Jon F. Harrison - US grants

9317784 Harrison Regulation of pH is one of the most critical aspects of organismal homeostasis. Although acid-base status affects a wide variety of cellular processes, including enzyme catalysis, ionic balance, membrane transport, and hormone-receptor interactions, our knowledge of this aspect of insect physiology is quite limited. Previous research by Dr. Harrison has shown that locusts regulate extracellular pH quite closely, and that acid- base loads resulting from diet, starvation, or injections of HCl are excreted. A major goal of the proposed research is to determine the specific region(s) of the alimentary canal/hindgut complex responsible for the regulated excretion of acid-base loads. This research will also test whether changes in the secretion of acid-base by the midgut can be directly induced by changes in acid-base status. It is generally assumed (in insects and mammals) that excretion of ammonium is functionally equivalent to acid excretion. However, this assumption has never been tested directly in insects, and recently has been extensively debated for mammals. The proposed study will test whether ammonium excretion by the hindgut of locusts is functionally equivalent to acid secretion in a simple, direct manner. Together, these experiments will provide the first organismal model of the most important mechanisms of long-term acid-base regulation in insects. ***

9521543 Temperature regulation is very important for many organisms, because rates of biochemical reactions vary with temperature. Careful thermoregulation is particularly important to flight performance. Flying bees have been thought to regulate temperature of their thorax, which houses their flight muscles, by varying rates of convective and evaporative heat loss. Recent studies, however, show that flying bees reduce rates of metabolic heat production as air temperature increases. Because metabolic heat is produced mainly by the activity of the flight muscles, power output for flight may also change with temperature. This research will measure flight performance, water balance, evaporative water loss and metabolic rate in freely hovering honey bees over a range of air temperatures. The data will be used to construct quantitative heat and water budgets for thermoregulation in flying bees. It will result in the first comprehensive models of thermal effects on heat balance, water balance and flight performance in insects. The research will increase understanding of environmental constraints on the distribution, abundance, and activity patterns of biologically and economically important flying insects.

Like all animals, insect cells must obtain oxygen from the atmosphere, and excrete the volatile waste product, carbon dioxide. Insects use a relatively unique type of respiratory system to engage in this process, the tracheal respiratory system. With the tracheal respiratory system, gases move between the atmosphere and the cells primarily via air-filled tubes called trachea. The goal of this study is to investigate the basic physiological mechanisms of function in the insect tracheal system, primarily using grasshoppers as model systems. Specifically, this project will assess the relationship between structure and function comparing insects of different sizes, and insect tissues of different metabolic rates. Tracheal structure will be measured using light and electron microscopy to quantify tracheal dimensions, while tracheal function will be assessed by monitoring gas exchange and ventilation volume in response to exposure to low or high oxygen levels. The relative importance of diffusion and convection in insect tracheal systems will be investigated by manipulating the diffusion rate of oxygen by changing the inert gas composition of the atmosphere. This research will be important for understanding the evolution of the insect tracheal system, and for developing a general understanding of the relationship between form and function in animal gas exchange systems. Because oxygen availability influences growth and development, this research will be relevant to the understanding of insect development, and the use of controlled atmospheres to reduce insect infestations. This research project will also contribute significantly to scientific training, as 2-3 Ph.D. students will be partially funded by this award.

