Oxygen toxicity is not related to mammalian body size

1. Small mammals have been used to study the effects of O2 toxicity. The aim of the present study was to investigate whether body size should be considered when applying the results of these studies to man. 2. Oxygen toxicity is enhanced as perfusion and metabolism increase: specific animal tissues of high perfusion are more susceptible to O2 toxicity. Exercise, high metabolic rate, and increased brain blood flow enhance O2 toxicity. 3. Increased specific O2 consumption and perfusion as body mass decreases may enhance O2 toxicity in small mammals. 4. Survival time in normobaric hyperoxia (1 atm O2) and the time to first appearance of convulsions in hyperbaric oxygen (4-5 atm) were collected from the literature and showed no relation to body size. 5. Known difference in antioxidant enzyme activity cannot explain the findings. 6. Independence of tissue PO2 on body size, or equal rates of free radical formation and degradation, are suggested as possible mechanisms. 7. Small mammals can serve as a good model for O2 toxicity in man.     

Predators as drivers of insect defenses

Insects have evolved various types of antipredator defenses. For example, many insects have evolved crypsis, and exhibit cryptic body colors and shapes for hiding from predators. Other insects produce toxins as a form of chemical defense against predators, and some toxic insects are aposematic, with conspicuous body colors for advertising their toxins. Insects can also develop hairs, spines or hard exoskeletons as morphological defenses to protect themselves from predation. In addition, insects can evolve behavioral defenses, in which insects exhibit autotomy or dropping, or feign death. This study investigated which predator types evoke these types of defenses, through a review of the effectiveness of antipredator defenses in insects against carnivorous animals that are commonly used as model predators in studies. These predators include other insects, spiders, fish, frogs, lizards, birds and mammals. The results provide the first step for clarifying the evolutionary drivers of antipredator defenses in insects. The following aspects should be considered for future studies: multiple predator species and sufficient replication, alternative prey and predator models, and tolerance to predators in insects.     

DEGREE OF SPECIALIZATION IS RELATED TO BODY SIZE IN HERBIVOROUS INSECTS: A PHYLOGENETIC CONFIRMATION

Numerous studies have suggested a general relationship between the degree of host specialization and body size in herbivorous animals. In insects, smaller species are usually shown to be more specialized than larger‐bodied ones. Various hypotheses have attempted to explain this pattern but rigorous proof of the body size–diet breadth relationship has been lacking, primarily because the scarceness of reliable phylogenetic information has precluded formal comparative analyses. Explicitly using phylogenetic information for a group of herbivores (geometrid moths) and their host plant range, we perform a comparative analysis to study the body size–diet breadth relationship. Considering several alternative measures of body size and diet breadth, our results convincingly demonstrate without previous methodological issues—a first for any taxon—a positive association between these traits, which has implications for evaluating various central aspects of the evolutionary ecology of herbivorous insects. We additionally demonstrate how the methods used in this study can be applied in assessing hypotheses to explain the body size–diet breadth relationship. By analyzing the relationship in tree‐feeders alone and finding that the positive relationship remains, the result suggests that the body size–diet breadth relationship is not solely driven by the type of host plant that species feed on.     

