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 comprehensive 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 ∼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 ∼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 basitarsal sulcus gland, a novel exocrine structure in ants

The basitarsus of the mid- and/or hindlegs of several Amblyoponinae ants shows a deep longitudinal groove or sulcus on its anterior face in workers and queens. Histological examination reveals this sulcus is associated with a conspicuous novel epithelial gland, which brings the number of exocrine glands in the legs of ants to 25. The ultrastructural characteristics of the gland show the presence of a well-developed smooth endoplasmic reticulum. This is indicative for the elaboration of a non-proteinaceous and thus possibly pheromonal secretion. Behavioural observations show that this secretion is collected by the tarsomeres and spread onto the brood and nest, suggesting a role in nestmate recognition. A similar basitarsal sulcus gland was also found in Nothomyrmecia, Paraponera and Tetraponera, which represents both a wide phylogenetic and ecological distribution, as it includes arboreal, ground-dwelling as well as subterranean taxa.

Three spectrally distinct photoreceptors in diurnal and nocturnal Australian ants

Ants are thought to be special among Hymenopterans in having only dichromatic colour vision based on two spectrally distinct photoreceptors. Many ants are highly visual animals, however, and use vision extensively for navigation. We show here that two congeneric day- and night-active Australian ants have three spectrally distinct photoreceptor types, potentially supporting trichromatic colour vision. Electroretinogram recordings show the presence of three spectral sensitivities with peaks (λmax) at 370, 450 and 550 nm in the night-active Myrmecia vindex and peaks at 370, 470 and 510 nm in the day-active Myrmecia croslandi. Intracellular electrophysiology on individual photoreceptors confirmed that the night-active M. vindex has three spectral sensitivities with peaks (λmax) at 370, 430 and 550 nm. A large number of the intracellular recordings in the night-active M. vindex show unusually broad-band spectral sensitivities, suggesting that photoreceptors may be coupled. Spectral measurements at different temporal frequencies revealed that the ultraviolet receptors are comparatively slow. We discuss the adaptive significance and the probability of trichromacy in Myrmecia ants in the context of dim light vision and visual navigation.

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.

Molecular phylogeny and biogeography of the spider ants, genus Leptomyrmex Mayr (Hymenoptera: Formicidae)

This study provides the first phylogenetic reconstruction of the ant genus Leptomyrmex Mayr, a prominent endemic component of rain forest and wet sclerophyll forest in Australia, New Guinea and New Caledonia. Five genes are used to reconstruct phylogeny and estimate of ages of diversification in order to test congruence of the history of nuclear and mitochondrial genes: three protein-coding nuclear genes: arginine kinase (argK, 897 bp), long wavelength rhodopsin (LW Rh, 546 bp) and wingless (Wg, 409 bp), as well as the large subunit ribosomal gene 28S (482 bp) and the mitochondrial gene cytochrome oxidase I (COI, 658 bp). Four different partitioning schemes were tested for optimal resolving power; results show that partitioning by gene, translational pattern and codon position were uniformly favoured over less complex partitions. Nuclear markers showed relatively minor sequence divergence and provided strongly supported topology; phylogeny based solely on mtDNA produced somewhat conflicting topology but offered little power to resolve species complexes. Monophyly of the genus Leptomyrmex was recovered, as was the sister-group relationship of 'micro-' and 'macro-'Leptomyrmex species. Divergence dating analyses estimate that Leptomyrmex arose in the Eocene (stem age ∼ 44 million years ago (ma)), and that the 'macro-' species diverged from the 'micro-' species in the early Oligocene (∼ 31 ma). Diversification of the crown group 'macro-' and 'micro-'Leptomyrmex occurred in the Miocene (∼ 15 ma and 7.9 ma, respectively). New Guinean and New Caledonian lineages appear to have diverged from Australian lineages only recently (∼ 4.7 ma and 10.3 ma, respectively), and the latter clade is inferred to have reached New Caledonia from Australia via long distance dispersal. These results challenge previous hypotheses of Leptomyrmex classification and assumptions about their historical dispersal, but are in agreement with the current knowledge of the geological history of Melanesia.

