Morphogenetic origin of natural variation

We studied individual pathways of gastrulation in two related amphibian species making an emphasis on the developmental dynamics of normal variation in the geometry of gastrulation movements. Analyzing the variation dynamics, we show that the linear succession of developmental stages is a secondary phenomenon disguising self-oscillations that lie at the heart of the dorsal blastopore lip morphogenesis. Characteristic features of the equations derived to describe the oscillations are, first, their dependence only on the movement geometry and, second, including of the dynamics of spatial variance directly into the movement equations, making it clear that the reasons for variability of morphogenesis are the same that for morphogenesis itself. The equations describing morphogenetic oscillations are mathematically similar to those describing natural selection in that the system tends to minimize its variance, individual or within-individual one, but the spatially uniform state turns to be unstable. Comparing of the dynamics of natural developmental variation in gastrulation in two frog species shows that, depending on the mechanics and geometry mass cell movements, different types of gastrulation movements have different proportions of the between- to within-individual differences, which strongly influences the choice of characters subject to evolution. Instead of being a source of constraints imposed on externally guided evolutionary trends, morphogenesis becomes a driving force of the adaptively silent, but directional evolution of the developing systems, which seems to be the only possible way of originating of the evolutionary novelties, both in evolution and ontogeny of the biological structures.     

DIFFERENTIATION AMONG NINE POPULATIONS OF PHLOX. I. ELECTROPHORETIC AND QUANTITATIVE VARIATION

The organization of genetic variation in Phlox drummondii was investigated using both allozyme electrophoresis and quantitative genetics. Variation at five polymorphic enzyme loci was characterized in nine populations, and variation in 16 morphological and life-history characters was examined using an analysis of full- and half-sibs in seven populations. Significant levels of genetic variation were found at enzyme loci and for metric characters. Significant heritabilities were observed for 15 of the 16 characters examined. Genetic differences among populations were revealed both by Nei's genetic distance and by phenotypic differences, summarized by discriminant analysis. Partitioning variance in allozyme frequencies among hierarchical levels of genetic organization indicated that 94% of this variance lay within populations, 4% between populations within varieties, and 2% between varieties. Partitioning phenotypic variance for metric characters indicated that 73% lay within populations, 24% lay between populations within varieties, and 3% lay between varieties. Thus, both electrophoretic and metric characters indicated that despite extensive genetic differentiation among populations, most of the evolutionary potential of the species lies within populations.     

Evolutionary divergence in directions of high phenotypic variance in the ostracode genus poseidonamicus

Trait variation and covariation are understood to influence the response of populations to natural selection on generational time scales, but their role, if any, in shaping long-term macroevolutionary divergence is still unclear. The present study uses the rich fossil record of the ostracode genus Poseidonamicus to reconstruct in great detail the evolutionary history of a set of landmark-based morphometric characters. This reconstruction included two kinds of evolutionary inferences: ancestor-descendant transitions among populations repeatedly sampled at the same location and divergence between lineages measured as independent contrasts on a phylogeny. This reconstructed history was then used to test if evolutionary changes were concentrated in directions (traits or combinations of traits) with high phenotypic variance. Two different statistics of association between evolution and variation tested the null hypothesis that evolutionary changes occur in random directions with respect to trait variability. The first of these measured the similarity between the directions of evolutionary change and the axis of maximum variance, and the second measured the degree to which evolutionary changes were concentrated in directions of high phenotypic variation. Randomization tests indicated that both kinds of evolutionary inferences (ancestor-descendant and phylogenetic contrasts) occurred preferentially in directions of high phenotypic variance (and close to the axis of maximal variation), suggesting that within-population variation can structure long-term divergence. This effect decayed after a few million years, but at least for one metric, never disappeared completely. These results are consistent with Schluter's genetic constraints model in which evolutionary trajectories on adaptive landscapes are deflected by variation within and covariation among traits.     

