Reference genome of the bicolored carpenter ant, Camponotus vicinus.

Carpenter ants in the genus Camponotus are large, conspicuous ants that are abundant and ecologically influential in many terrestrial ecosystems. The bicolored carpenter ant, Camponotus vicinus Mayr, is distributed across a wide range of elevations and latitudes in western North America, where it is a prominent scavenger and predator. Here, we present a high-quality genome assembly of C. vicinus from a sample collected in Sonoma County, California, near the type locality of the species. This genome assembly consists of 38 scaffolds spanning 302.74 Mb, with contig N50 of 15.9 Mb, scaffold N50 of 19.9 Mb, and BUSCO completeness of 99.2%. This genome sequence will be a valuable resource for exploring the evolutionary ecology of C. vicinus and carpenter ants generally. It also provides an important tool for clarifying cryptic diversity within the C. vicinus species complex, a genetically diverse set of populations, some of which are quite localized and of conservation interest.

Biogeography and evolution of social parasitism in Australian Myrmecia bulldog ants revealed by phylogenomics.

Studying the historical biogeography and life history transitions from eusocial colony life to social parasitism contributes to our understanding of the evolutionary mechanisms generating biodiversity in eusocial insects. The ants in the genus Myrmecia are a well-suited system for testing evolutionary hypotheses about how their species diversity was assembled through time because the genus is endemic to Australia with the single exception of the species M. apicalis inhabiting the Pacific Island of New Caledonia, and because at least one social parasite species exists in the genus. However, the evolutionary mechanisms underlying the disjunct biogeographic distribution of M. apicalis and the life history transition(s) to social parasitism remain unexplored. To study the biogeographic origin of the isolated, oceanic species M. apicalis and to reveal the origin and evolution of social parasitism in the genus, we reconstructed a comprehensive phylogeny of the ant subfamily Myrmeciinae. We utilized Ultra Conserved Elements (UCEs) as molecular markers to generate a molecular genetic dataset consisting of 2,287 loci per taxon on average for 66 out of the 93 known Myrmecia species as well as for the sister lineage Nothomyrmecia macrops and selected outgroups. Our time-calibrated phylogeny inferred that: (i) stem Myrmeciinae originated during the Paleocene âˆ¼ 58 Ma ago; (ii) the current disjunct biogeographic distribution of M. apicalis was driven by long-distance dispersal from Australia to New Caledonia during the Miocene âˆ¼ 14 Ma ago; (iii) the single social parasite species, M. inquilina, evolved directly from one of the two known host species, M. nigriceps, in sympatry via the intraspecific route of social parasite evolution; and (iv) 5 of the 9 previously established taxonomic species groups are non-monophyletic. We suggest minor changes to reconcile the molecular phylogenetic results with the taxonomic classification. Our study enhances our understanding of the evolution and biogeography of Australian bulldog ants, contributes to our knowledge about the evolution of social parasitism in ants, and provides a solid phylogenetic foundation for future inquiries into the biology, taxonomy, and classification of Myrmeciinae.

The global distribution of known and undiscovered ant biodiversity.

Invertebrates constitute the majority of animal species and are critical for ecosystem functioning and services. Nonetheless, global invertebrate biodiversity patterns and their congruences with vertebrates remain largely unknown. We resolve the first high-resolution (~20-km) global diversity map for a major invertebrate clade, ants, using biodiversity informatics, range modeling, and machine learning to synthesize existing knowledge and predict the distribution of undiscovered diversity. We find that ants and different vertebrate groups have distinct features in their patterns of richness and rarity, underscoring the need to consider a diversity of taxa in conservation. However, despite their phylogenetic and physiological divergence, ant distributions are not highly anomalous relative to variation among vertebrate clades. Furthermore, our models predict that rarity centers largely overlap (78%), suggesting that general forces shape endemism patterns across taxa. This raises confidence that conservation of areas important for small-ranged vertebrates will benefit invertebrates while providing a "treasure map" to guide future discovery.

Ant phylogenomics reveals a natural selection hotspot preceding the origin of complex eusociality.