The applicability of metapopulation theory to large mammals

Metapopulation theory has become a common framework in conservation biology and it is sometimes suggested that a metapopulation approach should be used for management of large mammals. However, it has also been suggested that metapopulation theory would not be applicable to species with long generations compared to those with short ones. In this paper, we review how and on what empirical ground metapopulation terminology has been applied to insects, small mammals and large mammals. The review showed that the metapopulation term sometimes was used for population networks which only fulfilled the broadest possible definition of a metapopulation, i.e. they were subpopulations connected by migrating individuals. We argue that the metapopulation concept should be reserved for networks that also show some kind of metapopulation dynamics. Otherwise it applies to almost all populations and loses its substance. We found much empirical support for metapopulation dynamics in both insects and small mammals, but not in large mammals. A possible reason is the methods used to confirm the existence of metapopulation dynamics. For insects and small mammals, the common approach is to study population turnover through patch occupancy data. Such data is difficult to obtain for large mammals, since longer temporal scales need to be covered to record extinctions and colonizations. Still, many populations of large mammals are exposed to habitat fragmentation and the resulting subpopulations sometimes have high risks of extinction. If there is migration between the subpopulations, the metapopulation framework could provide valuable information on their population dynamics. We suggest that a metapopulation approach can be interesting for populations of large mammals, when there are discrete breeding subpopulations and when these subpopulations have different growth rates and demographic fates. Thus, a comparison of the subpopulations’ demographic fates, rather than subpopulation turnover, can be a feasible alternative for studies of metapopulation dynamics in large mammals.     

Experimental manipulation of yolk testosterone affects digit length ratios in the ring-necked pheasant (Phasianus colchicus)

In humans, most of the mammals and one bird species studied so far, the relative length of individual digits is sexually dimorphic. Most studies of humans have been concerned with the ratio between second (2D) and fourth digits (4D), whereas some studies of humans and other mammals have also investigated other digit ratios. Inter- and intra-sexual variation in 2D:4D may depend on differential exposure to androgens during embryonic life, and the genetic mechanisms linking 2D:4D to androgens may be mediated by Hox genes. Because Hox genes are conserved in vertebrates, similar patterns of variation in digit ratios might be expected across vertebrate classes. The observation of correlations between digit ratios and physiological, psychological and performance traits in humans has generated interest in exploring the possibility that digit ratios are a marker of embryonic exposure to androgens, which have diverse consequences on several phenotypic traits. However, the hypothesis that digit ratios depend on androgen effects during development has never been tested experimentally. In this study, we increased testosterone concentration in ring-necked pheasant eggs and measured length ratios between the second, third and fourth digits of both feet in fully grown offspring. Females from testosterone-injected eggs had larger 2D:3D in the left foot, whereas this was not the case in males. The other digit ratios were unaffected by hormone treatment in both sexes. However, digit ratios showed no sexual dimorphism among controls. Thus, present results are consistent with the hypothesis that variation in testosterone levels during development affects digit ratios.     

A combined morphometric analysis of foot form and its association with sex,stature, and body mass

Objectives: Morphometric analysis of footprints is a classic means for orthopedic diagnosis. In forensics and physical anthropology, it is commonly used for the estimation of stature and body mass. We studied individual variation and sexual dimorphism of foot dimensions and footprint shape by a combination of classic foot measurements and geometric morphometric methods. Methods: Left and right feet of 134 healthy adult males and females were scanned twice with a 3D optical laser scanner, and stature as well as body mass were recorded. Foot length and width were measured on the 3D scans. The 2D footprints were extracted as the plantar‐most 2 mm of the 3D scans and measured with 85 landmarks and semilandmarks. Results: Both foot size and footprint shape are sexually dimorphic and relate to stature and body mass. While dimorphism in foot length largely results from dimorphism in stature, dimorphism in footprint shape partly owes to the dimorphism in BMI. Stature could be estimated well based on foot length (R² = 0.76), whereas body mass was more closely related to foot width (R² = 0.62). Sex could be estimated correctly for 95% of the individuals based on a combination of foot width and length. Discussion: Geometric morphometrics proved to be an effective tool for the detailed analysis of footprint shape. However, for the estimation of stature, body mass, and sex, shape variables did not considerably improve estimates based on foot length and width. Am J Phys Anthropol 157:582–591, 2015. © 2015 Wiley Periodicals, Inc.     

