EVOLUTION, Issue 5 2009
Reinmar Hager
Epigenetic effects attributed to genomic imprinting are increasingly recognized as an important source of variation in quantitative traits. However, little is known about their relative contribution to phenotypic variation compared to those of additive and dominance effects, and almost nothing about their role in phenotypic evolution. Here we address these questions by investigating the relative contribution of additive, dominance, and imprinting effects of quantitative trait loci (QTL) to variation in "early" and "late" body weight in an intercross of mice selected for divergent adult body weight. We identified 18 loci on 13 chromosomes; additive effects accounted for most of the phenotypic variation throughout development, and imprinting effects were always small. Genetic effects on early weight showed more dominance, less additive, and, surprisingly, less imprinting variation than that of late weight. The predominance of additivity of QTL effects on body weight follows the expectation that additive effects account for the evolutionary divergence between selection lines. We hypothesize that the appearance of more imprinting effects on late body weight may be a consequence of divergent selection on adult body weight, which may have indirectly selected for alleles showing partial imprinting effects due to their associated additive effects, highlighting a potential role of genomic imprinting in the response to selection. [source]

DOES LARGE BODY SIZE IN MALES EVOLVE TO FACILITATE FORCIBLE INSEMINATION?

EVOLUTION, Issue 11 2005
A STUDY ON GARTER SNAKES
Abstract A trend for larger males to obtain a disproportionately high number of matings, as occurs in many animal populations, typically is attributed either to female choice or success in male-male rivalry; an alternative mechanism, that larger males are better able to coercively inseminate females, has received much less attention. For example, previous studies on garter snakes (Thamnophis sirtalis parietalis) at communal dens in Manitoba have shown that the mating benefit to larger body size in males is due to size-dependent advantages in male-male rivalry. However, this previous work ignored the possibility that larger males may obtain more matings because of male-female interactions. In staged trials within outdoor arenas, larger body size enhanced male mating success regardless of whether a rival male was present. The mechanism involved was coercion rather than female choice, because mating occurred most often (and soonest) in females that were least able to resist courtship-induced hypoxic stress. Males do physically displace rivals from optimal positions in the mating ball, and larger males are better able to resist such displacement. Nonetheless, larger body size enhances male mating success even in the absence of such malemale interactions. Thus, even in mating systems where males compete physically and where larger body size confers a significant advantage in male-male competition, the actual selective force for larger body size in males may relate to forcible insemination of unreceptive females. Experimental studies are needed to determine whether the same situation occurs in other organisms in which body-size advantages have been attributed to male-male rather than male-female interactions. [source]

EMPIRICAL EVIDENCE FOR AN OPTIMAL BODY SIZE IN SNAKES

EVOLUTION, Issue 2 2003
Scott M. Boback
Abstract The concept of optimal size has been invoked to explain patterns in body size of terrestrial mammals. However, the generality of this phenomenon has not been tested with similarly complete data from other taxonomic groups. In this study we describe three statistical patterns of body size in snakes, all of which indicate an optimal length of 1.0 m. First, a distribution of largest body lengths of 618 snake species had a single mode at 1.0 m. Second, we found a positive relationship between the size of the largest member of an island snake assemblage and island area and a negative relationship between the size of the smallest member of an island snake assemblage and island area. Best-fit lines through these data cross at a point corresponding to 1.0 m in body length, the presumed optimal size for a one-species island. Third, mainland snake species smaller than 1.0 m become larger on islands whereas those larger than 1.0 m become smaller on islands. The observation that all three analyses converge on a common body size is concordant with patterns observed in mammals and partial analyses of four other disparate animal clades. Because snakes differ so strikingly from mammals (ectotherms, gape-limited predators, elongate body shape) the concordant patterns of these two groups provide strong evidence for the evolution of an optimal body size within independent monophyletic groups. However, snakes differ from other taxonomic groups that have been studied in exhibiting a body size distribution that is not obviously skewed in either direction. We suggest that idiosyncratic features of the natural history of ectotherms allow relatively unconstrained distributions of body size whereas physiological limitations of endotherms constrain distributions of body size to a right skew. [source]

A STATISTICAL TEST OF UNBIASED EVOLUTION OF BODY SIZE IN BIRDS

EVOLUTION, Issue 12 2002
Folmer Bokma
Abstract., Of the approximately 9500 bird species, the vast majority is small-bodied. That is a general feature of evolutionary lineages, also observed for instance in mammals and plants. The avian interspecific body size distribution is right-skewed even on a logarithmic scale. That has previously been interpreted as evidence that body size evolution has been biased. However, a procedure to test for unbiased evolution from the shape of body size distributions was lacking. In the present paper unbiased body size evolution is defined precisely, and a statistical test is developed based on Monte Carlo simulation of unbiased evolution. Application of the test to birds suggests that it is highly unlikely that avian body size evolution has been unbiased as defined. Several possible explanations for this result are discussed. A plausible explanation is that the general model of unbiased evolution assumes that population size and generation time do not affect the evolutionary variability of body size; that is, that micro- and macroevolution are decoupled, which theory suggests is not likely to be the case. [source]

