Relative Body Size Research Articles

Lizards perceived abiotic and biotic stressors independently when competing for shade in terrestrial mesocosms

Hormones such as glucocorticoids and androgens enable animals to respond adaptively to environmental stressors. For this reason, circulating glucocorticoids became a popular biomarker for estimating the quality of an environment, and circulating androgens are frequently used to indicate social dominance. Here, we show that access to thermal resources influence the hormones and behavior of male lizards (Sceloporus jarrovi). We exposed isolated and paired males to different thermal landscapes, ranging from one large patch of shade to sixteen smaller patches. Both the presence of a competitor and the patchiness of the thermal environment influenced hormone concentrations and movement patterns. When shade was concentrated in space, paired lizards competed more aggressively and circulated more corticosterone. Even without competitors, lizards circulated more corticosterone in landscapes with fewer patches of shade. Conversely, shifts in circulating testosterone depended only on the relative body size of a lizard; when paired, large males and small males circulated more and less testosterone, respectively. Furthermore, isolated males moved the farthest and covered the most area when shade was concentrated in a single patch, but paired males did the opposite. Because the total area of shade in each landscape was the same, these hormonal and behavioral responses of lizards reflect the ability to access shade. Thus, circulating glucocorticoids should reflect the thermal quality of an environment when researchers have controlled for other factors. Moreover, a theory of stress during thermoregulation would help ecologists anticipate physiological and behavioral responses to changing climates.

On the evolution of extreme structures: static scaling and the function of sexually selected signals

The ‘positive allometry hypothesis’ predicts that ornaments and weapons of sexual selection will scale steeply when among-individual variation in trait size is compared with variation in overall body size. Intuitive and striking, this idea has been explored in hundreds of contemporary animal species and sparked controversy in palaeobiology over the function of exaggerated structures in dinosaurs and other extinct lineages. Recently, however, challenges to this idea have raised questions regarding the validity of the hypothesis. We address this controversy in two ways. First, we suggest the positive allometry hypothesis be applied only to morphological traits that function as visual signals of individual body size. Second, because steep scaling slopes make traits better signals than other body parts, we propose that tests of the positive allometry hypothesis compare the steepness of the scaling relationships of focal, putative signal traits to those of other body parts in the same organism (rather than to an arbitrary slope of 1). We provide data for a suite of 29 extreme structures and show that steep scaling relationships are common when structures function as signals of relative body size, but not for comparably extreme structures that function in other contexts. We discuss these results in the context of animal signalling and sexual selection, and conclude that patterns of static scaling offer powerful insight into the evolution and function of disproportionately large, or extreme, animal structures. Finally, using data from a ceratopsid dinosaur and a pterosaur, we show that our revised test can be applied to fossil assemblages, making this an exciting and powerful method for gleaning insight into the function of structures in extinct taxa.

Body size structure of oribatid mite communities in different microhabitats

ABSTRACTSize scaling phenomena occur on different levels, from organisms to ecosystems. In predictive ecology, empirical data on body size relation have been used for decades to explain large-scale temporal and spatial patterns. More recently, community ecologists have started to use abundance-weighted mean body sizes as a tool to predict changes in species assemblages along gradients in above-ground systems. In soil and litter systems, however, body size of individuals or the body size structure of communities have rarely been addressed in this way. Here we use community data of oribatid mites from different forest ground microhabitats (dead wood, moss, and litter) in combination with body size measurements to describe some basic body-size relationships for decomposer mites. Generally, we found that the community body size (measured as an abundance-weighted mean of all species) as well as size distribution of sexual and parthenogenetic oribatids differed across microhabitats. Furthermore, our results showed that the abundance of oribatid mites in fragmented (moss), but not in continuous (dead wood, litter) microhabitats, can be predicted by the community body size. All these differences might be explained by specific microhabitat conditions like pore size and food resource quality, but also by the dominance and competitive or facultative interactions among certain species in a particular sample or habitat. Additionally, our results bring renewed attention to body size as an important predictor for patterns, structure, and energy translocation in terrestrial forest soil food webs.

