The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Deborah M Gordon - One of the best experts on this subject based on the ideXlab platform.
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gene expression variation in the brains of Harvester Ant foragers is associated with collective behavior
Communications Biology, 2020Co-Authors: Daniel A. Friedman, Ryan A York, Austin T Hilliard, Deborah M GordonAbstract:Natural selection on collective behavior acts on variation among colonies in behavior that is associated with reproductive success. In the red Harvester Ant (Pogonomyrmex barbatus), variation among colonies in the collective regulation of foraging in response to humidity is associated with colony reproductive success. We used RNA-seq to examine gene expression in the brains of foragers in a natural setting. We find that colonies differ in the expression of neurophysiologically-relevAnt genes in forager brains, and a fraction of these gene expression differences are associated with two colony traits: sensitivity of foraging activity to humidity, and forager brain dopamine to serotonin ratio. Loci that were correlated with colony behavioral differences were enriched in neurotransmitter receptor signaling & metabolic functions, tended to be more central to coexpression networks, and are evolving under higher protein-coding sequence constraint. Natural selection may shape colony foraging behavior through variation in gene expression.
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Measurement of natural variation of neurotransmitter tissue content in red Harvester Ant brains among different colonies
Analytical and Bioanalytical Chemistry, 2020Co-Authors: Mimi Shin, Deborah M Gordon, Daniel A. Friedman, B. Jill VentonAbstract:Colonies of the red Harvester Ant, Pogonomyrmex barbatus , regulate foraging activity based on food availability and local conditions. Colony variation in foraging behavior is thought to be linked to biogenic amine signaling and metabolism. Measurements of differences in neurotransmitters have not been made among Ant colonies in a natural environment. Here, for the first time, we quAntified tissue content of 4 biogenic amines (dopamine, serotonin, octopamine, and tyramine) in single forager brains from 9 red Harvester Ant colonies collected in the field. Capillary electrophoresis coupled with fast-scan cyclic voltammetry (CE-FSCV) was used to separate and detect the amines in individual Ant brains. Low levels of biogenic amines were detected using field-amplified sample stacking by preparing a single brain tissue sample in acetonitrile and perchloric acid. The method provides low detection limits: 1 nM for dopamine, 2 nM for serotonin, 5 nM for octopamine, and 4 nM for tyramine. Overall, the content of dopamine (47 ± 9 pg/brain) was highest, followed by octopamine (36 ± 10 pg/brain), serotonin (20 ± 4 pg/brain), and tyramine (14 ± 3 pg/brain). Relative standard deviations were high, but there was less variation within a colony than among colonies, so the neurotransmitter content of each colony might change with environmental conditions. This study demonstrates that CE-FSCV is a useful method for investigating natural variation in neurotransmitter content in single Ant brains and could be useful for future studies correlating tissue content with colony behavior such as foraging. Graphical abstract
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The physiology of forager hydration and variation among Harvester Ant (Pogonomyrmex barbatus) colonies in collective foraging behavior
Nature Publishing Group, 2019Co-Authors: Daniel A. Friedman, Michael J Greene, Deborah M GordonAbstract:Abstract Ants are abundAnt in desiccating environments despite their high surface area to volume ratios and exposure to harsh conditions outside the nest. Red Harvester Ant (Pogonomyrmex barbatus) colonies must spend water to obtain water: colonies lose water as workers forage outside the nest, and gain water metabolically through seeds collected in foraging trips. Here we present field experiments showing that hydrated P. barbatus foragers made more foraging trips than unhydrated nestmates. The positive effect of hydration on foraging activity is stronger as the risk of desiccation increases. Desiccation tests showed that foragers of colonies that reduce foraging in dry conditions are more sensitive to water loss, losing water and motor coordination more rapidly in desiccating conditions, than foragers of colonies that do not reduce foraging in dry conditions. Desiccation tolerance is also associated with colony reproductive success. Surprisingly, foragers that are more sensitive to water loss are from colonies more likely to produce offspring colonies. This could be because the foragers of these colonies conserve water with a more cautious response to desiccation risk. An Ant’s hydration status may influence its response to the olfactory interactions that regulate its decision to leave the nest to forage. Thus variation among Ant colonies in worker physiology and response to ambient conditions may contribute to ecologically significAnt differences among colonies in collective behavior
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regulation of Harvester Ant foraging as a closed loop excitable system
