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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
Social insect colonies exhibit striking diversity in social organization. Included in this overwhelming variation in structure are differences in colony queen number. The number of queens per colony varies both intra- and interspecifically and has major impacts on the social dynamics of a colony and the fitness of its members. To understand the evolutionary transition from single to multi-queen colonies, I examined a species which exhibits variation both in mode of colony founding and in the queen number of mature colonies. The California harvester ant Pogonomyrmex californicus exhibits both variation in the number of queens that begin a colony (metrosis) and in the number of queens in adult colonies (gyny). Throughout most of its range, colonies begin with one queen (haplometrosis) but in some populations multiple queens cooperate to initiate colonies (pleometrosis). I present results that confirm co-foundresses are unrelated. I also map the geographic occurrence of pleometrotic populations and show that the phenomenon appears to be localized in southern California and Northern Baja California. Additionally, I provide genetic evidence that pleometrosis leads to primary polygyny (polygyny developing from pleometrosis) a phenomenon which has received little attention and is poorly understood. Phylogenetic and haplotype analyses utilizing mitochondrial markers reveal that populations of both behavioral types in California are closely related and have low mitochondrial diversity. Nuclear markers however, indicate strong barriers to gene flow between focal populations. I also show that intrinsic differences in queen behavior lead to the two types of populations observed. Even though populations exhibit strong tendencies on average toward haplo- or pleometrosis, within population variation exists among queens for behaviors relevant to metrosis and gyny. These results are important in understanding the dynamics and evolutionary history of a distinct form of cooperation among unrelated social insects. They also help to understand the dynamics of intraspecific variation and the conflicting forces of local adaptation and gene flow.
ContributorsOverson, Rick P (Author) / Gadau, Jürgen (Thesis advisor) / Fewell, Jennifer H (Committee member) / Hölldobler, Bert (Committee member) / Johnson, Robert A. (Committee member) / Liebig, Jürgen (Committee member) / Arizona State University (Publisher)
Created2011
Description
ABSTRACT The elephant tree, Bursera microphylla, is at the northern limit of its range in central Arizona. This species is sensitive to frost damage thus limiting its occurrence in more northern areas of the southwest. Marginal populations of B. microphylla are found in mountain ranges of Central Arizona and are known to occur in the rugged mountain range system of the South Mountain Municipal Park (SMMP). Little is known of the distribution of this species within the park and details relevant to the health of both individual plants and the population such as diameter and number of trunks, height, and presence of damage have not been examined. This study was designed, in part, to test the hypothesis that favorable microhabitats at SMMP are created by particular combinations of abiotic features including aspect, slope, elevation and solar radiation. Data on abiotic factors, as well as specific individual plant locations and characteristics were obtained for 100 individuals. Temperature data was collected in vertical transects at different altitudinal levels. Some of these data were used in spatial analyses to generate a habitat suitability model using GIS software. Furthermore, collected data was analyzed using Matlab© software to identify potential trends in the variation of morphological traits. In addition, for comparative purposes similar information at one hundred computer-generated randomly chosen points throughout SMMP was obtained. The GIS spatial analyses indicated that aspect, slope, elevation, and relative solar radiance are strongly associated as major climatic components of the microhabitat of B. microphylla. Temperature data demonstrated that there are significant differences in ambient temperature among different altitudinal gradients with middle elevations being more favorable. Furthermore, analyses performed using Matlab© to explore trends of elevation as a factor indicated that multiple trunk plants are more commonly found at higher elevations than single trunk plants, there is a positive correlation of trunk diameter with elevation, and that canopy volume has a negative correlation with respect to elevation. It was concluded that microhabitats where B. microphylla occurs at the northern limit of its range require a particular combination of abiotic features that can be easily altered by climatic changes.
