Size-dependent Variation Research Articles

Quantitative Genetic Studies of Behavioral Evolution

This text examines the theory and methods of quantitative genetics and presents case studies that illustrate the many ways in which the methods can be applied. The author brings together current theoretical and empirical studies to show how quantitative genetics can illuminate topics as diverse as sexual selection, migration, sociality and aggressive behaviour. Nearly half of the chapters focus on conceptual issues, ranging from quantitative genetic models to the complementary roles of quantitative genetic and optimality approaches in evolutionary studies. Other chapters illustrate how to use the techniques by providing surveys of research fields, such as the evolution of mating behaviour, sexual selection, migration and size-dependent behavioural variation. The balance of the volume offers case studies of territoriality in fruit flies, cannibalism in flour beetles, mate-attractive traits in crickets, locomotor behaviour and physiology in the garter snake, and cold adaptation in the house mouse. Taken together, these studies document both the benefits and pitfalls of quantitative genetics. This book aims to show the advanced student and scholar of behavioural evolution and genetics the many powerful uses of quantitative genetics in behavioural research.

Flower Size-Dependent Variation in Seed Size: Theory and a Test

We developed an optimal-allocation model for the variation in seed size among and within plants of the same species and tested the predictions using naturally growing plants of Lilium auratum. In the model, we considered size-number trade-offs among seeds and assumed that pollen capture is an increasing but diminishing function of allocation to pollen capture mechanisms. We predicted that seed size is positively correlated with allocation to pollen capture. This is because the increased cost of pollen capture makes it more advantageous to increase seed size to enhance the establishment probability of individual seeds than to increase seed number. Field tests were consistent with the predictions. First, hand pollination increased seed number per fruit, which indicated that pollen capture limited seed production, as is assumed in the model analyses. Both ovule size and mean seed weight per fruit were positively correlated with corolla dry weight. In addition, mean seed weight per fruit was negatively correl...

Size-dependent variations in phytoplankton and protozoan community structure across the St. Lawrence River transition region

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 120:99-110 (1995) - doi:10.3354/meps120099 Size-dependent variations in phytoplankton and protozoan community structure across the St. Lawrence River transition region Frenette, J.-J., Vincent, W. F., Dodson, J. J., Lovejoy, C. We evaluated 2 contrasting perspectives on the St. Lawrence Estuary maximum turbidity zone (MTZ): the first being that it is a zone of stress and mortality for the plankton community, the second that it is a biologically productive area with a complex, structured food web. Two cruises were undertaken under different hydrologic regimes, one at the end of the spring flood period and the other during mean summer flow conditions. The same pattern of change in community structure of the phytoplankton and protozoa (2 to 200 um) was observed across the saltwater transition in both cruises: there was a shift in the size distribution of taxa towards dominance by larger cells and an increase in the number of taxa (including 'endemic taxa' confined to a specific salinity range) at the bottom of the transition zone. There was no evidence of a decline in evenness, nor of a shift towards a heterotroph-based food web that would result from the mortality of autotrophs advected into the MTZ. These changes imply a prolonged residence time for the cells in the MTZ and a combination of immigration and emigration pathways that favours larger particles and high taxon diversity. The results are consistent with a 'hydrodynamic entrapment' model. Our observations do not support the earlier views that the St. Lawrence MTZ is a region of unfavourable biological conditions. Conversely, the large average cell size combined with a longer cell-retention time in this region may contribute towards its productivity as a larval fish nursery. Estuary . Phytoplankton . Protozoa . Biovolume . Turbidity . Community Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 120. Publication date: April 20, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Interspecific Allometries of Critical Buckling Height and Actual Plant Height

Size-dependent variations in the critical buckling height Hcrit and actual height H of plants were determined for a total of 111 species with self-supporting stems ranging in diameter between 0.03 cm ≤ D ≤ 3.0m. For each species, experimentally determined values for the physical properties of stems (Young's elastic modulus and bulk tissue density) were used to compute Hcrit. For small species (D < 3 cm), empirically determined critical buckling loads were used to compute Hcrit by means of the Elastica equation and the more traditionally employed Greenhill formula; for larger species (D ≖ 3 cm), Greenhill's formula was used exclusively to estimate Hcrit. Within most of the size-range examined, the predicted values of Hcrit from the Elastica equation and Greenhill's formula were statistically indistinguishable. Regression analyses showed that the interspecific allometry of Hcrit parallels that of H such that the safety factor against the elastic mechanical failure of stems (i.e., Hcrit/H) under their own biomass was roughly constant. Since the safety factor against elastic buckling is independent of plant size, a general allometric “rule,” Hcrit/H ≈ 4, appears to govern the evolution of plant size.

