Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item

植物生态学报 , 2001,
Abstract: Two basic forces affect the evolution of plant mating systems.Selfing will be favored if it increases seed set when polle n is limiting (reproductive assurance) or increases siring success when pollen d evoted to selfing is more likely to accomplish fertilization than pollen devoted to outcrossing (automatic selection advantage). Experimental and observational studies, however, have yet to identify more precisely the set of ecological cond itions under which either of those advantages can be expressed. Pollen discounti ng reduces a selfers' success as an outcross pollen parent, i.e. lowering au tomatic selection advantage, and inbreeding depression is expected to reduce any advantage selfers might gain through reproductive assurance or automatic selection. Changes in a species' mating system are likely to induce evolutionary adjus tments in its resource allocation. Theory predicts that sex allocation, or the proportion of reproductive resources allocated to male function in hermaphroditic plants, decreases as the selfing rate increases, and that total reproductive al location increases with increased selfing if inbreeding depression is not so sev ere as to prevent the evolution of self-fertilization. In some extreme conditio ns, increased selfing may lead to severe change in life history, i.e. from peren niality to annuality. Sex allocation theory provides a general explanation for diversity in breeding systems, in particular, it explains why most flowering plan ts are hermaphroditic. While empirical evidence is abundant that supports the ex pected decrease in sex allocation as selfing rate increases, there has been no demonstration of the expected correlation between mating system and total reprodu ctive effort. Selfing tends both to reduce the level of genetic variability with in populations and to increase the amount of genetic differentiation among popul ations. A longtime conjecture that selfers may give up some long-term evolution ary flexibility has now been partially confirmed.
Preliminary studies on invasive model and outbreak mechanism of exotic species, Spartiona alterniflora Loisel.

DENG Zi-Fa,AN Shu-Qing,ZHI Ying-Biao,ZHOU Chang-Fang,CHEN Lin,ZHAO Cong-Jiao,FANG Shu-Bo,LI Hong-Li,

生态学报 , 2006,
Abstract: The invasive species, Spartina alterniflora Loisel., has been introduced to many countries because it accelerates sediment accretion and therefore can act as a seawall. However, the exceptional adaptability and reproductive ability of this species has led to its extensive dispersal into habitats where it has negative impacts on native species. Previous researchers have shown Allee effects in the establishment of S. alterniflora, in part due to inbreeding depression and rapid local adaptation, making this species a model plant for studying biological invasion from ecological and genetic perspectives. In China, the expansion of S. alterniflora, based on intentionally transplanted in multiple loci, has developed an understanding of the mode of point-source dispersal, suggesting multi-locus outbreaks and weak Allee effects. The episodic and continuous dispersal pattern of seeds plays an important role in maintaining, recruitment and expansion of S. alterniflora populations. Furthermore, expansion of S. alterniflora populations is also enhanced by clonal growth. It has proven very difficult to eradicate S. alterniflora, but timely monitoring combined with a clear understanding of the factors that promote invasion may alleviate the effect of this species in natural habitats.
Social and Population Structure in the Ant Cataglyphis emmae  [PDF]
Michael J. Jowers, Laurianne Leniaud, Xim Cerdá, Samer Alasaad, Stephane Caut, Fernando Amor, Serge Aron, Rapha?l R. Boulay
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0072941
Abstract: Dispersal has consequences not only for individual fitness, but also for population dynamics, population genetics and species distribution. Social Hymenoptera show two contrasting colony reproductive strategies, dependent and independent colony foundation modes, and these are often associated to the population structures derived from inter and intra-population gene flow processes conditioned by alternative dispersal strategies. Here we employ microsatellite and mitochondrial markers to investigate the population and social genetic structure and dispersal patterns in the ant Cataglyphis emmae at both, local and regional scales. We find that C. emmae is monogynous and polyandrous. Lack of detection of any population viscosity and population structure with nuclear markers at the local scale suggests efficient dispersal, in agreement with a lack of inbreeding. Contrasting demographic differences before and during the mating seasons suggest that C. emmae workers raise sexuals in peripheric nest chambers to reduce intracolonial conflicts. The high genetic differentiation recovered from the mtDNA haplotypes, together with the significant correlation of such to geographic distance, and presence of new nuclear alleles between areas (valleys) suggest long-term historical isolation between these regions, indicative of limited dispersal at the regional scale. Our findings on the ecological, social and population structure of this species increases our understanding of the patterns and processes involved under independent colony foundation.
