Impact of the Little Fire Ant,Wasmannia auropunctata,on Native Forest Ants in Gabon1

The Neotropical little fire ant, Wasmannia auropunctata, is notorious for its negative impacts on the native biota of tropical islands, such as the Galapagos and New Caledonia, where it has been introduced. Here, I evaluate the impact of exotic W. auropunctata populations on continental Africa. I surveyed ants at nine sites in Lopé National Park in Gabon, Central Africa, and found a highly significant correlation between ant diversity and length of infestation by W. auropunctata. I found many more native ant species present in areas not infested with W. auropunctata (39.0 ± 4.6) compared with areas infested by W. auropunctata for approximately 5–10 yr (7.0 ± 6.2 and 1.7 ± 1.2, respectively). In infested areas, W. auropunctata made up the bulk of specimens collected in every plot. This study demonstrates that the threat posed by W. auropunctata to biodiversity is as serious in continental ecosystems as it is in the more fragile island ecosystems of previous studies. Introductions near waterways are particularly devastating: in Lopé, the infested territory is most extensive along waterways and occurs in a pattern that strongly suggests moving water facilitates colonization.     

The Molecular Clockwork of the Fire Ant Solenopsis invicta

The circadian clock is a core molecular mechanism that allows organisms to anticipate daily environmental changes and adapt the timing of behaviors to maximize efficiency. In social insects, the ability to maintain the appropriate temporal order is thought to improve colony efficiency and fitness. We used the newly sequenced fire ant (Solenopsis invicta) genome to characterize the first ant circadian clock. Our results reveal that the fire ant clock is similar to the clock of the honeybee, a social insect with an independent evolutionary origin of sociality. Gene trees for the eight core clock genes, period, cycle, clock, cryptochrome-m, timeout, vrille, par domain protein 1 & clockwork orange, show ant species grouping closely with honeybees and Nasonia wasps as an outgroup to the social Hymenoptera. Expression patterns for these genes suggest that the ant clock functions similar to the honeybee clock, with period and cry-m mRNA levels increasing during the night and cycle and clockwork orange mRNAs cycling approximately anti-phase to period. Gene models for five of these genes also parallel honeybee models. In particular, the single ant cryptochrome is an ortholog of the mammalian-type (cry-m), rather than Drosophila-like protein (cry-d). Additionally, we find a conserved VPIFAL C-tail region in clockwork orange shared by insects but absent in vertebrates. Overall, our characterization of the ant clock demonstrates that two social insect lineages, ants and bees, share a similar, mammalian-like circadian clock. This study represents the first characterization of clock genes in an ant and is a key step towards understanding socially-regulated plasticity in circadian rhythms by facilitating comparative studies on the organization of circadian clockwork.     

Replication of the Endosymbiotic Bacterium Blochmannia floridanus Is Correlated with the Developmental and Reproductive Stages of Its Ant Host

The dynamics of replication of the intracellular endosymbiotic bacterium Blochmannia floridanus was determined during the larval development of its host ant Camponotus floridanus by real-time quantitative PCR. The bacteria were found to proliferate during pupation and immediately after the eclosion of the imagines (adult ants). In older workers the number of bacteria present in the midgut bacteriocytes decreased significantly. In contrast, the bacterial population in the ovaries was dependent on the reproductive state of the animal. An age-dependent degeneration of the midgut bacteriocytes was also investigated by microscopic techniques in males and female castes of the closely related ant species C. herculeanus and C. sericeiventris, respectively, with similar results and supports the concept of age-dependent degeneration of the midgut bacteriocytes in all castes.     

