Rick P Overson

PhD
PostDoc Position
Chicago Botanic Garden

Publications

  • Source
    Behavioral Ecology and Sociobiology 01/2013; · 2.75 Impact Factor
  • Robert A. Johnson, Rick P. Overson, Corrie Moreau
    [Show abstract] [Hide abstract]
    ABSTRACT: Pogonomyrmex magnacanthus Cole was described as a distinct species; unusually large eyes and a high ocular index (maximum eye diameter/head width) were listed as diagnostic characters. However, examination of numerous series of P. magnacanthus revealed that both characters were highly variable, and that these series consisted of P. magnacanthus plus an undescribed species, Pogonomyrmex hoelldobleri Johnson, Overson & Moreau sp. nov. This paper describes all three castes of P. hoelldobleri as well as the alate queen of P. mohavensis, which is very similar to that of P. hoelldobleri. A molecular phylogeny that consisted of 3,703 bp from one mitochondrial and five nuclear gene fragments supported the monophyly of P. hoelldobleri, P. magnacanthus, and P. mohavensis. Pogonomyrmex magnacanthus can be separated from other P. californicus group species based on: (1) its unusually large eyes, (2) a high ocular index, and (3) a malar ratio that is typically < 1.0. Pogonomyrmex hoelldobleri can be separated from other P. californicus group species based on the combination of: (1) eyes not unusually large, (2) cephalic rugae not forming circumocular whorls, but rather converging posterior to the eyes, usually near the vertex, (3) mandible with seven teeth, and (4) interrugal spaces on pronotal sides moderately to strongly granulate, dull to weakly shining. Pogonomyrmex mohavensis can be separated from other P. californicus group species based on the combination of: (1) eyes not unusually large, (2) cephalic rugae not forming circum-ocular whorls, but rather extending more or less directly to the vertex or converging only slightly near the vertex, (3) mandible with six teeth (a seventh sometimes occurs as a denticle between the basal and sub-basal teeth), and (4) interrugal spaces on pronotal sides smooth and shining to weakly punctate and moderately shining. We also provide field observations and distribution maps for P. magnacanthus, P. hoelldobleri, and P. mohavensis, and an updated key to P. californicus group species that occur in central and western North America.
    Zootaxa 01/2013; 3646(3):201-227. · 1.06 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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).
    Insectes Sociaux 01/2013; · 1.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A reproductive division of labor between subordinates and established reproductives is a hallmark of eusociality. In most groups, however, workers retain some reproductive capabilities. Across insect societies, measures of successful worker reproduction in the presence of a queen, with few exceptions, indicate that worker reproduction is kept at very low levels. There are, however, certain colony-level characteristics that may influence the degree to which worker reproduction is promoted, such as queen number, queen mating frequency, and physical presence of a queen in species with multiple nesting sites (polydomy). In this study, the level of worker reproduction in field colonies of the ant species Aphaenogaster cockerelli was measured. A. cockerelli is a monogynous and polydomous species, so worker reproduction across nesting sites was investigated. None of the 297 males sampled provided any evidence of worker reproduction. Worker reproduction would have been detectable if it was present at or above a level of 1.5 % of the total males per colony. An effective mating frequency for queens of this species was found to be 1.03. Although A. cockerelli colonies have many colony-level factors potentially promoting worker reproduction (workers with active, trophic egg-producing ovaries, a single singly-mated queen, workers who are physically separated from the queen), it is evident that worker reproduction is highly regulated. Synthesizing the extensive amount of policing and fertility signaling data previously reported on this species, A. cockerelli is presented as case study for how worker reproduction is repressed and cooperation is maintained in insect societies.
    Insectes Sociaux 01/2012; 59(3):411-416. · 1.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ants are some of the most abundant and familiar animals on Earth, and they play vital roles in most terrestrial ecosystems. Although all ants are eusocial, and display a variety of complex and fascinating behaviors, few genomic resources exist for them. Here, we report the draft genome sequence of a particularly widespread and well-studied species, the invasive Argentine ant (Linepithema humile), which was accomplished using a combination of 454 (Roche) and Illumina sequencing and community-based funding rather than federal grant support. Manual annotation of >1,000 genes from a variety of different gene families and functional classes reveals unique features of the Argentine ant's biology, as well as similarities to Apis mellifera and Nasonia vitripennis. Distinctive features of the Argentine ant genome include remarkable expansions of gustatory (116 genes) and odorant receptors (367 genes), an abundance of cytochrome P450 genes (>110), lineage-specific expansions of yellow/major royal jelly proteins and desaturases, and complete CpG DNA methylation and RNAi toolkits. The Argentine ant genome contains fewer immune genes than Drosophila and Tribolium, which may reflect the prominent role played by behavioral and chemical suppression of pathogens. Analysis of the ratio of observed to expected CpG nucleotides for genes in the reproductive development and apoptosis pathways suggests higher levels of methylation than in the genome overall. The resources provided by this genome sequence will offer an abundance of tools for researchers seeking to illuminate the fascinating biology of this emerging model organism.