Abiotic and Seasonal Factors Influencing Trace Metal Levels (Cd, Cu, Ni, Pb, and Zn) in the Freshwater AmphipodGammarus fasciatusin Two Fluvial Lakes of the St. Lawrence River

The potential use of the freshwater amphipod Gammarus fasciatus as a biomonitor of metal pollution has been assessed in two fluvial lakes of the St. Lawrence River. Metal (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) concentrations were measured twice at 22 sites in Lakes St. Pierre and St. Louis, both in oxic sediments and in amphipods. Concentrations of free-metal ions at the sediment–water interface were estimated from lake water pH and sediment/water sorption equilibria. Multiple linear regression models forecasting trace metal (Cd, Cu, Ni, Pb, and Zn) levels in amphipods were developed, using abiotic variables (sediment-bound metals, sediment organic carbon, free-metal ions, hydrogen ions, dissolved calcium, and dissolved organic carbon) and biotic (size class) variables. These models explained 73–81% of the observed variation, except in the case of Zn (68%) and Cu (61%), indicating that G. fasciatus is a promising biomonitor for Cd, Ni, and Pb in littoral environments. Seasonal patterns of amphipod contamination were identified for Fe, Ni, and Pb, summer concentrations being higher than those measured during the fall. Size-dependent variation in amphipod metal levels was found, smaller organisms being more contaminated than larger ones.

Neighbour effects on gender variation in Ambrosia artemisiifolia

In this study we tested the prediction that male gender allocation in natural populations of common ragweed (Ambrosia artemisiifolia L.) depends more on relative plant height within the neighbouring canopy than on absolute plant height. This is consistent with the assumption that success as a pollen donor for an anemophilous plant within a crowded population will be greater when neighbours are shorter than when neighbours are taller. Data on height and proximity of neighbours, irradiance, and target plant height, biomass, and gender allocation were collected from two natural populations. In one population, these data were also recorded for a group of target plants that had local neighbours artificially removed when the target plants were seedlings. Allocation to male flowers was most strongly positively correlated with height relative to that of close neighbours and with percent irradiance in natural populations. Numerous all-female plants were recorded among the smallest individuals that were suppressed by a dense overhead canopy of neighbours. No relationships were found between plant size and gender when plants were taller than their neighbours or when neighbours were artificially removed. Hence, previously reported size-dependent gender variation in this species may depend on the presence of neighbours. It is postulated that ragweed individuals may sense the presence of neighbours through the phytochrome system, and that effects of neighbours on light quantity and quality cues a shift to increased female function. However, plants that grew from the seedling stage without neighbours were heavier and more female but were not taller than plants with neighbours left intact. The interpretation of this effect is unclear but may reflect a change in plant architecture corresponding with the removal of neighbours. Key words: gender, plant height, plasticity, pollen dispersal, phytochrome, shading.

Growth and competition in clonal plants-persistence of shoot populations and species diversity