Sociogenomics of Cooperation and Conflict during Colony Founding in the Fire Ant Solenopsis invicta

One of the fundamental questions in biology is how cooperative and altruistic behaviors evolved. The majority of studies seeking to identify the genes regulating these behaviors have been performed in systems where behavioral and physiological differences are relatively fixed, such as in the honey bee. During colony founding in the monogyne (one queen per colony) social form of the fire ant Solenopsis invicta, newly-mated queens may start new colonies either individually (haplometrosis) or in groups (pleometrosis). However, only one queen (the “winner”) in pleometrotic associations survives and takes the lead of the young colony while the others (the “losers”) are executed. Thus, colony founding in fire ants provides an excellent system in which to examine the genes underpinning cooperative behavior and how the social environment shapes the expression of these genes. We developed a new whole genome microarray platform for S. invicta to characterize the gene expression patterns associated with colony founding behavior. First, we compared haplometrotic queens, pleometrotic winners and pleometrotic losers. Second, we manipulated pleometrotic couples in order to switch or maintain the social ranks of the two cofoundresses. Haplometrotic and pleometrotic queens differed in the expression of genes involved in stress response, aging, immunity, reproduction and lipid biosynthesis. Smaller sets of genes were differentially expressed between winners and losers. In the second experiment, switching social rank had a much greater impact on gene expression patterns than the initial/final rank. Expression differences for several candidate genes involved in key biological processes were confirmed using qRT-PCR. Our findings indicate that, in S. invicta, social environment plays a major role in the determination of the patterns of gene expression, while the queen''s physiological state is secondary. These results highlight the powerful influence of social environment on regulation of the genomic state, physiology and ultimately, social behavior of animals.     

Expression of the Foraging Gene Is Associated with Age Polyethism,Not Task Preference,in the Ant Cardiocondyla obscurior

One of the fundamental principles of social organization, age polyethism, describes behavioral maturation of workers leading to switches in task preference. Here we present a system that allows for studying division of labor (DOL) by taking advantage of the relative short life of Cardiocondyla obscurior workers and thereby the pace of behavioral transitions. By challenging same-age young and older age cohorts to de novo establish DOL into nurse and foraging tasks and by forcing nurses to precociously become foragers and vice versa we studied expression patterns of one of the best known candidates for social insect worker behavior, the foraging gene. Contrary to our expectations we found that foraging gene expression correlates with age, but not with the task foraging per se. This suggests that this nutrition-related gene, and the pathways it is embedded in, correlates with physiological changes over time and potentially primes, but not determines task preference of individual workers.     

Ant Species Identity has a Greater Effect than Fire on the Outcome of an Ant Protection System in Brazilian Cerrado

Although fire‐ and ant–plant interactions influence the community structure and dynamics of Neotropical savannas, no previous studies have considered their simultaneous effects on target host plants. We monitored the effect of ant exclusion for 3 years on leaf area loss to leaf chewing insects, thrips abundance, and reproductive output of the extrafloral nectary‐bearing shrub, Peixotoa tomentosa (Malpighiaceae). We predicted that the impact of ants on herbivores and plants would depend on the ant species, and that fire would reduce the effect of ants. We deliberately chose control plants that differed in their occupant ant species. Fire occurred in the second year of the study, allowing us to determine its effect on the benefit afforded by ants. Ants reduced leaf area loss and thrips abundance, and increased fruit and seed production in all 3 years. Some ant species were more effective than others, while plants with multiple ant species suffered higher leaf area loss than plants with a single ant species. In the year following the fire, leaf damage was greater than in the other years, regardless of the ant species, and the proportional effect of ants in reducing damage was less. Interactions affecting thrips abundance did not change following fire, nor was the benefit to the plant proportionally reduced. Overall, the identity of the ant species had a greater effect than did the occurrence of fire on the ant–herbivore–plant interaction: the identity of the ant species influenced leaf area loss, thrips numbers, and bud and seed production, while fire only modified the impact of ants on the amount of leaf area consumed by insect herbivores.     

Tissue Localization of the Endosymbiotic Bacterium “Candidatus Blochmannia floridanus” in Adults and Larvae of the Carpenter Ant Camponotus floridanus