NUPTIAL GIFTS AND THE EVOLUTION OF MALE BODY SIZE

EVOLUTION, Issue 3 2002
Kenneth M. Fedorka
Abstract In many insect systems, males donate nuptial gifts to insure an effective copulation or as a form of paternal investment. However, if gift magnitude is both body size-limited and positively related to fitness, then the opportunity exists for the gift to promote the evolution of large male size. In the striped ground cricket, Allonemobius socius, males transfer a body size-limited, somatic nuptial gift that is comprised primarily of hemolymph. To address the implications of this gift on male size evolution, we quantified the intensity and direction of natural (fecundity) and sexual (mating success) selection over multiple generations. We found that male size was under strong positive sexual selection throughout the breeding season. This pattern of selection was similar in successive generations spanning multiple years. Male size was also under strong natural selection, with the largest males siring the most offspring. However, multivariate selection gradients indicated that gift size, and not male size, was the best predictor of female fecundity. In other words, direct fecundity selection for larger gifts placed indirect positive selection on male body size, supporting the hypothesis that nuptial gifts can influence the evolution of male body size in this system. Although female size was also under strong selection due to a size related fecundity advantage, it did not exceed selection on male size. The implications of these results with regard to the maintenance of the female-biased size dimorphic system are discussed. [source]

Body Size and Risk of Extinction in Australian Mammals

CONSERVATION BIOLOGY, Issue 5 2001
Marcel Cardillo
For Australian terrestrial mammals this link is of particular interest because it is widely believed that species in the intermediate size range of 35,5500 g (the "critical weight range") have been the most prone to recent extinction. But the relationship between body size and extinction risk in Australian mammals has never been subject to a robust statistical analysis. Using a combination of randomization tests and phylogenetic comparative analyses, we found that Australian mammal extinctions and declines have been nonrandom with respect to body size, but we reject the hypothesis of a critical weight range at intermediate sizes. Small species appear to be the least prone to extinction, but extinctions have not been significantly clustered around intermediate sizes. Our results suggest that hypotheses linking intermediate body size with high risk of extinction in Australian mammals are misguided and that the focus of future research should shift to explaining why the smallest species are the most resistant to extinction. Resumen: El vínculo entre el tamaño del cuerpo y el riesgo de extinción ha sido el centro de mucha atención reciente. Para los mamíferos terrestres australianos este vínculo es de particular interés debido a que se cree ampliamente que las especies en un rango intermedio de tamaño de 35,5500 g (el rango de peso crítico) ha sido el más susceptible a extinciones recientes. Sin embargo, la relación entre extinciones, el tamaño y el riesgo de extinción en mamíferos australianos nunca ha sido sometida a un análisis estadístico robusto. Usando una combinación de pruebas aleatorizadas y análisis filogenéticos comparativos, encontramos que las extinciones y disminuciones de mamíferos australianos han sido no aleatorias con respecto al tamaño del cuerpo, pero rechazamos la hipótesis de un rango crítico a tamaños intermedios. Las especies pequeñas aparentan ser las menos susceptibles de extinción, pero las extinciones no se han agrupado significativamente alrededor de tamaños intermedios. Nuestros resultados sugieren que la hipótesis que vincula el tamaño intermedio de cuerpo con un alto riesgo de extinción en mamíferos australianos está mal planteada y que el centro de la investigación a futuro deberá enfocarse a explicar el porqué las especies más pequeñas son las más robustas a la extinción. [source]

Female Preferences for Sailfin and Body Size in the Sailfin Molly, Poecilia latipinna

ETHOLOGY, Issue 5 2004
R. David MacLaren
We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates. [source]

Female Choice, Female Reluctance to Mate and Sexual Selection on Body Size in the Dung Fly Sepsis cynipsea

ETHOLOGY, Issue 7 2000
Wolf U. Blanckenhorn
We investigated the mechanisms of sexual selection in the common dung fly Sepsis cynipsea and how these affect selection on body size at the population level. Because of the presumed costs associated with mating, we predicted that there would be a decrease in the general reluctance of females to mate with any particular male at higher male densities at the mating site, a fresh cow pat, resulting in indirect female choice and a decrease in the strength of sexual selection. In contrast, classical direct female choice and male-male competition should result in increased selection intensities because more opportunities for choice and competition exist at higher densities. Female reluctance to mate and female assessment of males are expressed in prominent female behaviour to repel mates in several insect species, including S. cynipsea. Laboratory pair-wise choice experiments showed that large males were more likely to obtain copulations, which also ensued more promptly, suggesting female assessment of male quality (direct female choice). There was a basic influence of male activity but little further effect of male scramble competition on the outcome of mating. Another laboratory experiment showed a decrease in female shaking duration per male, associated with an asymptote in the shaking duration per female, as male density and harassment increased, but did not show the increase in mating frequency predicted by the female reluctance hypothesis. A study estimating sexual selection differentials in the field showed that directional selection for larger males was present overall and was negatively related to seasonally mediated variation in male density. Our study suggests that direct female choice in combination with indirect female choice (due to an interaction of female reluctance to mate and male persistence) is most consistent with the behavioural and selection patterns observed in S. cynipsea, but male effects cannot be definitively excluded. [source]