9977047
Elser
The IRC-EB Program seeks to promote research that integrates across multiple levels of biological organization and across diverse types of habitats and organisms. Such work should articulate general principles that can begin to re-unify the increasingly fragmented wealth of biological knowledge that this century has generated. This project involves a diverse team of researchers that includes a physiologist, a microbial ecologist, theoretical biologists, evolutionary biologists, limnologists, and a terrestrial ecosystem ecologist. It involves an explicit, conceptually organized, integration from genes to ecosystems, from microbes to metazoans, and from lakes to deserts. This project will use a framework of biological stoichiometry to assess how the fundamental chemical balance required for growth links the genetics and physiology of organisms to ecosystem dynamics. Biological stoichiometry is the study of the balance of energy and multiple chemical elements in living systems. Accumulating research suggests a characteristic biogeochemical signature of rapid organism growth, manifested in biomass C:N:P stoichiometry, which is driven by the fundamental association of rapid growth with P-rich ribosomal RNA. In addition, considerable data are accumulating that indicate that organism C:N:P stoichiometry is a key mediator of ecological dynamics, including trophic dynamics and biogeochemical cycling in ecosystems. Thus, there appears an opportunity to use principles of chemical stoichiometry to derive the causal connections between the genetics and cellular physiology of growth with major ecological implications. This 4-year project will make this attempt via three closely intertwined components. In Component 1 (Organismal Biology) the coupling of growth, biochemical composition (RNA concentration), and C:N:P will be examined in a suite of organisms whole nutritional physiology has not been well studies (bacteria, protozoa, fungi, insects, worms). Patterns of C:N:P variation and growth will be assessed in these taxa relative to patterns known from better-studied groups. How terrestrial and aquatic metazoan herbivores with contrasting C:N:P composition cope with food resources that are stoichiometrically imbalanced with respect to their requirements. These studies will examine both behavioral and physiological adjustments by animals in response to stoichiometric food quality. Component 2 (Evolution) will consider organism growth, C:N:P, and biochemical allocation in an evolutionary context in both terrestrial (Drosophila) and aquatic (Daphnia) realms. How these phenotypic traits, as well as key genotypic features associated with the genetics of the ribosome (such as rDNA intergenic spacer length and gene dosage) are arrayed on known phylogenetic trees will be investigated. Drosophila and Daphnia will be subjected to artificial selection on growth rate, and how growth rate, C:N:P, RNA allocation, and ribosomal genotypes change in concert will be examined. At the end of these divergent selection regimes, the consequences of selection for physiological, behavioral, and ecological features will be assessed for each taxon. The implication of growth-C:N:P coupling in theoretical studies that permit in situ evolution of ecological communities under multiple resource limitations will be determined. Finally, Component 3 will place considerations of genetics and physiology of C:N:P and growth in an ecological context by sampling a wide range of ecosystem types (lake, desert, grassland, forest) for key stoichiometric parameters. The main goal in these studies is to determine whether the C:N:P stoichiometry of primary producer and detritus biomass is associated with particular patterns of primary consumer biomass, C:N:P, and diversity.

Dissertation Research: Mechanisms and Significance of Ontogenetic Changes in Respiratory Function During Insect Locomotion

Jon Harrison and Scott Kirkton

The goal of this research is to examine how body size affects the respiratory physiology of active insects. Initial results show that larger/older grasshoppers fatigue quicker during repeated jumping, which suggests possible problems with oxygen delivery to the muscle. This project utilizes American locusts (Schistocerca americana) to determine how structural changes in both the respiratory tracheal system and the jumping muscle vary with body size during development. The tracheal structure will be measured using light and electron microscopy, while the leg muscle metabolic biochemistry will be measured using enzymatic assays. The amount of oxygen consumed during jumping will be measured for the whole animal using flow-through respirometry and leg muscle oxygen levels will be measured with electron paramagnetic resonance. The results of this project will help understand the general relationship between body size and tracheal function and provide a test of the hypothesis that gigantic insects of the Paleozoic Era were made possible by increased atmospheric oxygen levels.

Genetic and Phenotypic Variation in Foraging Behavior of African and European
Honey Bees

Principle Investigators: Jennifer H. Fewell and Jon F. Harrison, Arizona State University