Characterization of polymorphic microsatellites in the giant bulldog ant, Myrmecia brevinoda and the jumper ant, M. pilosula

The ant genus Myrmecia Fabricius (Hymenoptera: Formicidae) is endemic to Australia and New Caledonia, and has retained many biological traits that are considered to be basal in the family Formicidae. Here, a set of 16 dinucleotide microsatellite loci were studied that are polymorphic in at least one of the two species of the genus: the giant bulldog ant, M. brevinoda Forel, and the jumper ant, M. pilosula Smith; 13 are novel loci and 3 are loci previously published for the genus Nothomyrmecia Clark (Hymenoptera: Formicidae). In M. brevinoda, the total of 12 polymorphic microsatellites yielded a total of 125 alleles, ranging from 3 to 18 with an average of 10.42 per locus; the observed and expected heterozygosities ranged from 0.4000 to 0.9000 and from 0.5413 to 0.9200, respectively. In M. pilosula, the 9 polymorphic loci yielded a total of 67 alleles, ranging from 3 to 12 with an average of 7.44 per locus; the observed and expected heterozygosities ranged from 0.5625 to 0.9375 and from 0.4863 to 0.8711, respectively. Five loci were polymorphic in both target species. In addition, 15 out of the 16 loci were successfully amplified in M. pyriformis. These informative microsatellite loci provide a powerful tool for investigating the population and colony genetic structure of M. brevinoda and M. pilosula, and may also be applicable to a range of congeners considering the relatively distant phylogenetic relatedness between M. pilosula and the other two species within the genus Myrmecia.

Insect biodiversity and conservation in Australasia

Australasia, which consists of Australia and the adjacent islands of the southwestern Pacific Ocean, has an insect diversity approximately proportional to the land mass. This diversity is distinctive, with some major groups missing and others having radiated. Iconic species are familiar to most people living in Australia and New Zealand, and a range of insects once contributed to Aboriginal Australian culture and diet. Conservation of Australasian entomological biodiversity is an increasing challenge for contemporary scientists. Examples are provided of insect conservation schemes from New Guinea, New Zealand, and Australia. Funding for insect biodiversity studies beyond flagship species is needed.

Episodes in insect evolution

This article derives from a society-wide symposium organized by Timothy Bradley and Adriana Briscoe and presented at the 2009 annual meeting of the Society for Integrative and Comparative Biology in Boston, Massachusetts. David Grimaldi provided the opening presentation in which he outlined the major evolutionary events in the formation and subsequent diversification of the insect clade. This presentation was followed by speakers who detailed the evolutionary history of specific physiological and/or behavioral traits that have caused insects to be both ecologically successful and fascinating as subjects for biological study. These include a review of the evolutionary history of the insects, the origins of flight, osmoregulation, the evolution of tracheal systems, the evolution of color vision, circadian clocks, and the evolution of eusociality. These topics, as covered by the speakers, provide an overview of the pattern and timing of evolutionary diversification and specialization in the group of animals we know as insects.

Phylogeny of colletid bees (Hymenoptera: Colletidae) inferred from four nuclear genes

Colletidae comprise approximately 2500 species of bees primarily distributed in the southern continents (only two colletid genera are widely distributed: Colletes and Hylaeus). Previously published studies have failed to resolve phylogenetic relationships on a worldwide basis and this has been a major barrier to the progress of research regarding systematics and evolution of colletid bees. For this study, data from four nuclear gene loci: elongation factor-1alpha (F2 copy), opsin, wingless, and 28S rRNA were analyzed for 122 species of colletid bees, representing all subfamilies and tribes currently recognized; 22 species belonging to three other bee families were used as outgroups. Bayesian, maximum likelihood, and parsimony methods were employed to investigate the phylogenetic relationships within Colletidae and resulted in highly congruent and well-resolved trees. The phylogenetic results show that Colletidae are monophyletic and that all traditionally recognized subfamilies (except Paracolletinae) are also strongly supported as monophyletic. Our phylogenetic hypothesis provides a framework within which broad questions related to the taxonomy, biogeography, morphology, evolution, and ecology of colletid bees can be addressed.

