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Widespread Phenomenon (widespread + phenomenon)
Selected AbstractsThe effect of single vegetation elements on wind speed and sediment transport in the Sahelian zone of Burkina FasoEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2007J. K. Leenders Abstract Soil loss caused by wind erosion is a widespread phenomenon in the Sahelian zone of West Africa. According to Sahelian farmers, scattered vegetation standing in amongst the crop has the potential for a wind erosion control strategy. This study was conducted to study the effect of single vegetation elements on the pattern of average wind speed and sediment transport. This was done by two experiments that were carried out during the rainy seasons of 2002 and 2003 in north Burkina Faso, West Africa. Wind speeds were measured using three sonic anemometers, at a sampling frequency of 16 Hz. Sediment transport was determined by calculating the mass fluxes from 17 MWAC catchers. In this study, a shrub was defined as a vegetation element with branches until ground and a tree as a vegetation element with a distinctive trunk below a canopy. Behind shrubs wind speed near the soil surface was reduced up to approximately seven times the height of the shrub. The observed reduction in wind speed in the area where wind speed was reduced was 15 per cent on average. At the sides of the shrub, wind speed was increased, by on average 6 per cent. As the area of increase in wind speed is one-third of the area of decrease in wind speed, the net effect of a shrub is a reduction in wind speed. A similar pattern was visible for the pattern of sediment transport around a shrub. Downwind of a shrub, sediment transport was diminished up to seven times the height of the shrub. Probably most of this material was trapped by the shrub. Trees showed a local increase of wind around the trunk, which is expected to relate to an increase in sediment transport around the trunk. Mass flux measurements of sediment transport were not made, but visual observations in the field substantiate this. Behind the canopy of a tree, a tree acts similarly to a shrub regarding its effects on average wind speed, but as a tree is generally a larger obstacle than a shrub the extent of this effect is larger than for shrubs. Thus, whereas shrubs are more effective than trees regarding their direct effect on soil loss by trapping sand particles near the soil surface, trees are more effective in affecting soil loss indirectly by reducing the wind speed downwind more effectively than shrubs. Therefore, to reduce soil loss in an area, the presence of both trees and shrubs is crucial. Copyright © 2007 John Wiley & Sons, Ltd. [source] Achieving high sexual size dimorphism in insects: females add instarsECOLOGICAL ENTOMOLOGY, Issue 3 2007TOOMAS ESPERK Abstract 1.,In arthropods, the evolution of sexual size dimorphism (SSD) may be constrained by a physiological limit on growth within each particular larval instar. A high SSD could, however, be attained if the larvae of the larger sex pass through a higher number of larval instars. 2.,Based on a survey of published case studies, the present review shows that sex-related difference in the number of instars is a widespread phenomenon among insects. In the great majority of species with a sexually dimorphic instar number, females develop through a higher number of instars than males. 3.,Female-biased sexual dimorphism in final sizes in species with sexually dimorphic instar number was found to considerably exceed a previously estimated median value of SSD for insects in general. This suggests a causal connection between high female-biased SSD, and additional instars in females. Adding an extra instar to larval development allows an insect to increase its adult size at the expense of prolonged larval development. 4.,As in the case of additional instars, SSD is fully formed late in ontogeny, larval growth schedules and imaginal sizes can be optimised independently. No conflict between selective pressures operating in juvenile and adult stages is therefore expected. 5.,In most species considered, the number of instars also varied within the sexes. Phenotypic plasticity in instar number may thus be a precondition for a sexual difference in instar number to evolve. [source] Kinship Discrimination and Effects on Social Rank and Aggressiveness Levels in Iberian Red Deer HindsETHOLOGY, Issue 12 2007Francisco Ceacero Kin recognition is a widespread phenomenon that allows individuals to benefit by enhancing their inclusive fitness, and one of its most common forms is reducing aggressiveness towards relatives. We carried out an experiment with Iberian red deer hinds (Cervus elaphus hispanicus) in order to examine kin biases in dominance behaviour and its consequences on social rank. Three enclosed groups (n = 36, 23 and 21, respectively) were monitored during two lactation seasons and social rank hierarchies were assessed by analysing aggressive interactions matrices with Matman 1.1 software. Aggressive interactions between related hinds was significantly smaller than expected (,2 = 5.02, df = 1, p = 0.025), not only between mother and daughter but also in second and third kinship degrees. Although rates of aggressiveness were similar to data published relating free-ranging C. e. scoticus, aggressive interactions with relatives were significantly smaller (,2 = 39.0, df = 1, p < 0.001). This reduction