Evolution of sociality in a primitively eusocial lineage of bees

Lifetime monogamy and the evolution of eusociality

All evidence currently available indicates that obligatory sterile eusocial castes only arose via the association of lifetime monogamous parents and offspring. This is consistent with Hamilton's rule (br(s) > r(o)c), but implies that relatedness cancels out of the equation because average relatedness to siblings (r(s)) and offspring (r(o)) are both predictably 0.5. This equality implies that any infinitesimally small benefit of helping at the maternal nest (b), relative to the cost in personal reproduction (c) that persists throughout the lifespan of entire cohorts of helpers suffices to establish permanent eusociality, so that group benefits can increase gradually during, but mostly after the transition. The monogamy window can be conceptualized as a singularity comparable with the single zygote commitment of gametes in eukaryotes. The increase of colony size in ants, bees, wasps and termites is thus analogous to the evolution of multicellularity. Focusing on lifetime monogamy as a universal precondition for the evolution of obligate eusociality simplifies the theory and may help to resolve controversies about levels of selection and targets of adaptation. The monogamy window underlines that cooperative breeding and eusociality are different domains of social evolution, characterized by different sectors of parameter space for Hamilton's rule.

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.

Risk-sensitive foraging and the evolution of cooperative breeding and reproductive skew

Background

Group formation and food sharing in animals may reduce variance in resource supply to breeding individuals. For some species it has thus been interpreted as a mechanism of risk avoidance. However, in many groups reproduction is extremely skewed. In such groups resources are not shared equally among the members and inter-individual variance in resource supply may be extreme. The potential consequences of this aspect of group living have not attained much attention in the context of risk sensitive foraging.

Results

We develop a model of individually foraging animals that share resources for reproduction. The model allows analyzing how mean foraging success, inter-individual variance of foraging success, and the cost of reproduction and offspring raising influence the benefit of group formation and resource sharing. Our model shows that the effects are diametrically opposed in egalitarian groups versus groups with high reproductive skew. For individuals in egalitarian groups the relative benefit of group formation increases under conditions of increasing variance in foraging success and decreasing cost of reproduction. On the other hand individuals in groups with high skew will profit from group formation under conditions of decreasing variance in individual foraging success and increasing cost of reproduction.

Conclusion

The model clearly demonstrates that reproductive skew qualitatively changes the influence of food sharing on the reproductive output of groups. It shows that the individual benefits of variance reduction in egalitarian groups and variance enhancement in groups with reproductive skew depend critically on ecological and life-history parameters. Our model of risk-sensitive foraging thus allows comparing animal societies as different as spiders and birds in a single framework.

Social complexity in bees is not sufficient to explain lack of reversions to solitary living over long time scales

Background

The major lineages of eusocial insects, the ants, termites, stingless bees, honeybees and vespid wasps, all have ancient origins (≥ 65 mya) with no reversions to solitary behaviour. This has prompted the notion of a 'point of no return' whereby the evolutionary elaboration and integration of behavioural, genetic and morphological traits over a very long period of time leads to a situation where reversion to solitary living is no longer an evolutionary option.

Results

We show that in another group of social insects, the allodapine bees, there was a single origin of sociality > 40 mya. We also provide data on the biology of a key allodapine species, Halterapis nigrinervis, showing that it is truly social. H. nigrinervis was thought to be the only allodapine that was not social, and our findings therefore indicate that there have been no losses of sociality among extant allodapine clades. Allodapine colony sizes rarely exceed 10 females per nest and all females in virtually all species are capable of nesting and reproducing independently, so these bees clearly do not fit the 'point of no return' concept.

Conclusion

We argue that allodapine sociality has been maintained by ecological constraints and the benefits of alloparental care, as opposed to behavioural, genetic or morphological constraints to independent living. Allodapine brood are highly vulnerable to predation because they are progressively reared in an open nest (not in sealed brood cells), which provides potentially large benefits for alloparental care and incentives for reproductives to tolerate potential alloparents. We argue that similar vulnerabilities may also help explain the lack of reversions to solitary living in other taxa with ancient social origins.

