Dolichoderine Ants Research Articles

Pollination of Richea dracophylla (Ericaceae) and the role of the nocturnal ant Notoncus hickmani (Formicinae)

AbstractOur observation of large numbers of ants Notoncus hickmani (Formicinae) on the flowers of a Tasmanian endemic shrub Richea dracophyllum (Ericacea) during the night in winter prompted us to carry out a more extensive study of pollination of R. dracophyllum at two sites. Terminal panicles bear inflorescences of 300+ flowers whose petals are fused into calyptrae covering the reproductive organs, and the calyptrae must be removed before pollination can occur. To exclude birds, we placed mesh bags over some inflorescences. Inflorescences with exclusion bags had a high proportion of retained calyptra and the numbers of viable seeds were greatly reduced. We found R. dracophyllum to have a very long flowering period (more than 6 months) and a range of floral visitors, including honey‐eaters (Meliphagidae) and flying insects. At one site we observed large numbers (up to 100) of N. hickmani on inflorescences between dusk and midnight during winter at air temperatures down to 2.5°C. They fed on nectar from flowers that had lost their calyptra where they were exposed to pollen from the anthers and scanning electron microscopy showed high numbers of pollen grains being carried on the ants. The feeding behaviour of these ants would facilitate pollination between adjacent flowers (geitonogamy). Smaller numbers of dolichoderine ants (Iridomyrmex bicknelli?) were observed during the daytime in spring but mainly fed under partially detached calyptrae where they had little exposure to pollen. We suggest that R. dracophylla is pollinated by a range of species and functional groups—birds, flying insects and ants, and that the pollinating species will vary during the year and between sites, although insects depend on birds to remove the calyptrae. Ant pollination is rare, nocturnal ant pollination is extremely rare, and pollination by nocturnal cryophilic ants has not been documented previously.

Linking Colony Size with Foraging Behavior and Brain Investment in Odorous Ants (Formicidae: Dolichoderinae)

Superorganisms represent a unique level of biological organization in which the phenotype of the reproductive unit, the colony, results from traits expressed at the level of individual workers. Because body size scaling has important consequences for cell diversity and system complexity in solitary organisms, colony size is a trait of particular interest in superorganism evolution. In some instances, division of labor and worker polymorphism scale with colony size, but in general little is known about how colony size drives differences in individual-level behavior or neural traits. Ants represent the greatest diversity of superorganisms and provide a manner of natural experiment to test trends in trait evolution across multiple instances of colony size expansion. In this study, we control for environmental differences and worker size polymorphism to test if colony size correlates with measures of foraging behavior and brain size in dolichoderine ants. We present data from 3 species ranked by colony size. Our results suggest colony size correlates with measures of exploratory behavior and brain investment, with small-colony ants showing higher exploratory drive and faster exploration rate than the larger colony species, and greater relative investment in the primary olfactory brain region, the antennal lobe, than the larger colony species.

Iridoids and volatile pheromones of Tapinoma darioi ants: chemical differences to the closely related species Tapinoma magnum

Tapinoma species, and more general dolichoderine ants, are able to produce a variety of volatile compounds they use as chemical defense, alarm, and communication pheromones. Among these, iridoids and volatile ketones are the predominant molecule classes produced by the anal glands of these ants. A recent taxonomic revision of the genus Tapinoma in Europe revealed that the supercolonial species Tapinoma nigerrimum consists of a complex of four cryptic species. Two of them, Tapinoma magnum and the newly described Tapinoma darioi, are closely related species that evolutionary diverged recently. In this work, we determine and characterize the chemical profile of pheromones and volatile compounds of two Tapinoma species. From a chemical point of view, T. darioi and T. magnum show both qualitative and quantitative differences in the pheromones produced, supporting the taxonomic revision of the T. nigerrimum complex. Our data confirm T. darioi and T. magnum as separate species also from a biochemical point of view demonstrating the value of chemotaxonomy as a suitable tool for integrative studies of species differentiation even for closely related taxa.