The evolution of eusociality has allowed ants to become one of the most conspicuous and ecologically dominant groups of organisms in the world. A large majority of the current ∼14,000 ant species belong to the formicoids,1 a clade of nine subfamilies that exhibit the most extreme forms of reproductive division of labor, large colony size,2 worker polymorphism,3 and extended queen longevity.4 The eight remaining non-formicoid subfamilies are less well studied, with few genomes having been sequenced so far and unclear phylogenetic relationships.5 By sequencing 65 genomes, we provide a robust phylogeny of the 17 ant subfamilies, retrieving high support to the controversial leptanillomorph clade (Leptanillinae and Martialinae) as the sister group to all other extant ants. Moreover, our genomic analyses revealed that the emergence of the formicoids was accompanied by an elevated number of positive selection events. Importantly, the top three gene functions under selection are linked to key features of complex eusociality, with histone acetylation being implicated in caste differentiation, gene silencing by RNA in worker sterility, and autophagy in longevity. These results show that the key pathways associated with eusociality have been under strong selection during the Cretaceous, suggesting that the molecular foundations of complex eusociality may have evolved rapidly in less than 20 Ma.

The ant genus Tetraponera (Hymenoptera: Formicidae) in the Afrotropical region: taxonomic review and key to species.

The arboreal ant genus Tetraponera is widely distributed in the Paleotropics. Five species groups were previously recognized in the Afrotropical region (including Madagascar), and two of these were revised. This paper provides a taxonomic treatment of the remaining species. A survey of the T. allaborans group on the African mainland leads to the recognition of fourteen species: T. clypeata (Emery) (= T. braunsi (Forel) syn. nov.); T. continua (Forel) (= T. claveaui (Santschi) syn. nov.); T. cortina sp. nov.; T. dispar sp. nov.; T. emeryi (Forel) (= T. braunsi durbanensis (Forel) syn. nov.); T. exactor sp. nov.; T. furtiva sp. nov.; T. gerdae (Stitz); T. liengmei (Forel); T. mayri (Forel); T. pedana sp. nov.; T. penzigi (Mayr) (= T. scotti Donisthorpe syn. nov. = T. zavattarii (Menozzi) syn. nov. = T. penzigi praestigiatrix Santschi syn. nov.); T. pumila sp. nov.; and T. tessmanni (Stitz). A full revision of the Malagasy species of the T. allaborans group is deferred, but the following new synonymy is established: T. hysterica (Forel) = T. hysterica inflata (Emery) syn. nov.; T. longula (Emery) = T. sahlbergii deplanata (Forel) syn. nov.; T. mandibularis (Emery) = T. flexuosa (Santschi) syn. nov.; T. morondaviensis (Forel) = T. arrogans (Santschi) syn. nov. = T. demens (Santschi) syn. nov. = T. hysterica dimidiata (Forel) syn. nov.; and T. sahlbergii = T. sahlbergii spuria (Forel) syn. nov. = T. plicatidens (Santschi) syn. nov. In the T. ambigua group the following synonymy is reinstated (syn. rev.): T. ambigua (Emery) = T. erythraea (Emery) = T. bifoveolata (Mayr) = T. angolensis Santschi; and T. ophthalmica (Emery) = T. unidens Santschi. A new species is described in the Madagascar-endemic T. grandidieri group: T. elegans sp. nov. Scrutiny of the T. natalensis group indicates the occurrence of ten species: T. andrei (Mayr), T. anthracina (Santschi), T. caffra (Santschi), T. insularis sp. nov., T. kosi sp. nov., T. mocquerysi (Andr), T. natalensis (F. Smith), T. redacta sp. nov., T. schulthessi (Santschi), and T. setosa sp. nov. T. insularis is known only from Madagascar, while the other nine species are confined to the African mainland. The following new synonymy is proposed for the T. natalensis group (senior synonym cited first): T. anthracina = T. poultoni Donisthorpe syn. nov. = T. triangularis (Stitz) syn. nov.; T. mocquerysi = T. mocquerysi biozellata (Karavaiev) syn. nov. = T. mocquerysi elongata (Stitz) syn. nov. = T. emacerata (Santschi) syn. nov. = T. triangularis illota (Santschi) syn. nov. = T. ledouxi Terron syn. nov. = T. lemoulti (Santschi) syn. nov. = T. mocquerysi lepida Wheeler syn. nov. = T. monardi (Santschi) syn. nov. = T. emacerata oberbecki (Forel) syn. nov. = T. emacerata odiosa (Forel) syn. nov.; and T. natalensis = T. angusta (Arnold) syn. nov. = T. capensis (F. Smith) syn. nov. = T. natalensis cuitensis (Forel) syn. nov. = T. mocquerysi lutea (Stitz) syn. nov. = T. natalensis obscurata (Emery) syn. nov. = T. prelli (Forel) syn. nov. = T. natalensis usambarensis (Forel) syn. nov. The extensive synonymy under T. mocquerysi and T. natalensis reflects the conviction that previous taxonomists underestimated the extent of intraspecific variation in these taxa, but further study and testing of this conclusion is warranted. An illustrated worker- and queen-based key is provided for all species of Tetraponera occurring in Africa and Madagascar, except the Malagasy members of the T. allaborans group.