Nonplantigrade Foot Posture: A Constraint on Dinosaur Body Size

Dinosaurs had functionally digitigrade or sub-unguligrade foot postures. With their immediate ancestors, dinosaurs were the only terrestrial nonplantigrades during the Mesozoic. Extant terrestrial mammals have different optimal body sizes according to their foot posture (plantigrade, digitigrade, and unguligrade), yet the relationship of nonplantigrade foot posture with dinosaur body size has never been investigated, even though the body size of dinosaurs has been studied intensively. According to a large dataset presented in this study, the body sizes of all nonplantigrades (including nonvolant dinosaurs, nonvolant terrestrial birds, extant mammals, and extinct Nearctic mammals) are above 500 g, except for macroscelid mammals (i.e., elephant shrew), a few alvarezsauroid dinosaurs, and nondinosaur ornithodirans (i.e., the immediate ancestors of dinosaurs). When nonplantigrade tetrapods evolved from plantigrade ancestors, lineages with nonplantigrade foot posture exhibited a steady increase in body size following Cope’s rule. In contrast, contemporaneous plantigrade lineages exhibited no trend in body size evolution and were largely constrained to small body sizes. This evolutionary pattern of body size specific to foot posture occurred repeatedly during both the Mesozoic and the Cenozoic eras. Although disturbed by the end-Cretaceous extinction, species of mid to large body size have predominantly been nonplantigrade animals from the Jurassic until the present; conversely, species with small body size have been exclusively composed of plantigrades in the nonvolant terrestrial tetrapod fauna.     

Effects of body size and temperature on population growth

For at least 200 years, since the time of Malthus, population growth has been recognized as providing a critical link between the performance of individual organisms and the ecology and evolution of species. We present a theory that shows how the intrinsic rate of exponential population growth, rmax, and the carrying capacity, K, depend on individual metabolic rate and resource supply rate. To do this, we construct equations for the metabolic rates of entire populations by summing over individuals, and then we combine these population-level equations with Malthusian growth. Thus, the theory makes explicit the relationship between rates of resource supply in the environment and rates of production of new biomass and individuals. These individual-level and population-level processes are inextricably linked because metabolism sets both the demand for environmental resources and the resource allocation to survival, growth, and reproduction. We use the theory to make explicit how and why rmax exhibits its characteristic dependence on body size and temperature. Data for aerobic eukaryotes, including algae, protists, insects, zooplankton, fishes, and mammals, support these predicted scalings for rmax. The metabolic flux of energy and materials also dictates that the carrying capacity or equilibrium density of populations should decrease with increasing body size and increasing temperature. Finally, we argue that body mass and body temperature, through their effects on metabolic rate, can explain most of the variation in fecundity and mortality rates. Data for marine fishes in the field support these predictions for instantaneous rates of mortality. This theory links the rates of metabolism and resource use of individuals to life-history attributes and population dynamics for a broad assortment of organisms, from unicellular organisms to mammals.     

miRNAs

The evolution of complex animals such as insects and mammals is achieved with surprisingly few additions in protein coding genes. MicroRNAs (miRNAs), a class of non-coding RNAs, have emerged as important regulators of organogenesis in insects, fish and mammals. The microRNA repertoire of animals has expanded significantly during evolution especially in vertebrates, insects and nematodes, accompanying the appearance of complex body plans. MicroRNAs therefore have gained enormous interest in recent years. They are now regarded as key modulators of gene expression in many tissues during embryogenesis, in adult organisms and in disease processes. Therefore, these small RNA molecules have entered the center stage of molecular biology and are promising candidates not only for the regulation of key biological processes such as proliferation and apoptosis, but also for therapy of human diseases.     

