Individual Body Size Research Articles

How Should Adult Handgrip Strength Be Normalized? Allometry Reveals New Insights and Associated Reference Curves.

Handgrip strength (HGS) is an important indicator of health. Because HGS is strongly associated with body size, most investigators normalize HGS for some measure of body size as a more sensitive indicator of strength within a population. We aimed to 1) identify the optimal body size dimension to remove (normalize) HGS for differences in body size among adults and 2) generate norm-referenced centiles for HGS using the identified body size dimension. Data were from the National Health and Nutrition Examination Survey, a representative sample of the US noninstitutionalized civilian population. Exclusions resulted in a final sample of 8690 adults 20 yr and older. HGS was measured using handheld dynamometry. Body size dimensions included body mass, height, and waist circumference. The most appropriate dimension(s) associated with HGS is identified using allometry. We fitted centile curves for normalized HGS using the generalized additive model for location, scale, and shape. Findings suggest that neither body mass nor body mass index is appropriate to normalize HGS. Incorporating all three body size dimensions of body mass, height, and waist circumference, or the reduced subsets of body mass and height, or height alone, suggests that the most appropriate normalizing (body size) dimension associated with HGS should be a cross-sectional or surface area measure of an individual's body size (i.e., L2, where L is a linear dimension of body size). Given that height was also identified as the signally best body size dimension associated with HGS, we recommend HGS be normalized by height2 (i.e., HGS/HT2). Centile curves for HGS/HT2 by age group and gender were therefore provided. Scaling adult HGS by height2 may help normalize strength for population-based research.

Size variation in wild Bactrocera tryoni (Diptera: Tephritidae): only a small amount is related to the host fruit

AbstractBody size is an indicator of fitness in fruit flies (Diptera: Tephritidae), with larger males and females having increased mating success and egg production, respectively. Based on laboratory studies, the larval diet and its nutritional composition are considered the most important factors influencing juvenile growth and subsequent adult body size. However, a very limited literature is less clear on the importance of larval diet as an adult size modifier of wild fruit flies. Bactrocera tryoni (Froggatt) is a polyphagous species with larvae feeding within the fruit of over 200 plant species. To test the impact of larval host on adult size in wild individuals of this species, we collected naturally infested fruit from the field and then reared out adults in the laboratory. The wing length and dry body weight of emergent flies were measured. Linear mixed models were used to analyse the difference in size depending on fruit type, larval density, sex and their interactions. Separate measurements of body size, wing length and dry body weight were significantly influenced by the larval host fruit collected from the field. However, only 7% and 24% of the variation of the wing discal–medial cell length and dry body weight, respectively, could be explained by larval host fruit type with high individual body size variation both within and between host fruit types. Fruit protein content was positively correlated, and water content negatively correlated, to wing discal–medial cell length. Unexpectedly, the parameters of wing length and dry body weight were only weakly correlated with each other. The results support the large body of laboratory‐based fruit fly diet work, which identifies protein as a key component of the larval diet, but do not support a general assumption that larval host is the key driver of adult body size variation in wild frugivorous tephritids. Rather, and in agreement with a small number of laboratory‐based trials, the importance of larval diet to adult fitness appears to become less important as the larval feeding environment becomes more complex.

Seasonal variations in the life cycle and morphology of Anisops breddini (Hemiptera: Notonectidae)

ABSTRACT Studies on temperature-dependent phenology and morphology of insects facilitate examination of the consequences of temperature on their growth, development and population dynamics. The effects of seasonal changes on the life cycle and morphometry of Anisops breddini were studied by rearing eggs to adults under laboratory conditions during the wet and dry seasons. The average incubation period of eggs, developmental durations of instars I–V and total developmental time were significantly less at warm temperature (wet season) than in cold temperature (dry season). However, the hatching percentage was significantly higher at warm temperature than in cold temperature. Morphometric measurements of nymphs and adults were also significantly less at warm temperature than in cold temperature. Laboratory reared individuals during the wet season at warm temperature had faster development and produced smaller individuals as compared with the dry season. The developmental durations and body size of the experimental individuals were significantly negatively correlated with rearing temperature. The study further revealed that in warm temperature the developmental duration of the experimental individuals become shorter which in turn might increase the number of generations of this insect.

