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1.
《Ethology, Ecology and Evolution》2012,24(4):387-397
A variety of methods for measuring natural selection have been introduced recently, spurring a large number of empirical studies. Each method has its own strengths and weaknesses, and the use of different techniques in different ways has hampered comparisons among studies. I outline a method for integrating selection gradients, multiplicative fitness components and path analysis in a standardized way, to utilize the strengths of each technique and facilitate comparisons among studies. First, selection gradients are calculated using total lifetime fitness; these estimates can be used in equations to predict evolutionary change. Second, path analysis and multiplicative fitness components are used to understand the causes of selection. Examples of the method applied to studies of selection in an animal and a plant are given; use of this method allows comparisons to be made between the two studies of disparate taxa. 相似文献
2.
Nicholas Jordan 《Evolution; international journal of organic evolution》1991,45(8):1760-1772
Morphologically variable F2 genotypes derived from hybridization of coastal and inland ecotypes of the annual plant Diodia teres were used to identify selection on morphological traits in the natural habitat of each ecotype. These ecotypes occur in very different habitats, and have evolved pronounced morphological differentiation. Selection analysis can suggest whether present patterns of selection can explain morphological differences between ecotypes. F2 genotypes were characterized morphologically, clonally replicated, and transplanted into the habitat of each ecotype. Selection was measured on six morphological traits. Directional and stabilizing selection occurred on many traits; direction and strength of selection varied sharply at different stages of growth, as revealed by a path-analysis approach that divided selection into a set of independent components. Directional selection favored traits of the native population at the coastal habitat, but less so at the inland habitat. Selection was of sufficient strength to create the observed morphological differences between ecotypes in 25–100 generations, given constant selection and sufficient genetic variation. In effects on fitness, most traits were neither independent nor consistently interactive with other traits. Rather, many traits entered into strong but evanescent interactions affecting particular components of fitness. Observed interactions did not support the hypothesis that the morphology of each ecotype was functionally integrated to a high degree. 相似文献
3.
Jeffrey K. Conner Scott Rush Peter Jennetten 《Evolution; international journal of organic evolution》1996,50(3):1127-1136
Although the role of natural selection in the evolution of floral traits has been of great interest to biologists since Darwin, studies of selection on floral traits through differences in lifetime fitness have been rare. We measured selection acting on flower number, flower size, stigma exsertion, and ovule number per flower using field data on lifetime female fitness (seed production) in wild radish, Raphanus raphanistrum. The patterns of selection were reasonably consistent across three field seasons, with strong directional selection for increased flower production in all three years, weaker selection for increased ovule number per flower in two years, and selection for increased flower size in one year. The causes of the selection were investigated using path analysis combined with multiplicative fitness components. Increased flower production increased fruit production directly, and increased numbers of ovules per flower increased the number of seeds per fruit in all three years; pollinator visitation did not influence either of these fitness components. Increased flower size was associated with increases in both the number of fruit and the number of seeds per fruit in one year, with the latter relationship being stronger. Total lifetime seed production was affected more strongly by differences in fruit production than by differences in either the number of seeds per fruit or the proportion of fertilized seeds that were viable, but all three fitness components were positively correlated with total seed production. 相似文献
4.
5.
To compare the strength of natural selection on different traits and in different species, evolutionary biologists typically estimate selection differentials and gradients in standardized units. Measuring selection differentials and gradients in standard deviation units or mean-standardized units facilitates such comparisons by converting estimates with potentially varied units to a common scale. In this note, I compare the performance of variance- and mean-standardized selection differentials and gradients for a unique and biologically important class of traits: proportional traits, that can only vary between zero and one, and their complements (1 minus the trait) using simple algebra and analysis of data from a field-study using morning glories. There is a systematic, mathematical relationship between unstandardized and variance-standardized selection gradients for proportional traits and their complements, but such a general relationship is lacking for mean-standardized gradients, potentially leading investigators to mistakenly conclude that a proportional change in a trait would have little effect on fitness. Despite this potential limitation, mean-standardized selection differentials and gradients represent a useful tool for studying natural selection on proportional traits, because by definition they measure how proportional changes in the mean of a trait lead to proportional changes in relative fitness.Co-ordinating editor: I. Olivieri 相似文献
6.