Body size information in large-scale acoustic bat databases.

BackgroundCitizen monitoring programs using acoustic data have been useful for detecting population and community patterns. However, they have rarely been used to study broad scale patterns of species traits. We assessed the potential of acoustic data to detect broad scale patterns in body size. We compared geographical patterns in body size with acoustic signals in the bat species Pipistrellus pipistrellus. Given the correlation between body size and acoustic characteristics, we expected to see similar results when analyzing the relationships of body size and acoustic signals with climatic variables.MethodsWe assessed body size using forearm length measurements of 1,359 bats, captured by mist nets in France. For acoustic analyses, we used an extensive dataset collected through the French citizen bat survey. We isolated each bat echolocation call (n = 4,783) and performed automatic measures of signals, including the frequency of the flattest part of the calls (characteristic frequency). We then examined the relationship between forearm length, characteristic frequencies, and two components resulting from principal component analysis for geographic (latitude, longitude) and climatic variables.ResultsForearm length was positively correlated with higher precipitation, lower seasonality, and lower temperatures. Lower characteristic frequencies (i.e., larger body size) were mostly related to lower temperatures and northern latitudes. While conducted on different datasets, the two analyses provided congruent results.DiscussionAcoustic data from citizen science programs can thus be useful for the detection of large-scale patterns in body size. This first analysis offers a new perspective for the use of large acoustic databases to explore biological patterns and to address both theoretical and applied questions.

Childhood body size and midlife mammographic breast density in foreign-born and U.S.-born women in New York City

PurposeWe investigated whether childhood body size is associated with midlife mammographic density, a strong risk factor for breast cancer. MethodsWe collected interview data, including body size at age 10 years using a pictogram, and measured height and weight from 518 women, recruited at the time of screening mammography in New York City (ages 40–64 years, 71% Hispanic, 68% foreign-born). We used linear regression models to examine childhood body size in relation to percent density and areas of dense and nondense tissue, measured using a computer-assisted method from digital mammograms. ResultsIn models that adjusted for race/ethnicity, and age and body mass index at mammogram, the heaviest relative to leanest childhood body size was associated with 5.94% lower percent density (95% confidence interval [CI]: −9.20, −2.29), 7.69 cm2 smaller dense area (95% CI: −13.94, −0.63), and 26.17 cm2 larger nondense area (95% CI: 9.42, 43.58). In stratified analysis by menopausal status and nativity, the observed associations were stronger for postmenopausal and U.S.-born women although these differences did not reach statistical significance. ConclusionsHeavy childhood body size is associated with lower mammographic density, consistent with its associations with breast cancer risk. Suggestive findings by nativity require confirmation in larger samples.

Decomposing the effects of ocean environments on predator-prey body-size relationships in food webs.

Body-size relationships between predators and their prey are important in ecological studies because they reflect the structure and function of food webs. Inspired by studies on the impact of global warming on food webs, the effects of temperature on body-size relationships have been widely investigated; however, the impact of environmental factors on body-size relationships has not been fully evaluated because climate warming affects various ocean environments. Thus, here, we comprehensively investigated the effects of ocean environments and predator–prey body-size relationships by integrating a large-scale dataset of predator–prey body-size relationships in marine food webs with global oceanographic data. We showed that various oceanographic parameters influence prey size selection. In particular, oxygen concentration, primary production and salinity, in addition to temperature, significantly alter body-size relationships. Furthermore, we demonstrated that variability (seasonality) of ocean environments significantly affects body-size relationships. The effects of ocean environments on body-size relationships were generally remarkable for small body sizes, but were also significant for large body sizes and were relatively weak for intermediate body sizes, in the cases of temperature seasonality, oxygen concentration and salinity variability. These findings break down the complex effects of ocean environments on body-size relationships, advancing our understanding of how ocean environments influence the structure and functioning of food webs.