A fundamental question in integrative biology is how genetic variation relates to variation in an animal's survival and reproductive strategies. One way to answer this is to determine the genetic basis for behavioral differences between animal populations and then assess the ecological effects of those differences. This project examines foraging strategy differences between neotropical African-derived (Apis mellifera scutellata) and European (Apis mellifera ligustica) honey bees. It addresses to the questions of: (1) how genetic variation between African and European workers influences foraging strategy, and (2) how variation in worker foraging strategy affects differences in colony growth rates between the two subspecies.
Population-level research suggests that African honey bees out-compete European bees primarily through faster rates of colony growth and reproduction (swarming). Because honey bees are social insects, these differences in colony strategy are generated by collective differences in the behavior of the colony's individual workers. Prior research by the investigators suggests that a major behavioral difference between African and European workers is in foraging. African workers show a higher tendency than European workers to collect pollen. Because pollen is the primary food source for developing brood, this difference can have profound effects on colony growth. The first objective of this research is to understand the mechanisms producing individual differences in pollen and nectar foraging. The investigators will test the hypothesis that differences in resource choice between African and European foragers are driven by differences in their sensitivity to stimuli affecting pollen collection. They will determine whether co-fostered African workers respond more readily to stimuli known to affect pollen foraging, and examine differences between African and European workers in genomic regions (quantitative trait loci or QTL's) known to be associated with pollen foraging behavior in European bees.
Preliminary data also suggest that African and European workers differ in work effort during foraging, and that this variation may be mediated by differences in metabolic capacity. The second objective is to test the hypothesis that variation in metabolic rate between African and European honey bees is genetically based, and is linked to differences in resource preference and foraging effort. The researchers will compare metabolic rates, foraging load sizes and foraging rates of co-fostered African, European and hybrid workers to determine how these traits are inherited. Then, quantitative trait locus (QTL) mapping will be performed to locate genomic regions influencing variation in flight metabolic rates. These will be compared to known loci affecting body size and preference for pollen versus nectar collection.
The third objective is to determine whether variation in individual foraging behavior affects colony-level growth rates. The investigators will: (a) measure pollen intake rates and colony growth rates in African and European hives, and (b) experimentally manipulate the genotypes of the foragers in a hive (African versus European), to measure the effect of forager genotype on brood production. This research integrates behavior, physiology and genetics to generate a more complete understanding of the proximate mechanisms generating complex behavioral traits such as foraging. It also examines the consequences of individual behavioral differences on the ecological success of these competing subspecies.

DISSERTATION RESEAERCH: Effect of Body Size and Development on Gas Exchange Mechanisms in Insects: Diffusion vs. Convection

Jon F. Harrison
Kendra J. Greenlee

Delivery of oxygen in organisms occurs by two basic mechanisms, convection and diffusion. Determining the relative importance of these mechanisms is fundamental to understanding gas exchange in any organism. Convection occurs when pressure generated by respiratory muscles causes bulk movement of air. Diffusion occurs by passive movement of oxygen molecules from areas of high concentration to areas of lower concentration. For insects, the relative role of convection and diffusion in gas exchange is highly controversial. Past evidence supports the notion that some insects can sustain their energy demands through diffusion of oxygen alone. However, many insects exhibit pressure-generating behaviors, such as abdominal pumping in grasshoppers. In particular, it is thought that the relative importance of convection may increase with insect body size. In this study, the relative importance of diffusion and convection to insect gas exchange will be quantified by manipulating the ability of oxygen to diffuse using different carrier gases. Generally, air contains 21% oxygen and 79% nitrogen. Substituting helium or sulfur hexaflouride for nitrogen alters the oxygen diffusion coefficient, making it easier or more difficult, respectively, for oxygen to move by diffusion. The grasshoppers' metabolic response to lowered oxygen levels will be measured in all three carrier gases. If grasshoppers are breathing by diffusion, their metabolic responses should be strongly affected by these manipulations. Conversely, if grasshoppers breathe by convection, their metabolic responses to hypoxia will not be affected by variations in carrier gas. To test whether the relative importance of diffusion and convection varies with size, these experiments will be performed with juvenile (small) and adult (large) grasshoppers. To further test the importance of diffusion and convection in insects, grasshoppers will be anesthetized with ketamine to prevent abdominal pumping movements. If convection does become increasingly important in larger insects, ketamine is predicted to have a much stronger effect on metabolic responses to hypoxia in larger grasshoppers. Together, these experiments will provide the first empirical tests of the relative importance of diffusion and convection in insects of different sizes.

It has been hypothesized that the giant insects of the late Paleozoic were made possible by high atmospheric oxygen levels, and that current insect body sizes are constrained by our atmospheric oxygen level of 21%. This research will test this hypothesis with a series of experiments that examine the effect of single- and multi-generation exposure to different atmospheric O2 levels on insect size, developmental rate, tracheal structure and function. Most of these experiments use fruitflies (Drosophila melanogaster), but one broad comparative study of the developmental plasticity of 16 insect species in response to variation in atmospheric O2 levels is included.