of aggressiveness between related hinds was not the result of these hinds having a lower social rank: social rank was only related to age and weight, but not to kinship degree, calf sex or calving date. The decrease of aggressiveness towards first-, second- and third-degree relatives shows a complex kin recognition system in deer. Possible nepotistic roles in lactation include preventing milk thefts by non-kin and disturbing feeding of unrelated hinds. [source] SK channels and the varieties of slow after-hyperpolarizations in neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003Fivos Vogalis Abstract Action potentials and associated Ca2+ influx can be followed by slow after-hyperpolarizations (sAHPs) caused by a voltage-insensitive, Ca2+ -dependent K+ current. Slow AHPs are a widespread phenomenon in mammalian (including human) neurons and are present in both peripheral and central nervous systems. Although, the molecular identity of ion channels responsible for common membrane potential mechanisms has been largely determined, the nature of the channels that underlie the sAHPs in neurons, both in the brain and in the periphery, remains unresolved. This short review discusses why there is no clear molecular candidate for sAHPs. [source] PEAK SHIFT DISCRIMINATION LEARNING AS A MECHANISM OF SIGNAL EVOLUTIONEVOLUTION, Issue 6 2005Spencer K. Lynn Abstract "Peak shift" is a behavioral response bias arising from discrimination learning in which animals display a directional, but limited, preference for or avoidance of unusual stimuli. Its hypothesized evolutionary relevance has been primarily in the realm of aposematic coloration and limited sexual dimorphism. Here, we develop a novel functional approach to peak shift, based on signal detection theory, which characterizes the response bias as arising from uncertainty about stimulus appearance, frequency, and quality. This approach allows the influence of peak shift to be generalized to the evolution of signals in a variety of domains and sensory modalities. The approach is illustrated with a bumblebee (Bombus impatiens) discrimination learning experiment. Bees exhibited peak shift while foraging in an artificial Batesian mimicry system. Changes in flower abundance, color distribution, and visitation reward induced bees to preferentially visit novel flower colors that reduced the risk of flower-type misidentification. Under conditions of signal uncertainty, peak shift results in visitation to rarer, but more easily distinguished, morphological variants of rewarding species in preference to their average morphology. Peak shift is a common and taxonomically widespread phenomenon. This example of the possible role of peak shift in signal evolution can be generalized to other systems in which a signal receiver learns to make choices in situations in which signal variation is linked to the sender's reproductive success. [source] Individual differences in allocation of funds in the dictator game associated with length of the arginine vasopressin 1a receptor RS3 promoter region and correlation between RS3 length and hippocampal mRNAGENES, BRAIN AND BEHAVIOR, Issue 3 2008A. Knafo Human altruism is a widespread phenomenon that puzzled evolutionary biologists since Darwin. Economic games illustrate human altruism by showing that behavior deviates from economic predictions of profit maximization. A game that most plainly shows this altruistic tendency is the Dictator Game. We hypothesized that human altruistic behavior is to some extent hardwired and that a likely candidate that may contribute to individual differences in altruistic behavior is the arginine vasopressin 1a (AVPR1a) receptor that in some mammals such as the vole has a profound impact on affiliative behaviors. In the current investigation, 203 male and female university students played an online version of the Dictator Game, for real money payoffs. All subjects and their parents were genotyped for AVPR1a RS1 and RS3 promoter-region repeat polymorphisms. Parents did not participate in online game playing. As variation in the length of a repetitive element in the vole AVPR1a promoter region is associated with differences in social behavior, we examined the relationship between RS1 and RS3 repeat length (base pairs) and allocation sums. Participants with short versions (308,325 bp) of the AVPR1a RS3 repeat allocated significantly (likelihood ratio = 14.75, P = 0.001, df = 2) fewer shekels to the ,other' than participants with long versions (327,343 bp). We also implemented a family-based association test, UNPHASED, to confirm and validate the correlation between the AVPR1a RS3 repeat and monetary allocations in the dictator game. Dictator game allocations were significantly associated with the RS3 repeat (global P value: likelihood ratio ,2 = 11.73, df = 4, P = 0.019). The association between the AVPR1a RS3 repeat and altruism was also confirmed using two self-report scales (the Bardi,Schwartz Universalism and Benevolence Value-expressive Behavior scales). RS3 long alleles were associated with higher scores on both measures. Finally, long AVPR1a RS3 repeats were associated with higher AVPR1a human post-mortem hippocampal messenger RNA levels than short RS3 repeats (one-way analysis of variance (ANOVA): F = 15.04, P = 0.001, df = 14) suggesting a functional molecular genetic basis for the observation that participants with the long RS3 repeats allocate more money than participants