The distribution of endosymbiotic bacteria in different tissues of queens, males, and workers of the carpenter ant Camponotus floridanus was investigated by light and electron microscopy and by in situ hybridization. A large number of bacteria could be detected in bacteriocytes within the midguts of workers, young virgin queens, and males. Large amounts of bacteria were also found in the oocytes of workers and queens. In contrast, bacteria were not present in oocyte-associated cells or in the spermathecae of mature queens, although occasionally a small number of bacteria could be detected in the testis follicles of males. Interestingly, the number of bacteriocytes in mature queens was strongly reduced and the bacteriocytes contained only very few or no bacteria at all, although the endosymbionts were present in huge amounts in the ovaries of the same animals. During embryogenesis of the deposited egg, the bacteria were concentrated in a ring of endodermal tissue destined to become the midgut in later developmental stages. However, during larval development, bacteria could also be detected in other tissues although to a lesser extent. Only in the last-instar larvae were bacteria found exclusively in the midgut tissue within typical bacteriocytes. Tetracycline and rifampin efficiently cleansed C. floridanus workers of their symbionts and the bacteriocytes of these animals still remained empty several months after treatment had ceased. Despite the lack of their endosymbionts, these adult animals were able to survive without any obvious negative effect under normal cultivation conditions.     

Linking Temporal and Spatial Scales in the Study of an Argentine Ant Invasion

Our long-term study of an invasion of Argentine ants (Linepithema humile) in a 481-ha biological preserve in Northern California links multiple spatial and temporal scales. We have investigated, at local spatial scales of tens of meters, how nests spread and contract seasonally and from year to year. Microsatellite analysis shows population genetic structure on the scale of about 100 m. At the landscape scale, we have surveyed the spread and impact of Argentine ants in the biological preserve since 1993, and have found high variability both seasonally and from year to year. Here, we describe how seasonal patterns in nesting behavior at the local scale help to explain how the location of the invasion edge changes. Thus, the growth and spread of nests on the scale of tens of meters, from season to season, produce the dynamics of the invasion from year to year at the scale of hundreds of meters.     

GP-9s Are Ubiquitous Proteins Unlikely Involved in Olfactory Mediation of Social Organization in the Red Imported Fire Ant,Solenopsis invicta

The red imported fire ant (RIFA), Solenopsis invicta, is an invasive species, accidentally introduced in the United States that can cause painful (sometimes life-threatening) stings to human, pets, and livestock. Their colonies have two social forms: monogyne and polygyne that have a single and multiple functional queens, respectively. A major gene (Gp-9), identified as a putative pheromone-binding protein on the basis of a modest amino acid sequence identity, has been suggested to influence the expression of colony social organization. Monogyne queens are reported to possess only the GP-9B alleles, whereas polygyne queens possess both GP-9B and GP-9b. Thus, both social forms are reported to express GP-9B, with GP-9b being a marker expressed in polygynes but it is absent in monogynes. Here, we report two types of polygyne colonies, one that does not express GP-9b (monogyne-like) and the other expressing both proteins, GP-9B and GP-9b. Given their expression pattern, GP-9s are hemolymph proteins, which are more likely to be involved in the transport of lipids and small ligands within the homocoel. GP-9B existed in two forms, one of them is phosphorylated. The helical-rich content of the protein resembles the secondary structures of a beetle hemolymph protein and moth pheromone-binding proteins. An olfactory role is unlikely given the lack of specific expression in the sensillar lymph. In marked contrast to GP-9s, a chemosensory protein, SinvCSP, is demonstrated to be specifically expressed in the antennae. Within the antennae, expression of SinvCSP is restricted to the last two segments, which are known to house olfactory sensilla.     

Nest Relocation and Excavation in the Florida Harvester Ant,Pogonomyrmex badius

The Florida harvester ant (Pogonomyrmex badius) excavates deep nests in the sandy soils of the Gulf and Atlantic coastal plains. Nest relocations of over 400 colonies in a north Florida coastal plains pine forest were tracked and mapped from 2010 to 2013. Individual colonies varied from one move in two years to four times a year, averaging about one per year. Almost all moves occurred between May and November peaking in July when more than 1% of the colonies moved per day. Move directions were random, and averaged 4 m, with few moves exceeding 10 m. Distance moved was not related to colony size. Over multiple moves, paths were random walks around the original nest location. Relocation is probably intrinsic to the life history of this species, and the causes of relocation remain obscure— the architecture of old and new nests was very similar, and neither the forest canopy nor the density or size of neighbors was correlated with relocation. Monitoring entire relocations (n = 20) showed that they were usually completed in 4 to 6 days. Moves were diurnal, peaking in the mornings and afternoons dipping during mid-day, and ceasing before sundown. Workers excavated the new nest continuously during the daytime throughout the move and beyond. A minority of workers carried seeds, charcoal and brood, with seeds being by far the most common burden. The proportion of burdened workers increased throughout the move. Measured from year to year, small colonies gained size and large ones lost it. Colonies moving more than once in two years lost more size than those moving less often, suggesting that moving may bear a fitness cost. Colony relocation is a dramatic and consistent feature of the life history of the Florida harvester ant, inviting inquiry into its proximal and ultimate causes.     

