Home About us Contact
|
Home About us Contact | ||
|
|
||
Within-species Variation (within-specy + variation)
Selected AbstractsVARIATION OF SHELL SHAPE IN THE CLONAL SNAIL MELANOIDES TUBERCULATA AND ITS CONSEQUENCES FOR THE INTERPRETATION OF FOSSIL SERIESEVOLUTION, Issue 2 2000Sarah Samadi Abstract., Interpreting paleontological data is difficult because the genetic nature of observed morphological variation is generally unknown. Indeed, it is hardly possible to distinguish among several sources of morphological variation including phenotypic plasticity, sexual dimorphism, within-species genetic variation or differences among species. This can be addressed using fossil organisms with recent representatives. The freshwater snail Melanoides tuberculata ranks in this category. A fossil series of this and other species have been studied in the Turkana Basin (Kenya) and is presented as one of the best examples illustrating the punctuated pattern of evolution by the tenants of this theory. Melanoides tuberculata today occupies most of the tropics. We studied variation of shell shape in natural populations of this parthenogenetic snail using Raup's model of shell coiling. We considered different sources of variation on estimates of three relevant parameters of Raup's model: (1) variation in shell shape was detected among clones, and had both genetic and environmental bases; (2) sexual dimorphism, in those clones in which males occur, appeared as an additional source of shell variation; and (3) ecophenotypic variation was detected by comparing samples from different sites and years within two clones. We then tested the performance of discriminant function analyses, a classical tool in paleontological studies, using several datasets. Although the three sources of variation cited above contributed significantly to the observed morphological variance, they could not be detected without a priori knowledge of the biological entities studied. However, it was possible to distinguish between M. tuberculata and a related thiarid species using these analyses. Overall, this suggests that the tools classically used in paleontological studies are poorly efficient when distinguishing between important sources of within-species variation. Our study also gives some empirical bases to the doubts cast on the interpretation of the molluscan series of the Turkana Basin. [source] Among- and within-species variation in plant litter decomposition in contrasting long-term chronosequencesFUNCTIONAL ECOLOGY, Issue 2 2009David A. Wardle Summary 1Following major disturbances ecosystem development occurs but in the prolonged absence of disturbance a decline (retrogressive) phase follows in which productivity and nutrient availability diminishes. Although it is recognized that litter quality and decomposition rates decrease as retrogression proceeds, little is known about the extent to which this is driven among- vs. within-species variation across these sequences. 2We selected six long-term chronosequences that each included retrogressive stages, in New Zealand, Hawaii, Sweden, Alaska and Australia. Two involve significant species turnover across the sequence so that different species dominate at different stages, two involve low species turnover so that the same dominant species occur at all stages, and two involve some turnover of species but with certain species persisting throughout most of the sequence. 3For each chronosequence, we collected litter from each dominant plant species at each stage of that sequence. For each litter collection we measured concentrations of N and P, and performed laboratory decomposition bioassays to measure mass loss, N and P loss, and the response of mass loss to mixture with litters of coexisting species. 4We found that litter N and P concentrations often declined with increasing ecosystem age, both among- and within-species. However, the relative importance of among- and within-species effects varied across the six chronosequences. Rates of litter mass, N, and P loss during decomposition sometimes decreased with increasing ecosystem age, but most often at the among-species rather than the within-species level. 5Litter mixing effects often varied across chronosequence stages, but the magnitude and direction of these effects was inconsistent among sequences. Variation in litter mixing effects across chronosequence stages was driven mainly by among- rather than within-species variation. 6Although several recent studies have emphasized the role of within-species variation on ecosystem properties, our results point to among-species variation as a consistently important ecological driver, with within-species variation being important only for some variables and in some instances. As such they highlight that decomposition processes are most likely to be highly responsive to gradients of soil fertility (such as across chronosequences) when significant species turnover occurs across the gradient. [source] Population-level traits that affect, and do not affect, invasion successMOLECULAR ECOLOGY, Issue 6 2010N. J. SANDERS What allows some species to successfully colonize a novel environment while others fail? Numerous studies in invasion biology have sought to answer this question, but those studies have tended to focus on traits of species or individuals (e.g. body size, seed size, seed number), and these traits have largely been found to be weak predictors of invasion success. However, characteristics of colonizing populations (e.g. genetic diversity, density, age structure) might also be important for successful establishment, as the authors of a study published in this issue of Molecular Ecology show (Crawford & Whitney 2010). By experimentally manipulating the density and genetic diversity of colonizing populations of Arabidopsis thaliana, the authors found that genetic diversity, but not population density, increased colonization success. Importantly, the effects of genetic diversity on colonization success were both additive and non-additive, suggesting that traits associated with particular genotypes and complimentarity among genotypes contribute to colonization success. This research highlights the importance of considering within-species variation and characteristics of entire populations in predicting colonization success. [source] Effects of natural selection on patterns of DNA sequence variation at the transferrin, somatolactin, and p53 genes within and among chinook salmon (Oncorhynchus tshawytscha) populationsMOLECULAR ECOLOGY, Issue 7 2000Michael J. Ford Abstract This paper describes DNA sequence variation within and among four populations of chinook salmon (Oncorhynchus tshawytscha) at the transferrin, somatolactin and p53 genes. Patterns of variation among salmon species at the transferrin gene have been hypothesized to be shaped by positive natural selection for new alleles because the rate of nonsynonymous substitution is significantly greater than the rate of synonymous substitution. The twin goals of this study were to determine if the history of selection among salmon species at the transferrin gene is also reflected in patterns of intraspecific variation in chinook salmon, and to look for evidence of local adaptation at the transferrin gene by comparing patterns of nonsynonymous and synonymous variation among chinook salmon populations. The analyses presented here show that unlike patterns of variation between species, there is no evidence of greater differentiation among chinook salmon