The first goal of this research is to test whether D. melanogaster evolve different body sizes in response to variation in atmospheric O2 level (10, 20, 40% O2) in the lab. A second goal is to determine whether atmospheric O2 level can serve as a constraint on the evolution of large body size in D. melanogaster by selecting for large size in different O2 atmospheres. A third goal is to test for O2 delivery limitations, and potential compensatory responses of the respiratory system to variation in atmospheric oxygen level in fruitflies. Specifically these experiments will examine respiratory responses to rearing flies in 10, 20 and 40% O2 for one generation, multiple generations, or when selecting for large size. Atmospheric O2 effects on the capacity of the tracheal system to deliver oxygen will be measured morphologically with electron microscopy, and physiologically by measuring the lowest O2 level that permits normal metabolic rate. A fourth goal is to test three non-alternative hypotheses for why rearing O2 level affects individual fruitfly size: 1) The Direct O2 Limitation (DOL) Hypothesis that increasing O2 availability increases larval growth rates by increasing nutrient intake rates, 2) The O2 Cue (OC) Hypothesis, that increasing oxygen levels extend development rate by delaying the initiation of molting, and 3) The Cell Size (CS) hypothesis, that higher O2 levels increase fly size by increasing cell size at constant cell number. Finally, we will test for the generality of rearing O2 level on insect size and development rate. This comparative study of 16 species will also test whether O2 effects on these variables are influenced by insect size, developmental pattern, or habitat.

This project involves a unique system in which we can quantify the degree of physiological constraint (O2 availability) on the evolution of major life history traits (body size, developmental rate), and thus will be of interest to a wide array of evolutionary biologists, physiologists and ecologists. In addition, the possible control of atmospheric O2 on insect size (and historical insect gigantism) is of substantial interest to many non-biologists including paleogeologists, environmental scientists and the general public. Results will be widely disseminated through reviewed scientific papers in physiological and evolutionary journals as well as more general outlets such as Scientific American or Natural History. A web site on insect respiratory physiology and oxygen effects on insect size will be created and linked to the Insect Physiology On-line web site (http://lamar.colostate.edu/%7Einsects/index.html). Finally, this award will also fund postdoctoral, graduate, and undergraduate training programs for individuals from groups currently under-represented among biology professions.

This award will fund a workshop to discuss the scientific rationale for and design of a national facility (VAL, Variable Atmosphere Laboratory) to study the effects of atmospheric composition and climate on biological and earth processes. The tentative location of this facility would be the Arizona State University Polytechnic campus. VAL is envisioned as containing approximately 50 terrestrial and 20 aquatic "mini-worlds" in which atmospheric composition, temperature, humidity, UV radiation, atmospheric pressure and light cycle can be controlled. VAL would serve a wide variety of research fields, including geology, paleontology, ecology, plant physiology, animal physiology, astrobiology and environmental toxicology. Creation of VAL would provide the U.S. with the premier facility for experimental analysis of the effects of past and future climate change, and would be a critical step in rational planning for a sustainable earth. Educational outreach will be an important component of VAL. School groups will be able to tour the facility, and web cams and web-based data systems will allow school groups to observe and participate in on-going experiments. Educating students and the general public on the impacts of global change will be a central theme of VAL.

The purpose of the workshop is to gather diverse, expert opinion on the design and construction of VAL, with a special emphasis on the identification of: 1) the most important scientific problems that cannot currently be addressed in a cost-effective manner without VAL, and 2) key design features necessary for the success of VAL. Because of the breadth of fields encompassed by VAL, it is critical that the design and scientific rationale for VAL be considered by experts from diverse fields. The workshop will be held at the Center for Social Dynamics and Complexity at Arizona State University.

The product of the workshop will be a white paper, which will be submitted to a general US science journal, and will serve as the basis for proposals to fund construction of VAL. Construction of VAL will eventually require significant support from multiple agencies such as DOE, NASA, NIH, NOAA, EPA and NSF.