with the short repeats. This is the first investigation showing that a common human polymorphism, with antecedents in lower mammals, contributes to decision making in an economic game. The finding that the same gene contributing to social bonding in lower animals also appears to operate similarly in human behavior suggests a common evolutionary mechanism. [source] Potential role of radial glia in adult neurogenesis of teleost fishGLIA, Issue 1 2003Günther K.H. Zupanc Abstract Persistence of radial glia within the adult central nervous system is a widespread phenomenon among fish. Based on a series of studies in the teleost species Apteronotus leptorhynchus, we propose that one function of this persistence is the involvement of radial glia in adult neurogenesis, i.e., the generation and further development of new neurons in the adult central nervous system. In particular, evidence has been obtained for the involvement of radial glia in the guidance of migrating young neurons in both the intact and the regenerating brain; for a possible role as precursor cells from which new neurons arise; and for its role as a source of trophic substances promoting the generation, differentiation, and/or survival of new neurons. These functions contribute not only to the potential of the intact brain to generate new neurons continuously, and of the injured brain to replace damaged cells by newly generated ones, but they also provide an essential part of the cellular substrate of behavioral plasticity. GLIA 43:77,86, 2003. © 2003 Wiley-Liss, Inc. [source] Rapid climate change-related growth decline at the southern range edge of Fagus sylvaticaGLOBAL CHANGE BIOLOGY, Issue 11 2006ALISTAIR S. JUMP Abstract Studies on Fagus sylvatica show that growth in populations toward the southern limit of this species' distribution is limited strongly by drought. Warming temperatures in the Mediterranean region are expected to exacerbate drought where they are not accompanied by increases in precipitation. We studied levels of annual growth in mature F. sylvatica trees over the last half-century in the Montseny Mountains in Catalonia (northeast Spain). Our results show significantly lower growth of mature trees at the lower limit of this species' distribution when compared with trees at higher altitudes. Growth at the lower Fagus limit is characterized by a rapid recent decline starting in approximately 1975. By 2003, growth of mature trees had fallen by 49% when compared with predecline levels. This is not an age-related phenomenon, nor is it seen in comparable populations at higher altitudes. Analysis of climate-growth relationships suggests that the observed decline in growth is a result of warming temperatures and that, as precipitation in the region has not increased, precipitation is now insufficient to ameliorate the negative effects of increased temperatures on tree growth. As the climate-response of the studied forest is comparable with that of F. sylvatica forests in other southern European regions, it is possible that this growth decline is a more widespread phenomenon. Warming temperatures may lead to a rapid decline in the growth of range-edge populations and a consequent retreat of the species distribution in southern Europe. Assessment of long-term growth trends across the southern range edge of F. sylvatica therefore merits further attention. [source] The global trend in plant twining directionGLOBAL ECOLOGY, Issue 6 2007Will Edwards ABSTRACT Aim, To examine, at a global scale, patterns in the direction in which climbing plants twine. We tested three hypotheses: (1) that twining direction is determined randomly; (2) that twining direction is determined by apices following the apparent movement of the sun across the sky; and (3) that twining direction is determined by the Coriolis effect. Location, Seventeen sites spanning nine countries, both hemispheres and 65° of latitude. Methods, Twining direction was recorded for the first c. 100 stems encountered along transects through natural vegetation at each site. Results, Ninety-two per cent of the 1485 twining stems we recorded grew in right-handed helices, i.e. they twined in an anticlockwise direction. This is significantly (P < 0.001) different from random. The proportion of stems twining right-handedly (anticlockwise) was independent of both latitude (P= 0.33) and hemisphere (P= 0.63). These data are inconsistent with the idea that twining direction is determined by either the relative passage of the sun through the celestial sphere or by the Coriolis effect. Thus, we reject all three of our hypotheses. Main conclusions, The predominance of right-handed helical growth in climbing plants cannot be explained by hypotheses attempting to link plant growth behaviour and global location. One alternative hypothesis for our findings is that the widespread phenomenon of anticlockwise twining arises as a function of microtubule orientation operating at a subcellular level. [source] Assessing the extent of genome-wide intralocus sexual conflict via experimentally enforced gender-limited selectionJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2008E. H. MORROW Abstract Intralocus sexual conflict, which occurs when a trait is selected in opposite directions in the two sexes, is a taxonomically widespread phenomenon. The strongest genetic evidence for a gender load due to intralocus sexual conflict comes from the Drosophila melanogaster laboratory model