Climate change-driven body size shrinking in a social wasp

1. Climate change is expected to produce shifts in species distributions as well as behavioural, life-history, and/or morphological adaptations to find suitable conditions or cope with the altered environment. Most of our knowledge on this issue comes from studies on vertebrates, mainly endotherm species. However, it remains uncertain how small ectotherms, such as insects, respond to increased temperature. 2. This study tested whether climate change over the last 100 years (1904–2013) has affected morphological and functional traits in workers of the social wasp Dolichovespula sylvestris in the Iberian Peninsula. 3. Head width and forewing length, as well as body mass and wing area (assuming no change in shape), decreased over time and with increased mean annual temperature, even when controlling for geographical location and altitude. Interestingly, wing size decreased with a steeper slope compared with body size. If there is no change in wing shape, this would lead to an invariable wing loading (body mass:wing area ratio) over time, with potential consequences on flying ability of more recent (and thus smaller) wasp individuals. 4. These results suggest that recent climate change is leaving morphological signatures in social wasps, increasing the evidence for this phenomenon in insects. The data furthermore suggest that the known efficient thermoregulatory ability of social insect colonies may not successfully buffer the effect of global warming.     

Climate change and shrinking salamanders: alternative mechanisms for changes in plethodontid salamander body size

An increasing number of studies have demonstrated relationships between climate trends and body size change of organisms. In many cases, climate might be expected to influence body size by altering thermoregulation, energetics or food availability. However, observed body size change can result from a variety of ecological processes (e.g. growth, selection, population dynamics) or imperfect observation of biological systems. We used two extensive datasets to evaluate alternative mechanisms for recently reported changes in the observed body size of plethodontid salamanders. We found that mean adult body size of salamanders can be highly sensitive to survey conditions, particularly rainfall. This systematic bias in the detection of larger or smaller individuals could result in a signature of body size change in relation to reported climate trends when it is simply observation error. We also identify considerable variability in body size distributions among years and find that individual growth rates can be strongly influenced by weather. Finally, our study demonstrates that measures of mean adult body size can be highly variable among surveys and that large sample sizes may be required to make reliable inferences. Identifying the effects of climate change is a critical area of research in ecology and conservation. Researchers should be aware that observed changes in certain organisms can result from multiple ecological processes or systematic bias due to nonrandom sampling of populations.     

Neural tube closure: the curious case of shrinking junctions

Your brain and spinal cord began as a flat sheet, which narrowed, elongated, and rolled up to form a tube. A new study identifies a key molecular link underlying vertebrate neural tube formation, connecting planar cell polarity patterning to contraction of specific cell-cell junctions.     

Armor and anesthesia: exposure, feeling, and the soldier's body

For many civilians, the high-tech weapons, armor, and military medicine with which U.S. soldiers are equipped present an image of lethal capacity and physical invulnerability. But, as this article explores, soldiers themselves just as often associate the life-sustaining technology of modern warfare with feelings that range from a pragmatic ambivalence about exposure to harm all the way to profoundly unsettling vulnerability. This article, based on fieldwork among soldiers and military families at the U.S. Army's Ft. Hood, examines sensory and affective dimensions of soldiers' intimate bodily relationships with the technologies that alternately or even simultaneously keep them alive and expose them to harm. I argue that modern military discipline and technology conspire to cultivate soldiers as highly durable, capable, unfeeling, interchangeable bodies, or what might be called, after Susan Buck-Morss (1992), anesthetic subjects. But for soldiers themselves, their training, combat environment, protective gear, and weapons are a rich font of both emotional and bodily feeling that exists in complex tension with the also deeply felt military imperative to carry on in the face of extreme discomfort and danger.     

Age-related size invariance in perception of illusory and fragmented contours

We investigated invariant perception to sizes of images. Observers were secondary school students aged 7–17 years and adults. Two types of stimuli were used: fragmented line drawing of common objects and discs with deleted sectors which represented illusory Kanizsa contours, when discs were in particular positions. In experiments with fragmented images, we found an improvement in image recognition with observer’s age, increasing up to 13–14 years. The probability of recognition of fragmented line drawings increased significantly with decreasing stimulus size for children aged 7–12 years, indicating that size invariance at recognition for fragmented line drawings was absent in these children. However, size invariance was found for observers aged 7–12 years and for adults in this task. Upon the Kanizsa illusion appearance, the ratio of the separation between discs and disc diameter was smaller when we used larger disc diameters. This ratio increased with increasing age of observers. The obtained results provide evidence for the absence of size invariance when perceiving the Kanizsa illusion under our experimental conditions.     