Newly discovered sister lineage sheds light on early ant evolution

Ants are the world's most conspicuous and important eusocial insects and their diversity, abundance, and extreme behavioral specializations make them a model system for several disciplines within the biological sciences. Here, we report the discovery of a new ant that appears to represent the sister lineage to all extant ants (Hymenoptera: Formicidae). The phylogenetic position of this cryptic predator from the soils of the Amazon rainforest was inferred from several nuclear genes, sequenced from a single leg. Martialis heureka (gen. et sp. nov.) also constitutes the sole representative of a new, morphologically distinct subfamily of ants, the Martialinae (subfam. nov.). Our analyses have reduced the likelihood of long-branch attraction artifacts that have troubled previous phylogenetic studies of early-diverging ants and therefore solidify the emerging view that the most basal extant ant lineages are cryptic, hypogaeic foragers. On the basis of morphological and phylogenetic evidence we suggest that these specialized subterranean predators are the sole surviving representatives of a highly divergent lineage that arose near the dawn of ant diversification and have persisted in ecologically stable environments like tropical soils over great spans of time.

A DNA and morphology based phylogenetic framework of the ant genus Lasius with hypotheses for the evolution of social parasitism and fungiculture

BACKGROUND

Ants of the genus Lasius are ecologically important and an important system for evolutionary research. Progress in evolutionary research has been hindered by the lack of a well-founded phylogeny of the subgenera, with three previous attempts disagreeing. Here we employed two mitochondrial genes (cytochrome c oxidase subunit I, 16S ribosomal RNA), comprising 1,265 bp, together with 64 morphological characters, to recover the phylogeny of Lasius by Bayesian and Maximum Parsimony inference after exploration of potential causes of phylogenetic distortion. We use the resulting framework to infer evolutionary pathways for social parasitism and fungiculture.

RESULTS

We recovered two well supported major lineages. One includes Acanthomyops, Austrolasius, Chthonolasius, and Lasius pallitarsis, which we confirm to represent a seventh subgenus, the other clade contains Dendrolasius, and Lasius sensu stricto. The subgenus Cautolasius, displaying neither social parasitism nor fungiculture, probably belongs to the second clade, but its phylogenetic position is not resolved at the cutoff values of node support we apply. Possible causes for previous problems with reconstructing the Lasius phylogeny include use of other reconstruction techniques, possibly more prone to instabilities in some instances, and the inclusion of phylogenetically distorting characters.

CONCLUSION

By establishing an updated phylogenetic framework, our study provides the basis for a later formal taxonomic revision of subgenera and for studying the evolution of various ecologically and sociobiologically relevant traits of Lasius, although there is need for future studies to include nuclear genes and additional samples from the Nearctic. Both social parasitism and fungiculture evolved twice in Lasius, once in each major lineage, which opens up new opportunities for comparative analyses. The repeated evolution of social parasitism has been established for other groups of ants, though not for temporary social parasitism as found in Lasius. For fungiculture, the independent emergence twice in a monophyletic group marks a novel scenario in ants. We present alternative hypotheses for the evolution of both traits, with one of each involving loss of the trait. Though less likely for both traits than later evolution without reversal, we consider reversal as sufficiently plausible to merit independent testing.