Review of the ant genus Technomyrmex Mayr, 1872 in the Arabian Peninsula (Hymenoptera, Formicidae).

The taxonomy of the dolichoderine ants of the genus Technomyrmex Mayr, 1872 is revised for the Arabian Peninsula. Six species are treated, T.albipes (F. Smith, 1861), T.difficilis Forel, 1892, T.briani Sharaf, 2009, T.vexatus (Santschi, 1919), T.montaseri Sharaf, Collingwood & Aldawood, 2011, and T.setosus Collingwood, 1985. The successful tramp species T.difficilis Forel, 1892 is recorded for the first time from the Kingdom of Saudi Arabia (KSA) and Yemen, representing new records for the Palearctic Region. Technomyrmexvexatus (Santschi, 1919) is a new species record for Yemen. The queen caste of the rare endemic species, T.briani Sharaf, 2009 is described for the first time. A neotype for KSA endemic T.setosusCollingwood 1985 is designated based on a specimen collected from the type locality, the Asir Mountains, KSA, including new information on habitats and distribution. A male cast of Technomyrmex, possibly of T.setosus, is also described. An illustrated key based on the worker caste of the Arabian species of Technomyrmex is given. New geographical records and a distribution map for the treated species are presented.

Aphid–Buchnera–Ant symbiosis; or why are aphids rare in the tropics and very rare further south?

ABSTRACTAt least since the Cretaceous Terrestrial Revolution, the geographical distribution of aphids, particularly in the Northern Hemisphere, has been strongly affected by the low thermal tolerance of their obligatory bacterial symbiont,Buchnera aphidicola, which was why the aphids switched to obligate parthenogenesis in low latitudes. Hormaphidids and greenideids penetrated into the tropics only after the Oligocene strengthening of climate seasonality, and specialisations of the tropical representatives of these families did not allow them to spread further south (in the case of cerataphidines), or only allowed in few cases (in the case of greenideids).Aphids suffered from the Mesozoic–Cenozoic boundary extinction event much more strongly than other insects. The extinction was roughly coincidental with the establishment of the tight symbiosis of aphids with formicine and dolichoderine ants, which was accompanied by the flourishing of all three groups.In the Cretaceous, all of the representatives of extant and subfamilies occupied positions that were subordinate to Armaniinae and Sphecomyrminae. Prior to large ant colonies evolving their efficient ant–aphid mutualism, the aphids remained unprotected before the growing ant predation. The origin of the aphid trophobiosis with large colonies of Formicinae and Dolichoderinae has resulted in the steep decline of aphids left beyond that ant–aphid symbiotic network. By at least the basal Eocene (unlike the Late Cretaceous), ant proportions in the entomofauna increased sharply, and evident dominants emerged. Even now, aphid milkers from small colonies (hundreds of specimens) never protect their symbionts, and homopteran-tending ants are more likely to be dominant, with large colonies of 104–105workers.The mutualistic ant–aphid system failed to cross the tropical belt during the Cenozoic because ofBuchnera's low heat tolerance. As a result, the native southern temperate aphid fauna consists now of seven genera only, five of which are Late Cretaceous relicts. Some of them had relatives in Late Cretaceous amber of the Northern Hemisphere.

Partner choice through concealed floral sugar rewards evolved with the specialization of ant-plant mutualisms.