Functional diversity of small-mammal postcrania is linked to both substrate preference and body size

Selective pressures favor morphologies that are adapted to distinct ecologies, resulting in trait partitioning among ecomorphotypes. However, the effects of these selective pressures vary across taxa, especially because morphology is also influenced by factors such as phylogeny, body size, and functional trade-offs. In this study, we examine how these factors impact functional diversification in mammals. It has been proposed that trait partitioning among mammalian ecomorphotypes is less pronounced at small body sizes due to biomechanical, energetic, and environmental factors that favor a “generalist” body plan, whereas larger taxa exhibit more substantial functional adaptations. We title this the Divergence Hypothesis (DH) because it predicts greater morphological divergence among ecomorphotypes at larger body sizes. We test DH by using phylogenetic comparative methods to examine the postcranial skeletons of 129 species of taxonomically diverse, small-to-medium-sized (<15 kg) mammals, which we categorize as either “tree-dwellers” or “ground-dwellers.” In some analyses, the morphologies of ground-dwellers and tree-dwellers suggest greater between-group differentiation at larger sizes, providing some evidence for DH. However, this trend is neither particularly strong nor supported by all analyses. Instead, a more pronounced pattern emerges that is distinct from the predictions of DH: within-group phenotypic disparity increases with body size in both ground-dwellers and tree-dwellers, driven by morphological outliers among “medium”-sized mammals. Thus, evolutionary increases in body size are more closely linked to increases in within-locomotor-group disparity than to increases in between-group disparity. We discuss biomechanical and ecological factors that may drive these evolutionary patterns, and we emphasize the significant evolutionary influences of ecology and body size on phenotypic diversity.     

Age related size invariance in perception of illusory and fragmented contours

We investigated invariant perception to sizes of images. Observers were schoolmates of 7-17 years and adults. Two types of stimuli were used: fragmented line drawing of common objects and discs with deleted sectors, which represented illusory Kanizsa contours when discs were in particular positions. In experiments with fragmented images, we found an improvement in image recognition with observers' age, increasing up to 13-14 years. The probability of recognition of fragmented line drawings increased significantly with decreasing stimulus size for children of 7-12 years, indicating that size invariance at recognition for fragmented line drawings was absent in these children. However, size invariance was found for observers of 13-17 years and for adults in this task. At Kanizsa illusion appearance, the ratio of the separation between discs and disc diameter was smaller when we used larger disc diameters. This ratio increased with increasing age of observers. Obtained results provide evidence for the absence of size invariance when perceiving the Kanizsa illusion in our experimental conditions.     

On being the right size: food-limited feedback on optimal body size

An insular population of white-tailed deer Odocoileus virginianus introduced in 1896 to predator-free Anticosti Island, Quebec, has caused long-term changes in the plant community. Food quality declined as did body weight. Although different parameters of reproduction changed, overall reproductive rates remained similar, thus maintaining deer density and promoting further change in habitat. These results show (i) long-term feedbacks on carrying capacity, (ii) the mechanism for reduction of body mass, and (iii) the lack of strong reduction in reproductive rates to regulate the population at high density, a feature of Eutherians. They are relevant to mechanisms determining the evolution of vertebrate body sizes.     

Shoaling in juvenile guppies: the effects of body size and shoal size

While factors affecting shoal mate choice have been examined extensively in adult guppies (Poecilia reticulata), few studies have focused on the shoaling behavior of juveniles. In this study, juvenile guppies were tested for their ability to shoal as well as their response to shoal mates of different body size and to shoals with different numbers of individuals. In dichotomous choice tests, 10-day-old guppies (mean body length=8.83 mm), 30-day-old guppies (13.17 mm) and 50-day-old guppies (18.6mm) were given the opportunity to swim near shoals of five fish or an empty chamber. In most cases, the juvenile fish demonstrated shoaling behavior, swimming near a group of fish rather than an empty chamber, regardless of the age of the stimulus shoal. When presented with two shoals, one of similar age and body size and one of dissimilar age and body size, only the 50-day-old guppies showed a significant preference for the age-matched shoal. Similarly, when choosing between a large shoal and a small shoal, only the 50-day-old guppies spent significantly more time near the larger shoal. Thus, while juveniles at each age shoaled, only 50-day-old fish demonstrated the shoal mate discrimination seen in adult fish.     