Geometry and mechanics of teleost gastrulation and the formation of primary embryonic axes

Examination of normal shaping dynamics and immediate and long-term responses to blastoderm cutting in zebrafish and loach embryos prior to the onset of gastrulation and during the course of epiboly revealed that anteroposterior (AP) and dorsoventral (DV) polarity formation is connected with shaping of the blastoderm circumferential region, which stretches along and shrinks across its movement axes and originates the non-isotropic fields of tensile stresses. Based on data from cutting experiments and quantitative morphology, we reconstructed the movement-shaping patterns of epiboly and embryonic shield formation. We revealed that AP and DV axes originate as a mass cell movement subject to the movement-shaping equivalence principle, which means the spatial series of differently shaped areas corresponding to the time succession of the same area shaping. Maintenance of the main body axes in orthogonal orientation depends on the mechanical equilibrium principle allowing for converting shape asymmetry into that of tensile stresses and vice versa. The causal relationship between the main movement-shaping axes and that of embryonic polarity was proved in cutting experiments in which the DV axis direction was subject to rearrangement so as to adjust to the new direction of mass cell movement axes induced by healing the wound in the blastoderm circumferential region.     

Quantitative morphological evidence for incipient species within Lutzomyia quinquefer (Diptera: Psychodidae)

Morphological variation among geographic populations of the New World sand fly Lutzomyia quinquefer (Diptera, Phlebotominae) was analyzed and patterns detected that are probably associated with species emergence. This was achieved by examining the relationships of size and shape components of morphological attributes, and their correlation with geographic parameters. Quantitative and qualitative morphological characters are described, showing in both sexes differences among local populations from four Departments of Bolivia. Four arguments are then developed to reject the hypothesis of environment as the unique source of morphological variation: (1) the persistence of differences after removing the allometric consequences of size variation, (2) the association of local metric properties with meristic and qualitative attributes, rather than with altitude, (3) the positive and significant correlation between metric and geographic distances, and (4) the absence of a significant correlation between altitude and general-size of the insects.     

Comparison of variability of Rana temporaria (Amphibia, Anura) gastrula from different populations developing under the conditions of antropogenic pollution

The gastrulation of Rana temporaria embryos was studied at the natural spawning sites of Moscow city and Moscow district by means of morphometric analysis. We demonstrated that anthropogenic pollution plays an important role in morphogenesis of Anura. The measurements of embryos from the Moscow ponds made it possible to show an increased variability of gastrulation. Moreover, the level of gastrulation variability depends on the degree of pollution of a spawning pond and is coupled with increased correlations between the morphological features. This increase of correlations could be due to: (1) an increased number of correlating features (appearance of new correlations) and (2) strengthening of the existing correlations. The first way makes the gastrulation process more coordinated, and the second one causes the appearance of morphological structures, which are normally formed only at the next developmental stages.     

濒危植物马蹄参枝叶形态变异与环境因子的相关性分析

调查马蹄参在湖南、广东、广西、云南4省9个天然种群20项枝叶的形态指标在种群内和种群间的表型变异,运用相关分析揭示枝和叶形态指标间以及与环境因子之间的相关性,并进行聚类分析(UPGMA)和主成分分析.结果表明:各性状在种群内和种群间均存在一定变异性.广西花坪自然保护区两个种群(HP1,HP2)枝叶形态性状(尤其是枝)的...     

Estimates of hierarchical variation in flower morphology in natural populations ofScleranthus annuus (Caryophyllaceae), an inbreeding annual

The variation in two sets of morphological characters of the flowers of the highly inbreedingScleranthus annuus (Caryophyllaceae) was assessed using 15–20 plants from each of 20 natural populations from the southernmost region of Sweden. The stamen fertility data set consisted of 10 characters describing the degree of fertility of the ten stamens/staminoids, while the sepal/gynoecium data set comprised 10 sepal characters, together with style and stigma length. Substantial variation was found in both the degree of development and the fertility of the stamens, the degree of variability in stamen fertility being related to stamen position within the flower. Considerable variation was found in the characters of the sepal and the gynoecium. Hierarchical analyses of variance indicated that 29% of the variation in total male reproductive effort was distributed among populations, 28% among plants within populations and 43% represented within-plant variation. The corresponding averages for the characters from the sepal/gynoecium data set are 26, 38, and 35%: a greater proportion of the total variance in female reproductive characters is accounted for by among individual variation than is the case with the male reproductive characters. Significance tests of Mahalanobis distances derived by canonical variate analyses indicated that all populations were significantly separated using the sepal/gynoecium data set, while only 50% of the pairwise comparisons on the basis of the stamen fertility data set were significant. Cluster analysis did not reveal any aggregation of the populations. The incongruence of the two data sets and their ability to discriminate between the populations is discussed.     