Compositional heterogeneity and outgroup choice influence the internal phylogeny of the ants.

Knowledge of the internal phylogeny and evolutionary history of ants (Formicidae), the world's most species-rich clade of eusocial organisms, has dramatically improved since the advent of molecular phylogenetics. A number of relationships at the subfamily level, however, remain uncertain. Key unresolved issues include placement of the root of the ant tree of life and the relationships among the so-called poneroid subfamilies. Here we assemble a new data set to attempt a resolution of these two problems and carry out divergence dating, focusing on the age of the root node of crown Formicidae. For the phylogenetic analyses we included data from 110 ant species, including the key species Martialis heureka. We focused taxon sampling on non-formicoid lineages of ants to gain insight about deep nodes in the ant phylogeny. For divergence dating we retained a subset of 62 extant taxa and 42 fossils in order to approximate diversified sampling in the context of the fossilized birth-death process. We sequenced 11 nuclear gene fragments for a total of ∼7.5 kb and investigated the DNA sequence data for the presence of among-taxon compositional heterogeneity, a property known to mislead phylogenetic inference, and for its potential to affect the rooting of the ant phylogeny. We found sequences of the Leptanillinae and several outgroup taxa to be rich in adenine and thymine (51% average AT content) compared to the remaining ants (45% average). To investigate whether this heterogeneity could bias phylogenetic inference we performed outgroup removal experiments, analysis of compositionally homogeneous sites, and a simulation study. We found that compositional heterogeneity indeed appears to affect the placement of the root of the ant tree but has limited impact on more recent nodes. Our findings have implications for outgroup choice in phylogenetics, which should be made not only on the basis of close relationship to the ingroup, but should also take into account sequence divergence and other properties relative to the ingroup. We put forward a hypothesis regarding the rooting of the ant phylogeny, in which Martialis and the Leptanillinae together constitute a clade that is sister to all other ants. After correcting for compositional heterogeneity this emerges as the best-supported hypothesis of relationships at deep nodes in the ant tree. The results of our divergence dating under the fossilized birth-death process and diversified sampling suggest that the crown Formicidae originated during the Albian or Aptian ages of the Lower Cretaceous (103-124 Ma). In addition, we found support for monophyletic poneroids comprising the subfamilies Agroecomyrmecinae, Amblyoponinae, Apomyrminae, Paraponerinae, Ponerinae, and Proceratiinae, and well-supported relationships among these subfamilies except for the placement of Proceratiinae and (Amblyoponinae + Apomyrminae). Our phylogeny also highlights the non-monophyly of several ant genera, including Protanilla and Leptanilla in the Leptanillinae, Proceratium in the Proceratiinae, and Cryptopone, Euponera, and Mesoponera within the Ponerinae.

Long-term record of Argentine ant invasions reveals enduring ecological impacts.