ATMOSPHERIC OXYGEN INFLUENCES ON THE SIZE OF MODERN AND FOSSIL INSECTS (0746352)

Jon Harrison, PI

Recent geological models have suggested that oxygen levels varied significantly over the past 500 million years. These variations in atmospheric oxygen have been invoked to explain a vast array of evolutionary events, including major extinctions, changes in animal diversity, and the conquest of land by animals (reviewed by Berner, VandenBrooks and Ward, 2007). One of the most oft-cited and dramatic proposed effects of this oxygen variation is that increased oxygen levels during the Paleozoic allowed for increases in body size of vertebrates and insects. However, the intriguing hypothesis that hyperoxia was responsible for insect gigantism is weakened by two major problems: 1) the lack of statistical evidence that body size correlates with oxygen levels in the groups of animals that were present during these times of oxygen fluctuation and 2) a lack of modern physiological studies to support this hypothesis. Therefore, the PI will carry out a multi-faceted approach to the question of the impact of oxygen on insect development and evolution. He will measure body sizes of the three major fossil insect groups for which museum fossils are most abundant from the Carboniferous period through the Triassic period [Odonatoptera ? ancestors of modern dragonflies, Blattodea ? ancestors of modern cockroaches, and Palaeodictyopterida ? an extinct group], and perform the first statistical analysis of whether average or maximal insect size correlates with oxygen across this period. He will subsequently rear two species descended from these ancient taxa across the range of oxygen that occurred in the past - the dragonfly Anax junius, and the cockroach, Blatella germanica ? to better understand the effect of varying oxygen on modern physiology. The PI also will attempt to develop the first ever proxy for paleo-oxygen levels: the ratio of leg tracheal diameter to leg length in fossil insects. Recent studies using phase contrast x-ray synchrotron imaging at Argonne National Labs have shown that insect leg tracheal diameter depends on two factors: body size and atmospheric oxygen level. The PI will attempt to visualize leg tracheae in fossil insects preserved in amber, and then use the ratio of leg tracheal diameter to leg length for modern cockroaches reared in different oxygen levels to predict what the atmospheric oxygen concentration was when the fossilized insect lived. Development of an independent technique for assessing geologic atmospheric oxygen levels would be a major advance in geology and climate science and could help resolve current competing models.
Insect gigantism is of broad interest to the general public, and serves as a focal point to draw them into learning about fundamental processes of paleontology, evolution and physiology. The PI will leverage this interest to highlight ongoing research in paleontology and evolution by partnering with ASU Ask-A-Biologist web site (http://askabiologist.asu.edu/) and the Arizona Science Center to produce a new K-12 teaching resource. The PI is currently working closely with museums to develop the first exhibit on past and present climate change. He plans on incorporating this research on insect gigantism into an exhibit which will be of interest to museum goers of all ages.

Key uncertainties remain in understanding the effects of atmospheric and climatic change on ecosystems and health. Predicting the responses of the earth and biological systems to rising temperatures and the complex mixture of increasing gases (carbon dioxide, ozone, methane, nitrogen dioxide, sulfur dioxide) is challenging as it is difficult to control these multiple parameters and create replicated experiments, especially on a scale large enough to study biological communities. How elevations in trace gases will affect the capacity of communities to remove carbon dioxide from the atmosphere is unknown. Changes in atmospheric composition over geologic time have been hypothesized to drive major evolutionary changes, but these hypotheses are difficult to evaluate without experimental tests of atmospheric composition on organisms. Air pollutants have been implicated in the dramatic recent elevations in respiratory diseases like asthma, but facilities for experimentally testing the effect of atmospheric composition are insufficient. This award, jointly funded by the National Science Foundation's BIO and GEO directorates, will support a workshop to discuss the design and implementation of a national facility to study the effects of atmospheric composition and climate on biological and earth processes. The workshop participants constitute a diverse group of scientists in terms of scientific expertise, gender, geographic origin, ethnicity, and career stages. In addition, representatives from a variety of potential federal funding agencies will attend the workshop.

