Body shape and size divergence among populations of Poecilia vivipara in coastal lagoons of south-eastern Brazil

Geometric shape analyses were used to study body shape and size variation among populations of the livebearing fish Poecilia vivipara inhabiting the recently formed coastal lagoons of Grussaí and Iquipari in Northern Rio de Janeiro State, Brazil. The largest components of morphological variation among females were between different habitats in the same lagoon, whereas for males there were larger differences between lagoons than between habitats. The shape differences were mostly localized in the head region and midbody, which indicated different patterns of locomotion and foraging behaviour optimized for the habitat experienced by each population. The pattern of size variation was similar to that of size-independent shape variation.     

Inter- and intraspecific variation in grass phytolith shape and size: a geometric morphometrics perspective

Background and AimsThe relative contributions of inter- and intraspecific variation to phytolith shape and size have only been investigated in a limited number of studies. However, a detailed understanding of phytolith variation patterns among populations or even within a single plant specimen is of key importance for the correct taxonomic identification of grass taxa in fossil samples and for the reconstruction of vegetation and environmental conditions in the past. In this study, we used geometric morphometric analysis for the quantification of different sources of phytolith shape and size variation.MethodsWe used landmark-based geometric morphometric methods for the analysis of phytolith shapes in two extant grass species (Brachypodium pinnatum and B. sylvaticum). For each species, 1200 phytoliths were analysed from 12 leaves originating from six plants growing in three populations. Phytolith shape and size data were subjected to multivariate Procrustes analysis of variance (ANOVA), multivariate regression, principal component analysis and linear discriminant analysis.Key ResultsInterspecific variation largely outweighed intraspecific variation with respect to phytolith shape. Individual phytolith shapes were classified with 83 % accuracy into their respective species. Conversely, variation in phytolith shapes within species but among populations, possibly related to environmental heterogeneity, was comparatively low.ConclusionsOur results imply that phytolith shape relatively closely corresponds to the taxonomic identity of closely related grass species. Moreover, our methodological approach, applied here in phytolith analysis for the first time, enabled the quantification and separation of variation that is not related to species discrimination. Our findings strengthen the role of grass phytoliths in the reconstruction of past vegetation dynamics.     

Ontogenetic and environmental effects on otolith shape variability in three Mediterranean European eel (Anguilla anguilla, L.) local stocks

Otolith morphology is an efficient tool for the discrimination of fish stocks, populations and species when comparative genetic data are not available. Currently, the relationship between environmental factors and otolith shape is poorly characterized for the European eel (Anguilla anguilla), a highly migratory catadromous species constituting a single, randomly mating stock. The present study analyses the differences in otolith morphology between three Mediterranean eel local stocks from different environmental contexts (i.e. two brackish lagoons and one river). The relationship between otolith shape and otolith size was studied by means of Elliptic Fourier analysis and multivariate statistics. Otolith profile was digitally acquired and Cartesian coordinates were extracted. Partial Least Square (PLS) analysis pointed to continuous allometric growth in size and shape in otoliths from all three sites. In the three environments, shape variations occurred during growth as indicated by the presence of a significant and positive relationship between otolith size and the first PLS latent vector (i.e. which bears most of the information regarding otolith outline). Differences between smaller and larger sized otoliths were investigated using PLS Discriminant Analysis (PLSDA) and cluster analysis. Results indicate that otolith shape is highly uniform at smaller than at larger sizes. These shape differences apparently overlap the initial differentiation of the small otolith outlines acquired by eels during the growing phase as elvers in the marine environment. Data were discussed considering that the physical and chemical habitat variability in brackish lagoons and river could underlie a marked change in otolith shape during the animals' growth.     

Cranial morphological variation of Dromiciops gliroides (Microbiotheria) along its geographical distribution in south-central Chile: A three-dimensional analysis

We analyzed the variation in cranial morphology of the marsupial Dromiciops gliroides along its distribution in south-central Chile. We evaluated whether the cranial morphological variation is congruent with the phylogeographic structure previously observed in this species. We built three-dimensional models of 69 crania on which we digitized 30 landmarks. We used standard geometric morphometric methods to extract and analyze the shape and size components of the crania. Our data showed a subtle but consistent cranial size and shape variation along the studied distributional range, suggesting a geographic variation pattern rather than a phylogeographic structuring. Indeed, our multivariate analyses recovered a subtle morphological differentiation between island and mainland populations, contrary to what is suggested by a former phylogeographic study. We detected that either the cranial size variation, as well as the insularity and the latitude could be important factors underlying the cranial shape changes. We suggest that an interplay of historical and contemporary processes could be shaping the morphological pattern observed in this marsupial.     

