Seed-harvester Ant Pogonomyrmex Research Articles

Distribution and origin of intraspecific social variation in the California harvester ant Pogonomyrmex californicus

The California seed harvester ant Pogonomyrmex californicus exhibits striking differences in queen behavior and colony organization throughout its range. Most populations show the likely ancestral condition of single-queen colonies (monogyny). However, in one known population, cooperation between queens during colony founding (pleometrosis) occurs, and is suspected to persist to the mature colony stage (primary polygyny). To better understand this variation in social phenotype, we estimate relatedness among co-foundresses, measure the frequency of polygyny in adult colonies across three focal populations, and assess population genetic structure between populations. We additionally measure queen mating frequency (polyandry) across focal populations. With few possible exceptions, queens within pleometrotic associations are unrelated. We demonstrate a correlation between pleometrosis in incipient colonies and polygyny in adult colonies at the population level. Nuclear microsatellites and mtDNA barcoding indicate significant structure between focal populations. Queens from all three focal populations engage in relatively high levels of polyandry. These findings, when examined with previous data demonstrating that pleometrosis leads to polygynous colonies in the laboratory, strongly suggest that the same occurs in nature. However, the possibility of additional queen adoption in adult colonies (secondary polygyny) is not excluded. Thus, polygynous P. californicus colonies potentially represent long-term associations of unrelated family groups, containing multiple unrelated queens and their mixed-paternity offspring. Due to its pronounced variation in social behavior, P. californicus provides a unique opportunity to examine the evolutionary history and genetic underpinnings of cooperation among non-relatives, a strategy of intense interest in behavioral ecology.

Persistence of Horned Lizards (Phrynosoma spp.) in urban preserves of Central Arizona

Urbanization is rapidly enveloping isolated remnants of Sonoran Desert habitat in southern Arizona. Understanding the means by which herpetofauna can persist in these habitats in the face of multiple impacts is vital to conservation efforts to retain intact biotic communities, especially those with a high diversity of reptile species. We surveyed ten preserves in the Phoenix Metropolitan region for Desert (Phrynosoma platyrhinos) and Regal (Phrynosoma solare) horned lizards, members of an iconic group of lizards of the Southwest. At least one horned lizard species is found in preserves across the range in size, age and habitat axes we assessed, provided that their primary prey, seed-harvester ants (Pogonomyrmex rugosus) are present. Horned lizards are apparently absent from one large preserve where they were once present, perhaps as a result of a decline in seed-harvester ants, but they may have been absent from other preserves due to the lack of appropriate habitat for their prey rather than due to direct anthropogenic impacts.

Selection against Aerial Dispersal in Ants: Two Non-Flying Queen Phenotypes in Pogonomyrmex laticeps

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), produced only brachypterous queens. Brachypterous queens were significantly larger than ergatoid queens for 10 of 11 external characters, but both phenotypes had comparable reproductive potential, i.e., a spermatheca and a similar number of ovarioles. Using normal winged queens of the closely related P. uruguayensis for comparison, we determined that both queen phenotypes in P. laticeps had a full set of dorsal thoracic sclerites, albeit each sclerite was much reduced, whereas workers had a thorax without distinct dorsal sclerites. Sclerites were fused and immobile in ergatoid queens, while they were separable and fully articulated in brachypterous queens. Both phenotypes lacked the big indirect flight muscles, but brachypterous queens retained the tiny direct flight muscles. Overall, this dimorphism across populations indicates that there are alternative solutions to selective pressures against flying queens. We lack field data about colony founding strategy (independent or dependent) for either queen phenotype, but colonies at both sites produced numerous gynes, and we infer that all foundresses initiate colonies independently and are obligate foragers.

Identification of Cryptic Hosts for Two Inquiline Parasites of the Seed-Harvester Ant Pogonomyrmex and New Localities for P. anergismus (Hymenoptera: Formicidae)

The harvester ants Pogonomyrmex barbatus and P. rugosus serve as hosts for the parasitic ants P. anergismus and P. colei. Recent molecular studies demonstrated that morphology is unreliable for identification of hosts because the hosts contain cryptic species. Using mitochondrial-DNA sequences, we determined identity of 15 of 16 known populations of hosts, and in 9 instances, the identity of the particular host colony. Hosts are composed of 6 reproductively isolated lineages. While P. colei is known only from a single host, P. anergismus occurs in five distinct hosts and appears to have a much broader geographic range. We report seven new locality records for P. anergismus. Range extensions for P. anergismus in the United States consist of southwestern Texas including Big Bend National Park, northwestern Texas, central New Mexico, and south-central Arizona. We discuss factors that may influence dispersal of parasitic ants and host-parasite co-evolution.