A test of two hypotheses explaining the seasonality of reproduction in temperate mammals

1. Two proposed hypotheses about energy allocation were tested to explain the patterns of seasonal reproduction found in temperate mammals. The two hypotheses predict either that total demand for energy is greater during reproduction than during winter (when thermoregulatory costs are high) (Increased Demand Hypothesis) or that total costs during winter are greater than or equal to total costs during reproduction (Reallocation Hypothesis).
2. Data were compiled from the literature on summer (non-reproducing) and winter metabolic rates of temperate mammals, and were used on litter sizes and a published equation to predict metabolic rates during lactation.
3. All three measures of metabolic rate scaled to body mass with slopes significantly less than one. Metabolic rates during winter averaged ≈ 2 times greater than those of non-reproducing mammals during summer. On average, predicted metabolic rates during lactation were not significantly greater than during winter, but for some individual species they clearly were.
4. It is suggested that neither the Reallocation nor the Increased Demand Hypothesis can fully explain seasonal reproductive patterns in temperate mammals.     

Mosquitoes cool down during blood feeding to avoid overheating

Temperature is one of the most important factors affecting the life of insects [1]. For instance, high temperatures can have deleterious effects on insects' physiology. Therefore, many of them have developed various strategies to avoid the risk of thermal stress [2]. They can seek a fresher environment or adjust their water loss, but hematophagous insects, such as mosquitoes, must confront the issue of thermal stress at each feeding event on a warm-blooded host [3]. To better understand to what extent mosquitoes are exposed to thermal stress while feeding, we conducted a real-time infrared thermographic analysis of mosquitoes' body temperature during feeding on both warm blood and sugar solution. First, our results highlighted differences in temperature between the body parts of the mosquito (i.e., heterothermy) during blood intake, but not during sugar meals. We also found that anopheline mosquitoes can decrease their body temperature during blood feeding thanks to evaporative cooling of fluid droplets, which are excreted and maintained at the end of the abdomen. This mechanism protects the insect itself, probably as well as the sheltered microorganisms, both symbionts and parasites, from thermal stress. These findings constitute the first evidence of thermoregulation among hematophagous insects and explain the paradox of fresh blood excretion during feeding.     

Ankle and foot power in gait analysis: Implications for science,technology and clinical assessment

In human gait analysis studies, the entire foot is typically modeled as a single rigid-body segment; however, this neglects power generated/absorbed within the foot. Here we show how treating the entire foot as a rigid body can lead to misunderstandings related to (biological and prosthetic) foot function, and distort our understanding of ankle and muscle-tendon dynamics. We overview various (unconventional) inverse dynamics methods for estimating foot power, partitioning ankle vs. foot contributions, and computing combined anklefoot power. We present two case study examples. The first exemplifies how modeling the foot as a single rigid-body segment causes us to overestimate (and overvalue) muscle-tendon power generated about the biological ankle (in this study by up to 77%), and to misestimate (and misinform on) foot contributions; corroborating findings from previous multi-segment foot modeling studies. The second case study involved an individual with transtibial amputation walking on 8 different prosthetic feet. The results exemplify how assuming a rigid foot can skew comparisons between biological and prosthetic limbs, and lead to incorrect conclusions when comparing different prostheses/interventions. Based on analytical derivations, empirical findings and prior literature we recommend against computing conventional ankle power (between shank-foot). Instead, we recommend using an alternative estimate of power generated about the ankle joint complex (between shank-calcaneus) in conjunction with an estimate of foot power (between calcaneus-ground); or using a combined anklefoot power calculation. We conclude that treating the entire foot as a rigid-body segment is often inappropriate and ill-advised. Including foot power in biomechanical gait analysis is necessary to enhance scientific conclusions, clinical evaluations and technology development.     

How flies get their size: genetics meets physiology

Body size affects important fitness variables such as mate selection, predation and tolerance to heat, cold and starvation. It is therefore subject to intense evolutionary selection. Recent genetic and physiological studies in insects are providing predictions as to which gene systems are likely to be targeted in selecting for changes in body size. These studies highlight genes and pathways that also control size in mammals: insects use insulin-like growth factor (IGF) and Target of rapamycin (TOR) kinase signalling to coordinate nutrition with cell growth, and steroid and neuropeptide hormones to terminate feeding after a genetically encoded target weight is achieved. However, we still understand little about how size is actually sensed, or how organ-intrinsic size controls interface with whole-body physiology.     