This paper reviews studies on growth and size-structure dynamics of shoots and clones in clonal plants in comparison with those in non-clonal plants, and discusses the characteristics of clonal plants. The mode of competition between individuals (symmetric versus asymmetric, degree of competitive asymmetry), growth dynamics of individuals, allocation pattern between organs and spatial pattern of individuals are closely correlated with each other in non-clonal plant populations. Theoretical and field studies based on the diffusion model revealed that plants of “height-growth” type (mostly early-successional tree species) and plants of “diameter-growth” type (mostly late-successional tree species) tend to exhibit asymmetric competition and symmetric competition respectively. Moreover, asymmetrically competing plants show smaller effects of variation in individual growth rate and spatial pattern on the size-structure dynamics of the population than symmetrically competing plants. Thefefore, the spatial pattern of inviduals should be considered especially for plants undergoing symmetric competition. These results for non-clonal plants should have a significant implication also for the growth dynamics and competition in clonal plants. The mean growth rate of shoots [G(t,x) function] and hence the mode of competition between shoots differs among clonal plant species as in non-clonal plants. However, a large magnitude and size-independence (or slightly negative size-dependence) of the variation in growth rate of shoots [D(t,x) function], especially at the early stage in a growing season is a common characteristic of many clonal plant species, in contrast to the positively size-dependent variation in individual growth rate in non-clonal plants. This type of variation in shoot growth rate leads to the persistence of stable shoot populations even when the mean growth rate function is changed, and also in cases where the shoot population structure would be unstable in the absence of variation in growth rate. It is suggested that competition between clones is symmetric in most clonal plant species, which brings about small-scale spatio-temporal changes in species abundance and hence species diversity.

Ab initio models for ZnS surfaces: Influence of cluster size on surface properties.

The feasibility of the cluster method is studied using two-dimensional ZnS surface models. We used the translational symmetry of electron integrals in the Hartree-Fock valence method as it enables studies of large systems, containing several hundred atoms. The results show that the influence of boundaries and empty vacancies are limited only to a small area, and thus relatively small models can be used to simulate infinite systems. The properties are converging monotonically as the size of the model increases. However, in some cases small, size-dependent variations exist. Augmenting the minimal valence basis set with Zn 4p polarization functions decreases the influence of boundaries, and the charge distribution of surface becomes more uniform.

Size-Dependent Variations in Plant Growth Rates and the "¾ Power Rule"

Size-dependent variations in morphological and physiological variables adduced to influence growth rate (e.g., cell surface area and volume, chlorophyll a concentration per cell) were determined by reevaluating published data from unicellular and multicellular plants and animals. With respect to cell volume, reduced major axis regression of the available data indicated that cell surface area decreases roughly as the 0.69-power, the concentration of Chl a decreased roughly as the 0.80-power, and cell mass decreased as the 0.77-power. Computer simulations indicated that the scaling exponent for cell surface area was the consequence of size-dependent variations in cell geometry and aspect ratio (i.e., cell length/width) rather than the result of geometric similitude among cells differing in size. The anisometric relation between cell mass and volume indicated that bulk cell density declines with increasing cell volume. Reanalyses of published data showed that growth rate and weight-specific growth rate scale as the ¾- and negative ¼-power, respectively, with respect to the body mass of unicellular and multicellular plants and animals. It is speculated that the anisometric relation between the growth rate and mass of unicellular plants is attributable to a “dilution” of metabolically active cellular constituents with increasing cell size in combination with the scaling of surface area with respect to volume (and therefore cell mass). It is further speculated that similar biological scalings may account for the ¾-power rule obtained for taxonomically and ecologically diverse multicellular plants and animals.

Age and size-dependent variation in the seasonal timing and probability of reproduction among mature female pumpkinseed,Lepomis gibbosus

In this study, we used pumpkinseed,Lepomis gibbosus, populations in two east-central Ontario lakes to test for age and size-dependent effects on the probability and timing of reproduction of mature females. Pumpkinseed body size characteristics differed in the two lakes; Little Round Lake harbours a stunted population and Beloporine Lake does not. Age-class distribution of mature females was determined by a maturity assessment on fish collected just prior to spawning and at the mid-spawning period, combined with an early-season capture-mark-recapture survey. Spawning females were collected throughout the breeding season to assess age and size-related temporal trends, and to compare their age and size distribution with that of mature females at large. The proportion of age 2 females in Little Round Lake that actually spawned was considerably lower than the proportion of mature age 2 females at large. Furthermore, age 2 females that spawned in this lake did not do so until late in the breeding season. In contrast, the proportion of young/small females spawning in Beloporine Lake was comparable to the proportion of young/small mature females at large, and both small and large females spawned throughout the breeding season. Small mature females in Little Round Lake may have had no other option but to spawn late in the season because of their poor body condition. In Beloporine Lake, condition factor early in the breeding season in age 2–4 females was higher than that of Little Round Lake females, suggesting that limited energy reserves in the spring may have prevented young Little Round Lake females from early spawning. Our results show that the likelihood and timing of reproduction are both age and size-dependent in some populations. Small individuals that delay seasonal maturation and spawn late in the summer probably contribute little to the population due to the restricted growth and reduced overwinter survival of their progeny.