The Old Ladies of the Seed Harvester ant Pogonomyrmex Rugosus: Foraging Performed by Two Groups of Workers.

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.

Populations composed entirely of hybrid colonies: bidirectional hybridization and polyandry in harvester ants

In eusocial Hymenoptera, haplodiploid life cycles, obligate sterile castes, and polyandry may facilitate selection for hybridization. We analyzed a broad hybrid zone between the ecologically distinct seed-harvester ants Pogonomyrmex occidentalis (Cresson) and Pogonomyrmex maricopa (Wheeler) using mitochondrial (mt)DNA sequence data, eight morphological markers, and 14 random amplified polymorphic DNA (RAPD) markers. Average mtDNA sequence divergence among parental species was 11.34%, indicating secondary contact. RAPD markers were significantly correlated with morphological variation, confirming the interspecific hybrid origin of all morphologically putative hybrid colonies. A morphological hybrid index indicates an abundance of both F1 hybrids and parental morphotypes within colonies. Individual character frequencies plotted against distance show coincident and concordant clines, suggesting little to no introgression. The structure of the hybrid zone is two-fold. Within the western region, stark reversals in character frequencies coincide with overt soil differences, indicating a mosaic hybrid zone structure. The eastern region is a riparian habitat where four adjacent populations were composed entirely of hybrid colonies. These habitat associations suggest that hybrid worker genomes permit dispersal into intermediate environments that select against one or both parental species. The present study suggests that, in addition to retaining reproductive compatibility, ecologically distinct species of ants may generate hybrid colonies maintained by environmental selection. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 320–336.

Low queen mating frequency in the seed-harvester ant Pogonomyrmex (Ephebomyrmex) pima: implications for the evolution of polyandry

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 seed-harvester ants of the genus Pogonomyrmex. Previous studies of queen mating frequency in Pogonomyrmex have focused on monogynous (one queen per colony) species in the subgenus Pogonomyrmex. We performed a genetic mother–offspring analysis of mating frequency in Pogonomyrmex (Ephebomyrmex) pima, a queen-dimorphic species with dealate and intermorph queens that differ in colony structure (intermorph colonies contain multiple queens). Our results demonstrate that both dealate and intermorph queens of P. (E.) pima are typically single maters, unlike their congeners analyzed thus far. Polyandry appears to be a derived trait in Pogonomyrmex, but comparative tests between P. (E.) pima queen morphs and across the genus provide no evidence that it evolved as an adaptation to increase genetic diversity within colonies or to obtain more sperm, respectively.

Population and colony structure and morphometrics in the queen dimorphic harvester ant, Pogonomyrmex pima

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.

DISTRIBUTION AND EVOLUTION OF GENETIC CASTE DETERMINATION IN Pogonomyrmex SEED-HARVESTER ANTS

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 phenotypes: those with GCD, no evidence of GCD, and mixed (both GCD and non-GCD colonies present). The GCD phenotype was geographically widespread across the range of both morphospecies, occurring in 20 of 46 sampled populations. Molecular data suggest three reproductively isolated and cryptic lineages within each morphospecies, and no present hybridization. Mapping the GCD phenotype onto a mtDNA phylogeny indicates that GCD in P. rugosus was acquired from P. barbatus, suggesting that interspecific hybridization may not be the causal agent of GCD, but may simply provide an avenue for GCD to spread from one species (or subspecies) to another. We hypothesize that the origin of GCD involved a genetic mutation with a major effect on caste determination. This mutation generates genetic conflict and results in the partitioning and maintenance of distinct allele (or gene set) combinations that confer differences in developmental caste fate. The outcome is two dependent lineages within each population; inter-lineage matings produce workers, while intra-lineage matings produce reproductives. Both lineages are needed to produce a caste-functional colony, resulting in two reproductively isolated yet interdependent lineages. Pogonomyrmex populations composed of dependent lineages provide a unique opportunity to investigate genetic variation underlying phenotypic plasticity and its impact on the evolution of social structure.

