Pogonomyrmex

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Deborah M Gordon - One of the best experts on this subject based on the ideXlab platform.

  • gene expression variation in the brains of harvester ant foragers is associated with collective behavior
    Communications Biology, 2020
    Co-Authors: Daniel A. Friedman, Ryan A York, Austin T Hilliard, Deborah M Gordon
    Abstract:

    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.

  • experimental modulation of external microbiome affects nestmate recognition in harvester ants Pogonomyrmex barbatus
    PeerJ, 2016
    Co-Authors: Andy Dosmann, Nassim Bahet, Deborah M Gordon
    Abstract:

    Social insects use odors as cues for a variety of behavioral responses, including nestmate recognition. Past research on nestmate recognition indicates cuticular hydrocarbons are important nestmate discriminators for social insects, but other factors are likely to contribute to colony-specific odors. Here we experimentally tested whether external microbes contribute to nestmate recognition in red harvester ants (Pogonomyrmex barbatus). We changed the external microbiome of ants through topical application of either antibiotics or microbial cultures. We then observed behavior of nestmates when treated ants were returned to the nest. Ants whose external microbiome was augmented with microbial cultures were much more likely to be rejected than controls, but ants treated with antibiotics were not. This result is consistent with the possibility that external microbes are used for nestmate recognition.

  • the rewards of restraint in the collective regulation of foraging by harvester ant colonies
    Nature, 2013
    Co-Authors: Deborah M Gordon
    Abstract:

    Desert harvester ant colonies regulate their foraging activity and this collective behaviour appears to be under selection; colonies that forage less when conditions are poor have greater reproductive success, and the regulation of foraging behaviour appears to be inherited from parent to offspring colonies. Ant colonies are sometimes thought of as superorganisms, implying that they are subject to natural selection at a colony level. In a long-term (27-year) study of the association between collective behaviour and reproductive success in colonies of the red harvester ant, Pogonomyrmex barbatus, Deborah Gordon has found that, yes, they can show this superorganism characteristic. In times of drought, harvester ants tend not to forage as much as they do in times of plenty; they seem to bide their time until circumstances improve. This trait of restraint is passed on to daughter colonies, showing that it can indeed be regarded as a colony-level trait. Collective behaviour, arising from local interactions1, allows groups to respond to changing conditions. Long-term studies have shown that the traits of individual mammals and birds are associated with their reproductive success2,3,4,5,6, but little is known about the evolutionary ecology of collective behaviour in natural populations. An ant colony operates without central control, regulating its activity through a network of local interactions7. This work shows that variation among harvester ant (Pogonomyrmex barbatus) colonies in collective response to changing conditions8 is related to variation in colony lifetime reproductive success in the production of offspring colonies. Desiccation costs are high for harvester ants foraging in the desert9,10. More successful colonies tend to forage less when conditions are dry, and show relatively stable foraging activity when conditions are more humid. Restraint from foraging does not compromise a colony’s long-term survival; colonies that fail to forage at all on many days survive as long, over the colony’s 20–30-year lifespan, as those that forage more regularly. Sensitivity to conditions in which to reduce foraging activity may be transmissible from parent to offspring colony. These results indicate that natural selection is shaping the collective behaviour that regulates foraging activity, and that the selection pressure, related to climate, may grow stronger if the current drought in their habitat persists.

  • harvester ant colony variation in foraging activity and response to humidity
    PLOS ONE, 2013
    Co-Authors: Deborah M Gordon, Katherine N Dektar, Noa Pinterwollman
    Abstract:

    Collective behavior is produced by interactions among individuals. Differences among groups in individual response to interactions can lead to ecologically important variation among groups in collective behavior. Here we examine variation among colonies in the foraging behavior of the harvester ant, Pogonomyrmex barbatus. Previous work shows how colonies regulate foraging in response to food availability and desiccation costs: the rate at which outgoing foragers leave the nest depends on the rate at which foragers return with food. To examine how colonies vary in response to humidity and in foraging rate, we performed field experiments that manipulated forager return rate in 94 trials with 17 colonies over 3 years. We found that the effect of returning foragers on the rate of outgoing foragers increases with humidity. There are consistent differences among colonies in foraging activity that persist from year to year.