Modelling the Influence of Age, Body Size and Sex on Maximum Oxygen Uptake in Older Humans

EXPERIMENTAL PHYSIOLOGY, Issue 2 2000
Patrick J. Johnson
The purpose of this study was to describe the influence of body size and sex on the decline in maximum oxygen uptake (V,O2,max) in older men and women. A stratified random sample of 152 men and 146 women, aged 55-86 years, was drawn from the study population. Influence of age on V,O2,max, independent of differences in body mass (BM) or fat-free mass (FFM), was investigated using the following allometric model: V,O2,max= BMb (or FFMb) exp(a + (c × age) + (d × sex)) [epsilon]. The model was linearised and parameters identified using standard multiple regression. The BM model explained 68.8% of the variance in V,O2,max. The parameters (± s.e.e., standard error of the estimate) for lnBM (0.563 ± 0.070), age (-0.0154 ± 0.0012), sex (0.242 ± 0.024) and the intercept (-1.09 ± 0.32) were all significant (P < 0.001). The FFM model explained 69.3% of the variance in V,O2,max, and the parameters (± s.e.e) lnFFM (0.772 ± 0.090), age (-0.0159 ± 0.0012) and the intercept (-1.57 ± 0.36) were significant (P < 0.001), while sex (0.077 +/, 0.038) was significant at P = 0.0497. Regardless of the model used, the age-associated decline was similar, with a relative decline of 15% per decade (0.984 exp(age)) in V,O2,max in older humans being estimated. The study has demonstrated that, for a randomly drawn sample, the age-related loss in V,O2,max is determined, in part, by the loss of fat-free body mass. When this factor is accounted for, the loss of V,O2,max across age is similar in older men and women. [source]

Body frame dimensions are related to obesity and fatness: Lean trunk size, skinfolds, and body mass index

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 1 2010
Maciej Henneberg
We explore relationships between BMI and skinfolds and anthropometric variables reflecting variation in lean body frame. Data on the middle class adult Australian women (n = 1260) collected in 2002 during a National Body Size and Shape Survey were used. Standard measurements of stature, weight, skeletal dimensions (shoulder width, hip width, chest width, and depth, limb lengths), circumferences of head, trunk, limbs and triceps, subscapular and abdominal skinfolds were taken. Techniques for measurements of skeletal frame minimized the inclusion of adipose tissue thickness. Analysis of variance and parametric and nonparametric correlations were used. Vertical dimensions show weak correlations with fatness, while body frame circumferences and transverse dimensions are consistently, significantly, and substantially correlated with fatness, each explaining from 3 to 44% of variation in skinfold thickness. Skeletal dimensions explain up to 50% of variation in skinfold thickness (multiple regression). Especially high correlations with skinfold thickness occur for chest width, depth, and hip width (r range from 0.42 to 0.66). Body frame dimensions reflect largely trunk volume and the trunk/limb proportions. Larger lean trunk size is associated with greater fatness. Since the size of the abdominal cavity, and thus the gastrointestinal system (GI), is reflected in the trunk size, we speculate that larger frame may predispose to obesity in two ways: (1) larger stomachs require greater bulk of food to produce feeling of satiety as mediated through antral distension, (2) larger GIs may absorb more nutrients. Frame size may help to detect the risk of obesity among young adults. Am. J. Hum. Biol. 2010. © 2009 Wiley-Liss, Inc. [source]

Influence of maternal stature, pregnancy age, and infant birth weight on growth during childhood in Yucatan, Mexico: A test of the intergenerational effects hypothesis,

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2009
Maria Inês Varela-Silva
In developing nations, obesity has increased dramatically in the last decade, but a high prevalence of stunting still coexists. The intergenerational influences hypothesis (IIH) is one explanation for this. We test the IIH regarding variation in maternal stature, mother's age at pregnancy, and infant birth weight in relation to risk for overweight and stunting in 206 Maya children (4,6 years old) from Mérida, Yucatan, Mexico. The Maya children are compared with growth references (Frisancho 2008: Anthropometric Standards: An Interactive Nutritional Reference of Body Size and Body Composition for Children and Adults. Ann Arbor, MI: The University of Michigan Press. 335 pp) for height, weight, and body mass index (BMI). Almost 70% of the mothers are shorter than 150 cm. Mothers' height and child's birth weight predict overweight. Children with a mother shorter than 150 cm are less than half as likely (OR = 0.44) to be overweight compared to children whose mothers are equal to or taller than 150 cm. Children with birth weights below 3,000 g are only a third as likely to be overweight (OR = 0.28) than their peers within the range of normal birth weight (3,000,3,500 g). Sex of the child, mother's height, and birth weight predict stunting. Girls are only 40% as likely as boys to be stunted. Children with a mother below 150 cm are 3.6 times more likely of being stunted. Children with birth weights below 3000 g are over 3 times more likely to be stunted relative to children with birth weights within the normal range. Mother's age at pregnancy is not a predictor of overweight or stunting. Our findings conform the IIH and with similar studies of populations undergoing nutritional/epidemiological transitions from traditional to globalized lifestyles. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source]