ContributorsCordova, Cesar, M.S (Author) / Steele, Kelly P. (Thesis advisor) / Tridane, Abdessaman (Committee member) / Miller, William (Committee member) / Brady, Ward (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
The repression of reproductive competition and the enforcement of altruism are key components to the success of animal societies. Eusocial insects are defined by having a reproductive division of labor, in which reproduction is relegated to one or few individuals while the rest of the group members maintain the colony and help raise offspring. However, workers have retained the ability to reproduce in most insect societies. In the social Hymenoptera, due to haplodiploidy, workers can lay unfertilized male destined eggs without mating. Potential conflict between workers and queens can arise over male production, and policing behaviors performed by nestmate workers and queens are a means of repressing worker reproduction. This work describes the means and results of the regulation of worker reproduction in the ant species Aphaenogaster cockerelli. Through manipulative laboratory studies on mature colonies, the lack of egg policing and the presence of physical policing by both workers and queens of this species are described. Through chemical analysis and artificial chemical treatments, the role of cuticular hydrocarbons as indicators of fertility status and the informational basis of policing in this species is demonstrated. An additional queen-specific chemical signal in the Dufour's gland is discovered to be used to direct nestmate aggression towards reproductive competitors. Finally, the level of actual worker-derived males in field colonies is measured. Together, these studies demonstrate the effectiveness of policing behaviors on the suppression of worker reproduction in a social insect species, and provide an example of how punishment and the threat of punishment is a powerful force in maintaining cooperative societies.
ContributorsSmith, Adrian A. (Author) / Liebig, Juergen (Thesis advisor) / Hoelldobler, Bert (Thesis advisor) / Gadau, Juergen (Committee member) / Johnson, Robert A. (Committee member) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
Two nearly homogenous 60 acre watersheds near Heber, Arizona, within the Apache-Sitgreaves National Forest, were burned at moderate and high severities during the 2002 Rodeo-Chediski wildfire. Each watershed had 30 permanent plots located on it from earlier studies. In 2011, nearly 10 years following the fire, the plots were re-measured to determine how fire severity affects the long term vegetative recovery of this ecosystem; specifically herbaceous production and tree regeneration and density. Canopy cover, litter depth, herbaceous weight, herbaceous cover and shrub cover are vital indicators of herbaceous production, and were found to be significantly different between the sites. Canopy cover and litter depth were found to be significantly higher on the moderate site while herbaceous weight, herbaceous cover and shrub cover were found to be significantly higher on the high site. Tree densities of the three present tree species, ponderosa pine, alligator juniper, and gambel oak, were measured and divided into five size classes to distinguish the diversity of the communities. The mean densities for each species and size class were analyzed to determine if there were any statistically significant differences between the sites. Ponderosa pine saplings (regeneration) were found to have no significant differences between the sites. Juniper and oak saplings were found to be significantly higher on the high site. The remaining four ponderosa pine size classes were found to be significantly higher on the moderate site while the remaining four size classes for juniper and oak were found to have no statistical differences between the sites. Further analysis of the tree proportions revealed that the ponderosa pine species was significantly higher on the moderate site while juniper and oak were significantly higher on the high site. Species specific proportion analysis showed that the ponderosa pine size classes were significantly different across the sites while the juniper and oak size classes showed no significant differences between the sites. Within the ponderosa pine size classes, saplings were found to be significantly higher on the high site while the remaining four classes were significantly higher on the moderate site.
ContributorsNeeley, Heidi L (Author) / Alford, Eddie (Thesis advisor) / Pyne, Stephen (Committee member) / Brady, Ward (Committee member) / Arizona State University (Publisher)
Created2012
Description
Human recreation on rangelands may negatively impact wildlife populations. Among those activities, off-road vehicle (ORV) recreation carries the potential for broad ecological consequences. A study was undertaken to assess the impacts of ORV on rodents in Arizona Uplands Sonoran Desert. Between the months of February and September 2010, rodents were trapped at 6 ORV and 6 non-ORV sites in Tonto National Forest, AZ. I hypothesized that rodent abundance and species richness are negatively affected by ORV use. Rodent abundances were estimated using capture-mark-recapture methodology. Species richness was not correlated with ORV use. Although abundance of Peromyscus eremicus and Neotoma albigula declined as ORV use increased, abundance of Dipodomys merriami increased. Abundance of Chaetodipus baileyi was not correlated with ORV use. Other factors measured were percent ground cover, percent shrub cover, and species-specific shrub cover percentages. Total shrub cover, Opuntia spp., and Parkinsonia microphylla each decreased as ORV use increased. Results suggest that ORV use negatively affects rodent habitats in Arizona Uplands Sonoran Desert, leading to declining abundance in some species. Management strategies should mitigate ORV related habitat destruction to protect vulnerable populations.
ContributorsReid, John Simon (Author) / Brady, Ward (Thesis advisor) / Miller, William (Committee member) / Bateman, Heather (Committee member) / Arizona State University (Publisher)
Created2012
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 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