  • aggression is task dependent in the red harvester ant Pogonomyrmex barbatus
    Behavioral Ecology, 2013
    Co-Authors: Shelby J Sturgis, Deborah M Gordon
    Abstract:

    In many animal species, the propensity for aggression is linked to social context. In social insects, aggressive interactions between colonies are related to the assessment of cuticular hydrocarbon profiles. We investigated how, in the red harvester ant, Pogonomyrmex barbatus, an individual ant’s task environment contributes to its hydrocarbon profile, and how task-specific differences in profiles are linked to aggression. We compared the hydrocarbon profiles of 200 individuals from 4 task groups and 10 colonies, and measured aggression of ants of specific task groups toward non–nest mates of neighboring and distant colonies. We found that task groups can be distinguished by their hydrocarbon profiles. Hydrocarbon profiles are more closely associated with task group membership than with colony identity. Ants of the patroller task group were more likely to be aggressive to non–nest mates than ants of any other task group. There was no correlation between the extent of aggression between task groups and the magnitude of difference in their hydrocarbon profiles. Nearby nests did not differ more in hydrocarbon profile than distant nests. Our results suggest that aggression in P. barbatus is task dependent and is not directly correlated with the magnitude of difference in hydrocarbon profiles.

Bert Hölldobler - One of the best experts on this subject based on the ideXlab platform.

  • Division of labor is associated with age-independent changes in ovarian activity in Pogonomyrmex californicus harvester ants
    Journal of insect physiology, 2013
    Co-Authors: Adam Gregory Dolezal, Bert Hölldobler, Joshua Johnson, Gro V. Amdam
    Abstract:

    Abstract An age-independent division of labor can develop in both the reproductive (queen) and non-reproductive (worker) castes of Pogonomyrmex californicus harvester ants, and individuals develop biases for in-nest activities or external foraging. Additionally, ant ovaries normally atrophy in foragers compared to nest-biased workers (nurses). However, it is not clear whether these ovarian changes are due to changes in behavior or age, since foragers are typically older individuals. Here, we clarify this relationship in P. californicus queens and workers by comparing ovarian activity in same-aged ants that exhibit divergent behavioral biases. We found that foraging individuals had significantly reduced ovarian activity compared to their nest-biased counterparts, thereby linking changes in the ants’ reproductive system to social task performance rather than to age. The general finding that ovarian physiology is associated with social insect behaviors is consistent with the hypothesis that reproductive physiology may have played an important role in the evolution of social insect behavior.

  • endocrine physiology of the division of labour in Pogonomyrmex californicus founding queens
    Animal Behaviour, 2009
    Co-Authors: Adam G Dolezal, Bert Hölldobler, Jurgen Gadau, Colin S Brent, Gro V. Amdam
    Abstract:

    The proximate controls of a behaviour in extant species can inform us about the evolutionary route towards that behavioural phenotype. In social insects, different behavioural phenotypes often correlate with divergent hormone levels, and, in honeybees (Apis mellifera), this insight has lead to the hypothesis that behavioural biases, or division of labour, emerged via co-option of endocrine regulatory systems that paced behavioural change during the reproductive cycle of solitary ancestors. Founding queens of the California harvester ant Pogonomyrmex californicus show discrete behavioural changes during colony founding, with a dichotomy between nest-biased behaviour and field-biased behaviour. Additionally, a division of labour can develop if queens found nests together, with one queen being nest-biased and another being field-biased. To determine whether behavioural diphenism can be associated with reproductive endocrine regulators in an ant, we measured ecdysteroid and juvenile hormone (JH) content in (1) single-founding queens showing normal behavioural progression and (2) cofounding queens showing a division of labour. We found that ecdysteroid levels did not correlate with behaviour. JH titres, on the other hand, were elevated during the foraging life stage of single-founding queens as well as in the cofounding queens with a behavioural bias towards foraging. Our results suggest that JH affects the propensity for foraging task replication in P. californicus, and provide evidence for a common evolutionary route towards social behaviour in ants and bees.