Population Dynamics of the Endangered, Long-Lived Perennial Species, Ligularia sibirica

Ligularia sibirica is a relict wetland perennial plant species of the Czech and Slovak Republic. Explaining variation in population growth rate and identifying the causes of that variation is important for effective protection of such an endangered species. Matrix models based on four years of data of 11 populations were used to identify the pattern of variation in the demographic vital rates of this species, and to examine the causes of the variation such as population size and habitat type. Further, the matrix model was used to determine the population growth rate, longevity and risk of extinction of each population and to identify the specific vital rates that most affect population growth rate. The results showed that population growth rates were significantly different between years and populations. Temporal variation was mostly due to variable survival of adult individuals, while spatial variation was mainly driven by fertility of one small currently expanding population. Further, most studied populations of L. sibirica are performing well and only those growing in nitrogen-rich habitats have a high extinction risk. The results also indicate that all populations have low adult mortality, long-lived individuals (61.3?years on average) and some populations also show features of remnant populations (i.e., the persistence of populations in severe conditions in spite of no reproduction). Our results imply that detailed demographic data are needed to understand the long-term prospects of these populations. These data may serve as an early warning system for this species long before an obvious decline occurs in the populations.     

Species complex delimitation and patterns of population structure at different geographic scales in Neotropical silver catfish (<Emphasis Type="Italic">Rhamdia</Emphasis>: Heptapteridae)

The Neotropical catfish genus Rhamdia inhabits rivers and lakes from Mexico to Argentina. Previous studies have found that the taxonomy of this genus, as well as that of R. quelen, remains controversial. The present study aims to contribute to the understanding of Rhamdia systematics by delimiting putative species, and to elucidate the pattern of genetic differentiation of Rhamdia at different geographic levels within the cis-andean region. Species boundaries were defined by Generalized Mixed Yule Coalescent and Automatic Barcode Gap Discovery methods, and by phylogenetic analyses of cytochrome b (cyt b) sequences. Moreover, we performed phylogeographic analyses based on cyt b sequences and microsatellite markers. Patterns of differentiation were analyzed at three nested geographic levels: in the main cis-andean basins (macrogeographic scale); in the second major Neotropical basin system (mesogeographic scale), which encompasses La Plata basin, Patos-Merin basin, and the coastal lagoons draining to SW Atlantic Ocean; and finally, in the three most important coastal lagoons for artisanal fisheries in Uruguay (microgeographic scale). Sixteen species were found within Rhamdia, divided into two clades (cis- and trans-andean clades), each composed of eight putative species. Cis-andean Rhamdia species have probably diverged due to vicariance events occurring between and within basins since late Miocene-Pleistocene. Microgeographic scale analysis based on cyt b and microsatellite data revealed a high genetic structuring among the studied coastal lagoons. Mitochondrial and microsatellite markers enabled to identify three different populations, corresponding to the three coastal lagoons analyzed, which would have diverged recently and could be considered as different Management Units.     

Fish populations of lentic environments of the Paraná River

Data on the fish populations of lentic water bodies in the Paraná River are given for different areas sampled over more than twenty years. Three kinds of environment are considered: small, medium and large lagoons. Each kind has a particular fish population, the characteristics of which are described. Fish populations are also considered in relation to the macrophytes along the Paraná River. In general Prochilodus lineatus is the most important species, both in numbers and in biomass, in the majority of the lagoons. Considerations related to size and age of fish species are also discussed.     

Biosystematic studies of theClosterium peracerosum-strigosum-littorale complex

Numerous homothallic clones of theClosterium peracerosum-strigosum-littorale complex from various localities were obtained in axenic cultures. From comparisons of morphological characters of their vegetative cells cultured under the defined standard conditions, we have concluded that frequently observed morphological variation among local populations of the complex results not merely from phenotypical modification caused by local ecological factors. On the basis of the presence or absence of a wall thickening at cell apices, the clones could be separated into 2 groups of different genetic constitution. The group without a wall thickening could be separated further into 2 subgroups on the basis of statistical analyses of cell size variation. Clone GA-2-2 was exceptionally variable in cell size and produced remarkably deviated forms such as so-called “dwarf” or “giant” cells. Re-cloning of single cells of such deviated forms gave rise to several subclones whose mean values of cell size were distinct from that of GA-2-2, but whose qualitative characters such as the sexual morphology and the presence of a wall thickening were indistinguishable. It was observed that in clones GA-2-15 and S-10-20 which lacked a wall thickening some subclones had mean values of cell sizes distinct from that of the original clones. It was observed that in these subclones cell size changes were accompanied by nuclear size changes. The problem of cell size variation has been discussed with special regards to polyploidy and speciation in the inbreeding populations of the complex.     

