness advantages associated with resistance mutations. The two main strategies adopted for delaying resistance are the refuge and pyramid strategies. Both can reduce heritability of resistance, but pyramids can also delay resistance by reducing genetic variation for resistance. Seasonal declines in the concentration of Bt toxins in transgenic cultivars, however, can increase the heritability of resistance. The fitness advantages associated with resistance mutations can be reduced by agronomic practices, including increasing refuge size, manipulating refuges to increase fitness costs, and manipulating Bt cultivars to reduce fitness of resistant individuals. Manipulating costs and fitness of resistant individuals on transgenic insecticidal crops may be especially important for thwarting evolution of resistance in haplodiploid and parthenogenetic pests. Field-evolved resistance to Bt crops in only five pests during the last 14 years suggests that the refuge strategy has successfully delayed resistance, but the accumulation of resistant pests could accelerate. [source] Patterns of reproductive effort and success in birds: path analyses of long-term data from European ducksJOURNAL OF ANIMAL ECOLOGY, Issue 2 2002Peter Blums Summary 1We tested ecological hypotheses about timing of breeding and reproductive effort in birds, by analysing > 15-year data sets for individually marked females in three species of Latvian ducks (northern shoveler, tufted duck, common pochard). 2Duckling survival and recruitment declined with advancing hatch date in pochard and tufted duck, after controlling for effects of female age and other factors with path analysis, a novel finding which indicates that fitness advantages associated with early hatching extended beyond the prefledging period. Logistic regression analysis suggested further that individual duckling prefledging survival was moderate in the earliest phase of the breeding season, greatest in mid-season and lowest later on. 3However, selection acting against early hatched ducklings was surpassed by strong directional selection favouring recruitment of the earliest hatching females. The absolute and relative numbers of female recruits produced by a breeding female declined sharply with advancing hatch date in all species. 4Unlike previous studies, an hypothesized intraspecific trade-off between duckling mass and brood size was detected, being very robust in two of three species. 5Unexpectedly, female age effects on recruitment were manifested only indirectly by several pathways, the most important being the earlier hatching dates of older females. Size-adjusted body mass (i.e. condition index) was positively related to reproductive success, and was 2,8-fold more influential than female size (indexed by wing length). 6Overall, fecundity-independent variables (e.g. hatching date, weather, indices of duckling production and habitat quality) generally had 2,10 times greater influence on recruitment rates than did fecundity-dependent variables such as female size or condition, duckling mass and brood size, suggesting a critical role for external environmental factors vs. individual female-specific traits in the recruitment process. [source] Ecological aspects of seed desiccation sensitivityJOURNAL OF ECOLOGY, Issue 2 2003John C. Tweddle Summary 1The ability of seeds to survive desiccation is an important functional trait and is an integral part of plant regeneration ecology. Despite this, the topic has received relatively little attention from ecologists. In this study, we examine the relationships between seed desiccation tolerance and two important aspects of plant regeneration ecology: habitat and dormancy. This is done by comparative analysis of a data set of 886 tree and shrub species from 93 families. 2The proportion of species displaying desiccation sensitive seeds declines as the habitat becomes drier, and possibly also cooler, although the latter observation requires cautious interpretation. Desiccation sensitivity is most common in moist, relatively aseasonal vegetation zones, but is infrequent in, though not absent from arid and highly seasonal habitats. 3The highest frequency of desiccation sensitivity occurs in non-pioneer evergreen rain forest trees, although 48% of the species examined have desiccation tolerant seeds. In contrast, all pioneer taxa within the data set have drying tolerant seeds. 4Desiccation sensitivity is more frequent in seeds that are non-dormant on shedding (c. 31%), than dormant (c. 9%). Highest frequencies of drying tolerance occur in seeds with physical or combinational dormancy, at 99% and 100%, respectively. 5Although there is an association between non-dormancy and desiccation sensitivity in both tropical and temperate zones, the relationship does not appear to be causal. 6Working from the hypothesis that seed desiccation sensitivity represents a derived state in extant species, we use the results to investigate and discuss possible ecological trade-offs and associated fitness advantages. These may explain the hypothesized repeated loss of this trait. The frequent association between large seed size and desiccation sensitivity is also considered. [source] Seasonal changes in female size and its relation to reproduction in the parasitoid Asobara tabidaOIKOS, Issue 2 2001Jacintha Ellers The relation between female size and fitness was studied in female Asobara tabida throughout the field season. The size of A. tabida females varied considerably, with average size being smallest in the middle of the season. There was a positive correlation of realized fecundity with size, and the fitness advantage of larger females increased later in the season. A possible explanation for this can be found in the energy expenditure during the season. Regression analysis showed that fat use increases with size of the female, but also with temperature. Temperature was low early and late in the season, but high in the middle. We argue that the high temperatures may constrain fitness advantages of large females because of their increased metabolic needs. Variation in the form of the fitness function within the season may moderate directional selection for larger females. [source] Thermal effects on reptile reproduction: adaptation and phenotypic plasticity in a montane lizardBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010RORY S. TELEMECO Interspecific comparisons suggest a strong association between cool climates and viviparity in reptiles. However, intraspecific comparisons, which provide an opportunity to identify causal pathways and to distinguish facultative (phenotypically plastic) effects from canalized (genetically fixed) responses, are lacking. We documented the reproductive traits in an alpine oviparous lizard, and manipulated thermal regimes of gravid females and their eggs to identify proximate causes of life-history variation. Embryonic development at oviposition was more advanced in eggs laid by females from high-elevation populations than in eggs produced by females from lower elevations. In the laboratory, experimentally imposed low maternal body temperatures delayed oviposition and resulted in more advanced embryonic development at oviposition. Warm conditions both in utero and in the nest increased hatching success and offspring body size. Our intraspecific comparisons support the hypothesis that viviparity has evolved in cold-climate squamates because of the direct fitness advantages that warm temperatures provide developing offspring. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 642,655. [source] | ||||||||||||||||||||||