Effect of a Founder Event on Variation in the Genetic Sex-Determining System of the Fire Ant Solenopsis Invicta

Effects of a recent founder event on genetic diversity in wild populations of the fire ant Solenopsis invicta were studied, with particular attention given to the genetic sex-determining system. Diploid males are far more common relative to haploid males in introduced populations than in native populations of fire ants, and queens that produce diploid males account for a significantly larger proportion of the mated queens in introduced than in native populations. Differences between native and introduced populations in attributes of the mating systems (i.e., queen mating frequency or level of inbreeding) can be excluded as factors contributing to these different levels of diploid male production. Thus, we conclude that diploid males have increased in frequency in introduced populations because of a loss of allelic diversity at the sex-determining locus (loci). This loss of sex alleles has generated a substantial increase in the estimated segregational genetic load associated with production of sterile diploid males in introduced populations over the load in native populations. The loss of allelic diversity in the sex-determining system in introduced S. invicta is paralleled by a loss of electrophoretically detectable rare alleles at protein-encoding loci. Such concordance between these different types of markers is predicted because each of the many sex alleles present in the native populations is expected to be rare. Estimates of expected heterozygosity (H(exp)) based on 76 electrophoretic loci do not differ significantly between the native and introduced fire ant populations, illustrating the lack of sensitivity of this measure for detecting many types of bottlenecks.     

Common Polymorphism in the Phosphatase PHLPP2 Results in Reduced Regulation of Akt and Protein Kinase C