Capital and income breeding and the evolution of colony founding strategies in ants

Ability to store resources that will be used for reproduction represents a potential life history adaptation because storage permits feeding and reproduction to be decoupled spatially and/or temporally. The two ends of a continuum involve acquiring all resources prior to reproduction (capital breeding) or acquiring all resources during the reproductive period (income breeding). Traditional life history theory examines tradeoffs between costs and benefits of such strategies, but this theory has not been integrated into life history studies of ants, even though founding queens have the analogous strategies of fully claustral (capital breeding) and semi-claustral (income breeding). This study demonstrates that facultatively semi-claustral queens of the seed-harvester ant Pogonomyrmex desertorum exhibit phenotypic plasticity during colony founding because unfed queens produced few, small minims, whereas ad libitum fed queens produced larger, heavier minims and additional brood. Fed queens also lost less mass than unfed queens despite their producing more brood. Overall, foraging provides queens with a suite of benefits that likely offset potential negative effects of foraging risk. Life history studies across a diverse array of taxa show that capital breeding is consistently associated with low availability and/or unpredictability of food, i.e., environmental conditions that favor prepackaging of reproductive resources. Such a broad and consistent pattern suggests that similar factors favored the evolution of fully claustral (capital breeding) colony founding in ants. Overall, these data suggest that ant researchers should revise their conventional view that fully claustral colony founding evolved because it eliminated the need for queens to leave the nest to forage. Instead, colony founding strategies should be examined from the perspective of environmental variation, i.e., availability and predictability of food. I also provide a functional scenario that could explain the evolution of colony founding strategies in ants.

Mating flight, metrosis, and semi-claustrality in the seed-harvester ant Pogonomyrmex salinus (Hymenoptera, Formicidae)

Here we examine dispersal, metrosis, and claustrality in the seed-harvester ant Pogonomyrmex salinus at an unusually large mating aggregation. We found that mode of queen dispersal from the mating aggregation is not a function of queen mass and that wing damage among queens was relatively rare. P. salinus is haplometrotic in the field and foundress queens placed together in forced associations eventually fight to the death. While queens of Pogonomyrmex salinus can survive claustrally, producing a single minim from their body reserves in the laboratory, fed queens produce up to four significantly larger minims along with concurrent larvae and pupae during the same period. Since queens forage in the field, we interpret claustrality as a secondary reserve strategy when foraging fails, and suggest that foraging is obligate for P. salinus queens in an overdispersed and temperate environment. Thus, nest founding strategies employed by P. salinus may be environmentally determined and represent a continuum between fully claustral and obligate foraging. We discuss our results with reference to theories of pleometrosis and claustral colony founding.

Colony founding by pleometrosis in the semiclaustral seed-harvester ant Pogonomyrmex californicus (Hymenoptera: Formicidae)

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.

Semi-claustral colony founding in the seed-harvester ant Pogonomyrmex californicus: a comparative analysis of colony founding strategies.

The evolution of queens that rear their first brood solely using body reserves, i.e. fully claustral, is viewed as a major advance for higher ants because it eliminated the need for queens to leave the nest to forage. In an apparently unusual secondary modification, the seed-harvester ant Pogonomyrmex californicus displays obligate queen foraging, i.e. queens must forage to garner the resources necessary to survive and successfully rear their first brood. I examined the potential benefits of queen foraging by comparing ecological and physiological traits between P. californicus and several congeners in which the queen can rear brood using only body reserves. The primary advantage of foraging appears to lie in providing the queens of P. californicus with the energy to raise significantly more brood than possible by congeners that use only body reserves; the workers reared in the first brood were also heavier in mass than that predicted by their head width. Other correlates of queen foraging in P. californicus relative to tested congeners included a significantly lower total fat content for alate queens, a small queen body size, and a low queen to worker body mass ratio. Queens also forage in several other well-studied species of Pogonomyrmex, suggesting the possibility that queen foraging may be more common than previously thought in higher ants.