Sexual size dimorphism varies substantially among populations and species but we have little understanding of the sources of selection generating this variation. We used path analysis to study how oviposition host affects selection on body size in a seed-feeding beetle (Stator limbatus) in which males contribute large ejaculates (nuptial gifts) to females. Females use nutrients in these ejaculates for egg production. Male body size, which affects ejaculate size, affects female fecundity and is thus under fecundity selection similar in magnitude to the fecundity selection on female body size. We show that when eggs are laid on a host on which larval mortality is low (seeds of Acacia greggii) fecundity predicts fitness very well and fecundity selection is the major source of selection on both male and female adult size. In contrast, when eggs are laid on a host on which larval mortality is high (seeds of Parkinsonia florida) fecundity poorly predicts fitness such that fecundity selection is relaxed on both male and female size. However, because egg size affects larval mortality on this poor host (P. florida) there is selection on female size via the female size --> egg size --> fitness path; this selection via egg size offsets the reduction in fecundity selection on female, but not male, body size. Thus, differences in host suitability (due to differences in larval mortality) affect the relative importance of two sources of selection on adult body size; fecundity selection on both male and female body size is lower on the poor quality host (P. florida) relative to the high quality host (A. greggii) whereas selection on female body size via effects of egg size on offspring survival (body size --> egg size --> fitness) is greater on the poor quality host relative to the high quality host. Because selection via the egg size path affects only females the difference in larval survival between hosts shifts the relative magnitude of selection on female vs. male size. Researchers working on other study systems should be alerted to the possible importance of subtle, but consequential, indirect selection on their study organisms. 相似文献
7.
We expand current methods for calculating selection coefficients using path analysis and demonstrate how to analyse nonlinear selection. While this incorporation is a straightforward extension of current procedures, the rules for combining these traits to calculate selection coefficients can be complex. We demonstrate our method with an analysis of selection in an experimental population of Arabidopsis thaliana consisting of 289 individuals. Multiple regression analyses found positive directional selection and positive nonlinear selection only for inflorescence height. In contrast, the path analyses also revealed positive directional selection for number of rosette leaves and positive nonlinear selection for leaf number and time of inflorescence initiation. These changes in conclusions came about because indirect selection was converted into direct selection with the change in causal structure. Path analysis has great promise for improving our understanding of natural selection but must be used with caution since coefficient estimates depend on the assumed causal structure. 相似文献
8.
Lynda D. Corkum 《Hydrobiologia》1992,239(2):101-114
This study was designed to test the biome dependency hypothesis, which predicts that similar assemblages of macroinvertebrates occur along rivers both within and among drainage basins if the basins occupy the same biome. Benthic macroinvertebrates were collected from three drainage basins within each of three biomes in Canada, the eastern deciduous forests (EDF) of southwestern Ontario, the grasslands of south-central Alberta, and the montane coniferous forests (MCF) of southeastern British Columbia. A total of 225 benthic samples (3 biomes × 3 rivers/biome × 5 sites/river × 5 samples/site) was collected in spring using a cylinder sampler.The significant interaction effect between biome and a site's location along a river indicated that spatial patterns of variation in total density and taxonomic composition were not spatially consistent among sites along rivers or among biomes. Total macroinvertebrate densities were equivalent between the EDF and grassland sites. However, total density was substantially lower at the MCF sites than at sites in the other two biomes. The greatest differences in taxonomic composition occurred among biomes, although significant differences also occurred for all other sources of variation examined. Macroinvertebrate composition was more strongly associated with local, site-specific factors (riparian vegetation and land use) than with longitudinal gradients. Distinct site-specific taxonomic assemblages were evident in EDF, but not in the other two biomes where land use was more homogeneous. 相似文献
9.
Fredric J. Janzen Hal S. Stern 《Evolution; international journal of organic evolution》1998,52(6):1564-1571
Understanding the mechanics of adaptive evolution requires not only knowing the quantitative genetic bases of the traits of interest but also obtaining accurate measures of the strengths and modes of selection acting on these traits. Most recent empirical studies of multivariate selection have employed multiple linear regression to obtain estimates of the strength of selection. We reconsider the motivation for this approach, paying special attention to the effects of nonnormal traits and fitness measures. We apply an alternative statistical method, logistic regression, to estimate the strength of selection on multiple phenotypic traits. First, we argue that the logistic regression model is more suitable than linear regression for analyzing data from selection studies with dichotomous fitness outcomes. Subsequently, we show that estimates of selection obtained from the logistic regression analyses can be transformed easily to values that directly plug into equations describing adaptive microevolutionary change. Finally, we apply this methodology to two published datasets to demonstrate its utility. Because most statistical packages now provide options to conduct logistic regression analyses, we suggest that this approach should be widely adopted as an analytical tool for empirical studies of multivariate selection. 相似文献
10.