The ecological effects of species introductions can change in magnitude over time, but an understanding of how and why they do so remains incompletely understood. Clarifying this issue requires consideration of how temporal variation in invader traits affects invasion impacts (e.g., through differential effects on the diversity and composition of native species assemblages). We examine the temporal dynamics of Argentine ant invasions in northern California by resurveying 202 sites first sampled 30-40 yr ago. To test how invasion impacts change over time, we estimated native ant richness and species composition at 20 riparian woodland sites that span a 30-yr invasion chronosequence. We then use these data to test how variation in two invader traits (aggression and relative abundance) is related to time since invasion and invasion impact. Native ant assemblages along the chronosequence exhibited reduced native ant richness and altered species composition (compared to uninvaded control sites), but the magnitude of these impacts was independent of time since invasion. These results are corroborated by additional temporal comparisons of native ant assemblages at riparian sites sampled 20-30 yr ago. Our findings together illustrate that the impacts of invasions can persist undiminished over at least a 30-yr time frame and remain evident at regional scales. Although neither invader trait varied with time since invasion, native ant richness declined as the relative abundance of the Argentine ant increased. This latter result supports the hypothesis that factors reducing invader abundance at particular sites can decrease invasion impacts, but also that such changes may be due to site-specific factors (e.g., abiotic conditions) that affect invader abundance rather than time since invasion per se. Future studies should attempt to differentiate factors that are intrinsic to the process of invasion (e.g., changes in invader populations) from long-term environmental changes (e.g., climate change) that represent extrinsic influences on the dynamics of invasion.

Phylogenomic Insights into the Evolution of Stinging Wasps and the Origins of Ants and Bees.

The stinging wasps (Hymenoptera: Aculeata) are an extremely diverse lineage of hymenopteran insects, encompassing over 70,000 described species and a diversity of life history traits, including ectoparasitism, cleptoparasitism, predation, pollen feeding (bees [Anthophila] and Masarinae), and eusociality (social vespid wasps, ants, and some bees) [1]. The most well-studied lineages of Aculeata are the ants, which are ecologically dominant in most terrestrial ecosystems [2], and the bees, the most important lineage of angiosperm-pollinating insects [3]. Establishing the phylogenetic affinities of ants and bees helps us understand and reconstruct patterns of social evolution as well as fully appreciate the biological implications of the switch from carnivory to pollen feeding (pollenivory). Despite recent advancements in aculeate phylogeny [4-11], considerable uncertainty remains regarding higher-level relationships within Aculeata, including the phylogenetic affinities of ants and bees [5-7]. We used ultraconserved element (UCE) phylogenomics [7, 12] to resolve relationships among stinging-wasp families, gathering sequence data from >800 UCE loci and 187 samples, including 30 out of 31 aculeate families. We analyzed the 187-taxon dataset using multiple analytical approaches, and we evaluated several alternative taxon sets. We also tested alternative hypotheses for the phylogenetic positions of ants and bees. Our results present a highly supported phylogeny of the stinging wasps. Most importantly, we find unequivocal evidence that ants are the sister group to bees+apoid wasps (Apoidea) and that bees are nested within a paraphyletic Crabronidae. We also demonstrate that taxon choice can fundamentally impact tree topology and clade support in phylogenomic inference.

The acacia ants revisited: convergent evolution and biogeographic context in an iconic ant/plant mutualism.

Phylogenetic and biogeographic analyses can enhance our understanding of multispecies interactions by placing the origin and evolution of such interactions in a temporal and geographical context. We use a phylogenomic approach-ultraconserved element sequence capture-to investigate the evolutionary history of an iconic multispecies mutualism: Neotropical acacia ants (Pseudomyrmex ferrugineus group) and their associated Vachellia hostplants. In this system, the ants receive shelter and food from the host plant, and they aggressively defend the plant against herbivores and competing plants. We confirm the existence of two separate lineages of obligate acacia ants that convergently occupied Vachellia and evolved plant-protecting behaviour, from timid ancestors inhabiting dead twigs in rainforest. The more diverse of the two clades is inferred to have arisen in the Late Miocene in northern Mesoamerica, and subsequently expanded its range throughout much of Central America. The other lineage is estimated to have originated in southern Mesoamerica about 3 Myr later, apparently piggy-backing on the pre-existing mutualism. Initiation of the Pseudomyrmex/Vachellia interaction involved a shift in the ants from closed to open habitats, into an environment with more intense plant herbivory. Comparative studies of the two lineages of mutualists should provide insight into the essential features binding this mutualism.