Fossil evidence for the early ant evolution

Ants are one of the most studied insects in the world; and the literature devoted to their origin and evolution, systematics, ecology, or interactions with plants, fungi and other organisms is prolific. However, no consensus yet exists on the age estimate of the first Formicidae or on the origin of their eusociality. We review the fossil and biogeographical record of all known Cretaceous ants. We discuss the possible origin of the Formicidae with emphasis on the most primitive subfamily Sphecomyrminae according to its distribution and the Early Cretaceous palaeogeography. And we review the evidence of true castes and eusociality of the early ants regarding their morphological features and their manner of preservation in amber. The mid-Cretaceous amber forest from south-western France where some of the oldest known ants lived, corresponded to a moist tropical forest close to the shore with a dominance of gymnosperm trees but where angiosperms (flowering plants) were already diversified. This palaeoenvironmental reconstruction supports an initial radiation of ants in forest ground litter coincident with the rise of angiosperms, as recently proposed as an ecological explanation for their origin and successful evolution.

New fossil ants in French Cretaceous amber (Hymenoptera: Formicidae)

Recent studies on the ant phylogeny are mainly based on the molecular analyses of extant subfamilies and do not include the extinct, only Cretaceous subfamily Sphecomyrminae. However, the latter is of major importance for ant relationships, as it is considered the most basal subfamily. Therefore, each new discovery of a Mesozoic ant is of high interest for improving our understanding of their early history and basal relationships. In this paper, a new sphecomyrmine ant, allied to the Burmese amber genus Haidomyrmex, is described from mid-Cretaceous amber of France as Haidomyrmodes mammuthus gen. and sp. n. The diagnosis of the tribe Haidomyrmecini is emended based on the new type material, which includes a gyne (alate female) and two incomplete workers. The genus Sphecomyrmodes, hitherto known by a single species from Burmese amber, is also reported and a new species described as S. occidentalis sp. n. after two workers remarkably preserved in a single piece of Early Cenomanian French amber. The new fossils provide additional information on early ant diversity and relationships and demonstrate that the monophyly of the Sphecomyrminae, as currently defined, is still weakly supported.

Dynamics of the evolution of Batesian mimicry: molecular phylogenetic analysis of ant-mimicking Myrmarachne (Araneae: Salticidae) species and their ant models

Batesian mimicry is seen as an example of evolution by natural selection, with predation as the main driving force. The mimic is under selective pressure to resemble its model, whereas it is disadvantageous for the model to be associated with the palatable mimic. In consequence one might expect there to be an evolutionary arms race, similar to the one involving host-parasite coevolution. In this study, the evolutionary dynamics of a Batesian mimicry system of model ants and ant-mimicking salticids is investigated by comparing the phylogenies of the two groups. Although Batesian mimics are expected to coevolve with their models, we found the phylogenetic patterns of the models and the mimics to be indicative of adaptive radiation by the mimic rather than co-speciation between the mimic and the model. This shows that there is strong selection pressure on Myrmarachne, leading to a high degree of polymorphism. There is also evidence of sympatric speciation in Myrmarachne, the reproductive isolation possibly driven by female mate choice in polymorphic species.

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.

A multidisciplinary approach reveals cryptic diversity in Western Palearctic Tetramorium ants (Hymenoptera: Formicidae)

Diversity of ants of the Tetramorium caespitum/impurum complex was investigated in a multidisciplinary study. Focusing on morphologically hardly distinguishable Western Palearctic samples, we demonstrate the genetic and phenotypic diversity, demarcate phylogenetic entities, and discuss the clades in terms of biogeography. Sequences of 1113bp of the mitochondrial COI gene revealed 13 lineages. COII data, worker morphometry and male genitalia morphology corroborated the COI results for seven lineages; the remaining six were disregarded because of small sample size. A comparison with published data on cuticular hydrocarbons showed correspondence. The seven entities show different distribution patterns, though some ranges overlap in Central Europe. Since no major discrepancy between the results of the different disciplines became apparent, we conclude that the seven entities within the T. caespitum/impurum complex represent seven species. Geographical evidence allows the identification of T. caespitum and T. impurum, and we therefore designate neotypes and redescribe the two species in terms of morphology and mtDNA. As the revision of about 50 taxon names would go beyond the scope of this study, we refer to the remaining five species under code names. We discuss our findings in terms of plesiomorphy and convergent evolution by visualizing the mtDNA phylogeny in morphological space.