populations at nonsynonymous compared to synonymous sites. There is also no evidence of a reduction of within-species variation due to the hitchhiking effect at the transferrin gene, although in some populations nonsynonymous and synonymous derived mutations are both at higher frequencies than expected under a simple neutral model. Population size weighted selection coefficients (4Ns) that are consistent with both the inter and intraspecific data range from ~10 to ~235, and imply that between 1 and 40% of new nonsynonymous mutations at the transferrin gene have been beneficial. [source] Within population variation and interrelationships between morphology, nutritional content, and secondary compounds of Rhamnus alaternus fruitsNEW PHYTOLOGIST, Issue 2 2002Ido Izhaki Summary ,,We studied within-species variation in and interrelations among morphological and chemical traits of ripe Mediterranean buckthorn ( Rhamnus alaternus ) fruit, a bird-dispersed species. ,,Principal component analysis revealed that larger fruits tended to be relatively rich in nonstructural carbohydrates (NSC), water and P but poor in protein and most minerals. Small fruits tended to be relatively rich in protein, structural carbohydrates, K and Zn while intermediate size fruits tended to be rich in lipids, Mg and Ca. Variation in chemical traits (organic compounds and minerals) was typically much higher than in morphological traits (e.g. fruit size) with the exception of NSC and water content, which varied little. This discrepancy might be explained by differences in environmental conditions between plant microsites that imposed greater variability on fruit nutrient composition than on fruit-morphological traits; and by lower selective pressure by birds on fruit chemical traits than on morphological traits. ,,Secondary metabolite (emodin) concentration was positively correlated with concentrations of NSC, supporting the nutrient/toxin titration model, which predicts that high levels of secondary metabolites in fruits should be off set by high nutritional rewards for dispersers. ,,Emodin concentration in leaves was much higher than in fruit pulp, which may indicate its differential adaptive roles in seed dispersal and against herbivores. [source] Mortality and fertility rates in humans and chimpanzees: How within-species variation complicates cross-species comparisonsAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Kristen Hawkes A grandmother hypothesis may explain why humans evolved greater longevity while continuing to end female fertility at about the same age as do the other great apes. With that grandmother hypothesis in mind, we sought to compare age-specific mortality and fertility rates between humans and chimpanzees, our closest living relatives, and found two puzzles. First, we expected that lower adult mortality in humans would be associated with slower senescence, but the rate of chimpanzee demographic aging falls within the human range. Second, we expected declines in age-specific fertility to be similar in the two species but instead of falling in the thirties as it does in women, fertility remains high into the forties in some chimpanzee populations. We report these puzzles using data from nine human populations and both wild and captive chimpanzees, and suggest that systematic differences in the heterogeneity of surviving adults may explain them. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Classifying the fire-response traits of plants: How reliable are species-level classifications?AUSTRAL ECOLOGY, Issue 3 2010LYNDSEY MARIE VIVIAN Abstract Plant species in fire-prone environments possess specific traits which allow them to survive fire. Species are commonly classified according to whether they survive fire and resprout or whether they are killed by fire and regenerate from seed. However, different populations of the same species have been shown to vary in their responses. Therefore, the classification of a species into a single category based on fire-response traits may not necessarily be representative of every population under every circumstance. This study examined the extent of within-species variation in fire-response traits of woody plants in south-eastern Australia after the 2003 fires. Species were then classified using two approaches: (i) using data from a field survey of fire-response traits, taking into account within-species variation; and (ii) using species' fire responses listed in a pre-existing fire-response database compiled from a variety of primary sources. Field data showed that the majority of species in the study area resprouted after fire with around one in 10 species variable in their resprouting response. Almost half of all species varied from site to site according to whether they regenerated from seed, either solely or in addition to resprouting. The numbers of species classified as resprouters and seed regenerators varied according to the classification method used. Differences were also found between the classification method when calculating the mean proportion of resprouters and seed regenerators across sites. The fire-response traits for some species from the database were found to differ from the observed field responses. This study demonstrated that the application of a fire-response trait, reported in a trait database, to an entire species, may not adequately represent the actual fire responses of the populations of interest. Rather than considering the fire-response traits of a species, accurate prediction may be better achieved by considering how different populations of plants will respond to fire. [source] The geographic structure of morphological variation in eight species of fiddler crabs (Ocypodidae: genus Uca) from the eastern United States and MexicoBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010MELANIE J. HOPKINS Species with larger geographic distributions are more likely to encounter a greater variety of environmental conditions and barriers to gene flow than geographically-restricted species. Thus, even closely-related species with similar life-history strategies might vary in degree and geographic structure of variation if they differ in geographic range size. In the present study, we investigated this using samples collected across the geographic ranges of eight species of fiddler crabs (Crustacea: Uca) from the Atlantic and Gulf coasts of North America. Morphological variation in the carapace was assessed using geometric morphometric analysis of 945 specimens. Although the eight Uca species exhibit different degrees of intraspecific variation, widespread species do not necessarily exhibit more intraspecific or geographic variation in carapace morphology. Instead, species with more intraspecific variation show stronger morphological divergence among populations. This morphological divergence is partly a result of allometric growth coupled with differences in maximum body size among populations. On average, 10% of total within-species variation is attributable to allometry. Possible drivers of the remaining morphological differences among populations include gene flow mediated by ocean currents and plastic responses to various environmental stimuli, with isolation-by-distance playing a less important role. The results obtained indicate that morphological divergence among populations can occur over shorter distances than expected based on dispersal potential. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 248,270. [source] | ||||||||||||||||||||||