Multigene phylogeny reveals eusociality evolved twice in vespid wasps

Eusocial wasps of the family Vespidae are thought to have derived their social behavior from a common ancestor that had a rudimentary caste-containing social system. In support of this behavioral scenario, the leading phylogenetic hypothesis of Vespidae places the eusocial wasps (subfamilies Stenogastrinae, Polistinae, and Vespinae) as a derived monophyletic clade, thus implying a single origin of eusocial behavior. This perspective has shaped the investigation and interpretation of vespid social evolution for more than two decades. Here we report a phylogeny of Vespidae based on data from four nuclear gene fragments (18S and 28S ribosomal DNA, abdominal-A and RNA polymerase II) and representatives from all six extant subfamilies. In contrast to the current phylogenetic perspective, our results indicate two independent origins of vespid eusociality, once in the clade Polistinae+Vespinae and once in the Stenogastrinae. The stenogastrines appear as an early diverging clade distantly related to the vespines and polistines and thus evolved their distinctive form of social behavior from a different ancestor than that of Polistinae+Vespinae. These results support earlier views based on life history and behavior and have important implications for interpreting transitional stages in vespid social evolution.

Changing paradigms in insect social evolution: insights from halictine and allodapine bees

Until the 1980s theories of social insect evolution drew strongly on halictine and allodapine bees. However, that early work suffered from a lack of sound phylogenetic inference and detailed information on social behavior in many critical taxa. Recent studies have changed our understanding of these bee groups in profound ways. It has become apparent that forms of social organization, caste determination, and sex allocation are more labile and complex than previously thought, although the terminologies for describing them are still inadequate. Furthermore, the unexpected complexity means that many key parameters in kin selection and reproductive skew models remain unquantified, and addressing this lack of information will be formidable. At the same time, phylogenetic questions have become more tractable, and DNA sequence-based studies have resolved questions that earlier studies could not resolve, radically changing our understanding of the number of origins and losses of sociality in these bees.

Recent and simultaneous origins of eusociality in halictid bees

Eusocial organisms are characterized by cooperative brood care, generation overlap and reproductive division of labour. Traits associated with eusociality are most developed in ants, termites, paper wasps and corbiculate bees; the fossil record indicates that each of these advanced eusocial taxa evolved in the Late Cretaceous or earlier (greater than 65 Myr ago). Halictid bees also include a large and diverse number of eusocial members, but, in contrast to advanced eusocial taxa, they are characterized by substantial intra- and inter-specific variation in social behaviour, which may be indicative of more recent eusocial evolution. To test this hypothesis, we used over 2400 bp of DNA sequence data gathered from three protein-coding nuclear genes (opsin, wingless and EF-1a) to infer the phylogeny of eusocial halictid lineages and their relatives. Results from relaxed molecular clock dating techniques that utilize a combination of molecular and fossil data indicate that the three independent origins of eusociality in halictid bees occurred within a narrow time frame between approximately 20 and 22 Myr ago. This relatively recent evolution helps to explain the pronounced levels of social variation observed within these bees. The three origins of eusociality appear to be temporally correlated with a period of global warming, suggesting that climate may have had an important role in the evolution and maintenance of eusociality in these bees.

No sympatric speciation here: multiple data sources show that the ant Myrmica microrubra is not a separate species but an alternate reproductive morph of Myrmica rubra

No aspect of speciation is as controversial as the view that new species can evolve sympatrically, among populations in close physical contact. Social parasitism has been suggested to yield necessary disruptive selection for sympatric speciation. Recently, mitochondrial DNA phylogeography has shown that the ant Myrmica microrubra is closely related to its host, Myrmica rubra, leading to the suggestion that sympatric speciation has occurred. We investigated the relationships between the two ant forms using mitochondrial and nuclear DNA sequences, microsatellite genotyping and morphometrics. Molecular phylogenetic and population structure analyses showed that M. microrubra does not evolve separately to its host but rather shares a gene pool with it. Probability analysis showed that mitochondrial DNA data previously adduced in favour of sympatric speciation do not in fact do so. Morphometrically, M. microrubra is most readily interpreted as a miniature queen form of M. rubra, not a separate species. Myrmica microrubra is not an example of speciation. The large (typical M. rubra) and small (M. microrubra) queen forms are alternative reproductive strategies of the same species. Myrmica microrubraSeifert 1993 is consequently synonymized here with M. rubra Linnaeus, 1758.