Intermolt development reduces oxygen delivery capacity and jumping performance in the American locust (<Emphasis Type="Italic">Schistocerca americana</Emphasis>)

Among animals, insects have the highest mass-specific metabolic rates; yet, during intermolt development the tracheal respiratory system cannot meet the increased oxygen demand of older stage insects. Using locomotory performance indices, whole body respirometry, and X-ray imaging to visualize the respiratory system, we tested the hypothesis that due to the rigid exoskeleton, an increase in body mass during the intermolt period compresses the air-filled tracheal system, thereby, reducing oxygen delivery capacity in late stage insects. Specifically, we measured air sac ventilation frequency, size, and compressibility in both the abdomen and femur of early, middle, and late stage sixth instar Schistocerca americana grasshoppers. Our results show that late stage grasshoppers have a reduced air sac ventilation frequency in the femur and decreased convective capacities in the abdomen and femur. We also used X-ray images of the abdomen and femur to calculate the total proportion of tissue dedicated to respiratory structure during the intermolt period. We found that late stage grasshoppers had a lower proportion of their body dedicated to respiratory structures, especially air sacs, which convectively ventilate the tracheal system. These intermolt changes make oxygen delivery more challenging to the tissues, especially critical ones such as the jumping muscle. Indeed, late stage grasshoppers showed reduced jump frequencies compared to early stage grasshoppers, as well as decreased mass-specific CO₂ emission rates at 3 kPa PO₂. Our findings provide a mechanism to explain how body mass changes during the intermolt period reduce oxygen delivery capacity and alter an insect’s life history.     

A laminar cortical model of stereopsis and 3D surface perception: closure and da Vinci stereopsis

A laminar cortical model of stereopsis and 3D surface perception is developed and simulated. The model describes how monocular and binocular oriented filtering interact with later stages of 3D boundary formation and surface filling-in in the LGN and cortical areas V1, V2, and V4. It proposes how interactions between layers 4, 3B, and 2/3 in V1 and V2 contribute to stereopsis, and how binocular and monocular information combine to form 3D boundary and surface representations. The model includes two main new developments: (1) It clarifies how surface-to-boundary feedback from V2 thin stripes to pale stripes helps to explain data about stereopsis. This feedback has previously been used to explain data about 3D figure-ground perception. (2) It proposes that the binocular false match problem is subsumed under the Gestalt grouping problem. In particular, the disparity filter, which helps to solve the correspondence problem by eliminating false matches, is realized using inhibitory interneurons as part of the perceptual grouping process by horizontal connections in layer 2/3 of cortical area V2. The enhanced model explains all the psychophysical data previously simulated by Grossberg and Howe (2003), such as contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, Panum's limiting case, the Venetian blind illusion, stereopsis with polarity-reversed stereograms, and da Vinci stereopsis. It also explains psychophysical data about perceptual closure and variations of da Vinci stereopsis that previous models cannot yet explain.     

Dielectric properties of insect tissues

In order to explain some effects of microwave irradiation on insects it is necessary to consider a mathematical model. The knowledge of dielectric properties of a typical insect tissue is crucial for such a model. A method based on shift of resonant frequency and of quality factor measurement in a resonator both before and after the insertion of samples was used. The method (measurements at a frequency of 2375 MHz) has been described in detail. A large number of measurements were performed on different kinds of typical insect tissues (cuticle, fat body, muscles, reproductive organs and eggs) for their dielectric properties. The values obtained compare well to those reported in the literature for some mammals. Differences seemed to depend on different water-to-fat content ratios. However, no simple dependence on the water content was found. Values obtained from insect tissue material have been discussed in detail.     