Hong Qian 《Quantitative Biology.》2014,2(1):47
Motivated by recent understandings in the stochastic natures of gene expression, biochemical signaling, and spontaneous reversible epigenetic switchings, we study a simple deterministic cell population dynamics in which subpopulations grow with different rates and individual cells can bi-directionally switch between a small number of different epigenetic phenotypes. Two theories in the past, the population dynamics and thermodynamics of master equations, separately defined two important concepts in mathematical terms: the fitness in the former and the (non-adiabatic) entropy production in the latter. Both of them play important roles in the evolution of the cell population dynamics. The switching sustains the variations among the subpopulation growth, thus sustains continuous natural selection. As a form of Price’s equation, the fitness increases with (i) natural selection through variations and (ii) a positive covariance between the per capita growth and switching, which represents a Lamarchian-like behavior. A negative covariance balances the natural selection in a fitness steady state --- “the red queen” scenario. At the same time the growth keeps the proportions of subpopulations away from the “intrinsic” switching equilibrium of individual cells, thus leads to a continuous entropy production. A covariance, between the per capita growth rate and the “chemical potential” of subpopulation, counteracts the entropy production. Analytical results are obtained for the limiting cases of growth dominating switching and vice versa. 相似文献
11.
John R. Stinchcombe Anna K. Simonsen Mark. W. Blows 《Evolution; international journal of organic evolution》2014,68(4):1188-1196
Predicting the responses to natural selection is one of the key goals of evolutionary biology. Two of the challenges in fulfilling this goal have been the realization that many estimates of natural selection might be highly biased by environmentally induced covariances between traits and fitness, and that many estimated responses to selection do not incorporate or report uncertainty in the estimates. Here we describe the application of a framework that blends the merits of the Robertson–Price Identity approach and the multivariate breeder's equation to address these challenges. The approach allows genetic covariance matrices, selection differentials, selection gradients, and responses to selection to be estimated without environmentally induced bias, direct and indirect selection and responses to selection to be distinguished, and if implemented in a Bayesian‐MCMC framework, statistically robust estimates of uncertainty on all of these parameters to be made. We illustrate our approach with a worked example of previously published data. More generally, we suggest that applying both the Robertson–Price Identity and the multivariate breeder's equation will facilitate hypothesis testing about natural selection, genetic constraints, and evolutionary responses. 相似文献
12.
Wolf U. Blanckenhorn Max Reuter Paul I. Ward Andrew D. Barbour 《Evolution; international journal of organic evolution》1999,53(1):286-291
We show with a simulation that nonrepresentative sampling of two discrete fitness classes leads to biased estimates of selection. Systematic underestimation occurs if the selected class is overrepresented in the sample and overestimation if the unselected class is overrepresented. The bias is greater the stronger the selection intensity, the smaller the true fraction of individuals favored by selected, and the lower the sample size. We present a simple method that allows a posteriori statistical correction in cases of biased sampling given a separate estimate of the actual class representation, describe its practical implementation, and show that it works. 相似文献
13.
Lauren Schroeder Noreen von Cramon‐Taubadel 《Evolution; international journal of organic evolution》2017,71(11):2634-2649
Hominoid cranial evolution is characterized by substantial phenotypic diversity, yet the cause of this variability has rarely been explored. Quantitative genetic techniques for investigating evolutionary processes underlying morphological divergence are dependent on the availability of good ancestral models, a problem in hominoids where the fossil record is fragmentary and poorly understood. Here, we use a maximum likelihood approach based on a Brownian motion model of evolutionary change to estimate nested hypothetical ancestral forms from 15 extant hominoid taxa. These ancestors were then used to calculate rates of evolution along each branch of a phylogenetic tree using Lande's generalized genetic distance. Our results show that hominoid cranial evolution is characterized by strong stabilizing selection. Only two instances of directional selection were detected; the divergence of Homo from its last common ancestor with Pan, and the divergence of the lesser apes from their last common ancestor with the great apes. In these two cases, selection gradients reconstructed to identify the specific traits undergoing selection indicated that selection on basicranial flexion, cranial vault expansion, and facial retraction characterizes the divergence of Homo, whereas the divergence of the lesser apes was defined by selection on neurocranial size reduction. 相似文献
14.