Relationships between abiotic variables and geographic variation in skulls of pumas (Puma concolor: Mammalia, Felidae) in North and South America

Relationships between patterns of geographic variation in cranial morphology and selected abiotic variables were studied in the puma ( Puma concolor Linnaeus). Our dataset consisted of 11 cranial, 6 dental, and 2 mandibular measurements of 1700 adults, which were separated by gender and age class and analysed by univariate and multivariate statistical procedures. Variation in size was correlated with precipitation, but size was more highly correlated with latitude and temperature. The pattern of geographic variation in size of P. concolor is consistent with Bergmann's rule; populations with larger pumas occur more distant from the equator than populations with smaller pumas. A combination of climatic and biotic factors contribute to patterns of geographic variation in size of P. concolor in North and South America.     

Morphological variation in populations of Bletia purpurea (Orchidaceae) and description of the new species B. riparia

Bletia purpurea is the most widespread species in its genus. Morphological variation has been recognized throughout the range of its distribution. In this paper, the morphological variation from 63 populations (583 individuals) ofBletia purpurea is assessed to determine whether more than one species were present. Forty-four quantitative and qualitative characters were examined by univariate analyses and exploratory multivariate analyses. Univariate analyses indicate that quantitative characters such as lateral sepal width, petal. width, lip length, and lip width are significantly different for populations from Acazónica, Mexico. Floral parts in the populations from Acazónica are the smallest among all populations. Qualitative characters such as petals covering the lip midlobe and horizontal lip position are found exclusively in the same populations. We concluded that these populations should be described as a new species,B. riparia. Multivariate analyses indicated that morphological variation among the other populations cannot be ascribed to geographic distribution or ecological factors.     

Growth pattern and survival in populations of Poecilia vivipara (Teleostei; Poeciliidae) inhabiting an environmental gradient: a common garden study

We performed a common garden experiment to assess the existence of genetic differences on growth and body size between two populations of Poecilia vivipara inhabiting extremes of an environmental gradient caused by water salinity in lagoons of Northern Rio de Janeiro State, Brazil: the Campelo lagoon (freshwater) and Açu lagoon (brackish/saltwater). The two populations show extreme differences in average phenotypes for body size, shape and life history (freshwater populations with smaller body size, lower fecundity and larger reproductive allotment). Pregnant females were brought to the lab and the offspring from both groups were kept in a common recirculating system with freshwater. Standard length and survival were measured weekly over a period of 200 days and growth models were fitted and selected with information criteria. The offspring originally from the brackish water lagoon presented larger asymptotic length, higher maximum growth rate but lower survival than the offspring originally from the freshwater lagoon. Potential confounding variables such as density differences due to mortality and maternal effects (offspring size) were included as covariates in comparisons of growth rates between groups. The results are consistent with phenotypic differences among populations having some genetic basis, and with the existence of a trade-off between growth and maintenance due to the high growth/low survival observed in the group that changed from salt to freshwater. Comparisons of captive and natural populations suggest that the influence of environmental factors, such as salinity, food availability, fish density and predation should also be considered relevant to explain phenotypic variation in this system.     

Geographic variation in the essential oils and morphology of natural populations of Melaleuca alternifolia (Myrtaceae)

In recent decades, Melaleuca alternifolia has been grown in plantations for the commercial production of tea tree oil extracted from harvested leaf and stem material by steam distillation. Plantations are grown from seedlings raised from seeds collected from wild populations of this endemic Australian species. Considerable variation in morphology and leaf oil composition and yield has been observed and studies have demonstrated genetic and phenotypic heterozygosity between populations.Here we examine the variation in leaf oil chemical composition (chemotypes) between geographically defined locations of wild populations of M. alternifolia and investigate the relationships between tree size, chemotype and geographic location.Forty separate populations of M. alternifolia distributed amongst three river catchments (two in a warm moist coastal region and one in cool drier highlands) were studied. Total variation in tree size was significantly greater within individual sites than between them. However, the highland catchment populations exhibited significantly smaller mean tree size and a significantly different chemotype profile than the lowland populations. Contrary to the observation of lower genetic diversity, the highland catchment populations had greater chemotypic diversity. Furthermore, highly significant differences in population chemotypes were demonstrated between catchments.The possibilities that these differences could be ascribed to either genetic divergence or to environmental differences are discussed.     