This Doctoral Dissertation Enhancement award will support field research on grasshopper migration in China by Ph.D. student Arianne Cease of Arizona State University. Several specific questions will be addressed in this research including: 1) Do migratory forms of grasshopper result from superior or inferior diet quality? 2) Can transitions between migratory and nonmigratory forms be triggered by changes in specific plant characteristics, such as nitrogen, carbon, phosphorus, or alkaloid content? 3) Does overgrazing stimulate formation of migratory forms by lowering plant nutritional quality? To address these questions, the density and diet of Oedaleus asiaticus will be manipulated in the lab and observed in the field, and morphological, physiological and behavioral responses of developing grasshoppers will be recorded. This award will promote a highly interdisciplinary collaboration by a group of NSF-funded ecologists and insect physiologists with grasshopper biologists and grassland botanists in China. Collaborative activities funded by this award will include research at the Beijing Institute of Life Sciences and the State Key Laboratory of Integrated Management of Insect & Rodent Pests involving multiple Chinese and US scientists. Finally, this research will provide critical data necessary to understand and potentially prevent disastrous locust swarms.

During an outbreak year, swarming grasshoppers (locusts) can populate 11 million square miles of land worldwide, negatively affecting more than 60 countries and the livelihood of 1 out of every 10 people. Global climate change is predicted to increase precipitation variability and perhaps exacerbate locust outbreaks. While it is often hypothesized that dietary cues related to deteriorating environmental conditions might trigger locust swarms, the specific dietary cues that may cause this developmental plasticity are unknown. This research will investigate the question in China, using the grasshopper O. asiaticus, one of two economically important outbreak locusts in Asia. This research will also establish long-term international research ties and promote a globally engaged scientific workforce focused on an important agricultural problem.

Size is among the most important factors in determining the biology of an individual animal. Characteristics that correlate with body size include lifespan, metabolism, and growth. Despite the significance of these factors for fields ranging from field ecology to human medicine, scientists have not yet been able to explain the mechanistic link that generates these patterns throughout nature. Recent studies have demonstrated that size not only affects individual animals, but also entire societies such as social insect colonies. The central focus of this study is to test the hypothesis that behavioral organization influences the distribution of work within colonies and results in the allometric scaling of metabolic rate with colony size. Two sets of experiments will make it possible to test this hypothesis, first by measuring colonies as they naturally grow and second by artificially manipulating colony size. In both sets of experiments, metabolic rates, patterns of network connectivity, and and growth rates will be measured to develop an integrative perspective on how size affects whole colony energetics. This research will be conducted with the help of undergraduate students from minority backgrounds all of whom will have the opportunity to develop their own independent projects to develop and present at national conferences. A collaboration with the Estrella Mountain Regional Park in Maricopa County, AZ designed to educate and engage the general public with an interest in insect biodiversity will also be supported by this proposal.

One obvious pattern in animal biology is that insects and other arthropods are generally smaller than vertebrates. Why is this? More than 300 million years ago, in the late Paleozoic, giant insects up to 10-fold larger than those alive today roamed the earth. Recent findings from geologists have shown that the atmosphere had substantially more oxygen than today (31% vs. 21% today). These findings suggest that insects are small today (and were giant in the Paleozoic) because of the way they delivery oxygen to their tissues. This project tests this hypothesis by using fruit chafer beetles, the largest beetles living in the world today. Physiological and imaging experiments will be conducted to determine whether larger insects invest a greater fraction of their body as respiratory structure, and experience associated negative consequences (or trade-offs) such as reduced proportional sizes of the brain or digestive tract. A newly developed neural stimulating system will be used to assess respiratory function during the high demands of flight. 3D x-ray tomography and confocal microscopy will be used to measure the volume and structure of the respiratory system, brain, digestive tract, and muscles. Using such technologies, this project will test whether larger beetles must reduce the size and function of essential organs (such as the brain) in order to deliver oxygen to their tissues ? the limited by oxygen delivery hypothesis. Thus, this project has the potential to explain one of the most broad-scale patterns in animal biology. Understanding such physical limits on animal design is critical for development of new technologies for engineering micro-injection systems that utilize bio-inspired fluidic systems, and for understanding the potential effects of atmospheric changes on animals. This research project will also include educational and training components, including development of a web-based K-12 teaching resource, and research training for graduate, undergraduate, and high school students.