system, in which a negative genetic correlation between male and female lifetime fitness has been observed. Here, using a D. melanogaster model system, we utilize a novel modification of the ,middle class neighbourhood' design to relax selection in one sex, while maintaining selection in the other. After 26 generations of asymmetrical selection, we observed the expected drop in fitness of the non-selected sex compared to that of the selected sex, consistent with previous studies of intralocus sexual conflict in this species. However, the fitness of the selected sex also dropped compared to the base population. The overall decline in fitness of both the selected and the unselected sex indicates that most new mutations are harmful to both sexes, causing recurrent mutation to build a positive genetic correlation for fitness between the sexes. However, the steeper decay in the fitness of the unselected sex indicates that a substantial number of mutations are gender-limited in expression or sexually antagonistic. Our experiment cannot definitively resolve these two possibilities, but we use recent genomic data and results from previous studies to argue that sexually antagonistic alleles are the more likely explanation. [source] Colour variation and alternative reproductive strategies in females of the common lizard Lacerta viviparaJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2007E. VERCKEN Abstract Within-sex colour variation is a widespread phenomenon in animals that often plays a role in social selection. In males, colour variation is typically associated with the existence of alternative reproductive strategies. Despite ecological conditions theoretically favourable to the emergence of such alternative strategies in females, the social significance of colour variation in females has less commonly been addressed, relative to the attention given to male strategies. In a population of the common lizard, females display three classes of ventral colouration: pale yellow, orange and mixed. These ventral colours are stable through individual's life and maternally heritable. Females of different ventral colourations displayed different responses of clutch size, clutch hatching success and clutch sex-ratio to several individual and environmental parameters. Such reaction patterns might reflect alternative reproductive strategies in females. Spatial heterogeneity and presence of density- and frequency-dependent feedbacks in the environment could allow for the emergence of such alternative strategies in this population and the maintenance of colour variation in females. [source] Vesicular release of glutamate mediates bidirectional signaling between astrocytes and neuronsJOURNAL OF NEUROCHEMISTRY, Issue 4 2007Yingchun Ni Abstract The major excitatory neurotransmitter in the CNS, glutamate, can be released exocytotically by neurons and astrocytes. Glutamate released from neurons can affect adjacent astrocytes by changing their intracellular Ca2+ dynamics and, vice versa, glutamate released from astrocytes can cause a variety of responses in neurons such as: an elevation of [Ca2+]i, a slow inward current, an increase of excitability, modulation of synaptic transmission, synchronization of synaptic events, or some combination of these. This astrocyte-neuron signaling pathway might be a widespread phenomenon throughout the brain with astrocytes possessing the means to be active participants in many functions of the CNS. Thus, it appears that the vesicular release of glutamate can serve as a common denominator for two of the major cellular components of the CNS, astrocytes and neurons, in brain function. [source] Macrophage-Related Demyelination In Peripheral Nerves Of Mice Deficient In The Gap Junction Protein Connexin 32JOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 3 2002I Kobsar Mice deficient in the gap junction protein connexin 32 (Cx32) develop a slowly progressing demyelinating neuropathy, with enlarged periaxonal collars, abnormal non-compacted myelin domains and axonal sprouts. These mice serve as a model for the X-linked form of inherited demyelin- ating neuropathies in humans. Based on our previous findings that macrophages are involved in demyelination in other myelin mutants (i.e. mice heterozygously deficient in P0), we considered the possibility that macrophages might be also mediators of demyelination in Cx32-deficient mice. Indeed, we detected an age-related increase in the number of macrophages in demyelinating nerves of Cx32-deficient mice. In addition, immunoelectron microscopy revealed macrophages in an apposition to degenerating myelin reminiscent of a macrophage-mediated demyelinating neuropathy. We conclude that involvement of macrophages might be a widespread phenomenon in genetically-determined demyelination. [source] Diet and arterial hypertension: Is the sodium ion alone important?MEDICINAL RESEARCH REVIEWS, Issue 4 2002Michele Buemi Abstract Hypertension is a widespread phenomenon whose ultimate cause is still unknown. Many factors contribute to this disease, and partially for this reason, hypertension responds to different treatments in different individuals. It is difficult to generalize about therapies for general populations. In particular, the role of electrolytes in hypertension varies widely across individuals. This review focuses its attention on sodium, potassium, calcium, and magnesium ions in order to investigate whether these electrolytes