A Quantitative Comparison of the Similarity between Genes and Geography in Worldwide Human Populations

Multivariate statistical techniques such as principal components analysis (PCA) and multidimensional scaling (MDS) have been widely used to summarize the structure of human genetic variation, often in easily visualized two-dimensional maps. Many recent studies have reported similarity between geographic maps of population locations and MDS or PCA maps of genetic variation inferred from single-nucleotide polymorphisms (SNPs). However, this similarity has been evident primarily in a qualitative sense; and, because different multivariate techniques and marker sets have been used in different studies, it has not been possible to formally compare genetic variation datasets in terms of their levels of similarity with geography. In this study, using genome-wide SNP data from 128 populations worldwide, we perform a systematic analysis to quantitatively evaluate the similarity of genes and geography in different geographic regions. For each of a series of regions, we apply a Procrustes analysis approach to find an optimal transformation that maximizes the similarity between PCA maps of genetic variation and geographic maps of population locations. We consider examples in Europe, Sub-Saharan Africa, Asia, East Asia, and Central/South Asia, as well as in a worldwide sample, finding that significant similarity between genes and geography exists in general at different geographic levels. The similarity is highest in our examples for Asia and, once highly distinctive populations have been removed, Sub-Saharan Africa. Our results provide a quantitative assessment of the geographic structure of human genetic variation worldwide, supporting the view that geography plays a strong role in giving rise to human population structure.     

Morphological divergence patterns among populations of Poecilia vivipara (Teleostei Poeciliidae): test of an ecomorphological paradigm

The structure of body size and shape divergence among populations of Poecilia vivipara inhabiting quaternary lagoons in South-eastern Brazil was studied. This species is abundant throughout an environmental gradient formed by water salinity differences. The salinity gradient influences the habitat structure (presence of macrophytes) and the fish community (presence of large predators). Size and shape variation within and among populations was quantified by geometric morphometrics and analysed by indirect and direct gradient ordinations, using salinity and geography as a framework. Morphological divergence was associated with the salinity gradient. The evolutionary allometries observed were independent of within-group static allometries. Sexually dimorphic patterns were observed in size variation and within-population allometries. Specimens from freshwater (higher predation) sites presented smaller sizes, relatively longer caudal regions, lower anterior regions and a ventrally displaced eye. These features are consistent with an ecomorphological paradigm for aquatic organisms from populations subject to intense predation. A process of directional selection is postulated as the most likely force driving diversification among P. vivipara populations.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 799–812.     

Response to Phosphorus Limitation Varies among Lake Populations of the Freshwater Snail Potamopyrgus antipodarum

Local adaptation – typically recognized as higher values of fitness-related traits for native vs. non-native individuals when measured in the native environment - is common in natural populations because of pervasive spatial variation in the intensity and type of natural selection. Although local adaptation has been primarily studied in the context of biotic interactions, widespread variation in abiotic characteristics of environments suggests that local adaptation in response to abiotic factors should also be common. Potamopyrgus antipodarum, a freshwater New Zealand snail that is an important model system for invasion biology and the maintenance of sexual reproduction, exhibits local adaptation to parasites and rate of water flow. As an initial step to determining whether P. antipodarum are also locally adapted to phosphorus availability, we examined whether populations differ in their responses to phosphorus limitation. We found that field-collected juvenile P. antipodarum grew at a lower rate and reached an important size threshold more slowly when fed a relatively low vs. a relatively high- phosphorus diet. We also detected significant across-population variation in individual growth rate. A marginally significant population-by-dietary phosphorus interaction along with a two-fold difference across populations in the extent of suppression of growth by low phosphorus suggests that populations of P. antipodarum may differ in their response to phosphorus limitation. Local adaptation may explain this variation, with the implication that snails from lakes with relatively low phosphorus availability should be less severely affected by phosphorus limitation than snails from lakes with higher phosphorus availability.     

A concise review of geographic variation in adult body size in anadromous masu salmon, Oncorhynchus masou

Adult body size (size at maturity) is one of the key life history traits and is well known to sometimes correlate with latitude in anadromous salmonids. However, it is poorly understood whether geographic size patterns except for latitudinal trends occur or why such patterns have been shaped. The present paper briefly reviewed body size variation between anadromous returns of masu salmon Oncorhynchus masou in the Okhotsk group (10 populations along the Sea of Okhotsk coast), the Pacific group (2 populations along the Pacific Ocean coast) and the Sea of Japan group (24 populations along the Sea of Japan coast). The Okhotsk group was smaller than the Sea of Japan group. Although the statistical analysis detected no differences among the remaining combinations, the Okhotsk group was possibly smaller than the other groups because the size of the Pacific group seemed to be within range of the Sea of Japan group but tended to be larger than that of the Okhotsk group. Future research should first test whether size at maturity genetically differs between the Okhotsk group and the other two groups to explore further evolutionary factors shaping geographic size variation.     