Male Body Size and Mating Success and Their Relation to Larval Host Plant History in the Moth Rothschildia lebeau in Costa Rican Dry Forest

BIOTROPICA, Issue 2 2010
Salvatore J. Agosta
ABSTRACT The moth Rothschildia lebeau uses three tree species as its primary larval hosts in the tropical dry forest of northwestern Costa Rica. These hosts were shown previously to have different relative effects on caterpillar performance, resulting in an apparent host-related life history trade-off between large adult body size on the one hand but low offspring survival on the other. To further assess the potential ecological and evolutionary importance of this trade-off, an observational field study of the relationship between male body size and mating success was conducted. Across mating trials, larger males had a higher probability of being observed mating. Independent of the effect of size, the amount of wing damage an individual had sustained (a measure of relative age) was negatively correlated with the probability a male was observed mating. Within mating trials, the mated male tended to be larger than the average unmated male, but there was no difference in wing damage. Overall, results of this study were consistent with a positive effect of male body size on mating success, consistent with the idea that larval host plant history and its effects on adult body size matters in terms of adult male fitness. However, all sized males were observed mating over the course of the study, and the size advantage did not appear to be particularly strong. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source]

Importance of Body Size in Determining Dominance Hierarchies among Diverse Tropical Frugivores1

BIOTROPICA, Issue 1 2005
Aaron R. French
ABSTRACT Most studies examining dominance hierarchies have focused at the intraspecific level. While some examples of interspecific hierarchies have been noted, these have usually been limited to a few species in the same taxonomic group that utilize resources in similar ways. Here, we examine evidence for dominance interference competition among vertebrates comprising a diverse frugivore community, including 19 species of birds, squirrels, and primates in a mature Central African rainforest. A total of 38 fruiting trees from 18 species were observed for 2058 h to record dominance interactions between foraging vertebrates. We show that interference competition occurs within and between taxonomically diverse species of vertebrates at fruiting trees. The resulting cross-taxonomic dominance hierarchy includes larger vertebrates, such as primates and hornbills, as well as smaller ones, such as squirrels and parrots. Within this hierarchy, the dominance rank of each species is highly correlated with body mass, and is shown to significantly affect the number of fruits removed from a given tree. Because a majority of tropical tree species depend on vertebrates to disperse their seeds, and particular vertebrates may preferentially disperse the seeds of specific tree species, results may have important conservation implications for the maintenance of tree diversity in regions where populations of larger frugivores have been depressed or extirpated. [source]

Perceptions of Children's Body Sizes Among Mothers Living on the Texas-Mexico Border (La Frontera)

PUBLIC HEALTH NURSING, Issue 6 2006
Elizabeth Reifsnider
ABSTRACT Objectives: The objectives of this study were to quantify mothers' perceptions of their children's sizes and explore mothers' views of child growth, diet, activity, and health. Photographs of children from the Berkeley Longitudinal Growth Study (on Centers for Disease Control and Prevention [CDC] Web site) were used to stimulate discussion with mothers about child sizes. Design: A descriptive, cross-sectional study examined mothers' perceptions of their children's size and their beliefs about child size, growth, and health. Sample: The convenience sample included 25 mother,child dyads of 3-year-old children at two Head Start Centers in a county on the Texas,Mexico border. All mothers self-identified as Hispanic. Measurement: Photographs of children were shown to elicit mothers' perceptions of children's body sizes. The children and mothers were weighed and measured and their body mass indices (BMIs) were computed. The mothers were interviewed about their beliefs on child health, growth, and feeding. Results: No congruence was found between mothers' perceptions of child sizes in the pictures and their children's sizes. Conclusions: Using CDC photographs does not appear to be a useful way to educate mothers about child body sizes. A child who is happy, active, and can accomplish normal childhood activities is not considered by mothers as overweight, regardless of the child's BMI. [source]