play a role in the pathogenesis of arterial hypertension and its treatment. Some individuals are especially sensitive to sodium, and changing their intake of dietary sodium may lead to variations in the levels of the other electrolytes. These changes in electrolyte levels can complicate treatments for arterial hypertension in some patients. © 2002 Wiley Periodicals, Inc. Med Res Rev, 22, No. 4, 419,428, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/med.10013 [source] A novel DNA modification by sulphurMOLECULAR MICROBIOLOGY, Issue 5 2005Xiufen Zhou Summary Streptomyces lividans has a novel DNA modification, which sensitises its DNA to degradation during electrophoresis (the Dnd phenotype). The entire gene cluster (dnd) involved in this modification was localized on an 8 kb DNA fragment and was expressed in a S. lividans deletion mutant (dnd) and in several heterologous hosts. Disruption of the dnd locus abolishes the Dnd phenotype, and gain of the dnd locus conferred the Dnd phenotype respectively. Extensive analysis of the dnd gene cluster revealed five open reading frames, whose hypothetic functions suggested an incorporation of sulphur or a sulphur-containing substance into S. lividans genome, yet in an unknown manner. The Dnd phenotype was also discovered to exist in DNA of widespread bacterial species of variable origin and diverse habitat. Similarly organized gene clusters were found in several bacterial genomes representing different genera and in eDNA of marine organisms, suggesting such modification as a widespread phenomenon. A coincidence between the Dnd phenotype and DNA modification by sulphur was demonstrated to occur in several representative bacterial genomes by the in vivo35S-labelling experiments. [source] Working conditions and health status of child workers: Cross-sectional study of the students at an apprenticeship school in KocaeliPEDIATRICS INTERNATIONAL, Issue 1 2010Cigdem Caglayan Abstract Background:, Child labor remains a widespread phenomenon in today's world. The purpose of the present study was to describe the working conditions and health status of child workers in Kocaeli. Methods:, A cross-sectional research study has been carried out on 365 working children at the Kocaeli Occupational Training Center. Data were collected on working conditions, smoking habits, work accidents, perceived health status and psychological status using General Health Questionnaire-12. In order to evaluate the physical growth of children, their height and weight were measured. Results:, Most working children usually have a low level of education, low income and extended families. The mean age for children to start working was 14.8 ± 1.5 years and their daily working periods were 11.3 ± 1.3 h on average. Girls were found to have more psychopathology compared to boys on the GHQ-12 and the results were statistically significant. The height z score was less than ,2 SD at 6.9% while the weight z score was less than ,2 SD at 1.9%. According to body mass index (BMI) percentiles range, 3% of children were found to be underweight. A statistically significant and negative directional correlation was detected between body mass index z scores with age and daily working periods. Statistically significant but weak correlations were detected between height for age z scores and the starting age of work and also between weight for age z scores and chronological age. Conclusions:, Both the mental and the physical health of children were found to be negatively affected, by having to work at an early age, and by long working hours. For this reason, immediate and direct intervention should be taken to eradicate child labor, and protect children from unsafe and exploitative working conditions. [source] In vivo magnetic resonance imaging of xylem vessel contents in woody lianasPLANT CELL & ENVIRONMENT, Issue 8 2003M. J. CLEARWATER ABSTRACT Previous reports suggest that in some plant species the refilling of embolized xylem vessels can occur while negative pressure exists in the xylem. The aim of this experiment was to use non-destructive nuclear magnetic resonance imaging (MRI) to study the dynamics of xylem cavitation and embolism repair in-vivo. Serial 1H-MRI was used to monitor the contents of xylem vessels in stems of two dicotyledonous (Actinidia deliciosa and Actinidia chinensis, kiwifruit) and one monocotyledonous (Ripogonum scandens, supplejack) species of woody liana. The configuration of the horizontal wide bore magnet and probe allowed the imaging of woody stems up to 20 mm in diameter. Tests using excised stems confirmed that the image resolution of 78 µm and digital image subtraction could be used to detect the emptying and refilling of individual vessels. Imaging was conducted on both intact plants and excised shoots connected to a water supply. In the case of Ripogonum the excised shoots were long enough to allow the distal end of the shoot, including all leaves, to be exposed to ambient conditions outside the building while the proximal end was inside the MRI magnet. In total, six stems were monitored for 240 h while the shoots were subjected to treatments that included light and dark periods, water stress followed by re-watering, and the covering of all leaves to prevent transpiration. The sudden emptying of water-filled vessels occurred frequently while xylem water potential was low (below ,0.5 MPa for Actinidia, ,1.0 MPa for Ripogonum), and less frequently after