Mapping regions within cosmopolitan inversion In(3R)Payne associated with natural variation in body size in Drosophila melanogaster

Associations between genotypes for inversions and quantitative traits have been reported in several organisms, but little has been done to localize regions within inversions controlling variation in these traits. Here, we use an association mapping technique to identify genomic regions controlling variation in wing size within the cosmopolitan inversion In(3R)Payne in Drosophila melanogaster. Previous studies have shown that this inversion strongly influences variation in wing size, a trait highly correlated with body size. We found three alleles from two separate regions within In(3R)Payne with significant additive effects on wing size after the additional effect of the inversion itself had been taken into account. There were also several alleles with significant genotype-by-inversion interaction effects on wing size. None of the alleles tested had a significant additive effect on development time, suggesting different genes control these traits and that clinal patterns in them have therefore arisen independently. The presence of multiple regions within In(3R)Payne controlling size is consistent with the idea that inversions persist in populations because they contain multiple sets of locally adapted alleles, but more work needs to be done to test if they are indeed coadapted.     

Sediment resuspension dampens the effect of nutrient inputs on the phytoplankton community: a mesocosm experiment study

We sampled four populations of the robustly shelled Pleurocera canaliculata from large rivers and five pleurocerid populations bearing more fusiform shells (nominally P. acuta and P. pyrenellum) from smaller streams in a study area extending from upstate New York to northern Alabama, USA. Gene frequencies at 9 allozyme-encoding loci revealed that each population of P. acuta or P. pyrenellum was more genetically similar to the P. canaliculata population inhabiting the larger river immediately downstream than to any nominal conspecific. Thus, the extensive intraspecific variation in shell robustness displayed by these nine populations has apparently been rendered cryptic by taxonomic confusion. We then employed geometric morphometrics to explore a gradient in shell morphology from the acuta form to the typical canaliculata form in 18 historic samples collected down the length of Indiana’s Wabash River. The shell forms appeared generally distinctive on the major axes yielded by relative warp analysis (increasing robustness and decreasing spire elongation), although some overlap was apparent. MANCOVA returned a significant relationship between multivariate shape variation and stream size, as measured by drainage area. Possible drivers for this phenomenon include an environmental cline in the risk of dislodgement due to hydrodynamic drag and shifts in the community of predators.     

Allometric influence on phenotypic variation in the Song Sparrow (Melospiza melodia)

Song Sparrow ( Melospiza melodia ) populations found along the Pacific Coast of North America, from Baja California to the islands off the coast of Alaska, exhibit extensive morphological variation. With a multivariate analysis of size and shape, I describe a portion of this pattern and examine how it could be maintained despite gene flow among the populations. Because shape differences fall along geographic barriers, I suggest that similarities among Song Sparrow populations in multivariate shape reflect their pattern of genetic relatedness. A general pattern of Song Sparrow post-nestling growth allometry has been discovered: bill characteristics are positively allometric and all other characteristics are negatively allometric. In contrast to shape, multivariate patterns of body size variation do not correspond to geographic relationships. In combination with evidence of Song Sparrow phenotypic plasticity, it is proposed that multivariate body size is an environmentally plastic trait and that specific traits exhibit levels of phenotypic plasticity in proportion to their rate of growth with respect to body size. In this way local environmental factors which alter body size may change an entire suite of allometrically related traits and thus create striking patterns of morphological variation.     

Spatial variation of shell morphometrics in the subantarctic land snail <Emphasis Type="Italic">Notodiscus hookeri</Emphasis> from Crozet and Kerguelen Islands

The land snail Notodiscus hookeri, widely distributed in subantarctic islands, shows a large intraspecific variation in shell morphology. In the present work, shell size and form of individuals from populations located in Crozet and Kerguelen archipelagos were investigated by means of multivariate statistics. Variation in shell morphometrics was analysed after the partitioning of the overall variation into size and shape components by means of a principal component-based approach. Shell size shows a significant spatial heterogeneity, which seems essentially related to environmental pressures. Previous works pointed to a greater conchological variation between populations from Kerguelen but present observations show that intra-island variances are not significantly different in the two islands studied. Variation in shell shape splits the populations into two main entities because of different allometric relationships between two shell height components and all other measurements. However, using geographical affinities of populations as instrumental variables shows that more complex environmental features interfered in population clustering.