Phylogenetic relationships among species groups of the ant genus Myrmecia

Phylogenetic relationships among the nine species groups of the predominately Australian ant genus Myrmecia were inferred using 38 Myrmecia species and an outgroup using DNA sequences from two nuclear genes (622nt from 28S rRNA and 1907nt from the long-wave opsin gene). Nothomyrmecia macrops was selected as the most appropriate outgroup based on recent reliable studies showing monophyly of Myrmecia with Nothomyrmecia. The four species groups with an occipital carina (those of gulosa, nigrocincta, urens, and picta) were found to form a paraphyletic and basal assemblage out of which the five species groups lacking an occipital carina (those of aberrans, mandibularis, tepperi, cephalotes, and pilosula) arise as a strongly supported monophyletic assemblage. Monophyly was supported for four groups (those of gulosa, nigrocincta, picta, and mandibularis) but the situation is unclear for four others (those of urens, aberrans, tepperi, and pilosula). The aberrans group appears to be basal within the group lacking an occipital carina; a previous suggestion that it is the sister group to the rest of the genus is thus not supported.

Molecular systematics of basal subfamilies of ants using 28S rRNA (Hymenoptera: Formicidae)

For many years, the ant subfamily Ponerinae was hypothesized to contain the basal (early branching) lineages of ants. Recently the Ponerinae were reclassified into six poneromorph subfamilies based on morphological analysis. We evaluate this new poneromorph classification using 1240 base pairs of DNA sequence data obtained from 28S rRNA gene sequences of 68 terminal taxa. The molecular tree supported the monophyly of the ant family Formicidae, with 100% parsimony bootstrap (PB) support and posterior probabilities (PP) of 1.00, with the ant subfamily Leptanillinae as a sister group to all other ants (PB=62, PP=93). However, our analyses strongly support the polyphyly of the Poneromorph subfamilies (sensu Bolton). The Ectatomminae and Heteroponerinae are more closely related to the Formicoid subfamilies than to the rest of the poneromophs (PB=96, PP=100). The Amblyoponinae (PB=52, PP=96), Paraponerinae (PB=100, PP=100), Ponerinae (PB<50, PP=71), and Proceratiinae (PB=98, PP=100) appear as distinct lineages at the base of the tree and are identified as a poneroid grade. Monophyletic origins for the poneroid subfamilies Amblyoponinae, Paraponerinae, Ponerinae and Proceratiinae are supported in our analysis. However, the genus Platythyrea forms a distinct sister group to the Ponerini within the Ponerinae. The Heteroponerinae, based on our sample of Heteroponera, are associated with the subfamily Ectatomminae (PB=98, PP=100). Furthermore, our data indicate the genus Probolomyrmex belongs to the Proceratiinae as suggested by recent morphological analysis (PB=98, PP=100).

Phylogeny of the Ants: Diversification in the Age of Angiosperms

We present a large-scale molecular phylogeny of the ants (Hymenoptera: Formicidae), based on 4.5 kilobases of sequence data from six gene regions extracted from 139 of the 288 described extant genera, representing 19 of the 20 subfamilies. All but two subfamilies are recovered as monophyletic. Divergence time estimates calibrated by minimum age constraints from 43 fossils indicate that most of the subfamilies representing extant ants arose much earlier than previously proposed but only began to diversify during the Late Cretaceous to Early Eocene. This period also witnessed the rise of angiosperms and most herbivorous insects.