It's good to be queen: classically eusocial colony structure and low worker fitness in an obligately social sweat bee

Lasioglossum malachurum, a bee species common across much of Europe, is obligately eusocial across its range but exhibits clear geographic variation in demography and social behaviour. This variation suggests that social interactions between queens and workers, opportunities for worker oviposition, and patterns of relatedness among nest mates may vary considerably, both within and among regions. In this study, we used three microsatellite loci with 12-18 alleles each to examine the sociogenetic structure of colonies from a population at Agios Nikolaos Monemvasias in southern Greece. These analyses reveal that the majority of colonies exhibit classical eusocial colony structure in which a single queen mated to a single male monopolizes oviposition. Nevertheless, we also detect low rates of multiqueen nest founding, occasional caste switching by worker-destined females, and worker oviposition of both gyne and male-producing eggs in the final brood. Previous evidence that the majority of workers show some ovarian development and a minority (17%) have at least one large oocyte contrasts with the observation that only 2-3% of gynes and males (the so-called reproductive brood) are produced by workers. An evaluation of the parameters of Hamilton's Rule suggests that queens benefit greatly from the help provided by workers but that workers achieve greater fitness by provisioning and laying their own eggs rather than by tending to the queen's eggs. This conflict of interest between the queen and her workers suggests that the discrepancy between potential and achieved worker oviposition is due to queen interference. Comparison of relatedness and maternity patterns in the Agios Nikolaos Monemvasias population with those from a northern population near Tübingen, Germany, points to a north-south cline of increasingly effective queen control of worker behaviour.

Analysis of family-level relationships in bees (Hymenoptera: Apiformes) using 28S and two previously unexplored nuclear genes: CAD and RNA polymerase II

We analyzed a combined data set of two protein-coding nuclear genes (CAD and RNA polymerase II) and a nuclear ribosomal gene (28S D2-D4 region) for 68 bee species and 11 wasp outgroups. Our taxon sampling included all seven extant bee families, 17 of 20 subfamilies, and diverse tribes. Wasp outgroups included the two families most closely related to bees: Crabronidae and Sphecidae. We analyzed the combined and single gene data sets using parsimony and Bayesian methods, which yielded largely congruent results. Our results provide reasonably strong support for family and subfamily-level relationships among bees. Our data set strongly supports the sister-group relationship of the Colletidae and Stenotritidae, and places Halictidae as sister to this clade combined. Our analyses place the Melittidae and the long-tongued (LT) bee clade (Apidae+Megachilidae) near the base of the tree with Colletidae (and Stenotritidae) in a fairly highly derived position. This topology ("Melittidae-LT basal") was obtained in previous morphological studies under certain methods of character coding. A more widely accepted tree topology that places Colletidae (and/or Stenotritidae) as sister to all other bees ("Colletidae basal") is not supported by our data. The "Melittidae-LT basal" hypothesis may better explain patterns in the bee fossil record as well as historical biogeography of certain bee groups. Our results provide new insights into higher-level bee phylogeny and indicate that CAD, RNA polymerase II, and 28S are useful data sets for resolving Cretaceous-age divergences in bees and other Hymenoptera.

The evolutionary origin and elaboration of sociality in the aculeate Hymenoptera: maternal effects, sib-social effects, and heterochrony

We discuss the evolutionary origin and elaboration of sociality using an indirect genetic effects perspective. Indirect genetic effects models simultaneously consider zygotic genes, genes expressed in social partners (especially mothers and siblings), and the interactions between them. Incorporation of these diverse genetic effects should lead to more realistic models of social evolution. We first review haplodiploidy as a factor that promotes the evolution of eusociality. Social insect biologists have doubted the importance of relatedness asymmetry caused by haplodiploidy and focused on other predisposing factors such as maternal care. However; indirect effects theory shows that maternal care evolves more readily in haplodiploids, especially with inbreeding and despite multiple mating. Because extended maternal care is believed to be a precondition for the evolution of eusociality, the evolutionary bias towards maternal care in haplodiploids may result in a further bias towards eusociality in these groups. Next, we compare kin selection and parental manipulation and then briefly review additional hypotheses for the evolutionary origin of eusociality. We present a verbal model for the evolutionary origin and elaboration of sib-social care from maternal care based on the modification of the timing of expression of maternal care behaviors. Specifically, heterochrony genes cause maternal care behaviors to be expressed prereproductively towards siblings instead of postreproductively towards offspring. Our review demonstrates that both maternal effect genes (expressed in a parental manipulation manner) and direct effect zygotic genes (expressed in an offspring control manner) are likely involved in the evolution of eusociality. We conclude by describing theoretical and empirical advances with indirect genetic effects and sociogenomics, and we provide specific quantitative genetic and genomic predictions from our heterochrony model for the evolutionary origin and elaboration of eusociality.