Grazing and resource availability control soil nematode body size and abundance-mass relationship in semi-arid grassland.

Body size is a central functional trait in ecological communities. Despite recognition of the importance of above ground-below ground interactions, effects of above-ground herbivores on size and abundance-size relationships in soil fauna are almost uncharted. Depending on climate and soil properties, herbivores may increase basal resources of soil food webs, or reduce pore space, mechanisms expected to have contrasting effects on soil animal body size. We investigated how body size and shape of soil nematodes responded to mammalian grazers in three semi-arid grassland sites, along a gradient of soil texture and organic matter (OM) in a long-term herbivore removal study. We analysed nematode mass, length, diameter, body size distribution and biomass distribution. We formulated two mechanistic hypotheses to assess whether resource availability or pore space was the dominant abiotic control and modulated the effects of grazing. In ungrazed soils, average and maximum nematode size, as well as abundance and biomass of large nematodes, were greater in the high-OM than in the low-OM soil, and intermediate in the medium-OM soil. Grazing promoted larger sizes in the low-OM soil, where it had been shown to increase OM and microbial biomass, and led to more homogeneous average size and body size distribution across sites. The results support the hypothesis that nematode size was controlled by basal resource availability rather than by pore space. However, body shape might have been constrained by small pores in the fine-texture, high-OM soil, where nematodes were more elongated. Grazing may facilitate larger sizes in soil nematode communities by boosting basal resources where these are limiting, with important implications for estimations of nematode biomass and contribution to carbon and nutrient cycling. These findings contribute to the insofar-limited mechanistic understanding of how herbivores can shape functional traits of soil fauna and demonstrate that animals at one trophic level may control patterns in body size and abundance-size relationships in other trophic levels without a direct predator prey or competitive linkage between them.

Resource limitation alters effects of phenological shifts on inter-specific competition.

Phenological shifts can alter the relative arrival time of competing species in natural communities, but predicting the consequences for species interactions and community dynamics is a major challenge. Here we show that differences in relative arrival time can lead to predictable priority effects that alter the outcome of competitive interactions. By experimentally manipulating the relative arrival time of two competing tadpole species across a resource gradient, we found that delaying relative arrival of a species reduced the interaction asymmetry between species and could even reverse competitive dominance. However, the strength of these priority effects was contingent on the abundance of the shared resource. Priority effects were generally weak when resources were limited, but increased at higher resource levels. Importantly, this context dependency could be explained by a shift in per capita interaction strength driven by a shift in relative body sizes of competitors. These results shed new light into the mechanisms that drive variation in priority effects and help predict consequences of phenological shifts across different environments.

Interacting effects of predation risk and resource level on escape speed of amphibian larvae along a latitudinal gradient.

Fast-growing genotypes living in time-constrained environments are often more prone to predation, suggesting that growth-predation risk trade-offs are important factors maintaining variation in growth along climatic gradients. However, the mechanisms underlying how fast growth increases predation-mediated mortality are not well understood. Here, we investigated if slow-growing, low-latitude individuals have faster escape swimming speed than fast-growing high-latitude individuals using common frog (Rana temporaria) tadpoles from eight populations collected along a 1500km latitudinal gradient. We measured escape speed in terms of burst and endurance speeds in tadpoles raised in the laboratory at two food levels and in the presence and absence of a predator (Aeshna dragonfly larvae). We did not find any latitudinal trend in escape speed performance. In low food treatments, burst speed was higher in tadpoles reared with predators but did not differ between high-food treatments. Endurance speed, on the contrary, was lower in high-food tadpoles reared with predators and did not differ between treatments at low food levels. Tadpoles reared with predators showed inducible morphology (increased relative body size and tail depth), which had positive effects on speed endurance at low but not at high food levels. Burst speed was positively affected by tail length and tail muscle size in the absence of predators. Our results suggest that escape speed does not trade-off with fast growth along the latitudinal gradient in R.temporaria tadpoles. Instead, escape speed is a plastic trait and strongly influenced by the interaction between resource level and predation risk.