Climate-associated shifts in color and body size for a tropical bee pollinator

Habitat degradation and climatic changes are causing declines in bee populations, which in turn threaten wild plant reproductive success and the global food supply. We examined spatial and temporal variation in traits that may influence the way bees respond to environmental changes. For a color polymorphic species, we characterized proportions of three morphs and measured body size of individuals within sites of varying elevation over an 11-year sampling period. We found climate-associated variation in both color and body size, as well as temporal shifts in these traits that were associated with climatic conditions of sites. The proportion of bees that were red-orange increased relative to two other color morphs. Body size increased over time, and it increased more at drier sites. These results suggest that precipitation may be an important driver of trait shifts in tropical bees and motivate investigations of natural selection on color and body size due to differential climatic tolerances.

Altitudinal body size variation in Rana kukunoris: the effects of age and growth rate on the plateau brown frog from the eastern Tibetan Plateau

Body sizes in endothermic species tend to increase as temperature decreases in accordance with Bergmann’s rule. However, why do some species support Bergmann’s clines while others reverse it? This question should be solved by considering the relative contributions of mean age and growth rate on adult ectotherm body size. Here we studied altitudinal variation in mean body size, age, and growth rate in Rana kukunoris through 16 sites at different altitudes in the eastern Tibetan Plateau. Our results revealed that mean body size decreased as altitude increased in each sex, which fails to obey Bergmann’s rule, but supports the converse Bergmann’s rule. Frogs at lower altitudes tended to grow faster than individuals of the same species at higher altitudes. Conversely, age of adults did not significantly increase as altitude increased. Therefore, we suggest that lower growth rate limits the mean individual body size at the altitudes, explaining why this species follows the converse Bergmann’s rule. The effect of age cannot be ignored because decreasing body length with increasing altitudes is not significant when removing the effect of age.

Replacing native mammal assemblages with livestock in African savannahs, impacts dung beetle diversity and reduces body size

Replacement of complex assemblages of native mammal fauna with livestock species reduces niche heterogeneity. This negatively affects taxa such as dung beetles, which depend on them and can, in turn, affect ecosystem functioning. We assessed the response of dung beetle diversity, biomass and body condition to cattle-farming pressures in protected areas (PAs) and adjacent farms in the savannah biome of northern Namibia. We hypothesized that rich native mammal assemblages are essential to maintain dung beetle diversity and overall biomass. We further explored whether the low-quality dung resources on farms would lead to a decrease in individual body size for species found on both farms and PAs. Overall dung beetle richness increased with higher mammal richness but not relative abundance, demonstrating that a rich native vertebrate assemblage promotes dung beetle richness. Overall dung beetle biomass was lower on farms, but abundance showed no difference. Large-bodied dung specialist species, which are known to be functionally superior, were absent on farms while smaller generalist species proliferated. Furthermore, a large proportion of individuals of species common to both farms and PAs were physically smaller on farms, indicating reduced body condition. Our results show that a high diversity of native mammals maintains dung beetle diversity and higher biomass on PAs. A decrease in native dung on farms leads to reduced body mass, likely negatively impacting ecological function. These results suggest that the conservation of dung beetles and their functions in the expansive African savannah ecosystems is dependent on a complex mix of native mammal species.

Soil burrow characterization by 3D image analysis: Prediction of macroinvertebrate groups from biopore size distribution parameters

