Robert A Johnson

• Ph.D.
• Professor (Associate) at Arizona State University

surveys for ants on the Falkland Islands

This paper provides a taxonomic revision and a review of the biology for the 10 species of North American seed-harvester ants in the genus Veromessor. Two new synonomies are proposed: V. julianus subsp. clarior W.M. Wheeler and Creighton 1934 new synonym and V. julianus subsp. manni W.M. Wheeler and Creighton 1934 new synonym are synonomized under...

The eyes of insects display an incredible diversity of adaptations to enhance vision across the gamut of light levels that they experience. One commonly studied contrast is the difference in eye structure between nocturnal and diurnal species, with nocturnal species typically having features that enhance eye sensitivity such as larger eyes, larger...

Invertebrates constitute the majority of animal species and are critical for ecosystem functioning and services. Nonetheless, global invertebrate biodiversity patterns and their congruences with vertebrates remain largely unknown. We resolve the first high-resolution (~20-km) global diversity map for a major invertebrate clade, ants, using biodiver...

The eyes of insects display an incredible diversity of adaptations to enhance vision across the gamut of light levels that they experience. One commonly studied contrast is the difference in eye structure between nocturnal and diurnal species, with nocturnal species typically having features that enhance eye sensitivity such as larger eyes, larger...

This paper provides a taxonomic revision and reviews natural history for 35 South American species of the seed-harvesting ant genus Pogonomyrmex. Species treated herein mostly comprise the P. rastratus-group; four species are revived from synonomy, three taxa are elevated from subspecies to species, five taxa are synonymized, and 20 new species are...

The New World ant genus Myrmecocystus Wesmael, 1838 (Formicidae: Formicinae: Lasiini) is endemic to arid and semi-arid habitats of the western United States and Mexico. Several intriguing life history traits have been described for the genus, the best-known of which are replete workers, that store liquified food in their largely expanded crops and...

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...

Over 40 years ago, the dacetine ant Strumigenys arizonica was discovered in a nest of the fungus-growing ant Trachymyrmex arizonensis at Madera Canyon in the Santa Rita Mountains of the southwestern United States. This discovery suggested that the two species form compound nests, but this hypothesis has not been investigated. Here, we characterize...

Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the USA, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA-sequence and microsatellite-marker analyses of 474 cultivars...

The North American little black ant, Monomorium sp. AZ-02 (subfamily Myrmicinae), displays a dimorphism that consists of alate (winged) and ergatoid (wingless) queens. Surveys at our field site in southcentral Arizona, USA, demonstrated that only one queen phenotype (alate or ergatoid) occurred in each colony during the season in which reproductive...

(XLSX)

The ant genus Pogonomyrmex (Hymenoptera: Formicidae: Myrmicinae) comprises 71 described species that occur in North America, South America, and Hispaniola, and it is the nominal genus in the recently established tribe Pogonomyrmecini. A molecular phylogeny using 3,647 base pairs from fragments of one mitochondrial gene (cytochrome oxidase I) and fi...

Recently a new species of bombyliid fly, Marleyimyia xylocopae, was described by Marshall & Evenhuis (2015) based on two photographs taken during fieldwork in the Republic of South Africa. This species has no preserved holotype. The paper generated some buzz, especially among dipterists, because in most cases photographs taken in the field provide...

South American species in the seed-harvester ant genus Pogonomyrmex (subfamily Myrmicinae) are interesting biologically because of their numerous queen phenotypes and life histories. This paper provides a taxonomic revision and reviews the natural history for 21 South American species of Pogonomyrmex so that we can better study their rich and inter...

A fundamental and enduring problem in evolutionary biology is to understand how populations differentiate in the wild, yet little is known about what role organismal development plays in this process. Organismal development integrates environmental inputs with the action of gene regulatory networks to generate the phenotype. Core developmental gene...

We revise species of seed-harvester ants in the genus Pogonomyrmex (subfamily Myrmicinae) that occur on the Caribbean island of Hispaniola. Three species are recognized: P. aterrimus Wheeler (new status), P. saucius Wheeler and Mann, and P. schmitti Forel. Pogonomyrmex schmitti sublaevigatus Wheeler (= schmitti) and P. schmitti darlingtoni Wheeler...