PLOS Computational Biology, 2018Co-Authors: Renato Pagliara, Deborah M Gordon, Naomi Ehrich LeonardAbstract:Ant colonies regulate activity in response to changing conditions without using centralized control. Desert Harvester Ant colonies forage for seeds, and regulate foraging to manage a tradeoff between spending and obtaining water. Foragers lose water while outside in the dry air, but Ants obtain water by metabolizing the fats in the seeds they eat. Previous work shows that the rate at which an outgoing forager leaves the nest depends on its recent rate of brief Antennal contacts with incoming foragers carrying food. We examine how this process can yield foraging rates that are robust to uncertainty and responsive to temperature and humidity across minute-to-hour timescales. To explore possible mechanisms, we develop a low-dimensional analytical model with a small number of parameters that captures observed foraging behavior. The model uses excitability dynamics to represent response to interactions inside the nest and a random delay distribution to represent foraging time outside the nest. We show how feedback from outgoing foragers returning to the nest stabilizes the incoming and outgoing foraging rates to a common value determined by the volatility of available foragers. The model exhibits a critical volatility above which there is sustained foraging at a constAnt rate and below which foraging stops. To explain how foraging rates adjust to temperature and humidity, we propose that foragers modify their volatility after they leave the nest and become exposed to the environment. Our study highlights the importance of feedback in the regulation of foraging activity and shows how modulation of volatility can explain how foraging activity responds to conditions and varies across colonies. Our model elucidates the role of feedback across many timescales in collective behavior, and may be generalized to other systems driven by excitable dynamics, such as neuronal networks.
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regulation of Harvester Ant foraging as a closed loop excitable system
bioRxiv, 2018Co-Authors: Renato Pagliara, Deborah M Gordon, Naomi Ehrich LeonardAbstract:Ant colonies regulate activity in response to changing conditions without using centralized control. Harvester Ant colonies forage in the desert for seeds, and their regulation of foraging manages a tradeoff between spending and obtaining water. Foragers lose water while outside in the dry air, but the colony obtains water by metabolizing the fats in the seeds they eat. Previous work shows that the rate at which an outgoing forager leaves the nest depends on its recent experience of brief Antennal contact with returning foragers that carry a seed. We examine how this process can yield foraging rates that are robust to uncertainty and responsive to temperature and humidity across minutes to hour-long timescales. To explore possible mechanisms, we develop a low-dimensional analytical model with a small number of parameters that captures observed foraging behavior. The model uses excitability dynamics to represent response to interactions inside the nest and a random delay distribution to represent foraging time outside the nest. We show how feedback of outgoing foragers returning to the nest stabilizes the incoming and outgoing foraging rates to a common value determined by the "volatility" of available foragers. The model exhibits a critical volatility above which there is sustained foraging at a constAnt rate and below which there is cessation of foraging. To explain how the foraging rates of colonies adjust to temperature and humidity, we propose a mechanism that relies on foragers modifying their volatility after they leave the nest and get exposed to the environment. Our study highlights the importance of feedback in the regulation of foraging activity and points to modulation of volatility as a key to explaining differences in foraging activity in response to conditions and across colonies. Our results present opportunities for generalization to other contexts and systems with excitability and feedback across multiple timescales.
Walter R. Tschinkel - One of the best experts on this subject based on the ideXlab platform.
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vertical organization of the division of labor within nests of the florida Harvester Ant pogonomyrmex badius
PLOS ONE, 2017Co-Authors: Walter R. Tschinkel, Nicholas HanleyAbstract:In the Florida Harvester Ant, Pogonomyrmex badius, foragers occur only in the top 15 cm of the nest, whereas brood and brood-care workers reside mostly in the deepest regions, yet the food and seeds foragers collect must be transported downward 30 to 80 cm to seed chambers and up to 2 m to brood chambers. Using mark-recapture techniques with fluorescent printer's ink, we identified a class of workers that ranges widely within the vertical structure of the nest, rapidly moving materials dropped by foragers in the upper regions downward, and excavated soil from deeper upward. Within the nest, only 5% of foragers were recovered below 20 cm depth, but about 30% of transfer workers and 82% of unmarked workers were found there. Below 70 cm depth, 90% of workers were unmarked, and were probably involved mostly in brood care. During the summer, the transfer workers comprise about a quarter of the nest population, while foragers make up about 40%. Workers marked as transfer workers later appear as foragers, while those marked as foragers die and disappear from the foraging population, suggesting that transfer workers are younger, and age into foraging. The importance of these findings for laboratory studies of division of labor are discussed. The efficient allocation of labor is a key component of superorganismal fitness.