A review of the Pseudomyrmex ferrugineus and Pseudomyrmex goeldii species groups: acacia-ants and relatives (Hymenoptera: Formicidae).

The Pseudomyrmex ferrugineus group contains the Mesoamerican acacia-ants, an assemblage of species that inhabit and protect swollen-thorn acacias (Vachellia spp.). Recent phylogenetic studies have confirmed the existence of two generalist (dead twig-inhabiting) species that are embedded within the P. ferrugineus group. They are described here as P. evitus sp. nov. (occurring from Mexico to Costa Rica) and P. feralis sp. nov. (Guatemala). The morphological definition of the P. ferrugineus group is revised to incorporate additional variability in the worker and queen castes. The previous diagnosis of the males, based largely on features of the genitalia, requires little revision. Closely related to the P. ferrugineus group is a clade of five predominantly South American species, here designated and diagnosed as the P. goeldii group. The five species, P. goeldii (Forel), P. laevifrons Ward, P. micans sp. nov., P. obtusus sp. nov., and P. parvulus sp. nov., are characterized and illustrated. P. laevifrons and P. micans are closely related and difficult to distinguish, possibly reflecting incomplete isolation. Keys are provided for the identification of the species in both groups.

A revised phylogenetic classification of the ant subfamily Formicinae (Hymenoptera: Formicidae), with resurrection of the genera Colobopsis and Dinomyrmex.

The classification of the ant subfamily Formicinae is revised to reflect findings from a recent molecular phylogenetic study and complementary morphological investigations. The existing classification is maintained as far as possible, but some tribes and genera are redefined to ensure monophyly. Eleven tribes are recognized, all of which are strongly supported as monophyletic groups: Camponotini, Formicini, Gesomyrmecini, Gigantiopini, Lasiini (= Prenolepidii syn. n.), Melophorini (= Myrmecorhynchini syn. n.; = Notostigmatini syn. n.), Myrmelachistini stat. rev. (= Brachymyrmicini syn. n.), Myrmoteratini, Oecophyllini, Plagiolepidini, and Santschiellini stat. rev. Most of the tribes remain similar in content, but the generic composition of Lasiini, Melophorini, and Plagiolepidini is changed substantially. Species that have been placed in the genus Camponotus belong to three separate lineages. To ensure monophyly of this large, cosmopolitan genus we institute the following changes: Colobopsis and Dinomyrmex, both former subgenera of Camponotus, are elevated to genus level (stat. rev.), and two former genera, Forelophilus and Phasmomyrmex, are demoted to subgenus status (stat. n. and stat. rev., respectively) under Camponotus; two erstwhile subgenera of Phasmomyrmex, Myrmorhachis and Myrmacantha, become junior synonyms (syn. n.) of Camponotus (Phasmomyrmex); and the Camponotus subgenus Myrmogonia becomes a junior synonym (syn. n.) of Colobopsis. Dinomyrmex, represented by a single species from southeast Asia, D. gigas, is quite distinctive, but Camponotus and Colobopsis exhibit more subtle differences, despite being well separated phylogenetically. We identify morphological features of the worker caste that are broadly useful for distinguishing these two genera. Colobopsis species on the islands of New Caledonia and Fiji-regions with few native Camponotus species-tend to exceed these diagnostic bounds, but in this case regionally applicable character differences can be used to distinguish the two clades. Despite confusing similarities in the worker caste Colobopsis and Camponotus retain diagnostic differences in their larvae and pupae.

Phylogenomic methods outperform traditional multi-locus approaches in resolving deep evolutionary history: a case study of formicine ants.