xylem water potential approached zero at the end of water-stress treatments. No refilling of empty vessels was observed at any time in any of the species examined. It is concluded that embolism repair under negative pressure does not occur in the species examined here. Embolism repair may be more likely in species with narrower xylem vessels, but further experiments are required with other species before it can be concluded that repair during transpiration is a widespread phenomenon. [source] Public Values for River Restoration Options on the Middle Rio GrandeRESTORATION ECOLOGY, Issue 6 2009Matthew A. Weber Abstract River restoration is a widespread phenomenon. This reflects strong public values for conservation, though missing are studies explicitly justifying restoration expenditures. Public restoration benefits are not well quantified, nor are public preferences among diverse activities falling into the broad category "restoration." Our study estimates public values for restoration on the Middle Rio Grande, New Mexico. Stakeholder meetings and public focus groups guided development of a restoration survey mailed to Albuquerque area households. Four restoration categories were defined: fish and wildlife; vegetation density; tree type; and natural river processes. Survey responses supplied data for both choice experiment (CE) and contingent valuation (CV) analyses, two established environmental economics techniques for quantifying public benefits of conservation policies. Full restoration benefits are estimated at over $150 per household per year via the CE and at nearly $50 per household per year via CV. The CE allows value disaggregation among different restoration categories. The most highly valued category was tree type, meaning reestablishing native tree dominance for such species as Cottonwood (Populus deltoides) and eradicating non-native trees such as Saltcedar (Tamarix ramosissma). The high public values we have found for restoration offer economic justification for intensive riparian management, particularly native plant-based restoration in the Southwest. [source] EARNINGS AND LINGUISTIC PROFICIENCY IN A BILINGUAL ECONOMY*THE MANCHESTER SCHOOL, Issue 3 2005ANDREW HENLEY Bilingualism is a widespread phenomenon, yet its economic effects are under researched. Typically studies find that bilingual workers are disadvantaged. Governments often protect minority languages through official promotion of bilingualism, with potential economic consequences. This paper addresses the impact of bilingualism on earnings, using the example of Wales. Results show a positive raw differential of 8 to 10 per cent depending on definition of linguistic proficiency. This differential persists in earnings function estimates, which control for human capital and demographic characteristics as well as local area effects. The potential endogeneity of language choice and earnings is addressed through the use of appropriate instrumental variables. Results suggest that bilingualism may be exogenous to the determination of earnings. [source] Going Microlithic: A Levantine Perspective on the Adoption of Microlithic TechnologiesARCHEOLOGICAL PAPERS OF THE AMERICAN ANTHROPOLOGICAL ASSOCIATION, Issue 1 2002Michael P. Neeley The shift to microlithic technologies is a widespread phenomenon over much of the globe during the late Pleistocene and early Holocene. The occurrence of microliths in diverse geographical and temporal settings is a testament to their versatility and importance as a solution to the problems of survival. Using a perspective based on evolutionary theory, the adoption of microliths in the Levant is viewed from both a long-term, regional perspective involving resource procurement and a short-term, site-centered perspective focusing on mobility strategies. The results suggest that microliths are correlated with changes in forager behavior associated with resource procurement and mobility and that an evolutionary framework is useful for addressing this process. [source] Genome downsizing in polyploid plantsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2004I. J. LEITCH All else being equal, polyploids are expected to have larger C-values (amount of DNA in the unreplicated gametic nucleus) than their diploid progenitors, increasing in direct proportion with ploidy. This expectation is observed in some polyploid series, especially those newly formed, but there are examples suggesting that C-values in particular polyploids are less than expected. The availability of the Angiosperm DNA C-values database (http://www.rbgkew.org.uk/cval/homepage.html) has allowed this question to be addressed across a broad range of angiosperms and has revealed striking results deviating from expectation: (i) mean 1C DNA amount did not increase in direct proportion with ploidy, and (ii) mean DNA amount per basic genome (calculated by dividing the 2C value by ploidy) tended to decrease with increasing ploidy. These results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance. Recent advances in our understanding of the molecular events that take place following polyploid formation together with new data on how DNA amounts can both increase and decrease provide some insights into how genome downsizing may take place. The nature of the evolutionary forces that may be driving DNA loss are also discussed. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 651,663. [source] | ||||||||||||||||||||||||||||