Associations of body mass index and waist:hip ratio with hypertension.

Canada Fitness Survey data for people aged 20 to 69 years were analysed by means of linear discriminant analysis to determine the effect of age, weight relative to height (body mass index) and weight distribution (waist:hip ratio) on hypertension (defined as diastolic blood pressure of 90 mm Hg or more) for both sexes separately. All three variables had independent effects on hypertension, but partial correlation coefficients indicated that the contribution of waist:hip ratio was secondary to that of body mass index. The association of measurements of body fat (five skinfold measurements) with hypertension was also examined; overall these measurements gave no advantage over the more simply measured body mass index. The results confirm the importance of assessing the predominant location of body fat and the body mass index when examining excess weight in relation to disease.     

Geographic body size gradients in tropical regions: water deficit and anuran body size in the Brazilian Cerrado

A recent interspecific study found Bergmann's size clines for Holarctic anurans and proposed an explanation based on heat balance to account for the pattern. However, this analysis was limited to cold temperate regions, and exploring the patterns in warmer tropical climates may reveal other factors that also influence anuran body size variation. We address this using a Cerrado anuran database. We examine the relationship between mean body size in a grid of 1° cells and environmental predictors and test the relative support for four hypotheses using an AIC-based model selection approach. Also, we considered three different amphibian phylogenies to partition the phylogenetic and specific components of the interspecific variation in body size using a method analogous to phylogenetic eigen vector regression (PVR). To consider the potential effects of spatial autocorrelation we use eigenvector-based spatial filters. We found the largest species inhabiting high water deficit areas in the northeast and the smallest in the wet southwest. Our results are consistent with the water availability hypothesis which, coupled with previous findings, suggests that the major determinant of interspecific body size variation in anurans switches from energy to water towards the equator. We propose that anuran body size gradients reflect effects of reduced surface to volume ratios in larger species to control both heat and water balance.     

Being Barbie: the size of one's own body determines the perceived size of the world

A classical question in philosophy and psychology is if the sense of one's body influences how one visually perceives the world. Several theoreticians have suggested that our own body serves as a fundamental reference in visual perception of sizes and distances, although compelling experimental evidence for this hypothesis is lacking. In contrast, modern textbooks typically explain the perception of object size and distance by the combination of information from different visual cues. Here, we describe full body illusions in which subjects experience the ownership of a doll's body (80 cm or 30 cm) and a giant's body (400 cm) and use these as tools to demonstrate that the size of one's sensed own body directly influences the perception of object size and distance. These effects were quantified in ten separate experiments with complementary verbal, questionnaire, manual, walking, and physiological measures. When participants experienced the tiny body as their own, they perceived objects to be larger and farther away, and when they experienced the large-body illusion, they perceived objects to be smaller and nearer. Importantly, despite identical retinal input, this "body size effect" was greater when the participants experienced a sense of ownership of the artificial bodies compared to a control condition in which ownership was disrupted. These findings are fundamentally important as they suggest a causal relationship between the representations of body space and external space. Thus, our own body size affects how we perceive the world.     

Brain size and the diversification of body size in birds

Large brains are associated with increased cognitive skills, enabling animals to use new environments and resources more successfully. Such behavioral flexibility is theoretically expected to have macroevolutionary consequences. First, populations of big-brained individuals should more easily become established in new locations, increasing opportunities for allopatric speciation and decreasing chances that the species as a whole becomes extinct. Second, the ability to use new resources should place new selection pressures on populations, promoting adaptive diversification, a process termed "behavioral drive." In this article, we show that the average brain size of a bird family explains a significant fraction (R2 =0.12, P < .0001 , N= 120 families) of the rate at which body size diversifies within the family. The association is independent of the number of species in the family, geographic range, and correlates of speciosity, providing the first general support for the importance of behavioral drive in evolution.     