BACKGROUND: Ultraconserved elements (UCEs) have been successfully used in phylogenomics for a variety of taxa, but their power in phylogenetic inference has yet to be extensively compared with that of traditional Sanger sequencing data sets. Moreover, UCE data on invertebrates, including insects, are sparse. We compared the phylogenetic informativeness of 959 UCE loci with a multi-locus data set of ten nuclear markers obtained via Sanger sequencing, testing the ability of these two types of data to resolve and date the evolutionary history of the second most species-rich subfamily of ants in the world, the Formicinae. RESULTS: Phylogenetic analyses show that UCEs are superior in resolving ancient and shallow relationships in formicine ants, demonstrated by increased node support and a more resolved phylogeny. Phylogenetic informativeness metrics indicate a twofold improvement relative to the 10-gene data matrix generated from the identical set of taxa. We were able to significantly improve formicine classification based on our comprehensive UCE phylogeny. Our divergence age estimations, using both UCE and Sanger data, indicate that crown-group Formicinae are older (104-117 Ma) than previously suggested. Biogeographic analyses infer that the diversification of the subfamily has occurred on all continents with no particular hub of cladogenesis. CONCLUSIONS: We found UCEs to be far superior to the multi-locus data set in estimating formicine relationships. The early history of the clade remains uncertain due to ancient rapid divergence events that are unresolvable even with our genomic-scale data, although this might be largely an effect of several problematic taxa subtended by long branches. Our comparison of divergence ages from both Sanger and UCE data demonstrates the effectiveness of UCEs for dating analyses. This comparative study highlights both the promise and limitations of UCEs for insect phylogenomics, and will prove useful to the growing number of evolutionary biologists considering the transition from Sanger to next-generation sequencing approaches.

Macroevolutionary assembly of ant/plant symbioses: Pseudomyrmex ants and their ant-housing plants in the Neotropics.

Symbioses include some of the clearest cases of coevolution, but their origin, loss or reassembly with different partners can rarely be inferred. Here we use ant/plant symbioses involving three plant clades to investigate the evolution of symbioses. We generated phylogenies for the big-eyed arboreal ants (Pseudomyrmecinae), including 72% of their 286 species, as well as for five of their plant host groups, in each case sampling more than 61% of the species. We show that the ant-housing Vachellia (Mimosoideae) clade and its ants co-diversified for the past 5 Ma, with some species additionally colonized by younger plant-nesting ant species, some parasitic. An apparent co-radiation of ants and Tachigali (Caesalpinioideae) was followed by waves of colonization by the same ant clade, and subsequent occupation by a younger ant group. Wide crown and stem age differences between the ant-housing genus Triplaris (Polygonaceae) and its obligate ant inhabitants, and stochastic trait mapping, indicate that its domatium evolved earlier than the ants now occupying it, suggesting previous symbioses that dissolved. Parasitic ant species evolved from generalists, not from mutualists, and are younger than the mutualistic systems they parasitize. Our study illuminates the macroevolutionary assembly of ant/plant symbioses, which has been highly dynamic, even in very specialized systems.

The rise of army ants and their relatives: diversification of specialized predatory doryline ants.

BACKGROUND: Army ants are dominant invertebrate predators in tropical and subtropical terrestrial ecosystems. Their close relatives within the dorylomorph group of ants are also highly specialized predators, although much less is known about their biology. We analyzed molecular data generated from 11 nuclear genes to infer a phylogeny for the major dorylomorph lineages, and incorporated fossil evidence to infer divergence times under a relaxed molecular clock. RESULTS: Because our results indicate that one subfamily and several genera of dorylomorphs are non-monophyletic, we propose to subsume the six previous dorylomorph subfamilies into a single subfamily, Dorylinae. We find the monophyly of Dorylinae to be strongly supported and estimate the crown age of the group at 87 (74-101) million years. Our phylogenetic analyses provide only weak support for army ant monophyly and also call into question a previous hypothesis that army ants underwent a fundamental split into New World and Old World lineages. Outside the army ants, our phylogeny reveals for the first time many old, distinct lineages in the Dorylinae. The genus Cerapachys is shown to be non-monophyletic and comprised of multiple lineages scattered across the Dorylinae tree. We recover, with strong support, novel relationships among these Cerapachys-like clades and other doryline genera, but divergences in the deepest parts of the tree are not well resolved. We find the genus Sphinctomyrmex, characterized by distinctive abdominal constrictions, to consist of two separate lineages with convergent morphologies, one inhabiting the Old World and the other the New World tropics. CONCLUSIONS: While we obtain good resolution in many parts of the Dorylinae phylogeny, relationships deep in the tree remain unresolved, with major lineages joining each other in various ways depending upon the analytical method employed, but always with short internodes. This may be indicative of rapid radiation in the early history of the Dorylinae, but additional molecular data and more complete species sampling are needed for confirmation. Our phylogeny now provides a basic framework for comparative biological analyses, but much additional study on the behavior and morphology of doryline species is needed, especially investigations directed at the non-army ant taxa.