Obligate mutualisms require filtering mechanisms to prevent their exploitation by opportunists, but ecological contexts and traits facilitating the evolution of such mechanisms are largely unknown. We investigated the evolution of filtering mechanisms in an epiphytic ant-plant symbiotic system in Fiji involving Rubiaceae and dolichoderine ants, using field experiments, metabolomics, X-ray micro-computed tomography (micro-CT) scanning and phylogenetics. We discovered a novel plant reward consisting of sugary sap concealed in post-anthetic flowers only accessible to Philidris nagasau workers that bite through the thick epidermis. In five of the six species of Rubiaceae obligately inhabited by this ant, the nectar glands functioned for 10d after a flower's sexual function was over. Sugar metabolomics and field experiments showed that ant foraging tracks sucrose levels, which only drop at the onset of fruit development. Ontogenetic analyses of our focal species and their relatives revealed a 25-fold increase in nectary size and delayed fruit development in the ant-rewarding species, and Bayesian analyses of several traits showed the correlated evolution of sugar rewards and symbiosis specialization. Concealed floral nectar forestalls exploitation by opportunists (generalist ants) and stabilizes these obligate mutualisms. Our study pinpoints the importance of partner choice mechanisms in transitions from facultative to obligate mutualisms.

PREY-CAPTURE TECHNIQUES AND PREY PREFERENCES OF AELURILLUS AERUGINOSUS, A. COGNATUS, AND A. KOCHI, ANT-EATING JUMPING SPIDERS (ARANEAE: SALTICIDAE) FROM ISRAEL

ABSTRACT Aelurillus aeruginosus, A. cognatus, and A. kochi feed on ants in nature. Prey-capture techniques and prey preferences of each of these three species from Israel were studied in the laboratory using a wide range of ants and other insects. Each usually attacked ants head on, but there was no regular orientation of attacks on other insects. When attacking ants, but not other prey, each species tended to stab several times before holding on. In three different types of tests for prey preference, “well-fed” (fed 5 days prior to testing) and “starved” (fed 15 days prior to testing) individuals of each species took dolichoderine, formicine, and myrmicine ants in preference to a variety of other insects (Diptera, Hemiptera, Isoptera, and Pscoptera). When extra-starved (21-day fast), however, each species took ants and other insects indiscriminately. Testing with laboratory-reared salticids showed that preference and prey-capture behavior did not depend on prior experience with ants. When tested with dea...

Introduced fire ants can exclude native ants from critical mutualist-provided resources

Animals frequently experience resource imbalances in nature. For ants, one resource that may be particularly valuable for both introduced and native species is high-carbohydrate honeydew from hemipteran mutualists. We conducted field and laboratory experiments: (1) to test if red imported fire ants (Solenopsis invicta) competed with native ants for access to mutualisms with aphids, and (2) to quantify the effects of aphid honeydew presence or absence on colony growth of native ants. We focused on native dolichoderine ants (Formicidae, Dolichoderinae) because they are abundant ants that have omnivorous diets that frequently include mutualist-provided carbohydrates. At two sites in the southeastern US, native dolichoderine ants were far less frequent, and fire ants more frequent, at carbohydrate baits than would be expected based on their frequency in pitfall traps. A field experiment confirmed that a native ant species, Dorymyrmex bureni, was only found tending aphids when populations of S. invicta were suppressed. In the laboratory, colonies of native dolichoderine ants with access to both honeydew and insect prey had twice as many workers and over twice as much brood compared to colonies fed only ad libitum insect prey. Our results provide the first experimental evidence that introduced ants compete for access to mutualist-provided carbohydrates with native ants and that these carbohydrates represent critical resources for both introduced and native ants. These results challenge traditional paradigms of arthropod and ant nutrition and contribute to growing evidence of the importance of nutrition in mediating ecological interactions.

Population Growth ofAphis gossypiiandMyzus persicae(Hemiptera: Aphididae) in the Presence ofLinepithemahumile andTapinoma sessile(Hymenoptera: Formicidae)