Eusociality: origin and consequences

In this new assessment of the empirical evidence, an alternative to the standard model is proposed: group selection is the strong binding force in eusocial evolution; individual selection, the strong dissolutive force; and kin selection (narrowly defined), either a weak binding or weak dissolutive force, according to circumstance. Close kinship may be more a consequence of eusociality than a factor promoting its origin. A point of no return to the solitary state exists, as a rule when workers become anatomically differentiated. Eusociality has been rare in evolution, evidently due to the scarcity of environmental pressures adequate to tip the balance among countervailing forces in favor of group selection. Eusociality in ants and termites in the irreversible stage is the key to their ecological dominance and has (at least in ants) shaped some features of internal phylogeny. Their colonies are consistently superior to solitary and preeusocial competitors, due to the altruistic behavior among nestmates and their ability to organize coordinated action by pheromonal communication.

Sociality and the Rate of Molecular Evolution

The molecular clock does not tick at a uniform rate in all taxa but may be influenced by species characteristics. Eusocial species (those with reproductive division of labor) have been predicted to have faster rates of molecular evolution than their nonsocial relatives because of greatly reduced effective population size; if most individuals in a population are nonreproductive and only one or few queens produce all the offspring, then eusocial animals could have much lower effective population sizes than their solitary relatives, which should increase the rate of substitution of "nearly neutral" mutations. An earlier study reported faster rates in eusocial honeybees and vespid wasps but failed to correct for phylogenetic nonindependence or to distinguish between potential causes of rate variation. Because sociality has evolved independently in many different lineages, it is possible to conduct a more wide-ranging study to test the generality of the relationship. We have conducted a comparative analysis of 25 phylogenetically independent pairs of social lineages and their nonsocial relatives, including bees, wasps, ants, termites, shrimps, and mole rats, using a range of available DNA sequences (mitochondrial and nuclear DNA coding for proteins and RNAs, and nontranslated sequences). By including a wide range of social taxa, we were able to test whether there is a general influence of sociality on rates of molecular evolution and to test specific predictions of the hypothesis: (1) that social species have faster rates because they have reduced effective population sizes; (2) that mitochondrial genes would show a greater effect of sociality than nuclear genes; and (3) that rates of molecular evolution should be correlated with the degree of sociality. We find no consistent pattern in rates of molecular evolution between social and nonsocial lineages and no evidence that mitochondrial genes show faster rates in social taxa. However, we show that the most highly eusocial Hymenoptera do have faster rates than their nonsocial relatives. We also find that social parasites (that utilize the workers from related species to produce their own offspring) have faster rates than their social relatives, which is consistent with an effect of lower effective population size on rate of molecular evolution. Our results illustrate the importance of allowing for phylogenetic nonindependence when conducting investigations of determinants of variation in rate of molecular evolution.

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.

How do insect nuclear and mitochondrial gene substitution patterns differ? Insights from Bayesian analyses of combined datasets