Phylogenomics resolves evolutionary relationships among ants, bees, and wasps.

Eusocial behavior has arisen in few animal groups, most notably in the aculeate Hymenoptera, a clade comprising ants, bees, and stinging wasps [1-4]. Phylogeny is crucial to understanding the evolution of the salient features of these insects, including eusociality [5]. Yet the phylogenetic relationships among the major lineages of aculeate Hymenoptera remain contentious [6-12]. We address this problem here by generating and analyzing genomic data for a representative series of taxa. We obtain a single well-resolved and strongly supported tree, robust to multiple methods of phylogenetic inference. Apoidea (spheciform wasps and bees) and ants are sister groups, a novel finding that contradicts earlier views that ants are closer to ectoparasitoid wasps. Vespid wasps (paper wasps, yellow jackets, and relatives) are sister to all other aculeates except chrysidoids. Thus, all eusocial species of Hymenoptera are contained within two major groups, characterized by transport of larval provisions and nest construction, likely prerequisites for the evolution of eusociality. These two lineages are interpolated among three other clades of wasps whose species are predominantly ectoparasitoids on concealed hosts, the inferred ancestral condition for aculeates [2]. This phylogeny provides a new framework for exploring the evolution of nesting, feeding, and social behavior within the stinging Hymenoptera.

Relative roles of climatic suitability and anthropogenic influence in determining the pattern of spread in a global invader.

Because invasive species threaten the integrity of natural ecosystems, a major goal in ecology is to develop predictive models to determine which species may become widespread and where they may invade. Indeed, considerable progress has been made in understanding the factors that influence the local pattern of spread for specific invaders and the factors that are correlated with the number of introduced species that have become established in a given region. However, few studies have examined the relative importance of multiple drivers of invasion success for widespread species at global scales. Here, we use a dataset of >5,000 presence/absence records to examine the interplay between climatic suitability, biotic resistance by native taxa, human-aided dispersal, and human modification of habitats, in shaping the distribution of one of the world's most notorious invasive species, the Argentine ant (Linepithema humile). Climatic suitability and the extent of human modification of habitats are primarily responsible for the distribution of this global invader. However, we also found some evidence for biotic resistance by native communities. Somewhat surprisingly, and despite the often cited importance of propagule pressure as a crucial driver of invasions, metrics of the magnitude of international traded commodities among countries were not related to global distribution patterns. Together, our analyses on the global-scale distribution of this invasive species provide strong evidence for the interplay of biotic and abiotic determinants of spread and also highlight the challenges of limiting the spread and subsequent impact of highly invasive species.

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.

One nutritional symbiosis begat another: phylogenetic evidence that the ant tribe Camponotini acquired Blochmannia by tending sap-feeding insects.