THE SCALING OF PLANT AND ANIMAL BODY MASS, LENGTH, AND DIAMETER.

The interspecific scaling exponents of body mass M and diameter D with respect to length L were determined to evaluate the predictions of three scaling hypotheses (geometric, stress, and elastic similitude). The relation between M and L was determined for data from a total of 133 aquatic and terrestrial species (66 plant and 67 animal species); the relation between D and L was determined independently for a total of 753 aquatic and terrestrial species (667 plant and 86 animal species). Organisms were crudely classified as to their geometry (spheres, spheroids, cylinders) and shape (defined as the body slenderness factor, L/D) to examine whether geometry and shape evinced size-dependent variations. Regression indicated M = 1.29L2.95 (r2 = 0.91, N = 133; αRMA = 3.09 ± 0.088). The stress and elastic similitude (which respectively predict αRMA = 5 and αRMA = 4) were rejected; geometric similitude was not (αRMA = 3). For animals and plants, αRMA = 2.81 ± 0.061 (r2 = 0.98), and αRMA = 2.95 ± 0.093 (r2 = 0.94), respectively. For aquatics and terrestrial organisms, αRMA = 2.82 ±0.134 (r2 = 0.97, N = 36), and αRMA = 3.08 ±0.111 (r2 = 0.89, N = 97), respectively. These results were interpreted to support the hypothesis of geometric similitude. For the pooled plant and animals data, D = 0.05L1.00 (r2 = 0.95; αRMA = 1.03 ± 0.009), which was compatible with the hypothesis of geometric similitude. For plants, D = 0.05L1.06 (r2 = 0.95; αRMA = 1.09). For animals, D = 0.29L0.98 (r2 = 0.95; αRMA = 1.01 ± 0.025). Also, for aquatics, αRMA = 0.951 ± 0.151, whereas for terrestrial plants and animals, αRMA = 1.03 ± 0.089. Although the scaling exponent for D differed among individual groupings of animals and plants, the results of regression analyses were interpreted to indicate that, on the average, body diameter scaled isometrically with respect to length as predicted by geometric similitude. For the pooled data set, organic shape varied over 3 orders of magnitude; L varied over 9 orders of magnitude reflecting 22 orders of magnitude of M. In terms of body geometry and the absolute numbers of species in the total data set: spherical shaped species (L = D) < unassigned species < prolate spheroidal species < cylindrical (squat < slender) species. The largest organisms in the data set were slender (L/D > 20) cylindrical plants; the smallest organisms were spherical plants and animals. Although not subject to statistical inference, these data were interpreted to indicate that organic shape and geometry evince size-dependent variations. These variations as well as size-dependent changes in bulk density are hypothesized to account for the scaling exponents of M and D determined for individual plant and animal clades and grades.

First-Principles Determination of the Polarizabilities of Carbon Tubules as a Function of Length

ABSTRACTWe use the local-density-approximation to the density-functional theory to determine the axial polarizabilities of fullerene tubules as a function of length and winding topologies. Specifically, we present linear polarizabilities for tubules of composition C12H24, C36H24, C40H20 and C60H24. The size-dependent variation in the dipole-coupled gaps between pairs of occupied and unoccupied levels leads to enhancements in the polarizability per valence electron as the length of the tubule increases. The results are compared to recent densityfunctional based calculations of the linear and nonlinear polarizabilities for fullerene and benzene molecules.

Ab initio models for ZnS surfaces: the influence of cluster size on surface properties: II. Three-dimensional models

Models for zinc sulfide surfaces varying from 2D slabs to 3D zinc blende clusters containing several ZnS layers were studied. The energies and electronic properties are shown to converge monotonically as the model size increases. In some cases some size-dependent variation was found. The influence of edges and vacancies remains local, damping quickly beyond the neighboring atoms.