PHLPP2 (PH domain leucine-rich repeat protein phosphatase 2) terminates Akt and protein kinase C (PKC) activity by specifically dephosphorylating these kinases at a key regulatory site, the hydrophobic motif (Ser-473 in Akt1). Here we identify a polymorphism that results in an amino acid change from a Leu to Ser at codon 1016 in the phosphatase domain of PHLPP2, which reduces phosphatase activity toward Akt both in vitro and in cells, in turn resulting in reduced apoptosis. Depletion of endogenous PHLPP2 variants in breast cancer cells revealed the Ser-1016 variant is less functional toward both Akt and PKC. In pair-matched high grade breast cancer samples we observed retention of only the Ser allele from heterozygous patients (identical results were observed in a pair-matched normal and tumor cell line). Thus, we have identified a functional polymorphism that impairs the activity of PHLPP2 and correlates with elevated Akt phosphorylation and increased PKC levels.Breast cancer is diagnosed in ∼180,000 women and is the cause of 40,000 deaths each year in the U.S.² A prevalent underlying mechanism driving tumorigenesis is aberrant signal transduction pathways that result in constitutive activation of cell growth, proliferation, and survival pathways (2). A well characterized signal transduction pathway in breast cancer that promotes cellular survival, growth, and proliferation is the phosphatidylinositol 3-kinase/Akt pathway (3). This pathway is activated by a number of mechanisms, including gene amplification or gain of function mutations in upstream receptor protein-tyrosine kinases (4, 5), constitutive activation of hormone receptors (6), activating mutations in phosphatidylinositol 3-kinase and Akt (7, 8), and loss of function mutations in the regulatory phosphatase PTEN³ (phosphatase and tensin homolog on chromosome ten) (9). Thus, Akt is a major regulator of breast tumorigenesis.There are three isoforms of Akt present in humans. All three isoforms contain activating phosphorylation sites in the activation loop (Thr-308 in Akt1) and in the C-terminal hydrophobic motif (Ser-473 in Akt1) (10). Upon growth factor receptor stimulation, phosphatidylinositol 3-kinase becomes activated and phosphorylates the D3 position of, typically, phosphatidylinositol (4, 5) bisphosphate to generate phosphatidylinositol (3,4,5)-trisphosphate (11). This 3′-phosphorylated lipid recruits Akt to the plasma membrane by binding to its PH domain, resulting in conformational changes that allow access to the activation loop phosphorylation site (11). Constitutively bound phosphatidylinositol-dependent kinase-1 then phosphorylates Akt at Thr-308, accompanied by phosphorylation at Ser-473 resulting in a catalytically active kinase (12). Phosphorylation of Ser-473 depends on the mTORC2 complex (13-16). Signaling through this pathway is terminated by removal of the lipid second messenger phosphatidylinositol (3,4,5)-trisphosphate catalyzed by the phosphatase PTEN and by direct dephosphorylation of Akt by the recently-identified PHLPP family of phosphatases and protein phosphatase 2A-type phosphatases (17-20).The PHLPP family of phosphatases comprise three variants, the alternatively spliced PHLPP1α and PHLPP1β, and PHLPP2 (21). PHLPP1 and PHLPP2 specifically dephosphorylate the hydrophobic motif of specific Akt isozymes, thus decreasing Akt activity and promoting apoptosis (18, 19). PHLPP2 binds and dephosphorylates Akt1 and Akt3, whereas PHLPP1 binds and dephosphorylates Akt2 and Akt3 (18, 22). Their role in inactivating Akt suggests that both PHLPP1 and PHLPP2 could be potential tumor suppressors. Consistent with such a role, these phosphatases also dephosphorylate the hydrophobic motif of PKC, resulting in degradation of PKC. For this kinase, phosphorylation stabilizes the enzyme, so that the effect of depletion of the PHLPP phosphatases is to increase PKC protein levels (23). PKC is a well characterized oncogene, and loss of function of the PHLPP phosphatases could increase PKC protein levels and promote tumorigenesis (24). Providing further rationale that PHLPP2 could be a potential tumor suppressor, the phosphatase is located on chromosome 16q22.3, a region that encounters frequent loss of heterozygosity (LOH) in many primary and malignant breast tumors (25).Here we identify a non-synonymous polymorphism that results in an amino acid change from a Leu to a Ser at codon 1016 in the PP2C phosphatase domain of PHLPP2. Overexpression studies reveal the Ser-1016 variant has impaired phosphatase activity and is less effective at inducing apoptosis than the Leu-1016 variant. When comparing a pair-matched normal and breast cancer cell line or pair-matched normal and high grade tumor patient samples that are heterozygous, we observe preferential loss of the Leu allele in the tumor tissue or breast cancer cell line. This observation provides evidence that PHLPP2 could be one of the elusive tumor suppressor genes on chromosome 16q, and for heterozygous patients, loss of the more catalytically active Leu-1016 may promote breast tumorigenesis.     

Increase in Male Reproductive Success and Female Reproductive Investment in Invasive Populations of the Harlequin Ladybird Harmonia axyridis

Reproductive strategy affects population dynamics and genetic parameters that can, in turn, affect evolutionary processes during the course of biological invasion. Life-history traits associated with reproductive strategy are therefore potentially good candidates for rapid evolutionary shifts during invasions. In a series of mating trials, we examined mixed groups of four males from invasive and native populations of the harlequin ladybird Harmonia axyridis mating freely during 48 hours with one female of either type. We recorded the identity of the first male to copulate and after the 48 h-period, we examined female fecundity and share of paternity, using molecular markers. We found that invasive populations have a different profile of male and female reproductive output. Males from invasive populations are more likely to mate first and gain a higher proportion of offspring with both invasive and native females. Females from invasive populations reproduce sooner, lay more eggs, and have offspring sired by a larger number of fathers than females from native populations. We found no evidence of direct inbreeding avoidance behaviour in both invasive and native females. This study highlights the importance of investigating evolutionary changes in reproductive strategy and associated traits during biological invasions.     