Environmental gradients in a southern Europe estuarine system: Ria de Aveiro,Portugal implications for soft bottom macrofauna colonization 总被引:4,自引:0,他引:4
Four seasonal sampling surveys were carried out between December 1985 and September 1986 in Canal de Mira (Ria de Aveiro,
Portugal). A total of 40 sampling stations, distributed over 13 transects, was used. Salinity, temperature, dissolved oxygen
and pH of the water mass were measured. Sediment temperature, and salinity and pH of interstitial water were determined. Sediment
variables also included granulometric composition and organic matter contents. Bottom macrofauna samples were collected at
each station.
Ordination (PCA and MDS) and classification of the sampling stations were performed, using the physicochemical and the biological
data sets separately. Average linkage cluster analysis using the unweighted paired-group method, arithmetic averages, was
used for both sets of data.
With a salinity range from 35.1‰ to 0.0‰, Canal de Mira behaves like a tidally and seasonally poikilohaline estuary. Water
temperature (8.5–24.7°C) decreased along the channel towards its inner part during the cold season; an inverse and more pronounced
trend was observed during the hot season. Dissolved oxygen contents was generally high during the day (50% to 240% saturation).
Oversaturation was observed throughout the growing season, with peaks in areas with large amounts of rooted vegetation. The
pH values, largely correlated with dissolved oxygen, ranged from 6.8 to 8.9. Four types of sediment were present in Canal
de Mira, medium and muddy sands being dominant.
Two major gradients were identified: (i) a typical longitudinal estuarine gradient, associated with distance from the mouth,
representing physicochemical variables such as tidal amplitude, salinity and temperature; this gradient was accompanied by
an upstream increase in dominance; the community composition changes were mainly related to salinity; (ii) a lateral gradient,
related to current velocity, depth and sediment composition; the subtidal community had a comparatively low species richness
and abundance. Groups of stations could be recognized along the environmental gradients. Benthic community changes, however,
appeared to be gradual rather than marked by abrupt transitions. 相似文献
15.
John O. Reiss 《Evolutionary biology》2007,34(1-2):4-27
The metaphor of the adaptive landscape, introduced by Sewall Wright in 1932, has played, and continues to play, a central
role in much evolutionary thought. I argue that the use of this metaphor is tied to a teleological view of the evolutionary
process, in which natural selection directs evolution toward an improved future state. I argue further that the use of “relative
fitnesses” standardized to an arbitrary value, which is closely connected with the metaphor of an adaptive landscape, produces
a disconnect between the mean fitness of a population and any real property of that population. This allows for a vague and
ill-defined improvement to occur under the influence of selection. Instead, I suggest that relative fitnesses should be standardized
by the mean absolute fitness (expected population growth rate), so that they express the expected rate of increase in frequency,
rather than number. Under this definition, the mean relative fitness of all populations is always 1.0, and never changes as
long as the population continues to exist. 相似文献
16.
Susan A. Dudley 《Evolution; international journal of organic evolution》1996,50(1):92-102
I used phenotypic selection analysis to test the prediction from functional and comparative studies of plants that smaller leaves and more efficient water use are adaptive in drier environments. I measured selection gradients on leaf size and instantaneous water-use efficiency (a measure of carbon gain per unit water loss) in experimental populations of Cakile edentula var. lacustris placed into wet and dry environments in the field. Linear and nonlinear selection differed significantly between the two environments as predicted. Water-use efficiency was selected to be higher, and leaf area was selected toward a small intermediate optimum, in the dry environment. There was also significant positive correlational selection on water-use efficiency and leaf size, suggesting that the optimum leaf size in the dry environment is greater for plants with higher water-use efficiency. In contrast, neither leaf size nor water-use efficiency were selected in the wet environment, though larger leaves resulted in greater vegetative biomass. Path analysis of the linear selection gradients found that water-use efficiency affected plant fitness primarily because it increased vegetative biomass, as suggested by the hypotheses about the function of physiological traits. These results were not only consistent with the functional hypotheses but also with the observed genetic differentiation in water-use efficiency and leaf size between wet and dry site populations. 相似文献
17.