Conservation of Insect Diversity: a Habitat Approach

CONSERVATION BIOLOGY, Issue 6 2000
Jennifer B. Hughes
To explore the feasibility of basing conservation action on community-level biogeography, we sampled a montane insect community. We addressed three issues: (1) the appropriate scale for sampling insect communities; (2) the association of habitat specialization,perhaps a measure of extinction vulnerability,with other ecological or physical traits; and (3) the correlation of diversity across major insect groups. Using malaise traps in Gunnison County, Colorado, we captured 8847 Diptera (identified to family and morphospecies), 1822 Hymenoptera (identified to morphospecies), and 2107 other insects (identified to order). We sampled in three habitat types,meadow, aspen, and conifer,defined on the basis of the dominant vegetation at the scale of hundreds of meters. Dipteran communities were clearly differentiated by habitat type rather than geographic proximity. This result also holds true for hymenopteran communities. Body size and feeding habits were associated with habitat specialization at the family level. In particular, habitat generalists at the family level,taxa perhaps more likely to survive anthropogenic habitat alteration,tended to be trophic generalists. Dipteran species richness was marginally correlated with hymenopteran species richness and was significantly correlated with the total number of insect orders sampled by site. Because these correlations result from differences in richness among habitat types, insect taxa may be reasonable surrogates for one another when sampling is done across habitat types. In sum, community-wide studies appear to offer a practical way to gather information about the diversity and distribution of little-known taxa. Resumen:No existe ni el tiempo ni los recursos para diseñar planes de conservación para cada especie, particularmente para los taxones poco estudiados, no carismáticas, pero ecológicamente importantes que componen la mayoría de la biodiversidad. Para explorar la factibilidad de basar acciones de conservación en biogegrafía a nivel comunitario, muestreamos una comunidad de insectos de montaña. Evaluamos tres aspectos: (1) la escala adecuada para el muestreo de comunidades de insectos; (2) la asociación de especialización de hábitat,quizá una medida de vulnerabilidad de extinción,con otras características ecológicas o físicas; y (3) la correlación de la diversidad a lo largo de los grupos principales de insectos. Mediante el uso de trampas en el condado Gunnison, en Colorado, capturamos 8847 dípteros (identificados a nivel de familia y morfoespecies), 1822 himenópteros (identificadas hasta morfoespecies) y 2107 otros insectos (identificados a nivel de orden). Muestreamos tres tipos de hábitats,vega, álamos temblones y coníferas,definidos en base a la vegetación dominante a escala de cientos de metros. Las comunidades de dípteros estuvieron claramente diferenciadas por tipos de hábitat y no por la proximidad geográfica. Este resultado también se mantiene para las comunidades de himenópteros. El tamaño del cuerpo y los hábitos alimenticios estuvieron asociados con la especialización del hábitat a nivel de familia. En particular, los generalistas de hábitat a nivel de familia,los taxones que posiblemente tengan mayor probabilidad de sobrevivir alteraciones antropogénicas del hábitat,tendieron a ser generalistas tróficos. La riqueza de las especies de dípteros estuvo marginalmente correlacionada con la riqueza de especies de himenópteros y estuvo significativamente correlacionada con el número total de órdenes de insectos muestreadas por sitio. Debido a que estas correlaciones resultaron de diferencias en la riqueza de especies entre tipos de hábitats, los taxones de insectos podrían ser substitutos mutuos razonables cuando se muestrea entre diferentes tipos de hábitats. En resumen, los estudios a lo largo de comunidades parecen ofrecer una forma práctica de recolectar información sobre la diversidad y distribución de los taxones poco estudiados. [source]

Size-dependent species-area relationships in benthos: is the world more diverse for microbes?

ECOGRAPHY, Issue 3 2002
Andrey I. Azovsky
Using original and literature data on species richness, I compared the species-area relations for 5 different size classes of the Arctic benthos: macrofauna sensu lato, polychaetes, nematodes, ciliates and diatom algae. The data pool covered a wide range of areas from single samples to the whole seas. Both the slopes and intercepts of the curves depended significantly on the logarithm of the mean body size of the group. The number of small species (ciliates and diatom algae) showed relatively higher local diversity but increased more slowly with the area than the number of larger ones. Thus, both ,- and ,-components of species diversity of the marine benthos were size-dependent. As a consequence, the actual relations between number of species and their physical size are spatially scale-dependent: there are many more species of smaller size classes in any one local community, but at a global scope the situation changes drastically. The possible reasons are discussed, including dispersal efficiency, rates of speciation and size-dependent perception of environmental heterogeneity. Body size is suggested to be the important scaling factor in manifestation of so-called "general ecological laws". [source]

Body size determines the strength of the latitudinal diversity gradient

ECOGRAPHY, Issue 3 2001
Helmut Hillebrand
In most groups of organisms, the species richness decreases from the tropics to the poles. The mechanisms causing this latitudinal diversity gradient are still controversial. We present data from a comprehensive weighted meta-analysis on the strength of the latitudinal gradient in relation to body size. We sampled literature data on the correlation between species richness and latitude for a variety of organisms, ranging from trees to protozoa. In addition, own data on the presence of large-scale diversity patterns for diatoms were included, both for local and regional species richness. The strength of the latitudinal gradient was positively correlated to the size of the organisms. Strongest decreases of species richness to the poles was found for large organisms like trees and vertebrates, whereas meiofauna, protozoa and diatoms showed weak or no correlations between species richness and latitude. These results imply that latitudinal gradients are shaped by non-equilibrium (regional) processes and are persistent under conditions of dispersal limitation. [source]