Dosing for Fentanyl Infusion in Obese Children: Just Because It's What We Have Always Done Doesn't Mean It Is Right.

Dosing for Fentanyl Infusion in Obese Children: Just Because It's What We Have Always Done Doesn't Mean It Is Right.

Trait overdispersion and the role of sociality in the assembly of social spider communities across the Americas

Among the factors that may lead to differences in resource use among closely related species, body size and morphology have been traditionally considered to play a role in community assembly. Here we argue that for animals that live and forage in groups, level of sociality, reflecting differences in group size and cooperative tendencies, can be an additional and powerful dimension separating species in niche space. We compare 50+ communities of the social spider genus Anelosimus across the Americas against a null model that accounts for known effects of biotic and abiotic factors on the distribution of social systems in the genus. We show that these communities are more overdispersed than expected by chance in either or both body size and level of sociality, traits we have previously shown to be associated with differences in resource utilization (prey size, microhabitat, and phenology). We further show that the contribution of sociality to differences in the size of the prey captured is two to three times greater than that of body size, suggesting that changes in group size and cooperative tendencies may be more effective than changes in body size at separating species in niche space.

The Obesity Paradox in Cancer: How Important Is Muscle?

Although higher body mass index (BMI) increases the incidence of many cancers, BMI can also exhibit a null or U-shaped relationship with survival among patients with existing disease; this association of higher BMI with improved survival is termed the obesity paradox. This review discusses possible explanations for the obesity paradox, the prevalence and consequences of low muscle mass in cancer patients, and future research directions. It is unlikely that methodological biases, such as reverse causality or confounding, fully explain the obesity paradox. Rather, up to a point, higher BMI may truly be associated with longer survival in cancer patients. This is due, in part, to the limitations of BMI, which scales weight to height without delineating adipose tissue distribution or distinguishing between adipose and muscle tissue. Thus, cancer patients with higher BMIs often have higher levels of protective muscle. We assert that more precise measures of body composition are required to clarify the relationship of body size to cancer outcomes, inform clinical decision-making, and help tailor lifestyle interventions.

Interspecific geographic range size-body size relationship and the diversification dynamics of Neotropical furnariid birds

Among the earliest macroecological patterns documented, is the range and body size relationship, characterized by a minimum geographic range size imposed by the species' body size. This boundary for the geographic range size increases linearly with body size and has been proposed to have implications in lineages evolution and conservation. Nevertheless, the macroevolutionary processes involved in the origin of this boundary and its consequences on lineage diversification have been poorly explored. We evaluate the macroevolutionary consequences of the difference (hereafter the distance) between the observed and the minimum range sizes required by the species' body size, to untangle its role on the diversification of a Neotropical species-rich bird clade using trait-dependent diversification models. We show that speciation rate is a positive hump-shaped function of the distance to the lower boundary. The species with highest and lowest distances to minimum range size had lower speciation rates, while species close to medium distances values had the highest speciation rates. Further, our results suggest that the distance to the minimum range size is a macroevolutionary constraint that affects the diversification process responsible for the origin of this macroecological pattern in a more complex way than previously envisioned.

The relationship of age, activity, and body size on osteoarthritis in weight-bearing skeletal regions

This study examined the simultaneous impact of multiple underlying factors on OA expression in weight-bearing joints of the vertebrae and lower limb of a modern European skeletal sample (Lisbon and Sassari). OA was evaluated using standard ranked categorical scoring; composite OA scores derived through principal component analysis. Body size was calculated from postcranial measurements; torsional strength (J) of the femoral midshaft was calculated from three-dimensional surface models, size standardized and used as a proxy for activity. A standard multiple regression was applied.In all regions, the linear combination of age, body mass, stature, and J was significantly related to differences in OA. Across all joints, age was the strongest predictor; neither body size, nor activity variables demonstrated a statistical relationship with OA at the lumbar or knee; J demonstrated a negative correlation with pelvic OA.Variation in OA can be explained by age, stature, body mass, and structural adaptation related to habitual use. The negative correlation between femoral torsional strength with OA suggests that long-term, repetitive physical work capacity in childhood may be protective against OA development later in life. The multifactorial aetiology of OA requires incorporating multiple lines of evidence to interpret individual or population health from bone samples.