Anita Malhotra Roger S. Thorpe 《Biological journal of the Linnean Society. Linnean Society of London》1997,60(1):53-72
The anole fauna of the Lesser Antilles is depauperate in relation to that of the Greater Antilles, where complex communities characterized by adaptive specialization and convergent structure are present. Much of this adaptation is the result of changes in body size and shape, probably as a result of interspecific competition. Here we present data on variation in size and shape within a solitary Lesser Antillean species occupying an ecologically heterogenous island, and test the hypothesis that natural selection for varying environmental conditions is the cause of this variation. Univariate (analysis of variance), bivariate (analysis of covariance) and multivariate (multiple-group principal component analysis, canonical variate analysis) analysis showed that there is considerable geographic variation in size and shape within Anolis oculatus on Dominica. Partial Mantel tests rejected the null hypothesis of no association between size and shape and environmental variation. The possible proximate and evolutionary mechanisms responsible for these patterns are discussed. Despite these overall associations, a considerable amount of variation in shape appears to be unrelated to environmental variation. 相似文献
18.
Scheiner SM Donohue K Dorn LA Mazer SJ Wolfe LM 《Evolution; international journal of organic evolution》2002,56(11):2156-2167
Abstract.— Crucial to understanding the process of natural selection is characterizing phenotypic selection. Measures of phenotypic selection can be biased by environmental variation among individuals that causes a spurious correlation between a trait and fitness. One solution is analyzing genotypic data, rather than phenotypic data. Genotypic data, however, are difficult to gather, can be gathered from few species, and typically have low statistical power. Environmental correlations may act through traits other than through fitness itself. A path analytic framework, which includes measures of such traits, may reduce environmental bias in estimates of selection coefficients. We tested the efficacy of path analysis to reduce bias by re-analyzing three experiments where both phenotypic and genotypic data were available. All three consisted of plant species (Impatiens capensis, Arabidopsis thaliana , and Raphanus sativus) grown in experimental plots or the greenhouse. We found that selection coefficients estimated by path analysis using phenotypic data were highly correlated with those based on genotypic data with little systematic bias in estimating the strength of selection. Although not a panacea, using path analysis can substantially reduce environmental biases in estimates of selection coefficients. Such confidence in phenotypic selection estimates is critical for progress in the study of natural selection. 相似文献
19.
Ronan James O'Sullivan Tutku Aykanat Susan E. Johnston Adam Kane Russell Poole Ger Rogan Paulo A. Prodhl Craig R. Primmer Philip McGinnity Thomas Eric Reed 《Ecology and evolution》2019,9(12):7096-7111
Comparing observed versus theoretically expected evolutionary responses is important for our understanding of the evolutionary process, and for assessing how species may cope with anthropogenic change. Here, we document directional selection for larger female size in Atlantic salmon, using pedigree‐derived estimates of lifetime reproductive success as a fitness measure. We show the trait is heritable and, thus, capable of responding to selection. The Breeder's Equation, which predicts microevolution as the product of phenotypic selection and heritability, predicted evolution of larger size. This was at odds, however, with the observed lack of either phenotypic or genetic temporal trends in body size, a so‐called “paradox of stasis.” To investigate this paradox, we estimated the additive genetic covariance between trait and fitness, which provides a prediction of evolutionary change according to Robertson's secondary theorem of selection (STS) that is unbiased by missing variables. The STS prediction was consistent with the observed stasis. Decomposition of phenotypic selection gradients into genetic and environmental components revealed a potential upward bias, implying unmeasured factors that covary with trait and fitness. These results showcase the power of pedigreed, wild population studies—which have largely been limited to birds and mammals—to study evolutionary processes on contemporary timescales. 相似文献
20.
Natural selection can influence the evolution of sexual dimorphism through selection for sex-specific ecomorphological adaptations. The role of natural selection in the evolution of sexual dimorphism, however, has received much less attention than that of sexual selection. We examined the relationship between habitat structure and both male and female morphology, and sexual dimorphism in size and shape, across 21 populations of dwarf chameleon (genus Bradypodion). Morphological variation in dwarf chameleons was strongly associated with quantitative, multivariate aspects of habitat structure and, in most cases, relationships were congruent between the sexes. However, we also found consistent relationships between habitat and sexual dimorphism. These resulted from both differences in magnitude of ecomorphological relationships that were otherwise congruent between the sexes, as well as in sex-specific ecomorphological adaptations. Our study provides evidence that natural selection plays an important role in the evolution of sexual dimorphism. 相似文献