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Description
Division of labor, whereby different group members perform different functions, is a fundamental attribute of sociality. It appears across social systems, from simple cooperative groups to complex eusocial colonies. A core challenge in sociobiology is to explain how patterns of collective organization are generated. Theoretical models propose that division of labor self-organizes, or emerges, from interactions among group members and the environment; division of labor is also predicted to scale positively with group size. I empirically investigated the emergence and scaling of division of labor in evolutionarily incipient groups of sweat bees and in eusocial colonies of harvester ants. To test whether division of labor is an emergent property of group living during early social evolution, I created de novo communal groups of the normally solitary sweat bee Lasioglossum (Ctenonomia) NDA-1. A division of labor repeatedly arose between nest excavation and guarding tasks; results were consistent with hypothesized effects of spatial organization and intrinsic behavioral variability. Moreover, an experimental increase in group size spontaneously promoted higher task specialization and division of labor. Next, I examined the influence of colony size on division of labor in larger, more integrated colonies of the harvester ant Pogonomyrmex californicus. Division of labor scaled positively with colony size in two contexts: during early colony ontogeny, as colonies grew from tens to hundreds of workers, and among same-aged colonies that varied naturally in size. However, manipulation of colony size did not elicit a short-term response, suggesting that the scaling of division of labor in P. californicus colonies is a product of functional integration and underlying developmental processes, rather than a purely emergent epiphenomenon. This research provides novel insights into the organization of work in insect societies, and raises broader questions about the role of size in sociobiology.
ContributorsHolbrook, Carter Tate (Author) / Fewell, Jennifer H (Thesis advisor) / Gadau, Jürgen (Committee member) / Harrison, Jon F. (Committee member) / Hölldobler, Berthold (Committee member) / Johnson, Robert A. (Committee member) / Arizona State University (Publisher)
Created2011
Description
One hypothesis for the small size of insects relative to vertebrates, and the existence of giant fossil insects, is that atmospheric oxygen levels have constrained body sizes because oxygen delivery would be unable to match the needs of metabolically active tissues in larger insects. This study tested whether oxygen delivery becomes more challenging for larger insects by measuring the oxygen-sensitivity of flight metabolic rates and behavior during hovering for 11 different species of dragonflies that range in mass by an order of magnitude. Animals were flown in 7 different oxygen concentrations ranging from 30% to 2.5% to assess the sensitivity of their behavior and flight metabolic rates to oxygen. I also assessed the oxygen-sensitivity of flight in low-density air (nitrogen replaced with helium), to increase the metabolic demands of hovering flight. Lowered atmosphere densities did induce higher metabolic rates. Flight behaviors but not flight metabolic rates were highly oxygen-sensitive. A significant interaction between oxygen and mass was found for total flight time, with larger dragonflies varying flight time more in response to atmospheric oxygen. This study provides some support for the hypothesis that larger insects are more challenged in oxygen delivery, as predicted by the oxygen limitation hypothesis for insect gigantism in the Paleozoic.
ContributorsHenry, Joanna Randyl (Author) / Harrison, Jon F. (Thesis advisor) / Kaiser, Alexander (Committee member) / Rutowski, Ronald L (Committee member) / Arizona State University (Publisher)
Created2011
Description
In social insect colonies, as with individual animals, the rates of biological processes scale with body size. The remarkable explanatory power of metabolic allometry in ecology and evolutionary biology derives from the great diversity of life exhibiting a nonlinear scaling pattern in which metabolic rates are not proportional to mass, but rather exhibit a hypometric relationship with body size. While one theory suggests that the supply of energy is a major physiological constraint, an alternative theory is that the demand for energy is regulated by behavior. The central hypothesis of this dissertation research is that increases in colony size reduce the proportion of individuals actively engaged in colony labor with consequences for energetic scaling at the whole-colony level of biological organization. A combination of methods from comparative physiology and animal behavior were developed to investigate scaling relationships in laboratory-reared colonies of the seed-harvester ant, Pogonomyrmex californicus. To determine metabolic rates, flow-through respirometry made it possible to directly measure the carbon dioxide production and oxygen consumption of whole colonies. By recording video of colony behavior, for which ants were individually paint-marked for identification, it was possible to reconstruct the communication networks through which information is transmitted throughout the colony. Whole colonies of P. californicus were found to exhibit a robust hypometric allometry in which mass-specific metabolic rates decrease with increasing colony size. The distribution of walking speeds also scaled with colony size so that larger colonies were composed of relatively more inactive ants than smaller colonies. If colonies were broken into random collections of workers, metabolic rates scaled isometrically, but when entire colonies were reduced in size while retaining functionality (queens, juveniles, workers), they continued to exhibit a metabolic hypometry. The communication networks in P. californicus colonies contain a high frequency of feed-forward interaction patterns consistent with those of complex regulatory systems. Furthermore, the scaling of these communication pathways with size is a plausible mechanism for the regulation of whole-colony metabolic scaling. The continued development of a network theory approach to integrating behavior and metabolism will reveal insights into the evolution of collective animal behavior, ecological dynamics, and social cohesion.