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an illustrated guide to seeds found in nests of the florida Harvester Ant pogonomyrmex badius
PLOS ONE, 2017Co-Authors: Walter R. Tschinkel, Daniel J DominguezAbstract:The Florida Harvester Ant, Pogonomyrmex badius collects the seeds of many plAnt species and stores them in underground nest chambers for later consumption. Seeds taken from multiple nests in 1989, 2014 and 2015 were separated by size and species and identified through published keys, comparison with herbarium specimens and with identified seed collections. Harvester Ants stored at least 58 species of seeds from 20 plAnt families in their chambers. This paper presents images of each seed species in several aspects, their relative abundance in P. badius nests, their size relative to the smallest, and links to online data and images of the parent plAnt species, as well as to herbarium specimens. A number of seeds and plAnt families present at the site were not found in Ant nests. These data and images will be valuable for future studies and experiments to untangle the choices the Ants make in relation to what the plAnts and the seasons offer them.
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lifespan age size specific mortality and dispersion of colonies of the florida Harvester Ant pogonomyrmex badius
Insectes Sociaux, 2017Co-Authors: Walter R. TschinkelAbstract:Colonies of social insects such as Ants have species-typical life history attributes that include mature colony size, mortality rate, size at first reproduction, lifespan, reproductive investment and many others. A population of over 400 colonies of the Florida Harvester Ant, Pogonomyrmex badius, was repeatedly resurveyed over 6 years, producing a record of deaths, births, colony sizes and relocations. From these data the life span, growth rate and colony-size-specific mortality rates were determined. Colonies averaged about 2500 workers and ranged from less than 500 up to 10,000. The annual mortality rate of colonies decreased from about 25% for the smallest colonies, to about 6% for mid-sized colonies. Under steady-state assumptions, these extrapolate to lifespans of about 4 and 17 year, respectively. Over 90% of the largest colonies were still alive after 6 years, so that their lifespan could not be reliably determined, but probably exceeded 30 years or more. As new colonies grew, their probability of surviving increased, but many colonies stabilized at less than maximum size, thus remaining subject to the mortality rates characteristic of their size, not age. At the level of the whole population, colonies were significAntly clumped, probably as the result of habitat heterogeneity. Large colonies were associated with more open areas. Colonies with more and/or larger neighbors had moderately higher mortality rates. This rate increased as size asymmetry increased. The need for demographic data on Ant species with a range of mature colony sizes is discussed.
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the florida Harvester Ant pogonomyrmex badius relies on germination to consume large seeds
PLOS ONE, 2016Co-Authors: Walter R. Tschinkel, Christina L. KwapichAbstract:The Florida Harvester Ant, Pogonomyrmex badius, is one of many Ant species and genera that stores large numbers of seeds in damp, underground chambers for later consumption. A comparison of the sizes of seeds recovered from storage chambers with those of seed husks discarded following consumption revealed that the used seeds are far smaller than stored seeds. This difference in use-rate was confirmed in field and laboratory colonies by offering marked seeds of various sizes and monitoring the appearance of size-specific chaff. Because foragers collect a range of seed sizes but only open small seeds, large seeds accumulate, forming 70% or more of the weight of seed stores. Major workers increase the rates at which small and medium seeds are opened, but do not increase the size range of opened seeds. Experiments limiting Ant access to portions of natural seed chambers showed that seeds germinate during storage, but that the Ants rapidly remove them. When offered alongside non germinating seeds, germinating seeds were preferentially fed to larvae. The rate of germination during the annual cycle was determined by both burial in artificial chambers at various depths and under four laboratory temperatures. The germination rate depends upon the species of seed, the soil/laboratory temperature and/or the elapsed time. The seasonal soil temperature cycle generated germination patterns that vary with the mix of locally-available seeds. Taken together, exploitation of germination greatly increases the resources available to the Ants in space and time. While the largest seeds may have the nutritional value of 15 small seeds, the inability of workers to open large seeds at will precludes them from rapid use during catastrophic events. The Harvester Ant's approach to seed harvesting is therefore two-pronged, with both immediate and delayed payoffs arising from the tendency to forage for a wide variety of seeds sizes.