Sexual selection in the barn swallow (Hirundo rustica). V. Geographic variation in ornament size

Models of sexual selection in a cline predict the patterns of clinal variation in female mate preference and male secondary sexual characters. These predictions were tested for the nominate subspecies of the barn swallow Hirundo rustica which demonstrates clinal variation in morphology, with several characters in both sexes showing increasing size at higher latitudes. Sexual size dimorphism in the length of the tail ornament and the short, central tail feathers increase with increasing latitude while size dimorphism in other morphological characters is independent of latitude. The main reason for the two divergent patterns of sexual size dimorphism appears to be the higher foraging cost of having a long tail ornamental at low latitudes. The control of development decreases with increasing latitude as demonstrated by an increasing latitudinal cline in fluctuating asymmetry of tail length. Phenotypic variance in tail length increases with latitude in males, but not in females, as shown by the coefficients of variation. Clinal variation in morphology is not due to natural selection associated with a latitudinal increase in the distance between breeding and wintering areas. The geographic patterns of morphological variation suggest that the tail character has diverged geographically as a result of a sexual process of reliable signalling.     

Multiple scale patterns of shell and anatomy variability in land snails: the case of the Sicilian Marmorana (Gastropoda: Pulmonata, Helicidae)

Certain major aspects of phenotypic diversity are still largely unexplained. When phenotypic patterns do not relate to habitat variables, fine analysis of morphological patterns and their distribution sheds light on the origin of diversity. Among invertebrates, snails are an ideal model for studying the roles of the neutral processes and selection involved in creating diversity. To understand patterns and processes of variability on different scales (regional: areas; local: sites), morphological variability of two sets of characters (shell and genitalia) was quantified in a group of rock-dwelling land snails of the genus Marmorana (Pulmonata, Helicidae). To analyse shell variability, partitioning of the overall variation into size and shape components was analysed by a principal component-based approach. Shell shape and size variability is not significantly influenced by any environmental pressure. Variability at site scale is mainly attributed to shell size, which is a trait demonstrated to have a high degree of phenotypic plasticity. No sharp changes were observed for genitalia. Moreover, allometries between shell size and genitalia measurements involve a few populations. The observed multiple scale patterns are in line with the hypothesis that genital variance may be selectively controlled to maintain function.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 359–370.     

Environmentally Dependent Morphological Variability in Seven Apomictic Microspecies from Alchemilla L. (Rosaceae)

Apomictic microspecies, for example those of the genus Alchemilla, are often difficult to distinguish. Still, their differences are thought to be persistent due to apomixis. Apomicts are argued to have general-purpose genotypes. The present study aims to assess the variation of morphological characters of Alchemilla depending on environmental conditions both in nature and experimentally; to evaluate the efficacy of characters for identifying the different microspecies; to assess the similarity of different microspecies; and to determine if Alchemilla microspecies have general-purpose genotypes that are not dependent on environmental conditions. The variability of selected characters in seven microspecies of Alchemilla was studied in nature and five microspecies were grown in a common garden experiment. The growing conditions of the latter were subjected to various manipulations (fertilization, shading and irrigation). Typical natural habitats of Alchemilla exhibited only small differences. Environmental conditions therefore had little effect on morphological characters. Neither cultivation in the common garden nor manipulation of conditions therein had a significant impact on the discrimination of microspecies. However, the metric characters were larger in the garden relative to those observed in nature, particularly under fertilization. Fertilization affected most characters, whereas shading and irrigation did not. The most effective characters for discriminating between microspecies were the ratios of the metric characters. Two species pairs: A. vulgaris and A. micans, as well as A. glaucescens and A. hirsuticaulis were morphologically close; however, the species within these pairs could still be distinguished. The morphological characters of Alchemilla microspecies were only slightly dependent on the environmental conditions.     

Buffering effect of B-chromosome system of Trigonella foenum-graecum against different soil types

Summary Accessory (B–) chromosomes have been reported in many plants in various regions of the world. Studies on natural populations of certain plants like Phleum phleoides revealed that B-chromosomes were present in different frequencies in different habitats indicating a correlation between B-frequency and environmental conditions. The present experiment was performed to determine the response of B-chromosome carrier and non-carrier plants of Trigonella to different soil conditions. When the morphological data was subjected to analysis of variance, it was found that the carrier plants exhibited uniformity of characters in the different soil types, while the non-carrier plants exhibited considerable variability. The conclusion that can be drawn from this experiment is that B-chromosomes act as a buffering agent, neutralising the variability effect of different soil types.     