  • population wide lineage frequencies predict genetic load in the seed harvester ant Pogonomyrmex
    Proceedings of the National Academy of Sciences of the United States of America, 2006
    Co-Authors: Kirk E Anderson, Bert Hölldobler, Brendon M Mott, Jennifer H Fewell, Jurgen Gadau
    Abstract:

    Many populations of the seed-harvester ant Pogonomyrmex barbatus exhibit genetic caste determination (GCD) generated by the interbreeding of two distinct yet interdependent lineages. Same-lineage matings are genetically predestined to become female reproductives (gynes) whereas alternate-lineage matings become workers. The perpetuation of this system requires that reproductives of both lineages are available for mating and are thus part of the effective population. We label these dependent lineage populations, because each lineage depends on the alternate lineage for worker production. Here we investigate the potential costs associated with GCD in a population with highly skewed lineage frequencies. We reared colonies using newly mated queens from a GCD population and an ecologically equivalent Pogonomyrmex rugosus population with environmental caste determination. GCD founding queens suffer a genetic load from mating randomly and produce fewer brood with advanced development compared with environmental caste determination queens. Our results indicate that GCD queens acquiring a high proportion of same-lineage sperm are unlikely to found a colony successfully. Given model parameters of random mating and founding queens mating with three males on average, there was a close fit between theoretical expectations of variation in colony worker production based on mating and lineage frequencies and empirical deficits in worker production. As expected, severely decreased worker production was specific to the common lineage, suggesting that negative frequency-dependent selection acts to stabilize a dependent lineage system.

  • extremely high mating frequency in the florida harvester ant Pogonomyrmex badius
    Behavioral Ecology and Sociobiology, 2004
    Co-Authors: Frank E Rheindt, Jurgen Gadau, Christoph Peter Strehl, Bert Hölldobler
    Abstract:

    High effective multiple queen mating is a rare but taxonomically widespread phenomenon in eusocial Hymenoptera that has arisen convergently in several taxa. In ants, high effective mating frequencies have been confirmed in only two clades: the higher leaf-cutters (Atta, Acromyrmex) and the Pogonomyrmex seed harvesters. We analysed polyandry in Pogonomyrmex badius, which has a life-history unique within the genus, and report the highest numerical mating frequencies thus far recorded in ants. We also show that P. badius is characterized by one of the highest effective mating frequencies hitherto found in ants. It is now clear that all major sub-clades of Pogonomyrmex sensu stricto exhibit high levels of polyandry. Therefore, multiple mating must have arisen early in the evolution of the genus, and may have constituted a mechanism to increase offspring variability for queens that were confronted with increasingly complex levels of organization. Too few congeners have been investigated by the same method to be certain that polyandry in P. badius is really higher than in the rest of the genus. If so, research should concentrate on a possible link between high queen mating frequency and the distinct caste system found in P. badius.

  • Dufour gland secretion in the harvester ant genus Pogonomyrmex
    Chemoecology, 2004
    Co-Authors: Bert Hölldobler, E. David Morgan, Jurgen Liebig, Neil J Oldham, Yue Liu
    Abstract:

    Dufour gland secretions of the harvester ants Pogonomyrmex barbatus, P. rugosus and P. maricopa were investigated. The glandular blends exhibit species specific patterns, but more importantly, based on indiviual profiles of Dufour gland contents of colony members it is possible to separate the colonies from each other in each species. It is possible that these collective colony specific cues serve as longer lasting trunk route markers. Behavioral tests demon- strate that workers of P. rugosus prefer homing routes marked by members of their own colony to routes marked by a foreign conspecific colony.

Robert A Johnson - One of the best experts on this subject based on the ideXlab platform.

  • a taxonomic revision of south american species of the seed harvester ant genus Pogonomyrmex hymenoptera formicidae part i
    Zootaxa, 2015
    Co-Authors: Robert A Johnson
    Abstract:

    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 interesting ecology, life history, and evolution. Species treated herein comprise all South American species-groups except for the brevibarbis and rastratus-groups. The following taxa are raised to species: pencosensis Forel 1914 and serpens Santschi 1922. The following new synonomies are proposed: bruchi Forel 1913 is synonomized under coarctatus Mayr 1868 and cunicularius carnivora Santschi 1925 under serpens Santschi 1922. The following new species is described: tinogasta. This paper redescribes workers of all species, and I describe queens and diagnose males for the following species: bispinosus (ergatoid queen, male), inermis (queen, male), laticeps (male), lobatus (queen, male), micans (queen), naegelii (ergatoid queen), pencosensis (ergatoid queen), serpens (ergatoid queen), tinogasta (brachypterous queen), and uruguayensis (queen, male). A neotype was designated for the untraceable or possibly lost type of P. bispinosus, and a holotype or lectotype was designated from syntypes for all other previously described taxa in order to provide a single name-bearing specimen and to facilitate future taxonomic studies. Of the 21 species treated herein, five species have ergatoid (wingless) queens (bispinosus, cunicularius, pencosensis, serpens, mayri), two have brachypterous (short-winged) queens (mendozanus, tinogasta), and two have dimorphic queens (winged and ergatoid in naegelii, brachypterous and ergatoid in laticeps). I also provide keys for workers and queens (in English and Spanish), photographs of all castes, distribution maps, and a summary of known biology.