Invasive ant species can have dramatic impacts on native ants, through direct predation and by usurping common resources. Most invasive ants and many native ants use honeydew, produced by phloem-sucking hemipterans. Because colonies of invasive ants can become very large after establishment, these ants may facilitate greater hemipteran trophobiont population growth compared with their sympatric native ant counterparts. We examined the population growth of an aphid mutualist, Aphis gossypii, and a nonmutualist, Myzus persicae, exposed to two Dolichoderine ants, Linepithema humile, a globally widespread invasive species, and Tapinoma sessile, a widespread co-occurring native ant, in North America in an enemy-free laboratory study. L. humile worker foraging activity was at least twice that of T. sessile, and populations of the myrmecophile, A. gossypii, were greater when exposed to L. humile than T. sessile, possibly caused, in part, by more frequent encounters with L. humile. L. humile ignored M. persicae when A. gossypii was absent, whereas T. sessile preyed on it. Both ant species preyed on M. persicae when A. gossypii was also present. This suggested that both ants may assess nutritional gains from aphid species (i.e., honeydew versus body tissue), eliminating less productive aphids competing for host plant space. Through their impact on populations of hemipteran mutualists, we suggest that colonies of L. humile and perhaps other invasive ants may acquire more honeydew than native ants, thereby fueling colony growth that leads to numerical dominance and widespread success in introduced environments.

Phylogeny and Biogeography of Dolichoderine Ants: Effects of Data Partitioning and Relict Taxa on Historical Inference

Ants (Hymenoptera: Formicidae) are conspicuous organisms in most terrestrial ecosystems, often attaining high levels of abundance and diversity. In this study, we investigate the evolutionary history of a major clade of ants, the subfamily Dolichoderinae, whose species frequently achieve ecological dominance in ant communities. This group has also produced some of the world's most successful invasive ants. We use an extensive molecular data set ( approximately 9 kb of sequence data from 10 nuclear genes, covering 48 dolichoderine species and 6 outgroup taxa) to infer the phylogenetic relationships, divergence dates, and biogeographic history of these ants. We evaluate the effects of data partitioning and outgroup composition on phylogenetic inference by estimating relationships under a series of increasingly partitioned data sets and by running analyses both with and without Aneuretus simoni, a rare and localized species that is the nearest living relative of Dolichoderinae. We also examine the effects of excluding 2 data partitions with significant base composition heterogeneity. Our results reveal 4 well-supported and mutually exclusive clades of dolichoderines, corresponding to 4 newly defined tribes: Bothriomyrmecini (B), Dolichoderini (D), Leptomyrmecini (L), and Tapinomini (T). All Bayesian and likelihood analyses yield the same unrooted (ingroup-only) topology, ((D,L),(B,T)), with the outgroups attaching either on the Dolichoderini branch or on the Tapinomini branch. Placement of the root is highly sensitive to choice of model partition and to inclusion/exclusion of Aneuretus. Bayes' factors strongly favor the more partitioned models, and in these Tapinomini is recovered as sister to the remaining dolichoderines, but only if Aneuretus is included. Exclusion of Aneuretus precludes recovery of this topology in all but the most highly partitioned Bayesian analyses and then only with nonsignificant support, underscoring the importance of relict, taxonomically isolated taxa for phylogenetic inference. Removal of 2 partitions with heterogeneous base composition also markedly increases support for placement of the root on the Tapinomini branch. Our divergence date estimates and biogeographic analyses indicate that crown-group dolichoderines arose about 65 million years ago (Ma), although this was preceded by a substantial period (30 million years) of stem group evolution. The 4 extant tribes are estimated to have crown-group origins in the late Paleocene or Eocene (40-60 Ma). Tapinomini and Bothriomyrmecini originated in the Paleotropics and subsequently dispersed to other biogeographic regions. Crown-group Leptomyrmecini arose and diversified in the Neotropics, but they also gave rise to one clade that colonized Australia about 30 Ma and subsequently experienced a massive radiation on that continent. This event occurred later than the diversification of dolichoderines in the northern hemisphere, so that by the time dolichoderines came to dominate the Australian fauna they had already declined in abundance in the Holarctic region.