We analyzed 12 combined mitochondrial and nuclear gene datasets in seven orders of insects using both equal weights parsimony (to evaluate phylogenetic utility) and Bayesian methods (to investigate substitution patterns). For the Bayesian analyses we used relatively complex models (e.g., general time reversible models with rate variation) that allowed us to quantitatively compare relative rates among genes and codon positions, patterns of rate variation among genes, and substitution patterns within genes. Our analyses indicate that nuclear and mitochondrial genes differ in a number of important ways, some of which are correlated with phylogenetic utility. First and most obviously, nuclear genes generally evolve more slowly than mitochondrial genes (except in one case), making them better markers for deep divergences. Second, nuclear genes showed universally high values of CI and (generally) contribute more to overall tree resolution than mitochondrial genes (as measured by partitioned Bremer support). Third, nuclear genes show more homogeneous patterns of among-site rate variation (higher values of alpha than mitochondrial genes). Finally, nuclear genes show more symmetrical transformation rate matrices than mitochondrial genes. The combination of low values of alpha and highly asymmetrical transformation rate matrices may explain the overall poor performance of mitochondrial genes when compared to nuclear genes in the same analysis. Our analyses indicate that some parameters are highly correlated. For example, A/T bias was positively and significantly associated with relative rate and CI was positively and significantly associated with alpha (the shape of the gamma distribution). These results provide important insights into the substitution patterns that might characterized high quality genes for phylogenetic analysis: high values of alpha, unbiased base composition, and symmetrical transformation rate matrices. We argue that insect molecular systematists should increasingly focus on nuclear rather than mitochondrial gene datasets because nuclear genes do not suffer from the same substitutional biases that characterize mitochondrial genes.

A novel social polymorphism in a primitively eusocial bee

Halictine sweat bees (Hymenoptera, Halictidae) are model organisms for the evolution of altruism, reproductive castes, and eusocial colony organization. Halictine social behavior is not only extremely variable, but also ecologically and evolutionarily labile. Among social species, colony social organization ranges from communal societies of egalitarian females to eusocial and semisocial ones with reproductive queens and more or less sterile workers. A striking aspect of halictine social variation is the mutual exclusivity of communal and eusocial types of colony social organization within the same species, these two types of social behavior being characteristic of different genera and subgenera. We report a recently discovered exception to this rule in a population of Halictus sexcinctus (Fabricius) at Daimonia-Pyla in southern Greece, that contained both communal and eusocial colonies. Moreover, communal and eusocial females exhibit morphological differences that imply a preimaginal developmental switch, which could also underlie the two types of social behavior. That the communal and eusocial forms are not merely cryptic sister species with different social behavior is indicated by the comparison of mitochondrial DNA sequences of two sections of cytochrome oxidase I, which indicate that Greek specimens of both social types are more similar than they are to conspecifics from elsewhere in Europe. The phylogenetic position of Halictus sexcinctus suggests that this unusual communal/eusocial polymorphism may represent an unstable intermediate step in an evolutionary reversal from eusocial to solitary behavior.

Evolution and phylogenetic utility of alignment gaps within intron sequences of three nuclear genes in bumble bees (Bombus)

To test whether gaps resulting from sequence alignment contain phylogenetic signal concordant with those of base substitutions, we analyzed the occurrence of indel mutations upon a well-resolved, substitution-based tree for three nuclear genes in bumble bees (Bombus, Apidae: Bombini). The regions analyzed were exon and intron sequences of long-wavelength rhodopsin (LW Rh), arginine kinase (ArgK), and elongation factor-1alpha (EF-1alpha) F2 copy genes. LW Rh intron had only a few uninformative gaps, ArgK intron had relatively long gaps that were easily aligned, and EF-1alpha intron had many short gaps, resulting in multiple optimal alignments. The unambiguously aligned gaps within ArgK intron sequences showed no homoplasy upon the substitution-based tree, and phylogenetic signals within ambiguously aligned regions of EF-1alpha intron were highly congruent with those of base substitutions. We further analyzed the contribution of gap characters to phylogenetic reconstruction by incorporating them in parsimony analysis. Inclusion of gap characters consistently improved support for nodes recovered by substitutions, and inclusion of ambiguously aligned regions of EF-1alpha intron resolved several additional nodes, most of which were apical on the phylogeny. We conclude that gaps are an exceptionally reliable source of phylogenetic information that can be used to corroborate and refine phylogenies hypothesized by base substitutions, at least at lower taxonomic levels. At present, full use of gaps in phylogenetic reconstruction is best achieved in parsimony analysis, pending development of well-justified and generally applicable methods for incorporating indels in explicitly model-based methods.