  • a taxonomic revision of the seed harvester ant genus Pogonomyrmex hymenoptera formicidae on hispaniola
    Zootaxa, 2015
    Co-Authors: Robert A Johnson, Stefan Cover
    Abstract:

    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 (= aterrimus) are synonomized. We also describe the queen of P. aterrimus and P. saucius, and provide information on biology, distribution maps, and a key to workers and queens.

  • a new species of seed harvester ant Pogonomyrmex hoelldobleri hymenoptera formicidae from the mohave and sonoran deserts of north america
    Zootaxa, 2013
    Co-Authors: Robert A Johnson, Rick P Overson, C Moreau
    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. Pogonomyrnex inagnacanthus 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 < or = 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 circumocular 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.

  • The Old Ladies of the Seed Harvester ant Pogonomyrmex Rugosus: Foraging Performed by Two Groups of Workers
    Journal of insect behavior, 2008
    Co-Authors: Jan Oettler, Robert A Johnson
    Abstract:

    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.

  • low queen mating frequency in the seed harvester ant Pogonomyrmex ephebomyrmex pima implications for the evolution of polyandry
    Behavioral Ecology and Sociobiology, 2007
    Co-Authors: Tate C Holbrook, Robert A Johnson, Christoph Peter Strehl, Jurgen Gadau
    Abstract:

    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.

Blaine J Cole - One of the best experts on this subject based on the ideXlab platform.

  • mating for variety increases foraging activity in the harvester ant Pogonomyrmex occidentalis
    Molecular Ecology, 2008
    Co-Authors: Diane C Wiernasz, Jessica Hines, Dara G Parker, Blaine J Cole
    Abstract:

    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.

  • polyandry and fitness in the western harvester ant Pogonomyrmex occidentalis
    Molecular Ecology, 2004
    Co-Authors: Diane C Wiernasz, Christina L Perroni, Blaine J Cole
    Abstract:

    Using four highly polymorphic microsatellite markers (12–28 alleles), we gentoyped workers from 63 colonies of Pogonomyrmex occidentalis . Colonies have a single, multiply mated queen, and an average number of 6.3 patrilines per colony. Colony growth was measured over an 8-year period in the study population. Intracolonial relatedness and colony growth are correlated negatively, indicating a substantial fitness benefit to multiple mating.

  • recruitment limitation and population density in the harvester ant Pogonomyrmex occidentalis
    Ecology, 2002
    Co-Authors: Blaine J Cole, Diane C Wiernasz
    Abstract:

    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.

  • male size sperm transfer and colony fitness in the western harvester ant Pogonomyrmex occidentalis
    Evolution, 2001
    Co-Authors: Diane C Wiernasz, Amy K Sater, Allison J Abell, Blaine J Cole
    Abstract:

    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.

  • distribution of myrmecocystus mexicanus hymenoptera formicidae association with Pogonomyrmex occidentalis hymenoptera formicidae
    Annals of The Entomological Society of America, 2001
    Co-Authors: Blaine J Cole, Kevin L Haight, Diane C Wiernasz
    Abstract:

    Abstract We examined the spatial pattern of the ant Myrmecocystus mexicanus Wesmael. Although intraspecific dispersion is highly uniform, colonies were significantly associated with reproductively mature nests of the harvester ant Pogonomyrmex occidentalis (Cresson). Colonies of M. mexicanus were more likely to be found within 3 m of P. occidentalis and less likely to be found as far as 10 m away. The protein component of the diet of M. mexicanus at this site is almost exclusively dead or moribund workers of P. occidentalis. M. mexicanus appears to associate with one of its consistent food sources.

Jurgen Gadau - One of the best experts on this subject based on the ideXlab platform.