Although scientific literature focuses mainly on earthworms, all soil macroinvertebrates play an important role in modifying the architecture of the soil pore space and, in turn, in soil functions. Notwithstanding the fact that non-invasive technology, such as X-ray tomography, has long been used to differentiate non-biopores from biopores, it is still difficult to distinguish the specific contribution different macroinvertebrates make to the soil biopore system. Unlike the object-based image analysis approach, when applied to a soil pore system, mathematical morphology permits the user to obtain a very accurate pore size distribution consistent with the physical principle of water retention. The aim of this work was to evaluate the potential of the parameters of this kind of biopore size distribution to differentiate between the burrows of five different macroinvertebrate groups, namely Earthworms, Millipedes juliform, Centipedes, Campodeiform larvae and Elateriform larvae, inoculated into repacked soil mesocosms and incubated (14 days) in the field from where the soil animals were originally collected.A two-fold approach was proposed in this work so as to obtain parameters by both pore size population distributions and Weibull modelling of the cumulative distributions. Then a predictive discriminant analysis was performed on selected parameters by using macroinvertebrate groups as grouping variables and a very good prediction was obtained in both cases. The most useful parameters were the skewness and FFT indices in the first case and the shape parameter α of the Weibull model along with its RMSE in the second one. In addition, topological characterization was performed on gallery-shaped biopores. Vertical deviation was the only parameter that was independent of the individual body size and showed the statistically significant lowest value for the earthworms. The experiment and analyses performed in this work to explore the connection between macroinvertebrate groups and the corresponding biopore size distributions may represent a suitable methodological approach to performing a general investigation into the relationships between soil management and its impact on the system of soil macropores.

Social selection is density dependent but makes little contribution to total selection in New Zealand giraffe weevils.

Social selection occurs when traits of interaction partners influence an individual's fitness and can alter total selection strength. However, we have little idea of what factors influence social selection's strength. Further, social selection only contributes to overall selection when there is phenotypic assortment, but simultaneous estimates of social selection and phenotypic assortment are rare. Here, we estimated social selection on body size in a wild population of New Zealand giraffe weevils (Lasiorhynchus barbicornis). We measured phenotypic assortment by body size and tested whether social selection varied with sex ratio, density and interacted with the body size of the focal individual. Social selection was limited and unaffected by sex ratio or the size of the focal individual. However, at high densities social selection was negative for both sexes, consistent with size-based competitive interactions for access to mates. Phenotypic assortment was always close to zero, indicating negative social selection at high densities will not impede the evolution of larger body sizes. Despite its predicted importance, social selection may only influence evolutionary change in specific contexts, leaving direct selection to drive evolutionary change.

Long-term and seasonal changes in the life-history biology of the abyssal holothurian Pseudostichopus aemulatus from the Porcupine Abyssal Plain (North-East Atlantic)

Long-term interannual variations in the benthic community structure are well-known from abyssal plains in the North Atlantic and North Pacific, where rapid responses to changes in the environment by first-order opportunists modify overall species composition. To increase our knowledge of the long-term variations of deep-sea benthic communities in the North-East Atlantic, we studied the response of a second-order opportunist echinoderm, the holothurian Pseudostichopus aemulatus, before, during and after the “Amperima Event” – a four-year episode (1996–1999) where the first-order opportunistic holothurian, Amperima rosea, increased dramatically in density. We used a collection of 14 sampling times of deep-sea community assemblage over a sixteen-year period to understand the temporal variation (i.e., interannual and seasonal) in population structure (i.e., density and individual sizes) and reproduction (i.e., mean oocyte sizes, sex ratios, gonadal indices, and fecundity) in P. aemulatus. Samples were collected from the Porcupine Abyssal Plain (PAP) in the NE Atlantic Ocean at a depth of ca. 4850 m between 1989 and 2005 with a semi-balloon otter trawl (OTSB14) and an epibenthic sledge (BN1.5/C) at varying seasons. We measured individual body size, dissected organisms to prepare histological slides of their gonads, and measured the Feret oocyte diameter in females. We found changes in the life-history biology of P. aemulatus during the “Amperima Event”. Population density increased gradually from September 1997 until April 1999, when P. aemulatus reached a peak in density coinciding with the smallest mean body size observed (1998 and 1999) suggesting recruitment of juveniles. In 1997, before these changes in population structure, mean oocyte sizes were at their largest, suggesting a strong reproductive effort with individuals either preparing to spawn or spawning. This reproductive effort was minimal in the years after 1999, when we found the largest proportions of previtellogenic oocytes in individuals that were probably allocating their energy into growth rather than reproduction given their smaller size. The presence of gametes of all sizes across seasons and a broad range of individual sizes in various sampling times suggests no seasonal reproductive patterns. We suggest that feeding guild differences between various holothurian species explain the diverse life-history responses observed among holothurians competing for resources in a food-poor environment.