Complex sociogenetic organization and reproductive skew in a primitively eusocial sweat bee, Lasioglossum malachurum, as revealed by microsatellites

The sweat bees (Family Halictidae) are a socially diverse taxon in which eusociality has arisen independently numerous times. The obligate, primitively eusocial Lasioglossum malachurum, distributed widely throughout Europe, has been considered the zenith of sociality within halictids. A single queen heads a colony of smaller daughter workers which, by mid-summer, produce new sexuals (males and gynes), of which only the mated gynes overwinter to found new colonies the following spring. We excavated successfully 18 nests during the worker- and gyne-producing phases of the colony cycle and analysed each nest's queen and either all workers or all gynes using highly variable microsatellite loci developed specifically for this species. Three important points arise from our analyses. First, queens are facultatively polyandrous (queen effective mating frequency: range 1-3, harmonic mean 1.13). Second, queens may head colonies containing unrelated individuals (n = 6 of 18 nests), most probably a consequence of colony usurpation during the early phase of the colony cycle before worker emergence. Third, nonqueen's workers may, but the queen's own workers do not, lay fertilized eggs in the presence of the queen that successfully develop into gynes, in agreement with so-called 'concession' models of reproductive skew.

Elongation Factor 1 alpha resolves the monophyly of the haplodiploid ambrosia beetles Xyleborini (Coleoptera: Curculionidae)

Elongation Factor 1-alpha was used to test the monophyly of the wood boring beetle tribe Xyleborini, where all species are haplodiploid and perform regular inbreeding by brother-sister mating. Due to their feeding requirements, being highly dependent on ophiostomatoid fungi which they cultivate in wood tunnels, monophyly may be expected due to nutritional constraints. During the course of analyses, two copies of EF-1alpha were amplified in these beetles, differing in intron structure. The high similarity between paralogous amino acid sequences (93-94%) indicates a rather recent duplication in beetles, but phylogenetic analyses of different copies in insects rejected this hypothesis. Subsequent phylogenetic analyses of eighty orthologous sequences from Xyleborini and allied taxa, using the single-intron bearing copy, were greatly improved in resolution and node support by including the intron sequences (c. 60 bp). Most analyses resulted in a monophyletic Xyleborini, implying one origin of fungus feeding in this tribe. However, clear evidence for a polyphyletic Xyleborus and three more xyleborine genera calls for further revision of xyleborine classification.

Comparative social biology of basal taxa of ants and termites

Lacking a comprehensive fossil record, solitary representatives of the taxa, and/or a definitive phylogeny of closely related insects, comparison of the life history and social biology of basal, living groups is one of the few available options for developing inferences regarding the early eusocial evolution of ants and termites. Comparisons of a select group of basal formicid and isopteran taxa suggest that the reproductive organization of colonies and their patterns of division of labor were particularly influenced, in both groups, by nesting and feeding ecology. Opportunities for serial inheritance of the nest structure and colony population by kin may have been significant in the evolution of multiple reproductive forms and options. Disease has been a significant factor in the evolution of social organization in ants and termites, but the adaptive mechanisms of infection control differ. Evaluations of the convergent and divergent social biology of the two taxa can generate novel domains of research and testable hypotheses.

Phylogeography of the socially polymorphic sweat bee Halictus rubicundus (Hymenoptera: Halictidae)

The evolution of sociality in insects holds a central place in evolutionary theory. By examining the phylogenetic patterns of solitary and social behavior and how they correlate with ecological variables, we may identify factors important in the evolution of sociality. In this study, we investigated historical and biogeographical patterns of sociality in a socially polymorphic bee species (one that demonstrates both social and solitary nesting behavior). This unique system allows for a more powerful examination of evolutionary transitions in sociality than interspecific studies of obligately social and solitary species. We conducted a phylogenetic analysis among populations of the halictine bee Halictus rubicundus and then identified relationships among mitochondrial DNA sequence data, sociality, environmental conditions at the nesting site, and geographic location of populations of this species. Within North America, populations of H. rubicundus expressing social and solitary behavior belong to different genetic lineages. Sociality is also correlated with at least one environmental variable used in this study. Taken together, the results support the predictions for genetic control of sociality, but they are still consistent with social behavior at some level being determined by the environmental conditions at the nesting site.