Life-history variation in the annual arable weed Diplotaxis erucoides (Cruciferae)

Variation in life-history traits such as emergence, survival, time of flowering, and fecundity were studied in Diplotaxis erucoides, a mediterranean winter annual weed, by analyzing cohorts that emerged in autumn, early spring, and spring. The response of the plants to the environment, as reflected by plant architecture and pattern of biomass allocation, was also studied. Seedlings that germinate in autumn produced from 3 to 10 times more seeds than those that germinated in spring. The main factor affecting the number of seeds produced appears to be the life-span. Reduction of the growing period led to a decrease in both number and length of modular units, which resulted in decreased numbers of leaves, flowers, and fruits of each module. In semelparous D. erucoides plants, differences in the pattern of biomass allocation to reproduction are related to plant size. Our field data indicate that an increase of reproductive effort with size occurs in small individuals; however, a decrease occurs for vegetative biomass greater than 2 g and less than 5 g. Little variation in reproductive effort occurs when vegetative biomass is greater than 5 g. From a strategic point of view, size-dependent variation of reproductive effort in D. erucoides can be interpreted as good tactics to favour a higher proportion of resources devoted to reproduction in small individuals, thus ensuring some offspring. However, structural, developmental, and physiological constraints lead to stabilization or even a decrease in reproductive effort above a certain threshold size, when production of offspring is already ensured. Key words: phenotypic plasticity, plant architecture, biomass allocation, Diplotaxis erucoides.

Allocation of Organ Biomass in Perfect and Imperfect Flowers

Perianth MP, gynoecium MG, and androecium MA dry-weight biomass (in g) of 39 species of perfect flowers was measured. These data were pooled with published data from an additional 51 species and used to determine size-dependent variations in (MG and MA) in terms of the hypothesis that the quotient of MG and MA exceeds 1·0 for out-breeding (xenogamous) species and less than 1·0 for in-breeding (autogamous) species. Ordinary least square regression of the pooled data (n = 90) showed MG = 0·118 M0·916P (r2 = 0·884) and MA = 0·186 M0·975P (r2 = 0·865), indicating that the biomass of the gynoecium proportionally decrease as floral size increases. The exponents of these regressions indicate that the ratio of gynoecial to androecial biomass decreased with increasing floral size such that comparatively small flowers (MP < 0·0021 g) had MG/MA > 1·0 (predicted for 'out-breeders') while comparatively larger flowers (MP > 0·0021 g) had MG /MA < 1·0 (predicted for 'in-breeders'). Thus, on average, the type of breeding system was a size-dependent phenomenon.To test whether the biomass of a floral organ-type is a legitimate indicator of gender reproductive effort, the biomass (in g) of stamen filaments Mm and anther sacs MAS of 39 species was determined. Least square regression of these data showed MAS = 0·188 M0·854fil (r2 = 0·967), indicating that species with larger stamen filaments, on the average, bore proportionally smaller anther sacs and thereby cautioning against the uncritical use of the allocation of biomass to floral organ-type as a strict gauge of gender-function investment.To determine whether the loss of one gender-function results in proportional reallocation of biomass to the remaining gender-function, the size-dependency of androecial and gynoecial biomass was determined for a total of 33 perfect and imperfect flowers of Cucumis melo. Regression of the data obtained from perfect flowers yielded MA = 0·402 M1·47P (r2 = 0·898) and MG = 4·63 M1·36P (r2 = 0·842). Since MG/MA ∝ M0·11P , the biomass allocation to the gynoecium relative to the androecium decreased with increasing floral size. This result was consistent with the broad interpecific comparison based on 90 species with perfect flowers . Regression of the data for imperfect flowers yielded MA = 0·151 M1·02P (r2 = 0·675) and MG = 4·68 M1·47P (r2 = 0·996), indicating a near allometric relation for the androecium and a strong positive anisometry for the gynoecium. Thus, for flowers of comparable size, a loss of female gender obtains a modest to significant again in androecial biomass whereas the loss of male gender yields only a slight increase in gynoecial biomass.Collectively, the results of these studies indicate that biomass allocation patterns are size-dependent phenomena whose complexities have been largely ignored in the literature.

Divergent dispersal strategies in the freshwater bryozoan Plumatella repens: ramet size effects on statoblast numbers.