Factors explaining increased body size in common shrews (Sorex araneus) on Scottish islands

Aim  Island populations of small mammals are often characterized by a larger body size compared with neighbouring mainland or continental populations of the same species. A number of reasons have been put forward to explain this phenomenon. The aim of this study was to test which of these hypotheses can best explain the increase of body size in common shrews ( Sorex araneus ) on islands.
Location  The fieldwork for this study was carried out on the islands of the Inner Hebrides, Clyde Islands and the west coast of Scotland.
Methods  This study compared body sizes of common shrews from mainland and island sites on the west coast of Scotland, based on measurements of hind foot lengths. On 10 of the 13 islands sampled, common shrews were significantly larger than on the mainland. Body size did not vary significantly among mainland populations. We used the directional contrasts method to test the relative contributions of possible factors explaining the large body size observed in the island populations.
Results  We found that body size of common shrews on islands was positively related to distance from mainland, negatively related to average annual temperature, negatively related to island size, and may also be influenced by the presence or absence of pygmy shrews ( Sorex minutus ) on the island.
Main conclusions  Our results suggest a role for founder events, Bergmann's rule and K -selection in determining body size of common shrews on islands.     

How to make a sterile helper

The sterile worker castes found in the colonies of social insects are often cited as archetypal examples of altruism in nature. The challenge is to explain why losing the ability to mate has evolved as a superior strategy for transmitting genes into future generations. We propose that two conditions are necessary for the evolution of sterility: completely overlapping generations and monogamy. A review of the literature indicates that when these two conditions are met we consistently observe the evolution of sterile helpers. We explain the theory and evidence behind these ideas, and discuss the importance of ecology in predicting whether sterility will evolve using examples from social birds, mammals, and insects. In doing so, we offer an explanation for the extraordinary lifespans of some cooperative species which hint at ways in which we can unlock the secrets of long life.     

Stable isotope ecology in insects: a review

1. The use of stable isotope analysis (SIA) in ecological research has dramatically increased in recent years largely because it allows researchers to investigate ecological questions that have been previously difficult to address. 2. Ecological applications of SIA include estimating fundamental niche space and overlap, evaluating trophic or species level interactions, and investigating food web structure. Increasingly, researchers have been incorporating SIA in studies of animal migration, disease transmission, diet composition, nutrient assimilation, and body condition among others. 3. Studies using SIA to evaluate the ecology of terrestrial insects have lagged behind other taxonomic groups. This poor representation of stable isotope studies in publications likely stems from a lack of familiarity of entomologists with this technique. 4. An improved understanding of SIA, as well as the advantages and disadvantages specifically related to insect research, will benefit the field of entomology. In addition, insect-model systems provide unique opportunities for entomologists to incorporate SIA in their research to advance our knowledge of insect biology and the stable isotope ecology of insects. 5. We provide background information on stable isotopes, explain sources of isotopic variation, describe the processes of how isotopes are differentially routed and incorporated into an individual's tissues, explain the principles that influence isotopic fractionation and discrimination, highlight different methods and advancements in SIA, review innovative stable isotope studies, and provide an overview of common mistakes, considerations, and future directions entomologists can explore.     

Animal cell cultures in microsporidial research: their general roles and their specific use for fish microsporidia

The use of animal cell cultures as tools for studying the microsporidia of insects and mammals is briefly reviewed, along with an in depth review of the literature on using fish cell cultures to study the microsporidia of fish. Fish cell cultures have been used less often but have had some success. Very short-term primary cultures have been used to show how microsporidia spores can modulate the activities of phagocytes. The most successful microsporidia/fish cell culture system has been relatively long-term primary cultures of salmonid leukocytes for culturing Nucleospora salmonis. Surprisingly, this system can also support the development of Enterocytozoon bienusi, which is of mammalian origin. Some modest success has been achieved in growing Pseudoloma neurophilia on several different fish cell lines. The eel cell line, EP-1, appears to be the only published example of any fish cell line being permanently infected with microsporidia, in this case Heterosporis anguillarum. These cell culture approaches promise to be valuable in understanding and treating microsporidia infections in fish, which are increasingly of economic importance.