The Influence of the Mating System on the Maintenance of Genetic Variability in Polygenic Characters

The traditional models of the effect of assortative mating and inbreeding on the genetic variance of polygenic characters (Fisher 1918; Wright 1921) presume that there is no natural selection or mutation. In a large population, the genetic variance determined by additive genes may then increase by up to a factor of two with local inbreeding, and even more with assortative mating. The classical models are still used to interpret data from natural populations. But contrary to their assumptions, most metrical characters in natural populations are usually thought to be under a type of selection which depletes polygenic variation. Mutation is then necessary to maintain genetic variation. The present models show that with the additional features of mutation and selection, in a large population, the mating system has no influence on the amount of genetic variability maintained by additive genes.     

皂荚南方天然群体种实表型多样性

以系统揭示表型变异程度和变异规律为目的, 对皂荚(Gleditsia sinensis)南方分布区的10个天然群体的11个种实性状进行了比较分析。采用方差分析、多重比较、相关分析等多种分析方法, 对群体间和群体内的表型多样性以及与地理、环境因子的相关性进行了讨论。方差分析结果表明; 皂荚果实、种子等性状在群体间和群体内存在丰富的变异, 11个性状在群体间、群体内均达显著差异; 荚果性状在群体间和群体内的变异均大于种子性状, 11个性状的平均表型分化系数为20.42%, 群体内的变异(32.28%)大于群体间的变异(7.19%), 群体内的变异是皂荚的主要变异来源; 皂荚各性状平均变异系数为11.20%, 变异幅度为4.55%-18.38%。群体间荚果的变异(14.75%)高于群体间种子变异(6.95%), 表明种子变异稳定性高。荚果和种子各性状之间多呈极显著或显著正相关, 表现为荚果越大, 则种子越大, 种子的千粒重也越大; 荚果表现为同地理经度的南北变异, 种子则表现为同地理纬度的东西变异。研究结果为进一步开展皂荚遗传育种、保护生物学研究和皂荚种质资源利用奠定了基础。     

Comparison of variability of <Emphasis Type="Italic">Rana temporaria</Emphasis> (Amphibia,Anura) gastrula from different populations developing under the conditions of antropogenic pollution

The gastrulation of Rana temporaria embryos was studied at the natural spawning sites of Moscow city and Moscow district by means of morphometric analysis. We demonstrated that anthropogenic pollution plays an important role in morphogenesis of Anura. The measurements of embryos from the Moscow ponds made it possible to show an increased variability of gastrulation. Moreover, the level of gastrulation variability depends on the degree of pollution of a spawning pond and is coupled with increased correlations between the morphological features. This increase of correlations could be due to: (1) an increased number of correlating features (appearance of new correlations) and (2) strengthening of the existing correlations. The first way makes the gastrulation process more coordinated, and the second one causes the appearance of morphological structures, which are normally formed only at the next developmental stages.__________Translated from Ontogenez, Vol. 36, No. 2, 2005, pp. 110–122.Original Russian Text Copyright © 2005 by Severtsova, Severtsov.     

Fluctuating asymmetry and allozymic heterozygosity among natural populations of pocket gophers (Thomomys bottae)

Fluctuating asymmetry, or random deviations from bilateral symmetry, has been widely used as a measure of developmental stability. The relationship between fluctuating asymmetry (FA) and allozymic heterozygosity was evaluated using 18 natural populations of pocket gophers ( Thomomys bottae ). Heterozygosity in local populations of pocket gophers ranges over more than an order of magnitude (1.5—18.4%), making this burrowing rodent particularly apt for such studies. Two measures of FA in mensural skull characters were examined: absolute deviations between left and right sides and the variance of signed differences. After log transformations, levels of FA among individuals and populations were not related to size. Repeated-measures analyses of variance showed that FA was significant relative to measurement error, both across populations and within them. Asymmetries of different characters were uncorrelated, despite positive significant correlations among the characters themselves. FA levels varied only slightly among populations of gophers, and this variation was not significant for most characters. FA levels of populations were not correlated with allozymic heterozygosity, and analyses of variance in FA employing heterozygosity were not significant. Heterozygosity levels in these rodents appear more strongly related to aspects of population history (especially effective size and gene flow) than to developmental stability. Because so many genomic and environmental factors can affect morphological variation, caution is needed in interpreting correlations between genetic and phenetic variation.     