Foundress survival and brood production in the desert seed-harvester ants Pogonomyrmex rugosus and P. barbatus (Hymenoptera, Formicidae)

A three-factor laboratory experiment (2 species × 2 soil types × 4 moisture levels) demonstrated that water is the most important factor effecting colony establishment and growth in the two ecologically equivalent sister species of desert seed-harvester ants Pogonomyrmex rugosus and P. barbatus. All experimental indices, percent gyne survival, gyne live wet mass, percent of gynes producing workers, and mean number of individuals (workers, larvae, and pupae), increased from low to moderate moistures and then levelled off. Soil texture also displayed a significant effect as gyne wet mass was 5 - 10% higher across treatments in soils that had a higher clay content. The only species effect was that P. barbatus gynes were smaller but produced more workers and brood than those of P. rugosus. That P. rugosus survives longer under arid conditions was demonstrated by a significantly higher number of nests with live workers in the driest treatment; number of live gynes displayed a similar pattern but differences were not significant. Additionally, P. barbatus produced fewer workers than P. rugosus in the driest treatment, while this number was higher than P. rugosus at all other moisture levels. Metabolic rate was higher and workers eclosed sooner in P. barbatus compared to the larger P. rugosus.

Foraging in the seed-harvester ant genus Pogonomyrmex : are energy costs important?

Foraging in the seed-harvester ant genus Pogonomyrmex : are energy costs important?

Soil texture as an influence on the distribution of the desert seed-harvester ants Pogonomyrmex rugosus and Messor pergandei

Pogonomyrmex rugosus and Messor pergandei are ecologically similar species of desert seed-harvester ants that coexist in numerous areas throughout the Sonoran and Mohave Deserts. However, these two species also commonly segregate along physical gradients, with each species predominating in areas that differ in soil texture and/or topographic relief. Along gradients that included bajada and alluvial flat habitats, P. rugosus occurred alone in coarse-textured soils near mountains, while M. pergandei occurred alone in finer-textured soils further away. Conversely, along a vegetation gradient that included creosote bush and saltbush habitats, P. rugosus occurred alone in finer-textured soils than those occupied by either M. pergandei alone or both species in coexistence. However, in both situations clay content was significantly higher in areas occupied by P. rugosus alone, and at the latter site clay content was correlated with relative abundance of each species. Moreover, local distribution pattern of these two species may be related to the effects of clay on water retention, with retention being highest in areas occupied by P. rugosus alone. Differences in reproductive ecology may also affect these patterns as P. rugosus reproductive flights follow summer monsoon rains, while those of M. pergandei occur during the milder winter and spring.

Seed‐Harvester Ant Association with Shrubs: Competition for Water in the Mohave Desert?

Nests of the desert seed—harvester ant Pogonomyrmex rugosus are located preferentially near shrubs in some microhabitats at a Mohave Desert site, while nests of the same species are located preferentially away from shrubs at a Sonoran Desert site. At the Mohave site, nearest neighboring shrubs to ant nests show greater mortality than expected at random; this effect is reduced at the Sonoran site. The ants appear to be the cause of shrub mortality; workers defoliate shrubs and make no apparent use of severed leaves or stems. Shrub viability at the Mohave site is dependent upon distance from a P. rugosus nest and size of that nest. In the Mohave Desert, shrubs may initially provide valuable shade to starting colonies, yet later in colony ontogeny represent a significant competitor for water.

Water Loss in Chihuahuan Desert Ants

Previous articleNext article No AccessWater Loss in Chihuahuan Desert AntsWalter G. Whitford, Carol Ann Kay, and Aileen M. SchumacherWalter G. Whitford Search for more articles by this author , Carol Ann Kay Search for more articles by this author , and Aileen M. Schumacher Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 48, Number 4Oct., 1975 Article DOIhttps://doi.org/10.1086/physzool.48.4.30155664 Views: 1Total views on this site Citations: 23Citations are reported from Crossref Journal History This article was published in Physiological Zoology (1928-1998), which is continued by Physiological and Biochemical Zoology (1999-present). PDF download Crossref reports the following articles citing this article:Zac Hemmings, Nigel R Andrew Effects of microclimate and species identity on body temperature and thermal tolerance of ants (Hymenoptera: Formicidae), Austral Entomology 56, no.11 (Jul 2016): 104–114.https://doi.org/10.1111/aen.12215Amiel Vasl, Avi Shmida The adaptive role of nectarial appendages in Colchicum, Plant Systematics and Evolution 301, no.66 (Dec 2014): 1713–1723.https://doi.org/10.1007/s00606-014-1188-4Michal Holec, Jan Frouz, Richard Pokorný The influence of different vegetation patches on the spatial distribution of nests and the epigeic activity of ants (Lasius niger) on a spoil dump after brown coal mining (Czech Republic), European Journal of Soil Biology 42, no.33 (Jul 2006): 158–165.https://doi.org/10.1016/j.ejsobi.2005.12.005Robert A. 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