Evolution of body size: an optimization model

The growth of individuals is often described by bioenergetic equations which partition assimilated energy into maintenance, growth, reproduction, and so on. Such energy flows vary with body size. The bioenergetic equations in this paper, under the assumptions that organisms will adopt behavior that channels a maximum amount of energy into the production of surviving progeny, produce a model optimizing growth and reproduction. Using the Weierstrass theorem, we show that a solution of the optimization problem exists. The problem is further solved analytically using the Pontryagin maximum principle. The main conclusion of the paper is that in a given environment an optimal body size exists, one which maximizes the energy channeled to the production of progeny. This body size depends on the mortality rate, the maximum life span, and the derivative of the growth equation with respect to body size. The biological results predicted from the model are compared with ecological data for zooplankton and vertebrate species, which support the conclusions obtained.     

Lifetime selection on adult body size and components of body size in a waterstrider: opposing selection and maintenance of sexual size dimorphism

Abstract.— Sexual size dimorphism (SSD), the difference in body size between males and females, is common in almost all taxa of animals and is generally assumed to be adaptive. Although sexual selection and fecundity selection alone have often been invoked to explain the evolution of SSD, more recent views indicate that the sexes must experience different lifetime selection pressures for SSD to evolve and be maintained. We estimated selection acting on male and female adult body size (total length) and components of body size in the waterstrider Aquarius remigis during three phases of life history. Opposing selection pressures for overall body size occurred in separate episodes of fitness for females in both years and for males in one year. Specific components of body size were often the targets of the selection on overall body size. When net adult fitness was estimated by combining each individual's fitnesses from all episodes, we found stabilizing selection in both sexes. In addition, the net optimum overall body size of males was smaller than that of females. However, even when components of body size had experienced opposing selection pressures in individual episodes, no components appeared to be under lifetime stabilizing selection. This is the first evidence that contemporary selection in a natural population acts to maintain female size larger than male size, the most common pattern of SSD in nature.     

Brain stimulation: feeling the buzz

A recent study demonstrates that artificially generated patterns of brain activity are surprisingly easy to sense. Brain areas that differ substantially in their functional specialization are remarkably similar in their ability to support this awareness.     

Evolution of genetically correlated traits: tooth size and body size in baboons

Within a population, only phenotypic variation that is influenced by genes will respond to selection. Genes with pleiotropic effects are known to influence numerous traits, complicating our understanding of their evolution through time. Here we use quantitative genetic analyses to identify and estimate the shared genetic effects between molar size and trunk length in a pedigreed, breeding population of baboons housed at the Southwest National Primate Research Center. While crown area has a genetic correlation with trunk length, specific linear measurements yield different results. We find that variation in molar buccolingual width and trunk length is influenced by overlapping additive genetic effects. In contrast, mesiodistal molar length appears to be genetically independent of body size. This is the first study to demonstrate a significant genetic correlation between tooth size and body size in primates. The evolutionary implications are discussed.     

Mammalian reproductive strategies: A generalized relation of litter size to body size

Summary A generalized relationship of litter size to mammalian body size was predicted by a graph model. The model was used to generate hypotheses explaining specific features of variation in gestation time, relative litter weight, birth weight, and reproductive capacity. The predictions were tested by means of data from the literature.Mammals were assumed to maximize neonatal survival of offspring to the limits allowed by litter weight per female body weight. Gestation time correlated negatively with the foetal growth rate of relative litter weight. Gestation time did not correlate with the foetal growth rate of individual offspring.Relative litter weight correlated negatively with adult body weight. This relationship was explained by the higher assimilation rate per unit weight relative to metabolic rate in small mammals.Birth weight correlated positively with body weight. However, small mammals produce larger offspring than predicted by the linear relationship of birth weight to body weight in large mammals. There is obviously a minimum birth weight which cannot be decreased without special arrangements for parental care.The prediction of the relationship of litter size to body size was derived from the relations of relative litter weight and birth weight to body weight. In small mammals (less than 1 kg) litter the correlation was negative. When litter size was compared with body length, the correlation was positive in small mammals (less than 30 cm) and negative in large mammals. In both sets of data there was a negative overall correlation between litter size and body size.Reproductive capacity, defined as the number of offspring per season, correlated negatively with life-span.