How do animals decide when to stop growing and become adults? Body size profoundly affects many aspects of animal biology, yet the mechanisms by which animals determine their adult size remain among the fundamental unsolved problems of developmental biology. Holometabolous insects - the primary model for the study of size regulation in animals - do not grow as adults, so the size at which larvae initiate metamorphosis determines their adult size. A recent prominent hypothesis is that "the proximate mechanism setting limits to size during [larval] development is probably the onset of cellular hypoxia", presumably due to oxygen demand outstripping supply capacity. This research will test the role of oxygen in determination of adult body size in the fruit fly, Drosophila melanogaster, by examining the effect of manipulation of atmospheric oxygen levels on growth, timing of metamorphosis, and neuroendocrine function. In addition, epigenetic analyses will be conducted to test the role of candidate signaling pathways by which oxygen sensing might control developmental timing and body size.

Understanding how body size is determined is a fundamental question of biology because body size affects so many aspects of physiology, ecology and evolution. Body size strongly affects food requirements, competitive and reproductive capacities, value as a resource, drug clearance rates, and stress-tolerance of an animal. Yet, the mechanisms involved in determining when animals switch from the growing juvenile form to the reproductive adult form are not well-understood for any animal. In addition to providing new information on this topic that may be general for animals, this research with Drosophila may have specific applications relevant to insect control for agriculture and disease-prevention. This research will contribute to science training by funding research experiences for undergraduate, graduate and postdoctoral trainees. Finally, this project will support secondary education by development of an on-line biology laboratory and outreach to a local bioscience-focused high school. Results from this project will also be disseminated through peer reviewed publications and presentations at regional or national scientific meetings. Data associated with each publication will be posted on Dryad (www.datadryad.org).

Research has recently shown that overgrazing of livestock in a grassland in China lowered the nitrogen content of the grasses and that this caused a rise in the abundance of a locust likely to lead to locust swarms. This proposal will test whether this is also true for related species of locust in Australia and western Africa, and link both grazing practices and locust swarms to economics and social policy in the three contrasting regions. Three biologists and three social scientists will team up to help answer: (1) How do insect-nutrient relations and livestock grazing strategies interact to affect food prices, food security, and rangeland degradation? (2) How do property rights regimes affect the adaptive capacity of societies to respond to the link between overgrazing and locust outbreaks? Because both market forces and locust swarms operate over long distances, these effects are likely to be global.

Locust outbreaks have had devastating effects on food security, impacting crop and livestock yields. This proposal aims to develop new, sustainable strategies to understand and manage locust outbreaks, accounting for feedbacks among ecological, agricultural, and economic systems. Results will be translated directly into management and policy recommendations through collaborations with agricultural agencies. The project will also strengthen international scientific collaboration, train undergraduate and graduate students, and develop a multi-media outreach program for K-12 students and teachers.

The pattern of lower energy use per gram with increasing size (known as metabolic scaling) occurs across all animal groups, yet the mechanisms behind it are still not understood. Intriguingly, social insect colonies show the same level of reduced metabolism with increasing colony size. This project will combine experiments and mathematical models to determine the relationships between energy use and the organization of work in ant colonies. Ant colonies serve as an exemplar for this question, because their highly coordinated societies are organized around the work needed to sustain colony growth and maintenance, analogous to metabolic processes in organisms. Understanding the mechanisms underlying metabolic scaling has potential applications in physiology, medicine, and agriculture. The energy-based models and experiments in this project will be relevant well beyond social insect colonies, including informing human population scaling issues. The project will connect this research with a Mathematics and Social Biology Co-mentoring Program, to train research teams of undergraduates together in biology and mathematics. Students will participate in a formal training program on social biological principles and simulation modeling, and then participate as cross-disciplinary teams in collaborative research. Existing connections with research and minority programs at ASU will be used to recruit under-represented students into the program. Teaching modules on group size, social behavior, and metabolism for online K-12 use will also be developed in collaboration with ASU's Ask-a-Biologist outreach program. This project is co-funded by the Animal Behavior program in the Division of Integrative Organismal Systems, the Mathematical Biology program in the Division of Mathematical Sciences, and the BIOMAPS program for proposals at the interface of Biology, Math and the Physical Sciences.