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Limited flexibility and unusual longevity shape forager allocation in the Florida Harvester Ant (Pogonomyrmex badius)
Behavioral Ecology and Sociobiology, 2016Co-Authors: Christina L. Kwapich, Walter R. TschinkelAbstract:The benefits of behavioral flexibility in social insect societies are well known, but the advAntages of limited flexibility have seldom been considered. Florida Harvester Ant colonies maintain a stable forager population size for much of their active season, and despite seasonal variation in chronological age, foragers die within 27 days of initiating foraging. To determine how colonies balance forager mortality and forager replacement, we tested the relative influences of intrinsic and extrinsic factors on forager membership, retention, and longevity. Potential and realized forager longevity differed significAntly. Residual lifespan increased by 57 % when colonies were penned for 20 days, and up to 8-fold when foragers were retained in the laboratory. Increased forager longevity inhibited the movement of new workers into the forager population. In contrast, increased mortality and starvation did not stimulate the addition of new foragers and forager population size declined when mortality exceeded 4 % per day. Experimental increases in forager number, body fat, and the ratio of larvae to foragers did not induce behavioral reversion in existing foragers. These results suggest an unidirectional allocation strategy, with foragers that are less disposable and less behaviorally flexible than the well-studied honey bee. In P. badius , forager membership is maintained not by young Ants detecting increased demand, but by workers developing at rates that allow forager replacement and prevent excessive worker depletion. In the absence of a lifespan matched to predictable risks, opportunistic increases in forager survival may promote colony growth by inhibiting the scheduled and irreversible transitions of younger workers.
Jennifer H Fewell - One of the best experts on this subject based on the ideXlab platform.
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gene expression and variation in social aggression by queens of the Harvester Ant pogonomyrmex californicus
Molecular Ecology, 2016Co-Authors: Martin Helmkampf, Jennifer H Fewell, Alexander S Mikheyev, Yun Kang, Juergen GadauAbstract:A key requirement for social cooperation is the mitigation and/or social regulation of aggression towards other group members. Populations of the Harvester Ant Pogonomyrmex californicus show the alternate social phenotypes of queens founding nests alone (haplometrosis) or in groups of unrelated yet cooperative individuals (pleometrosis). Pleometrotic queens display an associated reduction in aggression. To understand the proximate drivers behind this variation, we placed foundresses of the two populations into social environments with queens from the same or the alternate population, and measured their behaviour and head gene expression profiles. A proportion of queens from both populations behaved aggressively, but haplometrotic queens were significAntly more likely to perform aggressive acts, and conflict escalated more frequently in pairs of haplometrotic queens. Whole-head RNA sequencing revealed variation in gene expression patterns, with the two populations showing moderate differentiation in overall transcriptional profile, suggesting that genetic differences underlie the two founding strategies. The largest detected difference, however, was associated with aggression, regardless of queen founding type. Several modules of coregulated genes, involved in metabolism, immune system and neuronal function, were found to be upregulated in highly aggressive queens. Conversely, nonaggressive queens exhibited a striking pattern of upregulation in chemosensory genes. Our results highlight that the social phenotypes of cooperative vs. solitary nest founding tap into a set of gene regulatory networks that seem to govern aggression level. We also present a number of highly connected hub genes associated with aggression, providing opportunity to further study the genetic underpinnings of social conflict and tolerance.
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the foundress s dilemma group selection for cooperation among queens of the Harvester Ant pogonomyrmex californicus
Scientific Reports, 2016Co-Authors: Zachary Shaffer, Stephen C Pratt, Takao Sasaki, Brian Haney, Marco A Janssen, Jennifer H FewellAbstract:The evolution of cooperation is a fundamental problem in biology, especially for non-relatives, where indirect fitness benefits cannot counter within-group inequalities. Multilevel selection models show how cooperation can evolve if it generates a group-level advAntage, even when cooperators are disadvAntaged within their group. This allows the possibility of group selection, but few examples have been described in nature. Here we show that group selection can explain the evolution of cooperative nest founding in the Harvester Ant Pogonomyrmex californicus. Through most of this species’ range, colonies are founded by single queens, but in some populations nests are instead founded by cooperative groups of unrelated queens. In mixed groups of cooperative and single-founding queens, we found that aggressive individuals had a survival advAntage within their nest, but foundress groups with such non-cooperators died out more often than those with only cooperative members. An agent-based model shows that the between-group advAntage of the cooperative phenotype drives it to fixation, despite its within-group disadvAntage, but only when population density is high enough to make between-group competition intense. Field data show higher nest density in a population where cooperative founding is common, consistent with greater density driving the evolution of cooperative foundation through group selection.