A Comparative Analysis of the Diets of a Genus of Freshwater Turtles across Africa

Pelusios (Testudines: Pleurodira) is an Afrotropical endemic genus of freshwater turtles that have adapted to a variety of habitats, with savannahs and forests being their two main habitat types. Although considered generally carnivorous, these turtles have rarely been subjected to detailed field surveys for determining their quantitative diet. In this paper, by using both the literature and original data, we analyze the diet of several Pelusios populations: three P. adansonii populations from South Sudan, one P. nanus from Zambia, seven P. castaneus from Nigeria, Benin and Togo, and four P. niger from Nigeria. All species were omnivorous but with a clear preponderance of the prey items being of animal origin (e.g., amphibians, fish, arthropods and annelids). Saturation curves revealed that the diet composition of all the surveyed populations was adequately assessed, and the diversity profiles indicated that all the populations were relatively similar in terms of overall dietary diversity. General Linear Models (GLM) showed a negative effect of vegetation cover on Anura adult consumption by turtles, and showed that the frequencies of Anura tadpoles, fish, reptiles and birds on Pelusios diets increased with the increase in vegetation cover. The GLM model also showed positive effects of individual body size on algae, Bivalvia, reptiles, birds and small mammal consumption by turtles, and underlined that the predation on Arachnida decreased with the increase in turtle body size. In all species, there were no significant intersexual dietary differences, whereas there were substantial ontogenetic dietary changes in three out of four species. Small-sized individuals of P. castaneus, P. niger and P. adansonii tended to feed mainly upon insects, with the adults also taking many fish and adult frogs, and in the case of P. niger, also birds and small mammals. Conversely, in P. nanus, the diet composition did not vary substantially from the juvenile to the adult age. All species appeared substantially generalist in terms of their diet composition, although the effects of season (wet versus dry) were not adequately assessed by our study.

Digit ratio in the common toad Bufo bufo: the effects of reduced fingers and of age dependency

IntroductionDespite the growing number of studies describing digit ratio patterns in tetrapods, knowledge concerning certain basic issues is still scarce. In lower vertebrates such as tailless amphibians (Anura), the numbering of individual fingers on the forelimbs and their homology with the fingers of other vertebrates pose an unsolved problem. Based on reviewed data on anuran limb development, we argue that the correct finger numbering scheme should be based on the assumption that the first finger, not the fifth finger, was reduced on the forelimbs. We analyzed the digit ratio in the common toad (Bufo bufo, Bufonidae), a species characterized by well-developed sexual dimorphism whereby females are larger than males, using both numbering schemes present in the literature.ResultsWe found that the digit ratio on hindlimbs differed significantly between the sexes only in the cases of left 2D:3D, with lower digit ratios in females, and of left 3D:4D, with lower digit ratios in males. We found that sex was the only significant variable for forelimbs, differentiating 2D:3D on the left forelimb, with lower digit ratios in females; 2D:4D on the right forelimb, with lower digit ratios in males; and 3D:4D on both forelimbs, with lower digit ratios in males. These results relate to variant II reflecting the hypothesis that the first digit was reduced during phylogenesis. There was no relationship between the body size (SVL) of individuals and any digit ratio, excluding 2D:4D on the right forelimbs in models with age variables. Additionally, for a subset of data where individual age was known, the models indicated that age was linked to significant differences in 2D:4D and 3D:4D on the left hindlimbs, while age, SVL, and sex influenced 2D:4D on the right forelimbs.ConclusionWe emphasize the importance of the problem of the correct numbering of forelimb digits in Anura and, under the assumption that it was the fifth digit that was reduced, argue that earlier results on digit ratio in this group should be interpreted with caution. The detected relationship between digit ratio and age in amphibians expands our knowledge, indicating that the age of individuals should be included in future digit ratio studies. This relationship may also apply to studies using digit ratio as a noninvasive indicator of endocrine disruption in amphibians.