Group size is one of the most fundamental attributes of sociality, with important effects on social organization and fitness. Previous work has found that larger harvester ant colonies (Pogonomyrmex californicus) exhibit allometric changes in task performance and activity patterns, including increased worker specialization. They additionally shift the allocation of effort, possibly away from more expensive tasks. Potentially coupled with this, colonies also show a consistent pattern of hypometric metabolic scaling, which matches that of organismal scaling patterns. Because task performance is directly linked to colony growth and metabolism, these results lead to the hypothesis that larger colonies achieve economies of scale in energy use from scaling changes in the organization of work. To examine how colony size influences work organization, the distribution of workers across tasks, individual task specialization, and worker activity levels will be measured in laboratory colonies of varying size. Colony metabolism, brood production and growth rates will be measured simultaneously to link behavioral organization to colony metabolic consequences. Additionally, colony demographics, including worker size and age distributions, will be assessed for their contributions to variation in metabolism. These parameters will be measured for: (a) colonies that vary in size but not age; (b) colonies changing in size ontogenetically over time; (c) size-manipulated colonies. The empirical research will be combined with simulation, differential equation and optimization models to ask how components of task organization and activity might interact to generate scaling changes in colony metabolism and productivity.

This project supports a symposium focused on the causal mechanisms responsible for the relationship between animal metabolic rate and body size, or metabolic scaling, to be held at the January 2022 meeting of the Society for Integrative and Comparative Biology. The symposium brings together an interdisciplinary and diverse group of senior and early-career scientists to discuss and synthesize the current understanding of this topic and to identify gaps for future investigations. One of the most important parameters explaining the structure and function of animals is their body size. Larger animals are not just scaled-up versions of small animals. They have lower heart rates, move their limbs more slowly during running, and eat and burn less fuel per pound. The tendency for larger animals to use less energy per pound is termed “hypometric metabolic scaling.” This size-related difference is critical for biomedical and veterinary procedures, agriculture, and ecology. For example, drug doses must be reduced in larger animals because they metabolize drugs more slowly, and scaling must be taken into account when estimating food needs of cattle and the crop consumption of locusts. While we know how body size affects patterns in animal structure, function, and metabolism, we lack an understanding of the molecular mechanisms explaining why these patterns occur, and the symposium addresses this gap. Symposium speakers will publish at least ten manuscripts related to metabolic scaling, and will together write a synthetic paper that outlines how ecological, biomechanical, and evolutionary processes create metabolic scaling. Development of a rigorous understanding of the evolutionary factors that drive metabolic scaling will contribute broadly to basic and applied biology.

Body size explains a large fraction of phenotypic variation in all animal groups, with many aspects of morphology, behavior, physiology, ecology, and evolution differing between small and large animals. However, biologists have a limited understanding of the causes of these scaling patterns. Of all scaling patterns, the hypometric scaling of metabolic rate has been particularly well-established, and the lower mass-specific energy turnover in larger animals is thought to drive many other observed scaling patterns such as lower mass-specific food consumption or smaller territories. This award will fund a symposium, “Causal Mechanisms of Metabolic Scaling,” at the Society for Integrative and Comparative Biology meeting in January 2022. This will be the first symposium to focus on how natural selection acts differentially on animals of different body sizes in ways that produce interspecific metabolic scaling patterns. The symposium will encourage connections across fields, by bringing together scientists who are paleontologists, behaviorists, physiologists, biomechanists, neuroscientists, and ecologists. This symposium will lead to the production of at least ten papers in the journal, Integrative and Comparative Biology. The speakers will also meet by zoom before and after the meeting, and in a workshop after the symposium, to prepare a synthesis paper, written collaboratively by all participants, that will synthesize the diverse perspectives that exist on metabolic scaling. The symposium promotes inclusive scientific training by including many scientists who are early-career and/or from groups currently under-represented in science.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.