Mixed Infections and Hybridisation in Monogenean Parasites  [PDF]
Bettina Schelkle, Patricia J. Faria, Mireille B. Johnson, Cock van Oosterhout, Joanne Cable
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0039506
Abstract: Theory predicts that sexual reproduction promotes disease invasion by increasing the evolutionary potential of the parasite, whereas asexual reproduction tends to enhance establishment success and population growth rate. Gyrodactylid monogeneans are ubiquitous ectoparasites of teleost fish, and the evolutionary success of the specious Gyrodactylus genus is thought to be partly due to their use of various modes of reproduction. Gyrodactylus turnbulli is a natural parasite of the guppy (Poecilia reticulata), a small, tropical fish used as a model for behavioural, ecological and evolutionary studies. Using experimental infections and a recently developed microsatellite marker, we conclusively show that monogenean parasites reproduce sexually. Conservatively, we estimate that sexual recombination occurs and that between 3.7–10.9% of the parasites in our experimental crosses are hybrid genotypes with ancestors from different laboratory strains of G. turnbulli. We also provide evidence of hybrid vigour and/or inter-strain competition, which appeared to lead to a higher maximum parasite load in mixed infections. Finally, we demonstrate inbreeding avoidance for the first time in platyhelminths which may influence the distribution of parasites within a host and their subsequent exposure to the host's localized immune response. Combined reproductive modes and inbreeding avoidance may explain the extreme evolutionary diversification success of parasites such as Gyrodactylus, where host-parasite coevolution is punctuated by relatively frequent host switching.
The importance of immune gene variability (MHC) in evolutionary ecology and conservation
Simone Sommer
Frontiers in Zoology , 2005, DOI: 10.1186/1742-9994-2-16
Abstract: Many natural populations are threatened not only by a dramatic reduction in total area of available habitat but also by increasing habitat fragmentation and degradation leading to declining population sizes and barriers to gene flow if exchange of individuals between subpopulations is restricted [1-3]. Small populations often suffer from reduction of genetic diversity due to genetic drift and inbreeding effects [4-6]. Negative effects such as increased rates of allelic loss, fixation of deleterious alleles and decreased average individual heterozygosity relative to the overall population were observed by both, theoretical and empirical studies [7,8]. The loss of genetic variation can lead to short-term reduction of fitness components such as survival, reproductive output, growth rates and to impaired ability to adapt to long-term changes in the environment [7,9-13]. An increasing number of studies indicates that host genetic diversity plays an important role in buffering populations against pathogens and widespread epidemics [6,14-20]. Study of the genetic effects of population fragmentation is therefore of central importance for conservation biology [21].Genetic studies of wild animals often employ neutral markers such as mitochondrial d-loop DNA (mtDNA), microsatellites or single nucleotide polymorphism (SNPs) to estimate the amount of variation present in individuals and populations [22-24]. While these markers are very informative for phylogenetic reconstructions and population history (bottleneck effects), for molecular clocks, to examine dispersal patterns of individuals (gene flow) and to classify individuals by relatedness and paternity analyses [25-28], the variation at neutral loci cannot provide direct information on selective processes involving the interaction of individuals with their environment or on the capacity for future adaptive changes [29,30]. However, these are issues of particular relevance in evolutionary ecology and conservation [31,32]. In
The Population Structure of Glossina palpalis gambiensis from Island and Continental Locations in Coastal Guinea  [PDF]
Philippe Solano ,Sophie Ravel,Jeremy Bouyer,Mamadou Camara,Moise S. Kagbadouno,Naomi Dyer,Laetitia Gardes,Damien Herault,Martin J. Donnelly,Thierry De Mee?s
PLOS Neglected Tropical Diseases , 2009, DOI: 10.1371/journal.pntd.0000392
Abstract: Background We undertook a population genetics analysis of the tsetse fly Glossina palpalis gambiensis, a major vector of sleeping sickness in West Africa, using microsatellite and mitochondrial DNA markers. Our aims were to estimate effective population size and the degree of isolation between coastal sites on the mainland of Guinea and Loos Islands. The sampling locations encompassed Dubréka, the area with the highest Human African Trypanosomosis (HAT) prevalence in West Africa, mangrove and savannah sites on the mainland, and two islands, Fotoba and Kassa, within the Loos archipelago. These data are discussed with respect to the feasibility and sustainability of control strategies in those sites currently experiencing, or at risk of, sleeping sickness. Principal Findings We found very low migration rates between sites except between those sampled around the Dubréka area that seems to contain a widely dispersed and panmictic population. In the Kassa island samples, various effective population size estimates all converged on surprisingly small values (10
Endocrine disruptor screening: regulatory perspectives and needs
Markus Hecker, Henner Hollert
Environmental Sciences Europe , 2011, DOI: 10.1186/2190-4715-23-15