    Proceedings of the National Academy of Sciences 01/2011; 108(14):5673-8. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Leaf-cutter ants are one of the most important herbivorous insects in the Neotropics, harvesting vast quantities of fresh leaf material. The ants use leaves to cultivate a fungus that serves as the colony's primary food source. This obligate ant-fungus mutualism is one of the few occurrences of farming by non-humans and likely facilitated the formation of their massive colonies. Mature leaf-cutter ant colonies contain millions of workers ranging in size from small garden tenders to large soldiers, resulting in one of the most complex polymorphic caste systems within ants. To begin uncovering the genomic underpinnings of this system, we sequenced the genome of Atta cephalotes using 454 pyrosequencing. One prediction from this ant's lifestyle is that it has undergone genetic modifications that reflect its obligate dependence on the fungus for nutrients. Analysis of this genome sequence is consistent with this hypothesis, as we find evidence for reductions in genes related to nutrient acquisition. These include extensive reductions in serine proteases (which are likely unnecessary because proteolysis is not a primary mechanism used to process nutrients obtained from the fungus), a loss of genes involved in arginine biosynthesis (suggesting that this amino acid is obtained from the fungus), and the absence of a hexamerin (which sequesters amino acids during larval development in other insects). Following recent reports of genome sequences from other insects that engage in symbioses with beneficial microbes, the A. cephalotes genome provides new insights into the symbiotic lifestyle of this ant and advances our understanding of host-microbe symbioses.
    PLoS Genetics 01/2011; 7(2):e1002007. · 8.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the draft genome sequence of the red harvester ant, Pogonomyrmex barbatus. The genome was sequenced using 454 pyrosequencing, and the current assembly and annotation were completed in less than 1 y. Analyses of conserved gene groups (more than 1,200 manually annotated genes to date) suggest a high-quality assembly and annotation comparable to recently sequenced insect genomes using Sanger sequencing. The red harvester ant is a model for studying reproductive division of labor, phenotypic plasticity, and sociogenomics. Although the genome of P. barbatus is similar to other sequenced hymenopterans (Apis mellifera and Nasonia vitripennis) in GC content and compositional organization, and possesses a complete CpG methylation toolkit, its predicted genomic CpG content differs markedly from the other hymenopterans. Gene networks involved in generating key differences between the queen and worker castes (e.g., wings and ovaries) show signatures of increased methylation and suggest that ants and bees may have independently co-opted the same gene regulatory mechanisms for reproductive division of labor. Gene family expansions (e.g., 344 functional odorant receptors) and pseudogene accumulation in chemoreception and P450 genes compared with A. mellifera and N. vitripennis are consistent with major life-history changes during the adaptive radiation of Pogonomyrmex spp., perhaps in parallel with the development of the North American deserts.
    Proceedings of the National Academy of Sciences 01/2011; 108(14):5667-72. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Las hormigas granívoras Pogonomyrmex barbatus y P. rugosus son hospederos de las hormigas parásitas P. anergismus y P. colei. Recientes trabajos moleculares demostraron que la morfología es poco fiable para la identificación de los hospederos porque los hospederos están compuestos de especies crípticas. Usando análisis de secuencias de ADN mitocondrial, determinamos la identidad de 15 de 16 poblaciones de hospederos, y en nueve casos la identidad de la colonia hospedera particular. Los hospederos son de seis linajes aislados reproductivamente. Mientras que para P. colei se conoce un solo hospedero, para P. anergismus se conocen cinco hospederos diferentes y parece tener un rango de distribución geográfica mucho más amplio. Reportamos siete nuevos registros de localidades para P. anergismus. Las extensiones de la distribución geográfica de P. anergismus en los Estados Unidos abarcan el suroeste de Texas incluyendo el parque nacional Big Bend, el noroeste de Texas, el centro de Nuevo México, y el centro sur de Arizona. Discutimos factores que podrían influir en la dispersión de las hormigas parásitas y en la co-evolución parásito-hospedero.
    The Southwestern Naturalist 12/2010; · 0.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The international conference 'Social Biomimicry: Insect Societies and Human Design', hosted by Arizona State University, USA, 18-20 February 2010, explored how the collective behaviour and nest architecture of social insects can inspire innovative and effective solutions to human design challenges. It brought together biologists, designers, engineers, computer scientists, architects and businesspeople, with the dual aims of enriching biology and advancing biomimetic design.
    Biology letters 04/2010; 6(4):431-3. · 3.35 Impact Factor
  • ROBERT A Johnson, RICK P Overson
    Journal of Hymenoptera Research 01/2009; 18(2):305-314. · 0.97 Impact Factor

48 Following View all

41 Followers View all