Hierarchical perception of fertility signals and nestmate recognition cues in two dolichoderine ants

In social insects, queens are likely to “honestly” inform their nestmates of their presence and fertility status through pheromonal communication. Cuticular hydrocarbons (CHCs) have been reported to be effective nestmate discriminators and strongly suspected to act as fertility signals, at least in some species. The use of the same chemical bouquet (i.e., the CHC profile) to convey two fundamentally different information seems puzzling. However, a recent threshold model proposes a hierarchy in the discriminating processes, i.e., fertility signals can only be perceived if nestmate recognition has been reached (Le Conte and Hefetz, Annu Rev Entomol 53:523-542, 2008). Here, we developed a simple behavioral bioassay based on chemical recruitment toward a queen placed outside the nest in two dolichoderine ants (Linepithema humile and Tapinoma erraticum), which allowed us to investigate the interplay between fertility signaling and colonial recognition. Using queen corpses of various origins (nestmates or aliens) and physiological states (fertile or infertile; mated or unmated), we demonstrated that nestmate recognition cues clearly override fertility signals under our experimental conditions. Indeed, while nestmate infertile queens were largely ignored by the workers, nestmate fertile queens (mated or not) induced worker recruitment, whereas alien fertile queens did not and were aggressed by the workers.

Technomyrmex (Formicidae: Dolichoderinae) in the New World: synopsis and description of a new species

A synopsis of dolichoderine ants of the genus Technomyrmex Mayr (Hymenoptera: Formicidae) in the New World is offered including notes, keys, pictures of all known species, and the description of T. gorgona sp. n. from SW Colombia. This is the first record of the genus from continental South America. Currently Technomyrmex comprises six species (two extinct, marked by *) in the New World: *T. caritatis Brandão & Baroni Urbani (Dominican amber), T. difficilis Forel (tramp species collected in Washington, Puerto Rico, Antigua and Nevis), T. fulvus (Wheeler) (Costa Rica, Panama and Colombia), T. gorgona sp. n. (Colombia), the first record for Colombia and South America, *T. hispaniolae (Wilson) (Dominican amber) and T. vitiensis Mann (tramp species collected in California).

Aggressive Interactions Between <I>Solenopsis invicta</I> and <I>Linepithema humile</I> (Hymenoptera: Formicidae) Under Laboratory Conditions

The Argentine ant, Linepithema humile (Mayr), and the red imported fire ant, Solenopsis invicta Buren, are natural agonists in their country of origin. Since the first report of L. humile in California in 1907 its range expanded statewide, displacing native ant species wherever it spread. Since the discovery of established populations of S. invicta in southern California in 1998, it has been restricted to discrete areas of southern California. However, as these discrete populations expand, they are encountering large populations of L. humile, which are effective competitors for available resources and are particularly aggressive in their encounters with other ant species such as S. invicta. Most Dolichoderine ants such as L. humile do not prefer to forage on baits made with defatted corn grit and soybean oil typically used in red imported fire ant control programs. Applications of these baits in areas where distributions of these species overlap might selectively affect populations of S. invicta and give L. humile a competitive advantage. Three laboratory experiments were conducted to determine the competitive outcomes between S. invicta pitted against L. humile: 1) agonistic behavior of workers in small arenas, 2) colony interactions with different population ratios, and 3) the effects of pyriproxyfen on the competitiveness of S. invicta against L. humile. Populations of S. invicta consisting of major workers killed more L. humile than did minors or a mixture of majors and minors. When paired against L. humile colonies consisting of 1,100 workers, colonies consisting of 38 S. invicta workers were easily defeated by L. humile. Colonies consisting of 450 S. invicta workers plugged their nest entrances, but they were ultimately defeated by L. humile after 13 d. The S. invicta colonies consisting of 1,100 workers took control of the bridge connecting the colonies, invaded the L. humile colony, killed the Argentine ant queens, and removed their brood. Pyriproxyfen-treated fire ant workers took significantly longer to chase the Argentine ants from a connecting bridge than did untreated fire ants. Thus, fire ant baits may have long-term effects on intercolonial aggression between S. invicta and L. humile, especially when Argentine ant populations are high in the summer.