Bison body size and climate change.

The relationship between body size and temperature of mammals is poorly resolved, especially for large keystone species such as bison (Bison bison). Bison are well represented in the fossil record across North America, which provides an opportunity to relate body size to climate within a species. We measured the length of a leg bone (calcaneal tuber, DstL) in 849 specimens from 60 localities that were dated by stratigraphy and 14C decay. We estimated body mass (M) as M = (DstL/11.49)3. Average annual temperature was estimated from δ18O values in the ice cores from Greenland. Calcaneal tuber length of Bison declined over the last 40,000 years, that is, average body mass was 37% larger (910 ± 50 kg) than today (665 ± 21 kg). Average annual temperature has warmed by 6°C since the Last Glacial Maximum (~24–18 kya) and is predicted to further increase by 4°C by the end of the 21st century. If body size continues to linearly respond to global temperature, Bison body mass will likely decline by an additional 46%, to 357 ± 54 kg, with an increase of 4°C globally. The rate of mass loss is 41 ± 10 kg per°C increase in global temperature. Changes in body size of Bison may be a result of migration, disease, or human harvest but those effects are likely to be local and short‐term and not likely to persist over the long time scale of the fossil record. The strong correspondence between body size of bison and air temperature is more likely the result of persistent effects on the ability to grow and the consequences of sustaining a large body mass in a warming environment. Continuing rises in global temperature will likely depress body sizes of bison, and perhaps other large grazers, without human intervention.

The role of mobile consumers in lake nutrient cycles: a brief review

We summarise current understanding of consumer recycling in lake nutrient cycles and expand on it by integrating emerging knowledge from food web ecology. The role of consumer nutrient recycling (CNR) is initially framed in the wider context of lake nutrient cycling, which includes hydrodynamic and biogeochemical processes, and their responses to global environmental change. Case studies are used to demonstrate that effects of CNR on lake ecosystems range widely, from reduced nutrient cycling rates to exacerbation of eutrophication. CNR depends on consumer biomass, body size and diet, remaining relatively consistent through the year and becoming important as other fluxes seasonally ebb. Universal patterns in food web structure, for example, consumer–resource biomass ratios, body size scaling and relationships between trophic level and diet breadth, are used to demonstrate the predictability of CNR effects. Larger, mobile, top predators excrete nutrients at a lower rate but over a wider range, linking nutrient cycles across habitats. Smaller-bodied, lower trophic level consumers have strong localised nutrient cycling effects associated with their limited mobility. Global environmental-change drivers that alter food web structure are likely to have the greatest impact on CNR rates and should direct future studies.

Early development and diets of non‐native juvenile Chinook Salmon (Oncorhynchus tshawytscha) in an invaded river of Patagonia, southern South America

AbstractChinook salmon (Oncorhynchus tshawytscha) have established populations in both the Atlantic and Pacific basins of southern South America. Yet, basic biological information about these salmon population is absent. Here, we documented relative densities, body size, condition and diet composition of juvenile Chinook Salmon from the Futaleufú River, Argentina. We sampled Chinook Salmon juvenile and environmental variables including daily river discharge, water temperature, electrical conductance, dissolved oxygen and total dissolved solids. We assessed individual variation in the diet of juvenile salmon over time. We estimated the incubation time before fry emergence to be around 101 days under a mean water temperature of 7.5°C. Salmon fry emerged during the Austral Winter (July‐August) in off‐channel habitats near the redds. Juvenile salmon were between 3.8 and 12.1 cm in length (TL) and their highest body condition occurred early during the Austral summer (December). Juvenile salmon abundances were positively associated with water temperature, but not flow. Diet analyses revealed a specialist feeding behaviour based on food pulses that included both aquatic and terrestrial insects; piscivory was not detected. Juvenile salmon co‐occurred with native fishes suggesting a potential for interspecific interference. Our findings provide baseline information for the future management of non‐native Chinook Salmon populations in the Southern Hemisphere and elsewhere.