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We combined behavioral analyses in the laboratory and field to investigate chemical communication in the formation of foraging columns in two Nearctic seed harvesting ants, Messor pergandei and Messor andrei. We demonstrate that both species use poison gland secretions to lay recruitment trails. In M. pergandei, the recruitment effect of the poison...

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 plu...

The genus Messor consists of 113 species of seed harvesting ants that are found in grasslands, semi-arid areas and savan-nahs in both the Old and New World. A full spectrum of foraging strategies occurs in Messor, ranging from individual to group foraging, with the latter having evolved several times. This paper reviews foraging strategies and the...

The South American seed-harvester ant Pogonomyrmex laticeps has dimorphic queens: ergatoid (permanently wingless) and brachypterous (short, non-functional wings). Surveys in western Argentina indicated that colonies near Chilecito, La Rioja Province, produced only ergatoid queens, while those near Punta Balasto, Catamarca Province (263 km away), pr...

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 f...

Hybridizing harvester ants of the Pogonomyrmex barbatus/rugosus complex have an exceptional genetic caste determination (GCD) mechanism. We combined computer simulations, population genomics, and linkage mapping using >1000 nuclear AFLP markers and a partial mtDNA sequence to explore the genetic architecture and origin of the dependent lineages. Ou...

Ant queens exhibit two primary strategies to initiate nests, independent colony founding (ICF) by solitary queens and dependent colony founding (DCF) when the queen starts a nest with a group of workers that disperse on foot from the parent nest. Numerous ant species have wingless (ergatoid) queens, and it is generally assumed that these species ex...

Pogonomyrmex mohavensis Johnson sp. nov. is described from the Mohave Desert of eastern California and western Nevada, USA. A mitochondrial phylogeny affirmed taxonomie validity of P. mohavensis, and inferred that it is most closely related to Pogonomyrmex snellingi. Field observations and a distribution map for P. mohavensis are also provided, alo...

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 for...

We used discriminant analysis to assess taxonomic status of three closely related, rare taxa within the cactus genus Escobaria (E. guadalupensis, E. sneedii var. sneedii, and E. sneedii var. leei). These three taxa consist of nine isolated populations; six of these populations consist of morphologically typical specimens (i.e., similar to the type...

We revise and key Trachymyrmex ants occurring in North America north of Mexico. We recognize nine species, including one new species from southern Arizona: T. arizonensis (Wheeler), T. carinatus Mackay & Mackay, T. desertorum (Wheeler), T. jamaicensis (André), T. nogalensis Byars, T. pomonae Rabeling & Cover sp. nov., T. septentrionalis (McCook), T...

We revise and key Trachymyrmex ants occurring in North America north of Mexico. We recognize nine species, including one new species from southern Arizona: T. arizonensis (Wheeler), T. carinatus Mackay & Mackay, T. desertorum (Wheeler), T. jamaicensis (André), T. nogalensis Byars, T. pomonae Rabeling & Cover sp. nov., T. septentrionalis (McCook), T...

The evolution of polyandry is a central problem in the study of insect mating systems, and both material and genetic benefits have been proposed to offset the presumed costs of multiple mating. Although most eusocial Hymenoptera queens mate with just one or occasionally two males, high levels of polyandry are exhibited by several taxa, including se...

The evolution of mating systems in eusocial Hymenoptera is constrained because females mate only during a brief period early in life, whereas inseminated queens and their stored sperm may live for decades. Considerable research effort during recent years has firmly established that obligate multiple mating has evolved only a few times: in Apis hone...

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 polymo...

We examined the distribution and ancestral relationships of genetic caste determination (GCD) in 46 populations of the seed-harvester ants Pogonomyrmex barbatus and P. rugosus across the east-to-west range of their distributions. Using a mtDNA sequence and two nuclear markers diagnostic for GCD, we distinguished three classes of population phenotyp...

Water is the most limiting factor in deserts, yet researchers have very different emphases on the relative importance of water, depending on the organisms that they study. For example, soil moisture is considered the most critical factor for recruitment of desert succulent plants, and numerous studies have linked plant distribution patterns with so...