Abstract: Since the middle of the 1990 s, there has been increasing awareness and concern regarding the exposure to chemicals that have the potential to interfere with the endocrine system, and thus, may cause health effects in people and wildlife. In fact, a great number of chemicals have been identified that were found to interact with the endocrine system of different animals in laboratory studies, and there are increasing reports of endocrine disruption in wild animals [1,2]. The potential role of endocrine disrupting chemicals in the environment has been discussed extensively for several years in both science and the broader public. On the one hand, there is evidence from various laboratory experiments that estrogenic or estrogen-like compounds have the potential of affecting development of the reproductive and nervous systems, as well as behavior and immune response in higher organisms [3,4]. On the other hand, it is still unclear if environmentally relevant concentrations of xenoestrogens can result in deleterious effects in wildlife populations, and to date - with few exceptions - there has been no direct evidence of such population relevant impacts in the wild [5,6]. In fact, few studies have attempted to explore the ecological relevance of the exposure to endocrine active chemicals under field conditions. One example is a recent whole-lake study that was conducted over 10 years at the Experimental Lakes Area in Canada that revealed clear evidence that the potent synthetic estrogen 17β-ethynylestradiol (EE2) affects fish populations and their supporting food web [7]. The population of the shortest-lived fish species, the fathead minnow, collapsed after two summers of EE2 additions. There is consequently an urgent need in understanding the relevance of lab-based experiments with endocrine disruptive chemicals (EDCs) in context with ecological scenarios.These reports and associated concerns regarding the ubiquitous presences of EDCs in the environment have sparked both
Dung Beetles Eat Acorns to Increase Their Ovarian Development and Thermal Tolerance  [PDF]
José R. Verdú,José L. Casas,Jorge M. Lobo,Catherine Numa
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0010114
Abstract: Animals eat different foods in proportions that yield a more favorable balance of nutrients. Despite known examples of these behaviors across different taxa, their ecological and physiological benefits remain unclear. We identified a surprising dietary shift that confers ecophysiological advantages in a dung beetle species. Thorectes lusitanicus, a Mediterranean ecosystem species adapted to eat semi-dry and dry dung (dung-fiber consumers) is also actively attracted to oak acorns, consuming and burying them. Acorn consumption appears to confer potential advantages over beetles that do not eat acorns: acorn-fed beetles showed important improvements in the fat body mass, hemolymph composition, and ovary development. During the reproductive period (October-December) beetles incorporating acorns into their diets should have greatly improved resistance to low-temperature conditions and improved ovarian development. In addition to enhancing the understanding of the relevance of dietary plasticity to the evolutionary biology of dung beetles, these results open the way to a more general understanding of the ecophysiological implications of differential dietary selection on the ecology and biogeography of these insects.
Comparative leaf anatomy in argentine Galactia species
Tourn,G. M.; Cosa,M. T.; Roitman,G. G.; Silva,M. P.;
Bolet?-n de la Sociedad Argentina de Bot??nica , 2009,
Abstract: a comparative study of anatomical characters of the leaves of argentine species of genera galactia was carried out in order to evaluate their potential value in taxonomy. in argentine 14 species and some varieties from sections odonia and collaearia can be found. section odonia: g. benthamiana mich., g. dubia dc., g. fiebrigiana burkart var. correntina burkart, g. glaucophylla harms, g. gracillima benth., g. latisiliqua desv., g. longifolia (jacq.) benth., g. marginalis benth., g. striata (jacq.) urban, g. martioides burkart, g. neesi d. c. var. australis malme, g. pretiosa burkart var. pretiosa, g. texana (scheele) a. gray and g. boavista (vell.) burkart from section collaearia. the characterization of sections is mainly based on reproductive characters, vegetative ones (exomorphological aspects) are scarcely considered. the present paper provides a description of anatomical characters of leaves in argentine species of galactia. some of them, may have diagnostic value in taxonomic treatment. special emphasis is placed on the systematic significance of the midvein structure. the aim of the present study, covering 10 species (named in bold), is a) to add more data of leaf anatomy characters, thus b) to evaluate the systematic relevance and/ or ecological significance.
Life at the margin: the mating system of Mediterranean conifers
G. Restoux, D. E. Silva, F. Sagnard, F. Torre, E. Klein,B. Fady
Web Ecology (WE) , 2008, DOI: 10.5194/we-8-94-2008
Abstract: Mixed mating, where a single tree progeny results from a mixture of selfing and outcrossing, is widespread in conifers and could be an evolutionary advantage at ecological margins when mating partners become scarce. This study analyzes how the mating system responds to bioclimate and density variations. We surveyed published data on the mating system of Abies, Picea and Pinus species when information on bioclimate and stand density was available. Our survey revealed that Mediterranean species demonstrate a lower selfing rate than other species and that the proportion of selfed versus outcrossed progeny is not fixed within species. The highest variability in mating types within populations was found when stand density was the most variable. To show how density affects the proportion of selfed versus outcrossed progeny, we used isozymes to genotype single tree seeds from a marginal Abies alba forest in Mediterranean France (Mont Ventoux) where low-to high-density stands are found. We then tested the adaptive potential of the different high and low density progenies by sowing them under controlled nursery conditions and measuring germination rate and seedling survival after 4 yr under 3 different water regimes. Although the mean value of outcrossing rate was typical for mixed mating conifers (tm = 0.85), individual outcrossing rates varied from 0.05 to 0.99 and were strongly correlated with stand type and density (tm from 0.87 in high-density to 0.43 in low-density marginal stands). Significantly fewer seeds from the low density marginal stand germinated (32% vs. 53% in the high density mature stand), although seedlings from the marginal stand had a better 4-yr survival (81%) than seedlings from the high-density mature stand (63%) when the three water regimes (from least to most stressful) were averaged. Trees from low density stands may be at a selective disadvantage because they produce more selfed progeny than trees from high-density stands. However, selfed seeds may be purged early on (at the embryo stage) and the remaining seeds tend to produce seedlings with better fitness. Variability of the selfing rate might thus be an adaptive strategy for species in highly contrasted environments where selection of both reproductive assurance and avoidance of inbreeding depression may be density dependent.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.