Evaluation of size-dependent variation in statoblast numbers in Plumatella repens indicates that this freshwater bryozoan employs divergent strategies in dispersing its asexual offspring in space and time. While the numbers of sessoblasts which were cemented to local substrates did not vary per unit ramet size, numbers of floatoblasts which disperse away from the parent to colonize substrates elsewhere varied in a size-dependent manner. Large ramets produced disproportionately more floatoblasts than did small ramets. In general, this result is consistent with the optimal dispersal predictions of three alternative theoretical models. However, the fact that the total number of sessoblasts in a ramet increased with ramet size appears to violate the "constant disperser principle" of one alternative model, and the occurrence of fusion in P. repens may violate the assumption of local competition for sites in another. In order to determine which model represents an appropriate description of dispersal in P. repens, future studies should evaluate the relative importance of local competition, cooperative phenomena like fusion, and mortality among dispersed and nondispersed offspring.

Inorganic nanoclusters in organic glasses — Novel materials for electro-optical applications

Polymer glasses which contain regularly arranged ultrasmall inorganic crystallites or clusters of CdS, CoS, NiS, ZnS have been prepared from functionalized diblock copolymers. Size and surface structure dependent variation of the ionization or redox potential respectively the band gap energy of the semiconductor particles in the polymeric glasses can be exploited to control photochemical processes and optical properties. The combination of anorganic and organic compounds provides a simple route to highly ordered, stable and processable materials with a wide range of properties. Regular arrangement of the clusters in a defined supermolecular lattice might be used for tayloring electromagnetic interactions and might provide new materials for infrared and microwave applications.

Historical and size-dependent genetic variation in hybrid mussel populations

Samples from the high and low shore were taken from mussel populations at two localities. Croyde Bay and Whitsand Bay in southwest England, within the zone of hybridisation of Mytilus edulis and Mytilus galloprovincialis, and analysed at five polymorphic allozyme loci. Strong correlations were observed between shell length and allele frequencies at both localities, with a higher frequency of alleles characterising M. galloprovincialis being found in larger mussels. Three hypotheses were considered as explanation of these results (1) differential mortality, (2) differential growth and (3) historical change within the hybrid zone. The last hypothesis was rejected because the pattern of length dependent allozyme variation was similar in samples taken in 1980–81 and 1986–87. The observation of small growth differences between M. edulis and M. galloprovincialis provided evidence against the second hypothesis. Thus, higher mortality of younger M. edulis was favoured as the cause of the length-dependent variation. Wave exposure and sand abrasion experienced by the mussels were thought to be the most likely selective factors. Strong correlations were also observed in these populations between shell length and allozyme heterozygosity. Analysis of genotype frequencies in small and large size classes of mussels provide evidence of a small added effect of heterozygosity, but no evidence of overdominance.

The chemistry and physics of molecular surfaces

This article reviews the results of several recent experiments performed in our laboratory designed to elucidate the fundamental chemical and physical properties of clusters of both transition metals and other refractory elements containing from one to several hundred atoms. The gas-phase reactivity of clusters towards a variety of reagents is explored using a fast-flow reactor system. Strong cluster size-dependent variations in reactivity are observed, especially for the case of hydrogen chemisorption. Measurement of cluster photoionization thresholds (IPs) provides a sensitive probe of the evolution of cluster electronic structure as a function of the number of constituent atoms.

Size-Dependent Effects in the Analysis of Reproductive Effort in Plants

Size-dependent variation in reproductive effort (RE) appears to be a common phenomenon in many plant species, but researchers have not fully appreciated the factors causing such variation and the potential significance of these patterns to plant ecology and life history. Data from desert winter annuals and the reexamination of published work indicate that many plant populations can be characterized by a significant linear relationship between absolute reproductive biomass and vegetative biomass. The form of this allometric relationship results in variable RE with size (monotonically increasing or decreasing) in many of these species. Both increasing and decreasing RE-with-size patterns are found in both iteroparous and semelparous species, but theoretical expectations for such patterns in different plants remain undeveloped. Some of the conclusions of previous studies of RE in plants may be in error if size-dependent effects were not taken into account. The graphical-regression approach presented here provides a simple means of testing for size-dependent effects within populations and for assessing the significance of differences in size-dependent patterns among populations.