BACKGROUND: Bacterial endosymbiosis has a recurring significance in the evolution of insects. An estimated 10-20% of insect species depend on bacterial associates for their nutrition and reproductive viability. Members of the ant tribe Camponotini, the focus of this study, possess a stable, intracellular bacterial mutualist. The bacterium, Blochmannia, was first discovered in Camponotus and has since been documented in a distinct subgenus of Camponotus, Colobopsis, and in the related genus Polyrhachis. However, the distribution of Blochmannia throughout the Camponotini remains in question. Documenting the true host range of this bacterial mutualist is an important first step toward understanding the various ecological contexts in which it has evolved, and toward identifying its closest bacterial relatives. In this study, we performed a molecular screen, based on PCR amplification of 16S rDNA, to identify bacterial associates of diverse Camponotini species. RESULTS: Phylogenetic analyses of 16S rDNA gave four important insights: (i) Blochmannia occurs in a broad range of Camponotini genera including Calomyrmex, Echinopla, and Opisthopsis, and did not occur in outgroups related to this tribe (e.g., Notostigma). This suggests that the mutualism originated in the ancestor of the tribe Camponotini. (ii) The known bacteriocyte-associated symbionts of ants, in Formica, Plagiolepis, and the Camponotini, arose independently. (iii) Blochmannia is nestled within a diverse clade of endosymbionts of sap-feeding hemipteran insects, such as mealybugs, aphids, and psyllids. In our analyses, a group of secondary symbionts of mealybugs are the closest relatives of Blochmannia. (iv) Blochmannia has cospeciated with its known hosts, although deep divergences at the genus level remain uncertain. CONCLUSIONS: The Blochmannia mutualism occurs in Calomyrmex, Echinopla, and Opisthopsis, in addition to Camponotus, and probably originated in the ancestral lineage leading to the Camponotini. This significant expansion of its known host range implies that the mutualism is more ancient and ecologically diverse than previously documented. Blochmannia is most closely related to endosymbionts of sap-feeding hemipterans, which ants tend for their carbohydrate-rich honeydew. Based on phylogenetic results, we propose Camponotini might have originally acquired this bacterial mutualist through a nutritional symbiosis with other insects.

How to prevent cheating: a digestive specialization ties mutualistic plant-ants to their ant-plant partners.

Mutualisms often involve reciprocal adaptations of both partners. Acacia ant-plants defended by symbiotic Pseudomyrmex ant mutualists secrete sucrose-free extrafloral nectar, which is unattractive to generalists. We aimed to investigate whether this extrafloral nectar can also exclude exploiters, that is nondefending ant species. Mutualist workers discriminated against sucrose whereas exploiters and generalists with no affinity toward Acacia myrmecophytes preferred sucrose, because mutualist workers lacked the sucrose-cleaving enzyme invertase, which is present in workers of the other two groups. Sucrose uptake induced invertase activity in workers of parasites and generalists, but not mutualists, and in larvae of all species: the mutualists loose invertase during their ontogeny. This reduced metabolic capacity ties the mutualists to their plant hosts, but it does not completely prevent the mutualism from exploitation. We therefore investigated whether the exploiters studied here are cheaters (i.e., have evolved from former mutualists) or parasites (exploiters with no mutualistic ancestor). A molecular phylogeny demonstrates that the exploiter species did not evolve from former mutualists, and no evidence for cheaters was found. We conclude that being specialized to their partner can prevent mutualists from becoming cheaters, whereas other mechanisms are required to stabilize a mutualism against the exploitation by parasites.

Evaluating alternative hypotheses for the early evolution and diversification of ants.

Ants are the world's most diverse and ecologically dominant eusocial organisms. Resolving the phylogeny and timescale for major ant lineages is vital to understanding how they achieved this success. Morphological, molecular, and paleontological studies, however, have presented conflicting views on early ant evolution. To address these issues, we generated the largest ant molecular phylogenetic data set published to date, containing approximately 6 kb of DNA sequence from 162 species representing all 20 ant subfamilies and 10 aculeate outgroup families. When these data were analyzed with and without outgroups, which are all distantly related to ants and hence long-branched, we obtained conflicting ingroup topologies for some early ant lineages. This result casts strong doubt on the existence of a poneroid clade as currently defined. We compare alternate attachments of the outgroups to the ingroup tree by using likelihood tests, and find that several alternative rootings cannot be rejected by the data. These alternatives imply fundamentally different scenarios for the early evolution of ant morphology and behavior. Our data strongly support several notable relationships within the more derived formicoid ants, including placement of the enigmatic subfamily Aenictogitoninae as sister to Dorylus army ants. We use the molecular data to estimate divergence times, employing a strategy distinct from previous work by incorporating the extensive fossil record of other aculeate Hymenoptera as well as that of ants. Our age estimates for the most recent common ancestor of extant ants range from approximately 115 to 135 million years ago, indicating that a Jurassic origin is highly unlikely.