ContributorsWaters, James S., 1983- (Author) / Harrison, Jon F. (Thesis advisor) / Quinlan, Michael C. (Committee member) / Pratt, Stephen C. (Committee member) / Fewell, Jennifer H. (Committee member) / Gadau, Juergen (Committee member) / Arizona State University (Publisher)
Created2012
Description
One hypothesis for why insects are smaller than vertebrates is that the blind-ended tracheal respiratory system challenges oxygen delivery for larger insects. Supporting this hypothesis, several studies have documented that larger insect species have larger gas transport structures than expected by isometric scaling. To further test this hypothesis, we performed the first inter-specific study of the scaling of spiracle size, using ten scarab beetle species, including some of the most massive insects. Using micro-CT, we measured the cross sectional area and depth of all eight spiracles. Areas of large spiracles in the anterior portion of the animal showed hypermetric scaling, varying approximately with mass^0.8. However, because diffusive capacities scaled with lower slopes than metabolic rates, larger beetles had a 10-fold higher required PO2 gradient across the spiracles to sustain oxygen consumption by diffusion. Despite this trend, calculations suggest that large beetles can exchange oxygen by diffusion across the spiracles at rest, but likely no beetles can do so during flight. Advective capacities through the spiracles scale with mass^1.8, suggestive of a switch toward greater use of convection and/or reduced required pressures in larger beetles.
ContributorsWagner, Julian Morgan (Author) / Harrison, Jon F. (Thesis director) / VandenBrooks, John (Committee member) / Miller, Laura (Committee member) / School of Mathematical and Statistical Sciences (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
The control, function, and evolution of sleep in animals has received little attention compared to many other fitness-relevant animal behaviors. Though natural selection has largely been thought of as the driving evolutionary force shaping sleep biology, sexual and social selection may also have transformative effects on sleep quantity and quality in animals. An overarching hypothesis is that increased levels of investment into inter-sexual choice and intra-sexual competition will reduce sleep. An alternative hypothesis is that sexual ornamentation (e.g. avian plumage coloration and song) may have evolved to communicate sleep health and may therefore be positively related to sleep investment. In this dissertation, I studied how sleep is related to components of sexual and social selection in animals (mostly in birds). I first reviewed the literature for empirical examples of how social and sexual selection drive animal sleep patterns and found support for this relationship in some common types of inter-individual interactions (e.g. mating, intra-sexual competition, parent-offspring interactions, group interactions); I also provided new ideas and hypotheses for future research. I then tested associations between sleep behavior with expression of ornaments (song and plumage coloration), using the house finch (Haemorhous mexicanus) as a model system. For both color and song, I found support for the hypothesis that individuals with exaggerated ornaments slept deeper and longer, suggesting that sleep is a critical resource for ornament elaboration and/or may be communicated by both types of sexual signal. Following this, I tested the phylogenetic association between sleep and social/sexual selection as well as other life-history traits across birds. I found that more territorial bird species sleep less, that polygynous birds sleep more than monogamous and polygynandrous birds, and that birds migrating longer distances sleep less and have less REM sleep. Finally, in the interest of applying basic knowledge about sleep biology to current global problems, I found support for the hypothesis that house finches from city environments have developed resilience to artificial light pollution at night. Altogether, I found that social, sexual, and life-history traits are indeed important and overlooked drivers of sleep behavior from multiple levels of analysis.