The evolution of worker caste diversity in social insects

Morphological diversification of workers is predicted to improve the division of labor within social insect colonies, yet many species have monomorphic workers. Individual-level selection on the reproductive capacities of workers may counter colony-level selection for diversification, and life-history differences between species (timing of caste determination, colony size, genetic variation available) may mediate the strength of this selection. We tested this through phylogenetically independent contrast analyses on a new data set for 35 ant species. Evidence was found that early divergence of queen-worker developmental pathways may facilitate the evolution of worker diversity because queen-worker dimorphism was strongly positively associated with diversity. By contrast, risks for colonies that invest in specialized workers and colony size effects on costs of worker reproduction seem unlikely to strongly affect the evolution of worker diversity because there was no significant association between colony size and diversity when controlling statistically for queen-worker dimorphism. Finally, worker diversity was greater in species with multiple lineages per colony, and it was negatively associated with relatedness in monogynous species. This could be due to high intracolonial genetic variance favoring the expression and evolution of great worker diversity or to diversity evolving more easily when there is selection for repression of worker reproduction (worker policing).

The rise of the ants: a phylogenetic and ecological explanation

In the past two decades, studies of anatomy, behavior, and, most recently, DNA sequences have clarified the phylogeny of the ants at the subfamily and generic levels. In addition, a rich new harvest of Cretaceous and Paleogene fossils has helped to date the major evolutionary radiations. We collate this information and then add data from the natural history of the modern fauna to sketch a history of major ecological adaptations at the subfamily level. The key events appear to have been, first, a mid-Cretaceous initial radiation in forest ground litter and soil coincident with the rise of the angiosperms (flowering plants), then a Paleogene advance to ecological dominance in concert with that of the angiosperms in tropical forests, and, finally, an expansion of some of the lineages, aided by changes in diet away from dependence on predation, upward into the canopy, and outward into more xeric environments.

Conflict over male parentage in social insects

Mutual policing is an important mechanism that maintains social harmony in group-living organisms by suppressing the selfish behavior of individuals. In social insects, workers police one another (worker-policing) by preventing individual workers from laying eggs that would otherwise develop into males. Within the framework of Hamilton's rule there are two explanations for worker-policing behavior. First, if worker reproduction is cost-free, worker-policing should occur only where workers are more closely related to queen- than to worker-produced male eggs (relatedness hypothesis). Second, if there are substantial costs to unchecked worker reproduction, worker-policing may occur to counteract these costs and increase colony efficiency (efficiency hypothesis). The first explanation predicts that patterns of the parentage of males (male parentage) are associated with relatedness, whereas the latter does not. We have investigated how male parentage varies with colony kin structure and colony size in 50 species of ants, bees, and wasps in a phylogenetically controlled comparative analysis. Our survey revealed that queens produced the majority of males in most of the species and that workers produced more than half of the males in less than 10% of species. Moreover, we show that male parentage does not vary with relatedness as predicted by the relatedness hypothesis. This indicates that intra- and interspecific variation in male parentage cannot be accounted for by the relatedness hypothesis alone and that increased colony efficiency is an important factor responsible for the evolution of worker-policing. Our study reveals greater harmony and more complex regulation of reproduction in social insect colonies than that expected from simple theoretical expectations based on relatedness only.

Workers of social insects prevent other workers laying eggs to increase colony efficiency and not -- as traditionally thought - purely because workers are more related to the queen of the colony

Single-copy nuclear genes recover cretaceous-age divergences in bees

We analyzed the higher level phylogeny of the bee family Halictidae based on the coding regions of three single-copy nuclear genes (long-wavelength [LW] opsin, wingless, and elongation factor 1-alpha [EF-1 alpha]). Our combined data set consisted of 2,234 aligned nucleotide sites (702 base pairs [bp] for LW opsin, 405 bp for wingless, and 1,127 bp for EF-1 alpha) and 779 parsimony-informative sites. We included 58 species of halictid bees from 33 genera, representing all subfamilies and tribes, and rooted the trees using seven outgroups from other bee families: Colletidae, Andrenidae, Melittidae, and Apidae. We analyzed the separate and combined data sets by a variety of methods, including equal weights parsimony, maximum likelihood, and Bayesian methods. Analysis of the combined data set produced a strong phylogenetic signal with high bootstrap and Bremer support and high posterior probability well into the base of the tree. The phylogeny recovered the monophyly of the Halictidae and of all four subfamilies and both tribes, recovered relationships among the subfamilies and tribes congruent with morphology, and provided robust support for the relationships among the numerous genera in the tribe Halictini, sensu Michener (2000). Using our combined nucleotide data set, several recently described halictid fossils from the Oligocene and Eocene, and recently developed Bayesian methods, we estimated the antiquity of major clades within the family. Our results indicate that each of the four subfamilies arose well before the Cretaceous-Tertiary boundary and suggest that the early radiation of halictid bees involved substantial African-South American interchange roughly coincident with the separation of these two continents in the late Cretaceous. This combination of single-copy nuclear genes is capable of recovering Cretaceous-age divergences in bees with high levels of support. We propose that LW opsin, wingless, and EF-1 alpha(F2 copy) may be useful in resolving relationships among bee families and other Cretaceous-age insect lineages.