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behavioral transitions with the evolution of cooperative nest founding by Harvester Ant queens
Behavioral Ecology and Sociobiology, 2014Co-Authors: Rick P Overson, Juergen Gadau, Rebecca M Clark, Stephen C Pratt, Jennifer H FewellAbstract:Research on the evolution of cooperative groups tends to explore the costs and benefits of cooperation, with less focus on the proximate behavioral changes necessary for the transition from solitary to cooperative living. However, understanding what proximate changes must occur, as well as those pre-conditions already in place, is critical to understand- ing the origins and evolution of sociality. The California Harvester Ant Pogonomyrmex californicus demonstrates population-level variation in colony founding over a close geographic range. In adjacent populations, queens either found nests as single individuals (haplometrosis) or form cooperative groups of nonrelatives (pleometrosis). We com- pared aggregation, aggression, and tolerance of queens from one pleometrotic and two haplometrotic populations during nest initiation, to determine which behaviors show an evolu- tionary shift and which are present at the transition to pleometrosis. Surprisingly, within-nest aggregative behavior was equally present among all populations. In nesting boxes with multiple available brood-rearing sites, both queen types readily formed and clustered around a single common brood pile, suggesting that innate attraction to brood (offspring) facilitates the transition to social aggregation. In contrast, queens from the three populations differed in their probabili- ties of attraction on the ground to nest sites occupied by other queens and in levels of aggression. Our results suggest that
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colony size effects on task organization in the Harvester Ant pogonomyrmex californicus
Insectes Sociaux, 2013Co-Authors: Juergen Gadau, C T Holbrook, T H Eriksson, Rick P Overson, Jennifer H FewellAbstract:Colony size is a fundamental attribute of insect societies that appears to play an importAnt role in their organization of work. In the Harvester Ant Pogonomyrmex californicus, division of labor increases with colony size during colony ontogeny and among unmanipulated colonies of the same age. However, the mechanism(s) integrating individual task specialization and colony size is unknown. To test whether the scaling of division of labor is an emergent epiphenomenon, as predicted by self-organizational models of task performance, we manipulated colony size in P. californicus and quAntified short-term behavioral responses of individuals and colonies. Variation in colony size failed to elicit a change in division of labor, suggesting that colony-size effects on task specialization are mediated by slower developmental processes and/or correlates of colony size that were missing from our experiment. In contrast, the proportional allocation of workers to tasks shifted with colony size, suggesting that task needs or priorities depend, in part, on colony size alone. Finally, although task allocation was flexible, colony members differed consistently in task performance and spatial tendency across colony size treatments. Sources of interindividual behavioral variability include worker age and genotype (matriline).
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division of labor increases with colony size in the Harvester Ant pogonomyrmex californicus
Behavioral Ecology, 2011Co-Authors: Tate C Holbrook, Phillip Barden, Jennifer H FewellAbstract:Size has profound consequences for the structure and function of biological systems, across levels of organization from cells to social groups. As tightly integrated units that vary greatly in size, eusocial insect colonies, in particular, are expected to exhibit social scaling relations. To address the question of how social organization scales with colony size, we quAntified task performance in variably sized colonies of the Harvester Ant Pogonomyrmex californicus. We found a positive scaling relationship between colony size and division of labor in 2 different contexts. First, individual workers were more specialized in older, larger colonies. Second, division of labor increased with colony size, independently of colony age. Moreover, the proportional allocation of workers to tasks shifted during colony ontogeny—older, larger colonies performed relatively less brood care—but did not vary with colony size among same-aged colonies. There were no colony-size effects on per capita activity or the distribution of activity across workers. Size-related changes in task performance were correlated with changes in the rate of encounter between nest mates. These results highlight the importance of colony size for the organization of work in insect societies and raise broader questions about the role of size in sociobiology. Key words: biological scaling, encounter rate, group size, social insects, task allocation, task specialization. [Behav Ecol]
Diane C Wiernasz - One of the best experts on this subject based on the ideXlab platform.