Aggressive Interactions Between Solenopsis invicta and Linepithema humile (Hymenoptera: Formicidae) Under Laboratory Conditions

The Argentine ant, Linepithema humile (Mayr), and the red imported fire ant, Solenopsis invicta Buren, are natural agonists in their country of origin. Since the first report of L. humile in California in 1907 its range expanded statewide, displacing native ant species wherever it spread. Since the discovery of established populations of S. invicta in southern California in 1998, it has been restricted to discrete areas of southern California. However, as these discrete populations expand, they are encountering large populations of L. humile, which are effective competitors for available resources and are particularly aggressive in their encounters with other ant species such as S. invicta. Most Dolichoderine ants such as L. humile do not prefer to forage on baits made with defatted corn grit and soybean oil typically used in red imported fire ant control programs. Applications of these baits in areas where distributions of these species overlap might selectively affect populations of S. invicta and give L. humile a competitive advantage. Three laboratory experiments were conducted to determine the competitive outcomes between S. invicta pitted against L. humile: 1) agonistic behavior of workers in small arenas, 2) colony interactions with different population ratios, and 3) the effects of pyriproxyfen on the competitiveness of S. invicta against L. humile. Populations of S. invicta consisting of major workers killed more L. humile than did minors or a mixture of majors and minors. When paired against L. humile colonies consisting of 1,100 workers, colonies consisting of 38 S. invicta workers were easily defeated by L. humile. Colonies consisting of 450 S. invicta workers plugged their nest entrances, but they were ultimately defeated by L. humile after 13 d. The S. invicta colonies consisting of 1,100 workers took control of the bridge connecting the colonies, invaded the L. humile colony, killed the Argentine ant queens, and removed their brood. Pyriproxyfen-treated fire ant workers took significantly longer to chase the Argentine ants from a connecting bridge than did untreated fire ants. Thus, fire ant baits may have long-term effects on intercolonial aggression between S. invicta and L. humile, especially when Argentine ant populations are high in the summer.

Rediscovery of a fossil dolichoderine ant lineage (Hymenoptera: Formicidae: Dolichoderinae) and a description of a new genus from South America

We describe a new genus, Gracilidris Wild & Cuezzo gen. nov., and a new species, G. pombero Wild and Cuezzo sp. nov., of dolichoderine ants (Hymenoptera: Formicidae: Dolichoderinae) from Paraguay, Brazil and Argentina based on the worker caste. These ants are morphologically similar to the extinct Gracilidris humilioides (Wilson 1985) comb. nov., known from a single Dominican amber fossil, that we redescribe and transfer to Gracilidris from Linepithema Mayr.

Prey‐capture techniques and prey preferences of Zenodorus durvillei, Z. metallescens and Z. orbiculatus, tropical ant‐eating jumping spiders (Araneae: Saiticidae) from Australia

Capture techniques and preferences of Zenodorus durvillei (Walckenaer), Z. metallescens (L. Koch) and Z. orbiculatus, Australian salticids that feed on ants in nature, were studied in the laboratory using a wide variety of ants and other insects. Each species adopted three prey‐capture modes: ambush, active pursuit in the open, and gleaning from spider webs. Large ants were sometimes stabbed several times before holding on. A variety of methods were used for testing preference. The potential of using this assortment of methods for assessing strength of preferences is discussed. Each species took dolichoderine, formicine, myrmecine, myrmicine and pseudomyrmecine ants in preference to a variety of other insects (aphids, bugs, caterpillars, crickets, flies, lacewings, mantises, mayflies, midges, mosquitoes, moths, plant and leaf hoppers, and termites). Testing with laboratory‐reared spiders showed that the development of preference for ants and ant‐specific prey‐capture behaviour did not depend on prior experience with ants. Tests with dead, motionless lures showed that each species could distinguish between ants and other types of prey independent of the different movement patterns of the prey. Preferences were intact after 7‐day and 14‐day fasts, but not after 21‐day fasts when prey were outside webs. When prey were in webs, preference for ants persisted even after 21‐day fasts. Findings are discussed in relation to other studies on specialised salticids and in relation to the structure and function of the salticid eye.