Tradeoffs in the Evolution of Caste and Body Size in the Hyperdiverse Ant Genus Pheidole

The efficient investment of resources is often the route to ecological success, and the adaptability of resource investment may play a critical role in promoting biodiversity. The ants of the “hyperdiverse” genus Pheidole produce two discrete sterile castes, soldiers and minor workers. Within Pheidole, there is tremendous interspecific variation in proportion of soldiers. The causes and correlates of caste ratio variation among species of Pheidole remain enigmatic. Here we test whether a body size threshold model accounts for interspecific variation in caste ratio in Pheidole, such that species with larger body sizes produce relatively fewer soldiers within their colonies. We evaluated the caste ratio of 26 species of Pheidole and found that the body size of workers accounts for interspecific variation in the production of soldiers as we predicted. Twelve species sampled from one forest in Costa Rica yielded the same relationship as found in previously published data from many localities. We conclude that production of soldiers in the most species-rich group of ants is regulated by a body size threshold mechanism, and that the great variation in body size and caste ratio in Pheidole plays a role in niche divergence in this rapidly evolving taxon.     

Genetic Analysis of Esterase Polymorphism in the Soybean Cyst Nematode, Heterodera glycines

The genetic basis of esterase polymorphism in Heterodera glycines was investigated through controlled matings and analysis of F₁ and F₂ progeny. Three nematode lines, each fixed for a different esterase phenotype, were isolated and purified through repeated directional selection and inbreeding. Each phenotype was characterized by its distinct pair of closely spaced bands of esterase activity. Single-female single-male crosses were conducted according to a modified agar-plate mating technique. F₁ progeny were homogeneous, exhibiting both parental esterase phenotypes (codominant heterozygotes) but no hybrid bands. Approximately 1,500 F₂ progeny segregated in a 1:2:1 ratio for expression of the esterase phenotypes of the female parental line, the heterozygote, and the male parental line. Apparently the three esterase phenotypes correspond to three codominant alleles of a single esterase locus. Reciprocal crosses gave similar results, suggesting no maternal inheritance.     

The Dynamics of Foraging Trails in the Tropical Arboreal Ant Cephalotes goniodontus

The foraging behavior of the arboreal turtle ant, Cephalotes goniodontus, was studied in the tropical dry forest of western Mexico. The ants collected mostly plant-derived food, including nectar and fluids collected from the edges of wounds on leaves, as well as caterpillar frass and lichen. Foraging trails are on small pieces of ephemeral vegetation, and persist in exactly the same place for 4–8 days, indicating that food sources may be used until they are depleted. The species is polydomous, occupying many nests which are abandoned cavities or ends of broken branches in dead wood. Foraging trails extend from trees with nests to trees with food sources. Observations of marked individuals show that each trail is travelled by a distinct group of foragers. This makes the entire foraging circuit more resilient if a path becomes impassable, since foraging in one trail can continue while a different group of ants forms a new trail. The colony’s trails move around the forest from month to month; from one year to the next, only one colony out of five was found in the same location. There is continual searching in the vicinity of trails: ants recruited to bait within 3 bifurcations of a main foraging trail within 4 hours. When bait was offered on one trail, to which ants recruited, foraging activity increased on a different trail, with no bait, connected to the same nest. This suggests that the allocation of foragers to different trails is regulated by interactions at the nest.     

Fecundity and the Behavioural Profile of Reproductive Workers in the Queenless Ant, Pachycondyla (= Ophthalmopone) berthoudi

Morphologically specialized queens are absent in Pachycondyla (=  Ophthalmopone ) berthoudi (ant subfamily Ponerinae). Instead, several of the workers mate and reproduce (gamergates). Gamergate proportion in nests commonly varies between nests and different times of the year. Individual fecundity of gamergates varies according to the number of these individuals in a nest, and we examined their behaviour in relation to fecundity in nests with different proportions of gamergates. In nests with high proportions of gamergates, they exhibited a diversity of behaviours inside the nest and in some cases could not be distinguished behaviourally from sterile workers. The fecundity of these gamergates was low and variable. In nests with low proportions, gamergates were relatively more fecund, and did not participate in colony labour. The behavioural profile of gamergates is therefore linked to their reproductive physiology, which is influenced by the number of mated individuals in the nest.