Body size and host range in European Heteroptera

ECOGRAPHY, Issue 1 2000
Martin Brändle
We used data on body size and host range of phytophagous Heteroptera in central Europe, an inverse measure of specialisation, to analyse the relationship of body size vs specialisation: 1) we found a clear positive relationship between body size and host range using species as independent data points. 2) However, a nested analysis of variance shows that most of the variance in body size occurred at higher taxonomic levels whereas most of the variance in host specialisation occurred between species. This suggests different phylogenetic inertia of body size and specialisation. Nevertheless, using means of different higher taxonomic levels there is still a significant positive correlation between body size and host range. 3) With more sophisticated methods of correcting for the phylogenetic relatedness between species, the positive correlation between body size and host range still holds, despite the different assumptions of each method. Thus, the relationship between body size and host range is a very robust pattern in true bugs. [source]

Seed weevils living on the edge: pressures and conflicts over body size in the endoparasitic Curculio larvae

ECOLOGICAL ENTOMOLOGY, Issue 3 2009
RAÚL BONAL
Abstract 1.,Body size in parasitic insects can be subjected to contrasting selective pressures, especially if they complete their development within a single host. On the one hand, a larger body size is associated with a higher fitness. On the other hand, the host offers a discrete amount of resources, thus constraining the evolution of a disproportionate body size. 2.,The present study used the weevil Curculio elephas as a study model. Larvae develop within a single acorn, feeding on its cotyledons, and larval body size is strongly related to individual fitness. 3.,The relationship between larval and acorn size was negatively exponential. Larval growth was constrained in small acorns, which did not provide enough food for the weevils to attain their potential size. Larval size increased and levelled off in acorns over a certain size (inflexion point), in which cotyledons were rarely depleted. When there were more than one larva per acorn, a larger acorn was necessary to avoid food depletion. 4.,The results show that C. elephas larvae are sometimes endoparasitic, living on the edge of host holding capacity. If they were smaller they could avoid food depletion more easily, but the fitness benefits linked to a larger size have probably promoted body size increase. The strong negative effects of conspecific competition may have possibly influenced female strategy of laying a single egg per seed. 5.,Being larger and fitter, but always within the limits of the available host sizes, may be one main evolutionary dilemma in endoparasites. [source]

Bergmann's rule in larval ant lions: testing the starvation resistance hypothesis

ECOLOGICAL ENTOMOLOGY, Issue 6 2003
Amy E. Arnett
Abstract., 1.,Body size of the ant lion Myrmeleon immaculatus follows Bergmann's rule , an increase in body size towards higher latitudes. The hypothesis that ant lion body size is larger in the north as an adaptation for starvation resistance was tested. 2.,In a laboratory experiment testing starvation resistance, survivorship curves differed among 10 ant lion populations for both a starved and a fed treatment. 3.,The average number of months survived by each population was correlated positively with latitude for both treatments. Across both treatments and all populations, large individuals survived longer than small individuals; however individuals from high latitudes had higher survivorship, even after factoring out variation due to initial body size. 4.,These results suggest that starvation resistance may be an adaptation for coping with reduced prey availability in high latitudes. Starvation resistance may contribute to latitudinal gradients in body size of ant lions and other ectotherms. [source]

Body size as an estimator of production costs in a solitary bee

ECOLOGICAL ENTOMOLOGY, Issue 2 2002
Jordi Bosch
Abstract 1. Body weight is often used as an estimator of production costs in aculeate Hymenoptera; however, due to differences between sexes in metabolic rates and water content, conversion of provision weight to body weight may differ between males and females. As a result, the cost of producing female progeny may often have been overestimated. 2. Provision weight and body weight loss throughout development were measured in a solitary bee, Osmia cornuta (Latreille), to detect potential differences between sexes in food weight/body weight conversion. 3. Male O. cornuta invest a larger proportion of larval weight in cocoon spinning, and presumably have higher metabolic rates than females during the larval period; however, this is compensated by a slightly longer larval period in females. 4. Overall, body weight loss throughout the life cycle does not differ significantly between sexes. As a result, cost production ratios calculated from provision weights and from adult body weights are almost identical. 5. The validity of other weight (cocoon, faeces) and linear (head width, intertegular span, wing length, cocoon length, and cell length) measures as estimators of production costs is also discussed. 6. Valid estimators of production costs vary across species due to differences in sex weight ratio, cocoon shape, provision size in reference to cell size, and adult body size. [source]

Effect of soil hardness on aggression in the solitary wasp Mellinus arvensis

ECOLOGICAL ENTOMOLOGY, Issue 5 2001
Jaboury Ghazoul
Summary 1. Two alternative nesting strategies are exhibited by soil-nesting Mellinus arvensis females, digging a new nest (diggers) and searching for an old unoccupied burrow (searchers). Wasps appear unable to distinguish between occupied and unoccupied nests, and aggressive interactions between searchers and nest owners at nest entrances are frequent. 2. In aggressive encounters, there is an advantage in size and residency status. 3. The costs associated with the two nesting strategies vary across geographically separated populations: nest digging incurs costs in terms of time, and these vary according to the hardness of the soil substrate; nest searching is variably costly in terms of risk of injury in aggressive encounters with nest-owning females. 4. Individual female wasps can switch between nesting strategies, and thus soil hardness, by affecting the cost of nest construction, affects the relative frequencies of the two nesting strategies within a population, favouring an increase in the searching strategy. This, in turn, affects the frequency and intensity of aggression between females at a nesting aggregation. 5. Female body size is correlated with soil hardness. As aggressive encounters are more frequent in sites with hard soil substrates, there is increased selective advantage in having large body size at these sites. 6. Body size is determined primarily by the availability of food resources during larval development, which is, to a degree, a function of the size of the adult female. There is a trade-off between provisioning a few cells with many provisions in each, leading to the development of few but large adults, as opposed to many cells with few provisions, leading to many small offspring. The relative advantage of these two provisioning strategies is, at least in part, a function of the hardness of the soil substrate. [source]