Phylogeny of ants (Formicidae) based on morphology and DNA sequence data

In order to reconstruct ants' phylogeny, we analysed DNA sequences for two nuclear genes, abdominal-A and Ultrabithorax, from 49 species of ants and two outgroups. As these genes control the development of the first segments of the abdomen in insects, which are very variable in ants (petiole, postpetiole, and gaster constriction), we hypothesized that the morphological variations between the subfamilies may be correlated with mutations of some abd-A or Ubx regions. Contrarily to our hypothesis, these sequences are highly conserved. The differences observed concern mainly third codon positions and present some saturation. Phylogenetic reconstructions were carried out using the genetic raw sequence data and by combining them with a set of morphological data (Total Evidence). Relations among subfamilies of ants remains poorly resolved with molecular data only, but adding these data to morphological characters confirms and reinforce the topology of : a Poneroid complex [Ponerinae, Cerapachyinae, Leptanillinae and army ants], a Formicoid complex [Dolichoderinae, Formicinae] and a Myrmecoid complex [Myrmicinae, Myrmeciinae, Pseudomyrmecinae, Nothomyrmeciinae]. Our molecular results allow resolution near the branch tips and three subfamilies (Dolichoderinae, Formicinae and Pseudomyrmecinae) always appear as monophyletic. The Formicinae and the Dolichoderinae have close relationships. The Camponotini appear as a strong clade inside the Formicinae. The Ponerinae are separated in two parts: the Ectatommini and all other tribes. The Cerapachyinae, Dorylinae, and Ecitoninae belong to the same clade, the Cerapachyinae being confirmed in their subfamily status. The Myrmicinae appears to be very heterogeneous, with the Attini forming a very stable and well-separated group.

Molecular phylogenetic analysis of ant subfamily relationship inferred from rDNA sequences

The relationships among ant subfamilies were studied by phylogenetic analysis of rDNA sequences of 15 species from seven subfamilies. PCR primers were designed on the basis of the rDNA sequence of the Australian bulldog ant, Myrmecia croslandi, previously determined. Phylogenetic trees were constructed using sequences of a fragment of 18S rDNA (1.8 kb), a fragment of 28S rDNA (0.7 kb excluding variable regions) and a combination of the 18S and 28S rDNAs, by neighbor-joining (NJ), maximum parsimony (MP) and maximum likelihood (ML). rDNA sequences corresponding to the same fragments from three non-ant hymenopteran species (a sawfly, a bee and a wasp) were employed as outgroups. These trees indicated that the ant subfamilies were clustered singly, and, among the seven subfamilies examined, Ponerinae and six other subfamilies are in a sister-groups relationship. The relationship among the six subfamilies, however, was not clarified. The phylogenetic trees constructed in the present study are not in contradiction to the tree from cladistic analysis of morphological data by Baroni Urbani et al. (1992) and the tree from morphological and molecular data (Ward and Brady, 2003), but are inconsistent with the traditional phylogeny. The present results thus raise a question as to the status of some traditionally employed "key" morphological characters. The present results also call for a reexamination of Amblyopone traditionally treated as a member of Ponerinae as belonging to a new subfamily.