Locomotion and righting behavior of sea stars: a study case on the bat star Asterina stellifera (Asterinidae)

Introduction: The locomotion behavior of an organism involves the integration of aspects like body symmetry, sensory and locomotor systems. Furthermore, various ecological factors seem to be related to locomotion characteristics, such as foraging strategy, migration trends, response to predators and competitors, and environmental stress. Objective: To analyze locomotion and the influence of body symmetry in the crawling and righting movements of the sea star Asterina stellifera. Methods: We carried out laboratory experiments in aquariums in the presence/absence of water current and on a horizontal and vertical surface. Results: The speed is similar to speed in other species of similar size. Both the speed and linearity of displacement were independent of individual body size. A water current leads to faster crawling and straight paths, but there is no rheotaxis: streams do not affect locomotion. Speed and linearity of displacement were independent of individual body size. The displacement pattern described here may be an adaptation of organisms that present dense populations in communities with high prey abundance, as is the case of A. stellifera. Conclusions: Like other asteroids, this species did not show an Anterior/Posterior plane of symmetry during locomotion, or righting movement: it does not tend to bilaterality.

Allometric scaling of faunal-mediated ecosystem functioning: A case study on two bioturbators in contrasting sediments

Soft-sediment biogeochemistry is influenced by the bioturbation activity of benthic invertebrates. We investigated whether the effect of two macrobenthos bioturbators, Limecola balthica and Hediste diversicolor, on sediment oxygen uptake can be described by allometric principles of metabolic activity scaling with animal body size and population biomass. Microcosms containing reconstructed populations to control density and individual body size were used to compare bioturbation effects and allometric scaling principles between a sandy and muddy sediment. Both species facilitated oxygen uptake in both sediment types, and a major portion of the variance in sediment metabolism (60–98%) could be explained by the per capita body size and density, and total population biomass. The allometric relationship with the stimulated sediment metabolism was similar in sand and mud for Hediste and strongly related to the increasing burrow ventilation rate with population biomass. Limecola irrigated less in mud but stimulated sediment metabolism more in mud in comparison to in sand. We discuss how physico-chemical differences between both sediment types, possible changes in activity, and size-dependent irrigation dynamics can explain the variable effects of Limecola on sediment metabolism. Overall, we provide empirical evidence that allometric laws can be used to upscale bioturbation effects on ecosystem functioning in marine soft sediments from the individual to the population level.

A new approach to assessing the space use behavior of macroinvertebrates by automated video tracking.

Individual space and resource use are central issues in ecology and conservation. Recent technological advances such as automated tracking techniques are boosting ecological research in this field. However, the development of a robust method to track space and resource use is still challenging for at least one important ecosystem component: motile aquatic macroinvertebrates. The challenges are mostly related to the small body size and rapid movement of many macroinvertebrate species and to light scattering and wave signal interference in aquatic habitats.We developed a video tracking method designed to reliably assess space use behavior among individual aquatic macroinvertebrates under laboratory (microcosm) conditions. The approach involves the use of experimental apparatus integrating a near infrared backlight source, a Plexiglas multi‐patch maze, multiple infrared cameras, and automated video analysis. It allows detection of the position of fast‐moving (~ 3 cm/s) and translucent individuals of small size (~ 5 mm in length, ~1 mg in dry weight) on simulated resource patches distributed over an experimental microcosm (0.08 m2).To illustrate the adequacy of the proposed method, we present a case study regarding the size dependency of space use behavior in the model organism Gammarus insensibilis, focusing on individual patch selection, giving‐up times, and cumulative space used.In the case study, primary data were collected on individual body size and individual locomotory behavior, for example, mean speed, acceleration, and step length. Individual entrance and departure times were recorded for each simulated resource patch in the experimental maze. Individual giving‐up times were found to be characterized by negative size dependency, with patch departure occurring sooner in larger individuals than smaller ones, and individual cumulative space used (treated as the overall surface area of resource patches that individuals visited) was found to scale positively with body size.This approach to studying space use behavior can deepen our understanding of species coexistence, yielding insights into mechanistic models on larger spatial scales, for example, home range, with implications for ecological and evolutionary processes, as well as for the management and conservation of populations and ecosystems. Despite being specifically developed for aquatic macroinvertebrates, this method can also be applied to other small aquatic organisms such as juvenile fish and amphibians.

Biogeographic position and body size jointly set lower thermal limits of wandering spiders.