Body size and invasion success in marine bivalves

ECOLOGY LETTERS, Issue 2 2002
Kaustuv Roy
The role of body size in marine bivalve invasions has been the subject of debate. Roy et al. found that large-bodied species of marine bivalves were more likely to be successful invaders, consistent with patterns seen during Pleistocene climatic change, but Miller et al. argued that such selectivity was largely driven by the inclusion of mariculture species in the analysis and that size-selectivity was absent outside of mariculture introductions. Here we use data on non-mariculture species from the north-eastern Pacific coast and from a global species pool to test the original hypothesis of Roy et al. that range limits of larger bivalves are more fluid than those of smaller species. First, we test the hypothesis that larger bivalve species are more successful than small species in expanding their geographical ranges following introduction into new regions. Second, we compare body sizes of indigenous and non-indigenous species for 299 of the 303 known intertidal and shelf species within the marine bivalve clade that contains the greater number of non-mariculture invaders, the Mytilidae. The results from both tests provide additional support for the view that body size plays an important role in mediating invasion success in marine bivalves, in contrast to Miller et al. Thus range expansions in Recent bivalves are consistent with patterns seen in Pleistocene faunas despite the many differences in the mechanisms. [source]

Impacts of nonpoint inputs from potato farming on populations of slimy sculpin (Cottus cognatus)

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2005
Michelle A. Gray
Abstract The potential influence of agricultural activity, particularly potato cultivation, on slimy sculpin populations (Cottus cognatus) was examined at 19 rivers of New Brunswick, Canada. Comparisons with forested streams resulted in differences in fish density, size, and reproductive performance. Young-of-the-year (YOY) sculpin were present only at two of 11 agricultural sites, though they were present at all nine forested sites. Sediment deposition was greatest at agricultural sites, with increased fine sediments deposited. Larger, coarse sands were deposited at two sites with active forest operations. Temperature had a stronger correlation than sedimentation with sculpin size and density in the agricultural region. Agricultural catchments were warmer than in forested catchments (median = 16.0 and 13.3°C, respectively). Body size of slimy sculpin was correlated positively and YOY densities correlated negatively with temperature, and sites with temperatures ,25°C were devoid of YOY sculpin. Our data indicate there is a significant effect of temperature on slimy sculpin populations in rivers of potato farming areas, highlighting the importance of examining indirect factors when investigating possible impacts of nonpoint source agricultural inputs. Indirect factors such as sediment deposition and temperature need to be considered in order to discriminate accurately the chronic impacts of agricultural chemicals on fish populations. [source]

Organochlorine pesticides and mercury in cottonmouths (Agkistrodon piscivorus) from northeastern Texas, USA,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2005
Thomas R. Rainwater
Abstract Dspite their ecological importance andglobal decline, snakes remain poorly studied in ecotoxicology. In this study, we examined organochlorine (OC) pesticide and mercury accumulation in cottonmouths (Agkistrodon piscivorus) living on a contaminated site in northeastern Texas (USA). Mercury and p,p,-dichlorodiphenyldichloroethylene (p,p,-DDE) were detected in all snakes examined. Other OCs, including p,p,-dichlorodiphenyltrichloroethane (p,p,-DDT), methoxychlor, aldrin, and heptachlor, also were detected, but less frequently. Concentrations of p,p,-DDE were higher in fat than in liver, while mercury concentrations were highest in liver, followed by kidney and tail clips. One animal contained the highest mercury concentration yet reported for a snake (8,610 ng/g). Mercury concentrations in liver and kidney were higher in males than females, while no intersex differences in p,p,-DDE concentrations were observed. Concentrations of p,p,-DDE in fat were correlated positively with body size in male cottonmouths but not females, suggesting a slower rate of accumulation in females. Body size strongly predicted mercury concentrations in liver, kidney, and tail clips of both sexes. Tail clips were strong predictors of mercury in liver and kidney in males but not females, suggesting possible sex-dependent differences in mercury toxicokinetics. Both long-term field studies and controlled laboratory investigations are needed to adequately assess the response of cottonmouths to chronic contaminant exposure. [source]

Abnormalities in sexual development of the amphipod Gammarus pulex (L.) found below sewage treatment works