ContributorsHutton, Pierce (Author) / McGraw, Kevin J (Thesis advisor) / Rutowski, Ronald L (Committee member) / Deviche, Pierre J (Committee member) / Sweazea, Karen L (Committee member) / Lesku, John A (Committee member) / Arizona State University (Publisher)
Created2021
Description
The alarming decline of insect pollinators is due in part to agrochemical exposure and climate warming. This thesis focuses on understanding how exposure to a commonly used fungicide and high air temperature affect the flight behavior and physiology of the very important commercial pollinator, Apis mellifera. I found that honey bees reared on pollen contaminated with field-realistic levels of a fungicide (Pristine®) commonly applied to almond blossoms before pollination had smaller thoraxes, possibly due to inhibition of protein digestion, plausibly reducing flight capability. By flying unloaded bees in low density air to elicit maximal performance, I found that consumption of high doses of fungicide during development inhibited maximal flight performance, but consumption of field-realistic doses did not.
To understand climatic-warming effects on honey bees, I flew unloaded foragers at various air densities and temperatures to assess the effects of flight muscle temperature (29 to 44°C) on maximal aerobic metabolism. Flight metabolic rate peaked at a muscle temperature of 39°C and decreased by ~2% per degree below and ~5% per degree above this optimum. Carrying nectar loads increased flight muscle temperatures and flight metabolism of foragers flying at air temperatures of 20 or 30°C. Yet, remarkably, bees flying at 40°C were able to carry loads without heating up or increasing metabolic rate. Bees flying at 40°C increased evaporative cooling and decreased metabolic heat production to thermoregulate. High speed video revealed that bees flying at 40°C air temperature lowered their wing beat frequency while increasing stroke amplitude, increasing flight efficiency. My data also suggests that cooler bees use wing kinematic strategies that increase flight stability and maneuverability while generating excess heat that warms their flight muscle toward optimum. High water loss rates during flight likely limit foraging in dry air temperatures above 46°C, suggesting that CTmax measures of resting honey bees significantly overestimate when high air temperature will negatively impact flight and foraging.
ContributorsGlass, Jordan Robert (Author) / Harrison, Jon F. (Thesis advisor) / Denardo, Dale F. (Committee member) / Dudley, Robert (Committee member) / Fewell, Jennifer H. (Committee member) / Arizona State University (Publisher)
Created2023
Description
Body size plays a pervasive role in determining physiological and behavioral performance across animals. It is generally thought that smaller animals are limited in performance measures compared to larger animals; yet, the vast majority of animals on earth are small and evolutionary trends like miniaturization occur in every animal clade. Therefore, there must be some evolutionary advantages to being small and/or compensatory mechanisms that allow small animals to compete with larger species. In this dissertation I specifically explore the scaling of flight performance (flight metabolic rate, wing beat frequency, load-carrying capacity) and learning behaviors (visual differentiation visual Y-maze learning) across stingless bee species that vary by three orders of magnitude in body size. I also test whether eye morphology and calculated visual acuity match visual differentiation and learning abilities using honeybees and stingless bees. In order to determine what morphological and physiological factors contribute to scaling of these performance parameters I measure the scaling of head, thorax, and abdomen mass, wing size, brain size, and eye size. I find that small stingless bee species are not limited in visual learning compared to larger species, and even have some energetic advantages in flight. These insights are essential to understanding how small size evolved repeatedly in all animal clades and why it persists. Finally, I test flight performance across stingless bee species while varying temperature in accordance with thermal changes that are predicted with climate change. I find that thermal performance curves varied greatly among species, that smaller species conform closely to air temperature, and that larger bees may be better equipped to cope with rising temperatures due to more frequent exposure to high temperatures. This information may help us predict whether small or large species might fare better in future thermal climate conditions, and which body-size related traits might be expected to evolve.
ContributorsDuell, Meghan (Author) / Harrison, Jon F. (Thesis advisor) / Smith, Brian H. (Thesis advisor) / Rutowski, Ronald (Committee member) / Wcislo, William (Committee member) / Conrad, Cheryl (Committee member) / Arizona State University (Publisher)
Created2018
Description
The ability to tolerate bouts of oxygen deprivation varies tremendously across the animal kingdom. Adult humans from different regions show large variation in tolerance to hypoxia; additionally, it is widely known that neonatal mammals are much more tolerant to anoxia than their adult counterparts, including in humans. Drosophila melanogaster are very anoxia-tolerant relative to mammals, with adults able to survive 12 h of anoxia, and represent a well-suited model for studying anoxia tolerance. Drosophila live in rotting, fermenting media and a result are more likely to experience environmental hypoxia; therefore, they could be expected to be more tolerant of anoxia than adults. However, adults have the capacity to survive anoxic exposure times ~8 times longer than larvae. This dissertation focuses on understanding the mechanisms responsible for variation in survival from anoxic exposure in the genetic model organism, Drosophila melanogaster, focused in particular on effects of developmental stage (larval vs. adults) and within-population variation among individuals.