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the structure of foraging activity in colonies of the Harvester Ant pogonomyrmex occidentalis
Behavioral Ecology, 2010Co-Authors: Blaine J Cole, Adrian A Smith, Zachary J Huber, Diane C WiernaszAbstract:The timing of activity by desert dwelling poikilotherms can be critical to survival. In the western Harvester Ant, colonies that have higher levels of genetic diversity forage for longer time periods in the morning than colonies with less diversity. We determined whether the advAntage of early foraging colonies was consistent by examining foraging behavior at other times of day and year. We used a combination of activity monitoring and temperature measurement at the nest entrance to quAntify foraging activity during the morning and evening summer foraging periods in both June and August. The duration of morning and evening foraging was significAntly positively correlated both within and across seasons—some colonies have a consistent advAntage in foraging. The temperature range over which colonies foraged was also consistent across time, suggesting that intercolony differences are a consequence of variation in the thermal ranges/preferences of the colony’s workers. The duration of foraging during this study was correlated with the duration of foraging measured 6 years earlier, suggesting that it is an aspect of colony phenotype. Key words: activity pattern, compensation, foraging, genetic diversity, Harvester Ants, Pogonomyrmex. [Behav Ecol]
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mating for variety increases foraging activity in the Harvester Ant pogonomyrmex occidentalis
Molecular Ecology, 2008Co-Authors: Diane C Wiernasz, Jessica Hines, Dara G Parker, Blaine J ColeAbstract:Multiple mating by females characterizes most insect species, but is relatively uncommon in social insects. Females may mate with multiple mates because they experience the direct benefits of increased survival or fecundity, to acquire high quality mates, or to lower the risk of reduced fecundity by mating with incompatible males. We used the extensive natural variation in mating frequency in the western Harvester Ant, Pogonomyrmex occidentalis, to test the hypothesis that increased mating by the queen leads to an increase in colony performance. Colonies with greater genetic diversity began to forage earlier in the day and foraged for longer time periods. The workers which initiated foraging were a nonrandom subset of the genotypes present in the colony. We used a statistical approach to correctly predict the direction and magnitude of the correlation between genetic diversity and colony foraging activity.
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recruitment limitation and population density in the Harvester Ant pogonomyrmex occidentalis
Ecology, 2002Co-Authors: Blaine J Cole, Diane C WiernaszAbstract:We evaluated the hypothesis that recruitment limitation is importAnt in determining density in Harvester Ant populations. Combining field observations and experiments, we conclude that the population density of Pogonomyrmex occidentalis is largely determined by recruitment limitation, and we demonstrate that variation in population density is a function of the dispersal patterns of foundress queens. The density of established colonies, the number of new colonies, and the number of foundress queens are all highly correlated in this population. The density of foundress queens predicts the density of new colonies in the following year. The density of propagules (foundress queens), new colonies, and established colonies is significAntly negatively correlated with the distance from the mating site that is the source of the propagules, and the distance from this source can be used to predict the local density of new and established colonies in this population. Finally, we show that the experimental addition of foundress queens significAntly increases the number of new colonies in supplemented vs. control plots. At the landscape level, the population is a mixture of areas with low and high density, with no evidence of overall density dependence. Density dependence is detectable only in local areas that receive sufficient propagules and, thus, depends on the proximity to the source of propagules. Consistent dispersal from a specific geographic site results in variation in population density independent of any variation in habitat quality.
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male size sperm transfer and colony fitness in the western Harvester Ant pogonomyrmex occidentalis
Evolution, 2001Co-Authors: Diane C Wiernasz, Amy K Sater, Allison J Abell, Blaine J ColeAbstract:Mating success in the western Harvester Ant, Pogonomyrmex occidentalis, increases with male size. We tested the hypothesis that increased mating success increases male fitness and the fitness of colonies that make large males by comparing the sperm content of males prior to and at the conclusion of the mating swarm. The number of sperm a male initially possesses is a function of male size, and large males transfer a greater proportion of their sperm than do small males. For colonies, the payoff per unit of investment is an increasing function of male size, and investment in large males is not equivalent to investing in a larger number of small males. Allocation ratios in species that show size variation in reproductives may need to be modified by the individual fitness functions.