  • high quality genome assembly and annotation of the california harvester ant Pogonomyrmex californicus buckley 1867
    bioRxiv, 2020
    Co-Authors: Jonas Bohn, Jurgen Gadau, Reza Halabian, Lukas Schrader, Victoria Shabardina, Yutaka Suzuki, Ulrich R Ernst, Raphael Stefffen, Wojciech Makalowski
    Abstract:

    The harvester ant genus Pogonomyrmex is endemic to arid and semiarid habitats and deserts of North and South America and California harvester ant Pogonomyrmex californicus is the most widely distributed Pogonomyrmex species in the North America. P. californicus colonies are usually monogynous, i.e. a colony has one queen. However, in a few populations in California, primary polygyny evolved, i.e. several queens cooperate in colony founding after their mating flights and continue to coexist in mature colonies. Here, we present high quality genome assembly and annotation of P. californicus. The size of the assembly is 241 Mb, which is in good agreement with previously estimated genome size and we were able to annotate 17,889 genes in total, including 15,688 protein-coding ones with BUSCO completeness at the 95% level. This high quality genome will pave the way for investigations of the genomic underpinnings of social polymorphism in queen number, regulation of aggression, and the evolution of adaptations to dry habitats in P. californicus.

  • phylogeography of Pogonomyrmex barbatus and p rugosus harvester ants with genetic and environmental caste determination
    Ecology and Evolution, 2015
    Co-Authors: Jurgen Gadau, Kirk E Anderson, Brendon M Mott
    Abstract:

    We present a phylogeographic study of at least six reproductively isolated lineages of new world harvester ants within the Pogonomyrmex barbatus and P. rugosus species group. The genetic and geographic relationships within this clade are complex: Four of the identified lineages show genetic caste determination (GCD) and are divided into two pairs. Each pair has evolved under a mutualistic system that necessitates sympatry. These paired lineages are dependent upon one another because their GCD requires interlineage matings for the production of F1 hybrid workers, and intralineage matings are required to produce queens. This GCD system maintains genetic isolation among these interdependent lineages, while simultaneously requiring co-expansion and emigration as their distributions have changed over time. It has also been demonstrated that three of these four GCD lineages have undergone historical hybridization, but the narrower sampling range of previous studies has left questions on the hybrid parentage, breadth, and age of these groups. Thus, reconstructing the phylogenetic and geographic history of this group allows us to evaluate past insights and hypotheses and to plan future inquiries in a more complete historical biogeographic context. Using mitochondrial DNA sequences sampled across most of the morphospecies’ ranges in the U.S.A. and Mexico, we conducted a detailed phylogeographic study. Remarkably, our results indicate that one of the GCD lineage pairs has experienced a dramatic range expansion, despite the genetic load and fitness costs of the GCD system. Our analyses also reveal a complex pattern of vicariance and dispersal in Pogonomyrmex harvester ants that is largely concordant with models of late Miocene, Pliocene, and Pleistocene range shifts among various arid-adapted taxa in North America.

  • colony size effects on task organization in the harvester ant Pogonomyrmex californicus
    Insectes Sociaux, 2013
    Co-Authors: Jurgen Gadau, C T Holbrook, T H Eriksson, Rick P Overson, Jennifer H Fewell
    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).

  • caste determination in a polymorphic social insect nutritional social and genetic factors
    The American Naturalist, 2008
    Co-Authors: Jurgen Gadau, Chris Smith, Kirk E Anderson, Chadwick V Tillberg, Andrew V Suarez
    Abstract:

    Abstract: We examined how dietary, social, and genetic factors affect individual size and caste in the Florida harvester ant Pogonomyrmex badius, which has three discrete female castes. The diet that a larva consumed, as indicated by δ13C, δ15N, and C:N, varied with caste. Both N content and estimated trophic position of dietary input was higher for major than for minor workers and was highest for gynes (reproductive females). The size and resources of a colony affected the size of only minor workers, not that of gynes and major workers. Approximately 19% of patrilines showed a bias in which female caste they produced. There were significant genetic effects on female size, and the average sizes of a major worker and a gyne produced by a patriline were correlated, but neither was correlated with minor worker size. Thus, genetic factors influence both caste and size within caste. We conclude that environmental, social, and genetic variation interact to create morphological and physiological variation among ...

  • low queen mating frequency in the seed harvester ant Pogonomyrmex ephebomyrmex pima implications for the evolution of polyandry
    Behavioral Ecology and Sociobiology, 2007
    Co-Authors: Tate C Holbrook, Robert A Johnson, Christoph Peter Strehl, Jurgen Gadau
    Abstract:

    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.

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