Microgeographical, inter-individual, and intra-individual variation in the flower characters of Iberian pear Pyrus bourgaeana (Rosaceae)

Flower characteristics have been traditionally considered relatively constant within species. However, there are an increasing number of examples of variation in flower characteristics. In this study, we examined the variation in attracting and rewarding flower characters at several ecological levels in a metapopulation of Pyrus bourgaeana in the Do?ana area (SW Spain). We answered the following questions: what are the variances of morphological and nectar characters of flowers? How important are intra-individual and inter-individual variance in flower characters? Are there microgeographical differences in flower characters? And if so, are they consistent between years? In 2008 and 2009, we sampled flowers of 72 trees from five localities. For six flower morphological and two nectar characteristics, we calculated coefficients of variation (CV). The partitioning of total variation among-localities, among-individuals, and within-individuals was estimated. To analyze differences among localities and their consistency between years, we conducted generalized linear mixed models. The CVs of nectar characters were always higher than those of morphological characters. As expected, inter-individual variation was the main source of variation of flower morphology, but nectar characters had significant variation at both intra- and inter-individual levels. For most floral traits, there were no differences among localities. Our study documents that variation is a scale-dependent phenomenon and that it is essential to consider intra- and inter-individual variance when investigating the causes and consequences of variation. It also shows that single year studies of floral characters should be viewed with caution.     

Morphological variation between red mullet populations in Greece

Morphometric variation in 15 characters of the red mullet Mullus barbatus samples from seven Greek localities was examined using multivariate analysis. ANOVA, stepwise discriminant analysis and cluster analysis revealed a rather high morphological variability between the populations studied. The discriminant analysis revealed that about 80% of the examined fish could be correctly classified into the seven areas. This variability could be explained in terms of genetic structuring of the populations and/or environmental conditions prevailing in each geographic area in combination with fish migration and egg/larvae transportation from one area to another. The results suggest that multivariate analysis when combined with other important biological parameters of red mullet may have important implications for the management of the Greek demersal fish resources.     

Morphological and genetic variation in Aegilops geniculata from Algeria

Aegilops geniculata Roth is an annual grass relative to cultivated wheats and is widely distributed in North Africa. In order to understand the diversity of this species, 14 populations collected in different bioclimatic areas in northern Algeria were analyzed using morphological and biochemical characters. Principal component analyses (PCA) based on the inflorescence characters and ecological parameters allowed the separation of populations in two mainly bioclimatic clusters characterized by different morphological patterns. Populations originated from humid and sub-humid coastal areas were characterized by vigorous spikes. Samples collected from intermediate and high mountains with humid and semi-arid conditions had long and lanceolate spikes. Individuals with small and narrow spikes were characteristics of steppic highlands in semi-arid conditions and high mountains with humid bioclimate. Individuals were distinguished successively by spike width, spike length, rachis length and awns number. Electrophoretic analyses of high molecular weight glutenin subunits (HMW-GS) based on the phenotypic variability and genetic distances revealed a significant variation within and between populations associated with bioclimatic conditions, in particular winter temperature. Genetic diversity was higher in populations growing under warm bioclimates than in those from cold bioclimates. These results suggest that a part of the variation for HMW glutenin variability is adaptive.     

Morphological variations of Caragana microphylla populations in the Xilingol steppe and their relationship with environmental factors

The morphological variations of branches, leaves, flowers, fruits and seeds of Caragana microphylla and their correlations with environmental factors were analyzed based on five natural populations in the Xilingol steppe, Inner Mongolia, China. Nested variation analysis showed that there were significant differences in all of the 28 morphological characters within and among populations in 16 morphological characters, and the variations within populations were much greater than those among populations in most morphological characters. Cluster analysis showed that the five populations of C. microphylla could be divided into two groups in morphological characters, and there was significant positive correlation between the divergence of morphological characters matrix and geographical distance matrix. Principal component analysis showed that leaflet length, area of a compound leaf, fresh-mass of a compound leaf, and shoot fresh-mass were main morphological characters that varied among C. microphylla populations. Spearman correlation analysis showed that there were significant correlations between some morphological characters and soil factors. Soil N:P ratio, available N content, total N content, organic matter content and soil water content were main factors that were associated with morphological characters of C. microphylla.