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2001
Melanie Yvette Gross
Abstract Increasing numbers of widely used industrial, agricultural, and natural chemicals are known to elicit endocrine-disrupting effects in a wide range of vertebrate and invertebrate species. The objective of this study was to determine whether the sexual development of the freshwater crustacean Gammarus pulex (L.) was affected below sewage treatment works (STW) previously known to contain endocrine-disrupting chemicals in their effluent. The gonadal structure, external sexual characteristics, and size of gammarids from exposed sites were compared to those of gammarids from a reference site. No significant difference was found in the gonadal structure of males collected below two STW. However, a highly significant number of females collected from a site known to elicit high estrogenic responses in vertebrates displayed an abnormal structure of oocytes in vitellogenesis. Body size was significantly shorter and male/female size differential was significantly reduced below one of the STW. Analysis of gnathopod and genital papillae length data suggests that different allometric relationships of these organs to body size exist between sample sites. [source]

Field Cricket Species Differences in the Temporal Patterns of Long-Distance Mate Attraction Signals

ETHOLOGY, Issue 9 2006
Susan M. Bertram
We quantify variation in the temporal components of long-distance mate attraction signals produced by a North American field cricket, Gryllus rubens Scudder. Total signaling time, trilling bout duration, and hourly bout number exhibit high repeatability within individuals. Extensive variation exists across individuals: some males never signal while others signal for several hours each night; of the signalers, average trilling bout duration ranges from <1 min to well over an hour; some males produce only one trilling bout in an evening while others produce three bouts every 2 h. Body size, weight, wing morphology, and condition do not appear to explain the variation. We compare the temporal signaling components of G. rubens with its sister species, G. texensis. Although G. rubens produce slightly more trills per hour with slightly shorter trilling bout durations, the temporal components of these long-distance mate attraction signals are surprisingly similar across species. [source]

SPATIAL AND TEMPORAL DYNAMICS IN A SEXUAL SELECTION MOSAIC

EVOLUTION, Issue 4 2008
Thomas P. Gosden
Selective regimes and phenotypic optima could either change smoothly and in a clinal fashion or be spatially organized in a more unpredictable mosaic pattern over the geographic landscape. When natural or sexual selection is driven by intra- or interspecific biotic interactions, fine-grained spatial variation in selective regimes could result in selection mosaics rather than clinal variation in selection. We investigated temporal variation and spatial organization in sexual selection on male body size along an ecological coastal-inland gradient of a polymorphic damselfly Ischnura elegans. Body size increased in a clinal fashion along this gradient: animals were smaller in size at the coast, but became larger in the inland areas. In contrast, the sexual selection regimes on male body size showed evidence of more fine-grained spatial organization with no evidence for a clinal pattern and low spatial autocorrelations between populations. These spatially fine-grained sexual selection regimes varied in sign and magnitude and were driven by a combination of the densities of heritable female color morphs and local female body sizes. We suggest that the spatial organization of the selective regimes can be interpreted as a sexual selection mosaic that is influenced by highly localized density- and frequency-dependent social interactions. [source]

Unstable release strategies in reared Atlantic salmon, Salmo salar L.

FISHERIES MANAGEMENT & ECOLOGY, Issue 3 2000
S. M. McKinnell
The effects of year, size, sexual maturity and release date on the probability of recapture of tagged Atlantic salmon, Salmo salar L., released from a Swedish hatchery in the Baltic Sea were examined. The probability of recapture varied among years for individuals which were juvenile when released (1988, 13.5%; 1989, 4.4%; 1990, 1.2%) or previously mature males (1988, 1.9%; 1989, 0.5%; 1990, 0.4%). Body size was positively associated with the probability of recapture in each release year for both life-history types. Inter-annual changes in recapture rates were similar for both large and small smolts. There was a significant effect of life-history type on recapture rates in 1988 and 1989, but not in 1990. There was a significant effect of release date on recapture rates in 1988 and 1990, but not in 1989. The maximum recapture rates were associated with different release dates in each year, i.e. 27 May 1988, 6 June 1989 and 21 June 1990. [source]

Body size and food thresholds for zero growth in Dreissena polymorpha: a mechanism underlying intraspecific competition

FRESHWATER BIOLOGY, Issue 12 2008
ALEXANDER WACKER
Summary 1. Dreissena polymorpha is an extraordinarily successful invasive species that shows high recruitment of small juvenile mussels on established mussel banks. Such juvenile settlement on, and overgrowth of, large adult mussels; however, leads to competition with adults, and often at high densities and low-food concentrations. 2. The concept of food thresholds for zero growth has been a powerful approach to explaining size-related exploitative competition in different zooplankton species. We applied it to investigate whether food threshold concentrations for zero growth (C0) differ between juvenile and adult zebra mussels. 3. By determining body mass growth at various concentrations of a diet mixture (Nannochloropsis limnetica and Isochrysis aff. galbana) we demonstrate that the threshold food concentration for growth of juvenile mussels (C0 = 0.08 mg C L,1) is substantially lower than that for adults (C0 = 0.36 mg C L,1). 4. This indicates that, at low food availability, juvenile zebra mussels are competitively superior to their larger conspecifics. Within zebra mussel banks plankton food is substantially depleted and so the observed mechanism might ensure juvenile success and therefore the regeneration of mussel banks in nature. [source]