The Fat Leading the Thin: Relative Body Size, Physical Activity Identification, and Behavioral Problems

Though sport and physical activity participation are key elements of a healthy lifestyle, anti-fat biases serve as barriers to active living, leaving a large population segment underserved. This stigma also creates thin body standards for people working in sport and physical activity, including instructors. In this study, the authors conducted an experiment to explore how instructor and participant body size interact to influence activity identification and subsequent intentions to be physically active. Results indicate that larger-bodied participants were more identified when working with a larger instructor. For thinner participants, there were no significant differences in identification related to instructor body size. Identification was positively related to future intentions in the activity. Implications for practice are discussed. Subscribe to JASM

Climatic factors shape plastic trade‐offs in the polyphenic black scavenger fly Sepsis thoracica (Diptera: Sepsidae)

AbstractAimTrade‐offs allow individuals to optimize their fitness by tailoring the investment into different traits to variable environmental conditions, such as along geographical gradients. Trade‐offs thus can help in adjusting to changing thermal and insolation profiles, especially in small ectotherms, whose body temperature typically follows environmental temperatures closely. Two traits usually involved in latitudinal adaptation are body size and melanism. Since both traits are costly, individuals need to optimize investment into each trait. Here, we studied how environmental factors influence this trade‐off in the short and long‐term.LocationEurope.MethodsWe raised flies from 15 latitudinal populations at three constant temperatures in a laboratory common garden to differentiate plastic and evolutionary responses to temperature. We further analysed how the different insolation components of the populations’ habitats influenced the evolution of the trade‐off.ResultsMale Sepsis thoracica (Diptera: Sepsidae) feature a sigmoid relationship between melanism and body size, defining two strikingly different male morphs: obsidian (small and black) and amber (large and orange). This relationship was altered by the developmental temperature, documenting its plasticity. The relationship further evolved across populations in response to the environmental characteristics of their habitat, notably temperature, insolation and UV radiation, suggesting that plasticity also has an underlying genetic basis. Nevertheless, melanism, but not body size, merely slightly increased with latitude.Main conclusionsAs the plastic and evolutionary responses of the relationship to temperature differed, plasticity does not necessarily follow the direction of evolution of this trade‐off, but rather adds to it. Our study evinces the role of several environmental factors in shaping the evolution of a plastic melanism—body size relationship defining a rare male polymorphism in temperate sepsid flies.

Allometric considerations when assessing aortic aneurysms in Turner syndrome: Implications for activity recommendations and medical decision-making.

In Turner syndrome, the potential to form thoracic aortic aneurysms requires routine patient monitoring. However, the short stature that typically occurs complicates the assessment of severity and risk because the relationship of body size to aortic dimensions is different in Turner syndrome compared to the general population. Three allometric formula have been proposed to adjust aortic dimensions, all employing body surface area: aortic size index, Turner syndrome-specific Z-scores, and Z-scores based on a general pediatric and young adult population. In order to understand the differences between these formula we evaluated the relationship between age and aortic size index and compared Turner syndrome-specific Z-scores and pediatric/young adult based Z-scores in a group of girls and women with Turner syndrome. Our results suggest that the aortic size index is highly age-dependent for those under 15 years; and that Turner-specific Z-scores are significantly lower than Z-scores referenced to the general population. Higher Z-scores derived from the general reference population could result in stigmatization, inappropriate restriction from sports, and increasing the risk of unneeded medical or operative treatments. We propose that when estimating aortic dissection risk clinicians use Turner syndrome-specific Z-score for those under fifteen years of age.