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colony size and reproduction in the western Harvester Ant pogonomyrmex occidentalis
Insectes Sociaux, 2000Co-Authors: Blaine J Cole, Diane C WiernaszAbstract:We report data from a four-year field study on the relationship between colony size and reproduction in the western Harvester Ant, Pogonomyrmex occidentalis. In all years, the likelihood of reproduction significAntly increased with increasing size in both field censuses during naturally-occurring mating flights and experimentally-watered colonies whose entire reproductive output was collected. However, the total amount of reproductive biomass was unrelated to colony size. We describe the size threshold for reproduction in P. occidentalis and show that it varies across years. Once colonies become reproductively mature, they reproduce consistently although not in every year. We describe a method for collecting the entire reproductive output for desert Ants whose reproductive flights are cued by rainfall.
Robert A. Johnson - One of the best experts on this subject based on the ideXlab platform.
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desiccation limits recruitment in the pleometrotic desert seed Harvester Ant veromessor pergandei
Ecology and Evolution, 2021Co-Authors: Robert A. JohnsonAbstract:The desert Harvester Ant Veromessor pergandei displays geographic variation in colony founding with queens initiating nests singly (haplometrosis) or in groups (pleometrosis). The transition from haplo- to pleometrotic founding is associated with lower rainfall. Numerous hypotheses have been proposed to explain the evolution of cooperative founding in this species, but the ultimate explanation remains unanswered. In laboratory experiments, water level was positively associated with survival, condition, and brood production by single queens. Queen survival also was positively influenced by water level and queen number in a two-factor experiment. Water level also was a significAnt effect for three measures of queen condition, but queen number was not significAnt for any measure. Foundress queens excavated after two weeks of desiccating conditions were dehydrated compared to alate queens captured from their natal colony, indicating that desiccation can be a source of queen mortality. Long-term monitoring in central Arizona, USA, documented that recruitment only occurred in four of 20 years. A discriminAnt analysis using rainfall as a predictor of recruitment correctly predicted recruitment in 17 of 20 years for total rainfall from January to June (the period for mating flights and establishment) and in 19 of 20 years for early plus late rainfall (January-March and April-June, respectively), often with a posterior probability > 0.90. Moreover, recruitment occurred only in years in which both early and late rainfall exceeded the long-term mean. This result also was supported by the discriminAnt analysis predicting no recruitment when long-term mean early and late rainfall were included as ungrouped periods. These data suggest that pleometrosis in V. pergandei evolved to enhance colony survival in areas with harsh abiotic (desiccating) conditions, facilitating colonization of habitats in which solitary queens could not establish even in wet years. This favorable-year hypothesis supports enhanced worker production as the primary advAntage of pleometrosis.
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effect of cuticular abrasion and recovery on water loss rates in queens of the desert Harvester Ant messor pergandei
The Journal of Experimental Biology, 2011Co-Authors: Robert A. Johnson, Alexander Kaiser, Michael C Quinlan, William P SharpAbstract:Factors that affect water loss rates (WLRs) are poorly known for organisms in natural habitats. Seed-Harvester Ant queens provide an ideal system for examining such factors because WLRs for mated queens excavated from their incipient nests are twofold to threefold higher than those of alate queens. Indirect data suggest that this increase results from soil particles abrading the cuticle during nest excavation. This study provides direct support for the cuticle abrasion hypothesis by measuring total mass-specific WLRs, cuticular abrasion, cuticular transpiration, respiratory water loss and metabolic rate for queens of the Ant Messor pergandei at three stages: unmated alate queens, newly mated dealate queens (undug foundresses) and mated queens excavated from their incipient nest (dug foundresses); in addition we examined these processes in artificially abraded alate queens. Alate queens had low WLRs and low levels of cuticle abrasion, whereas dug foundresses had high WLRs and high levels of cuticle abrasion. Total WLR and cuticular transpiration were lowest for alate queens, intermediate for undug foundresses and highest for dug foundresses. Respiratory water loss contributed ~10% of the total WLR and was lower for alate queens and undug foundresses than for dug foundresses. Metabolic rate did not vary across stages. Total WLR and cuticular transpiration of artificially abraded alate queens increased, whereas respiratory water loss and metabolic rate were unaffected. Overall, increased cuticular transpiration accounted for essentially all the increased total water loss in undug and dug foundresses and artificially abraded queens. Artificially abraded queens and dug foundresses showed partial recovery after 14 days.