A Molecular Framework for the Phylogeny of the Ant Subfamily Dolichoderinae

Partial sequences are reported for the mitochondrial genes for cytochrome oxidase subunits 2 and 3 and for cytochrome b, and the entire sequence of the gene for tRNALeuUUR for species from 14 genera of dolichoderine ants and from three outgroup genera. Considerable variation was observed between tRNA genes in the size of the TΨC arm and the DHU and anticodon loops and whether or not the TΨC stem possesses a GC pair. The outgroup taxa showed complete TAA CO1 stop codons, but dolichoderines have either TA or T. The outgroup taxa showed a noncoding gap between the CO1 and the tRNALeuUUR genes. A phylogeny-independent compatibility test using the amino acid sequences showed differences between the genes consistent with variation in evolutionary rates, according with other studies. Base compositions proved heterogeneous between species, hence phylogenetic analysis was restricted to the protein sequences using maximum likelihood and the mtREV24 replacement matrix. A maximum-likelihood consensus tree has similarities to those from morphological studies with some exceptions such Leptomyrmex falling within the dolichoderine genera rather than basally, and the accretion of genera formerly included under Iridomyrmex. Features of the tRNA genes and the CO1 termination codons agree quite well with the molecular phylogeny.

Ancient butterfly–ant symbiosis: direct evidence from Dominican amber

Although symbiotic association with ants is pervasive in the butterfly families Lycaenidae and Riodinidae the age of these symbioses has never been estimated explicitly. Here we report the first known fossil riodinid caterpillar. This fossil can be dated minimally between 15 and 20 Ma old, and confidently placed in the extant genus Theope . Differing little from modern day Theope , this fossil from Dominican amber provides direct evidence that secretory and acoustical organs used by modern caterpillars to mediate symbioses with ants have been highly developed at least since the Miocene. This fossil therefore becomes the point of reference for future studies using molecular clock methods for dating these symbioses within the riodinid butterflies. Modern evidence, and the abundance of dolichoderine ants in Dominican amber (now extinct in the West Indies) imply that specialized symbiotic relationships between Theope caterpillars and these ants were likely in existence at least 15 Ma ago. The current distribution of neotropical riodinid butterfly and ant faunas indicates the extinction in the West Indies of at least two unrelated taxa that formed a tightly linked symbiotic association, which persisted to the present elsewhere.

Stress tolerance in some Chacoan dolichoderine ants: implications for community organization and distribution

Stress-tolerance strategies in ants have been little studied in the context of ant communities. To examine this relationship, the behaviour and activity patterns of several dolichoderine ants,Forelius nigriventrisForel andDorymyrmex exsanguisForel and allies, with other members of a species-rich, scavenging ant assemblage in two habitats in the Argentine Chaco was studied. Both groups of dolichoderines were more active in the overgrazed-desertified habitat than in the forested habitat.Forelius nigriventriswas relatively thermophilic, andD. exsanguisand allies were active over a broad range of environmental conditions and were tolerant of cold conditions. These dolichoderines were subordinate in aggressive interactions with other species at baits, and were abundant at baits only when other species were absent. Competitive interactions may have led to stress tolerance in these ants. Stress tolerance on a local scale may also permit the geographic distribution of these ants (particularlyD. exsanguis) into zones of relatively harsh climate.

An electrophoretic analysis of Queen number in three species of Dolichoderine ants

For each of three species of dolichoderine ants, four mating system models were tested electrophoretically. The models tested were: (1) each colony is derived from one, singly-inseminated female, (2) each colony is derived from one female, inseminated twice, (3) colonies have two, coequal, singly-inseminated queens, and (4) colonies have three, coequal, singly-inseminated queens. From each of these models, expected frequencies of colonies of various genotypic compositions were calculated. Goodness of fit of actual colony types were then tested.