Most species encounter large variations in abiotic conditions along their distribution range. The physiological responses of most terrestrial ectotherms (such as insects and spiders) to clinal gradients of climate, and in particular gradients of temperature, can be the product of both phenotypic plasticity and local adaptation. This study aimed to determine how the biogeographic position of populations and the body size of individuals set the limits of cold (freezing) resistance of Dolomedes fimbriatus. We compared D. fimbriatus to its sister species Dolomedes plantarius under harsher climatic conditions in their distribution range. Using an ad hoc design, we sampled individuals from four populations of Dolomedes fimbriatus originating from contrasting climatic areas (temperate and continental climate) and one population of the sister species D. plantarius from continental climate, and compared their supercooling ability as an indicator of cold resistance. Results for D. fimbriatus indicated that spiders from northern (continental) populations had higher cold resistance than spiders from southern (temperate) populations. Larger spiders had a lower supercooling ability in northern populations. The red‐listed and rarest D. plantarius was slightly less cold tolerant than the more common D. fimbriatus, and this might be of importance in a context of climate change that could imply colder overwintering habitats in the north due to reduced snow cover protection. The lowest cold resistance might put D. plantarius at risk of extinction in the future, and this should be considered in conservation plan.

Testing Equid Body Mass Estimate Equations on Modern Zebras—With Implications to Understanding the Relationship of Body Size, Diet, and Habitats of Equus in the Pleistocene of Europe

The monodactyl horses of the genusEquusoriginated in North America during the Pliocene, and from the beginning of the Pleistocene, they have been an essential part of the large ungulate communities of Europe, North America and Africa. Understanding how body size ofEquusspecies evolved and varied in relation to changes in environments and diet thus forms an important part of understanding the dynamics of ungulate body size variation in relation to Pleistocene paleoenvironmental changes. Here we test previously published body mass estimation equations for the family Equidae by investigating how accurately different skeletal and dental measurements estimate the mean body mass (and body mass range) reported for extant Grevy's zebra (Equus grevyi) and Burchell's zebra (Equus quagga). Based on these tests and information on how frequently skeletal elements occur in the fossil record, we construct a hierarchy of best practices for the selection of body mass estimation equations inEquus. As a case study, we explore body size variation in Pleistocene EuropeanEquuspaleopopulations in relation to diet and vegetation structure in their paleoenvironments. We show a relationship between diet and body size inEquus: very large-sized species tend to have more browse-dominated diets than small and medium-sized species, and paleovegetation proxies indicate on average more open and grass-rich paleoenvironments for small-sized, grazing species ofEquus. When more than one species ofEquusco-occur sympatrically, the larger species tend to be less abundant and have more browse-dominated diets than the smaller species. We suggest that body size variation in PleistoceneEquuswas driven by a combined effect of resource quality and availability, partitioning of habitats and resources between species, and the effect of environmental openness and group size on the body size of individuals.

Effects of habitat quality on body size of the litter dwelling scorpion Tityus pusillus in fragmented rainforests of Brazil

Understanding how individual body size is affected by habitat quality allows us to assess the consequences of habitat loss and fragmentation on the morphology of arthropods. In this study, we examined the effect of habitat quality (litter depth and dry mass, understory density, canopy openness, and diameter at breast height of trees) on the body size of the litter dwelling scorpion Tityus pusillus Pocock, 1893 in fragmented rainforests of Brazil. The study was performed during the dry season in 10 forest fragments, and scorpions were collected with the aid of ultraviolet light lamps. Females, but not males, responded to the environmental attributes measured. Litter dry mass was positively related to individual body size of T. pusillus. These results suggest scorpion body size is sensitive to habitat structure. Environmental characteristics determine specific ranges of body size in scorpion populations, wherein smaller individuals inhabit sites that have less litterfall.