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The Old Ladies of the Seed Harvester Ant Pogonomyrmex Rugosus: Foraging Performed by Two Groups of Workers
Journal of insect behavior, 2008Co-Authors: Jan Oettler, Robert A. JohnsonAbstract:We examined temporal polyethism in Pogonomyrmex rugosus, predicting a pattern of decreasing age from foragers to nest maintenance workers to individuals that were recruited to harvest a temporary food source. Nest maintenance workers were younger than foragers, as indicated by their heavier mass and lower mandibular wear. In contrast, recruited foragers were similar in mass to foragers but they displayed higher mandibular wear, suggesting that they were at least as old as foragers. Longevity estimates for marked individuals of these two latter task groups showed mixed results. Higher mandibular wear of recruited foragers suggests that they did not follow the normal sequence for temporal polyethism, but rather that they functioned as seed-millers, which should more quickly abrade their dentition. This would be the first demonstration of specialist milling individuals in a monomorphic seed-Harvester Ant.
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population and colony structure and morphometrics in the queen dimorphic Harvester Ant pogonomyrmex pima
Insectes Sociaux, 2007Co-Authors: Robert A. Johnson, Christoph Peter Strehl, Juergen Gadau, C T HolbrookAbstract:The North American seed-Harvester Ant Pogonomyrmex (Ephebomyrmex) pima displays a dimorphism that consists of winged (alate) and wingless (intermorph) queens; both types of queens are fully reproductive. Microsatellite allele frequencies and a mitochondrial phylogeny demonstrate (1) alate and intermorph queens represent an intraspecific wing polymorphism, and (2) an absence of assortative mating and inbreeding by males. Surveys at our field site in southcentral Arizona, USA, demonstrated that only one type of queen (intermorph or dealate) occurred in each colony, including those excavated during the season in which reproductive sexuals were present. Colony structure appeared to vary by queen type as most intermorph colonies contained multiple mated queens. Alternatively, dealate queen colonies rarely contained a mated queen. Our inability to find mated dealate queens in these colonies probably resulted from difficulty in excavating the entire colony and reproductive queen, especially given that these colonies were only excavated over one day. A morphometric analysis demonstrated that intermorph queens are intermediate in size to that of workers and alate queens, but that intermorph queens retain all of the specialized anatomical features of alate queens (except for wings). Some colonies had queens that foraged and performed nest maintenance activities, and these queens sometimes accounted for a significAnt portion of colony foraging trips. Dissections revealed that these queens were uninseminated; some of these queens produced males in the laboratory.
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colony founding by pleometrosis in the semiclaustral seed Harvester Ant pogonomyrmex californicus hymenoptera formicidae
Animal Behaviour, 2004Co-Authors: Robert A. JohnsonAbstract:Pleometrosis, or colony founding via multiple queens, occurs in a localized population of the seed-Harvester Ant Pogonomyrmex californicus. In an apparently unusual secondary modification, queens of P. californicus are also obligate foragers; that is, queens must forage to garner the resources necessary to rear their first brood. Laboratory experiments measured the costs and benefits of pleometrosis and queen foraging in P. californicus in terms of queen survival, mass loss by queens and brood production. In all experiments, queen survival was positively associated with number of queens. Queen survival also varied with food level: survival was higher in fed treatments compared with unfed treatments at low queen numbers, whereas survival of unfed queens increased to the level of fed queens at higher queen numbers. Total mass loss of queens varied by food level, but not queen number, with fed queens losing about 50% less mass than unfed queens. Brood production also varied with queen number and food level. Total number of brood was positively associated with number of queens; at each queen number, fed queens produced more brood than unfed queens. The number of brood produced per queen, however, was similar across queen numbers. Fed queens also produced workers that were heavier than those produced by unfed queens, whereas head width of these minims was similar. Longer-term experiments revealed that these queen associations do not undergo queen reduction upon emergence of the first workers, but rather exhibit primary polygyny.