Vertebrate studies suggest that surviving anoxia requires the maintenance of ATP despite the loss of aerobic metabolism in a manner that prevents a disruption of ionic homeostasis. Instead, the abilities to maintain a hypometabolic state with low ATP and tolerate large disturbances in ionic status appear to contribute to the higher anoxia tolerance of adults. Furthermore, metabolomics experiments support this notion by showing that larvae had higher metabolic rates during the initial 30 min of anoxia and that protective metabolites were upregulated in adults but not larvae. Lastly, I investigated the genetic variation in anoxia tolerance using a genome wide association study (GWAS) to identify target genes associated with anoxia tolerance. Results from the GWAS also suggest mechanisms related to protection from ionic and oxidative stress, in addition to a protective role for immune function.
Vertebrate studies suggest that surviving anoxia requires the maintenance of ATP despite the loss of aerobic metabolism in a manner that prevents a disruption of ionic homeostasis. Instead, the abilities to maintain a hypometabolic state with low ATP and tolerate large disturbances in ionic status appear to contribute to the higher anoxia tolerance of adults. Furthermore, metabolomics experiments support this notion by showing that larvae had higher metabolic rates during the initial 30 min of anoxia and that protective metabolites were upregulated in adults but not larvae. Lastly, I investigated the genetic variation in anoxia tolerance using a genome wide association study (GWAS) to identify target genes associated with anoxia tolerance. Results from the GWAS also suggest mechanisms related to protection from ionic and oxidative stress, in addition to a protective role for immune function.
ContributorsCampbell, Jacob B (Author) / Harrison, Jon F. (Thesis advisor) / Gadau, Juergen (Committee member) / Call, Gerald B (Committee member) / Sweazea, Karen L (Committee member) / Rosenberg, Michael S. (Committee member) / Arizona State University (Publisher)
Created2018
Description
According to the World Health Organization, obesity has nearly tripled since 1975 and forty-one million children under the age of 5 are overweight or obese (World Health Organization, 2018). Exercise is a potential intervention to prevent obesity-induced cardiovascular complications as exercise training has been shown to aid nitric oxide (NO) production as well as preserving endothelial function in obese mice (Silva et al., 2016). A soil-derived organic mineral compound (OMC) has been shown to lower blood sugar in diabetic mice (Deneau et al., 2011). Prior research has shown that, while OMC did not prevent high fat diet (HFD)-induced increases in body fat in male Sprague-Dawley rats, it was effective at preventing HFD-induced impaired vasodilation (M. S. Crawford et al., 2019). Six-weeks of HFD has been shown to impair vasodilation through oxidative-stress mediated scavenging of NO as well as upregulation of inflammatory pathways including inducible nitric oxide synthase (iNOS) and cyclooxygenase (Karen L. Sweazea et al., 2010). Therefore, the aim of the present study was to determine whether OMC alters protein expression of iNOS and endothelial NOS (eNOS) in the vasculature of rats fed a control or HFD with and without OMC supplementation. Six-week old male Sprague-Dawley rats were fed either a standard chow diet (CHOW) or a HFD composed of 60% kcal from fat for 10 weeks. The rats were administered OMC at doses of 0 mg/mL (control), 0.6 mg/mL, or 3.0 mg/mL added to their drinking water. Following euthanasia with sodium pentobarbital (200 mg/kg, i.p.), mesenteric arteries and the surrounding perivascular adipose tissue were isolated and prepared for Western Blot analyses. Mesenteric arteries from HFD rats had more uncoupled eNOS (p = 0.006) and iNOS protein expression (p = 0.027) than rats fed the control diet. OMC was not effective at preventing the uncoupling of eNOS or increase in iNOS induced by HFD. Perivascular adipose tissue (PVAT) showed no significant difference in iNOS protein expression between diet or OMC treatment groups. These findings suggest that OMC is not likely working through the iNOS or eNOS pathways to improve vasodilation in these rats, but rather, appears to be working through another mechanism.
ContributorsNelson, Morgan Allen (Author) / Sweazea, Karen L (Thesis advisor) / Katsanos, Christos S (Committee member) / Baluch, Debra P (Committee member) / Arizona State University (Publisher)
Created2020