Artificial propagation and larval breeding tests of the african sharptooth catfish, Clarias gariepinus conducted in captive conditions

The African catfish Clarias gariepinus is the second most cultured species in many African countries, including Senegal. Despite its economic importance in local aquaculture, artificial propagation of the species that would allow obtaining quality seed throughout the year has not yet been mastered adequately. This study aimed at producing C. gariepinus quality and mass supply seed to enhance local production. Three different types of incubation (Macdonald's bottle, water lettuce and wire mesh frame) were tested to identify the most efficient and accessible method for the producers at low cost and with a high hatching rate. The hatching rates obtained for the three different incubation methods were 26.9%, 10.0% and 6.3% for the Macdonald bottle (MB), wire frame (WF) and water lettuce (WL), respectively, while the corresponding survival rates were 91.6%, 70.4% and 77.8%.77.8%. The high hatching rate obtained with the MB could be due to the influence of permanent water circulation, which is absent in the other two hatching systems. The survival rates decreased 15 days after hatching and were 3.24%, 2.04% and 7.16%, respectively. The survival rates obtained three days after hatching were satisfactory, but the significant decrease at 15 days after hatching especially during the post- weaning phase seems to be due to the food quality, and unrelated to the hatching system. The daily individual growth, weight gain and body size of the larvae was significantly higher for larvae fed with natural food compared those that received artificial food. These results indicate that larvae preferred and fed the natural food which was permanently available in the rearing tanks. The artificial food deposited on the bottom of the tank changes appearance over time and may not be appreciated and efficiently consumed by the larvae, which may negatively impact their growth performance.

A dynamic model of the body gas stores for carbon dioxide, oxygen, and inert gases that incorporates circulatory transport delays to and from the lung.

Many models of the body’s gas stores have been generated for specific purposes. Here, we seek to produce a more general purpose model that: 1) is relevant for both respiratory (CO2 and O2) and inert gases; 2) is based firmly on anatomy and not arbitrary compartments; 3) can be scaled to individuals; and 4) incorporates arterial and venous circulatory delays as well as tissue volumes so that it can reflect rapid transients with greater precision. First, a “standard man” of 11 compartments was produced, based on data compiled by the International Radiation Protection Commission. Each compartment was supplied via its own parallel circulation, the arterial and venous volumes of which were based on reported tissue blood volumes together with data from a detailed anatomical model for the large arteries and veins. A previously published model was used for the blood gas chemistry of CO2 and O2. It was not permissible ethically to insert pulmonary artery catheters into healthy volunteers for model validation. Therefore, validation was undertaken by comparing model predictions with previously published data and by comparing model predictions with experimental data for transients in gas exchange at the mouth following changes in alveolar gas composition. Overall, model transients were fastest for O2, intermediate for CO2, and slowest for N2. There was good agreement between model estimates and experimentally measured data. Potential applications of the model include estimation of closed-loop gain for the ventilatory chemoreflexes and improving the precision associated with multibreath washout testing and respiratory measurement of cardiac output.NEW & NOTEWORTHY A model for the body gas stores has been generated that is applicable to both respiratory gases (CO2 and O2) and inert gases. It is based on anatomical details for organ volumes and blood contents together with anatomical details of the large arteries. It can be scaled to the body size and composition of different individuals. The model enables mixed venous gas compositions to be predicted from the systemic arterial compositions.

Natural diet of Macrobrachium brasiliense (Crustacea, Decapoda) in a Cerrado stream

ABSTRACT Knowledge about the diet of a given species is essential to provide information on the growth and maintenance of populations in a natural environment. Macrobrachium brasiliense (Heller, 1862) is a species of freshwater prawn widely distributed in Brazil, being frequent in aquatic environments inserted in the Cerrado biome. The aim of this study was to evaluate the natural diet of a population of M. brasiliense, comparing the consumed food items according to sex, seasonality and body size of individuals. Monthly collections were carried out between September 2018 and August 2019. The individuals collected had their sex identified and the length of the cephalothorax measured. Stomach content was assessed based on the degree of repletion, the method of points and the frequency of occurrence. There was a high frequency of plant material in the stomach contents and a smaller but significant frequency of aquatic insects. There were no significant differences regarding the diet of males and females and between the dry and rainy seasons. It was observed an increase in total insect consumption with the increase in size of males and females of M. brasiliense. A diet preference for Trichoptera was recorded in both sampling periods for males and females. The results obtained confirm an omnivorous diet for the species and suggest that the composition and proportion of items may vary depending on the size of the individuals and the availability of the items in the environment.