"TOTAL EVIDENCE" AND THE EVOLUTION OF HIGHLY SOCIAL BEES

Abstract— Recent cladistic analyses of the relationships of the tribes of apine bees have produced conflicting results. The question of single or multiple origins of advanced eusociality in the group is thus unresolved. However, the previous studies have each treated only a limited part of the character data available. A "total evidence" analysis is essayed here, combining the published morphological characters with sequence data from rRNA and mtDNA. The resulting cladogram is: Euglossini + (Bombini + (Meliponini + Apini). This supports a single origin of advanced eusociality, from a stage of primitive eusociality.     

Behavioral Phylogeny of Corbiculate Apidae (Hymenoptera; Apinae), with Special Reference to Social Behavior

The phylogenetic relationships among the four tribes of corbiculate bees (Euglossini, Bombini, Meliponini, and Apini) are controversial. There is substantial incongruence between morphological and molecular data, and the single origin of eusociality is questionable. The use of behavioral characters by previous workers has been restricted to some typological definitions, such as solitary and eusocial. Here, I expand the term "social" to 42 characters and present a tree based only on behavioral characters. The reconstructed relationships were similar to those observed in morphological and "total evidence" analyses, i.e., Euglossini + (Bombini + (Meliponini + Apini)), all of which support a single origin of eusociality.     

Comparative morphology of the postmentum of bees (Hymenoptera: Apoidea) with special remarks on the evolution of the lorum

A comparative morphological study of the basal sclerites of the bee labium was undertaken. The term postmentum was applied to the basal sclerite of the bee labium. In contrast to recent interpretations, the undivided postmentum was found to be ancestral for bees and homologous with the single postmental sclerite of other Hymenoptera. This sclerite has previously been incorrectly indentified as two separate sclerites, usually termed mentum and lorum (= submentum), for many short-tongued bees (Colletidae, Halictidae, Andrenidae, Melittidae) and for the long-tongued families of bees (Anthophoridae, Fideliidae Megachilidae) excepting most members of the Apidae. The postmentum, divided into a true mentum and lorum, was found only in certain members of the Apidae. A phylogenetic implication resulting from this study shows that the Andrenidae may be the sister group to the MCL-T group (Melittidae, Ctenoplectridae and long-tongued families of bees). In addition, it is proposed that the Euglossinae should be the sister group to the Apinae (Meliponini, Apini and Bombini). This means that eusociality may be considered a synapomorphy for the Apinae.     

A re-evaluation of the phylogenetic relationships in the Apidae (Hymenoptera)

ABSTRACT .
The relationships between the four tribes in the bee family Apidae are re-examined. Characteristics of the postgena, presternum, antenna cleaner, arolium, female hind tibia and male genitalia, among others, support the placement of these tribes in three subfamilies: Meliponinae (Meliponini), Apinae (Apini) and Bombinae (Euglossini + Bombini). The Apinae is the sister group of the Bombinae. This tribal arrangement was originally proposed, using different characteristics, by Winston & Michener (1977).     

Task-partitioned nectar transfer in stingless bees: work organisation in a phylogenetic context

Abstract 1. The eusocial corbiculate bee tribes comprise the Apini (honey bees), Bombini (bumble bees), and Meliponini (stingless bees). Honey bee foragers ( Apis ) transfer nectar to receiver bees within the nest. This is an example of task partitioning, in which a task is split into sub-tasks connected by material transfer. Nectar transfer does not occur in Bombini. Although it is reported in some species of Meliponini, it has not been subject to detailed study.
2. Nectar transfer was investigated in five genera of Meliponini from Yucatan, Mexico ( Melipona , Trigona , Scaptotrigona , Nannotrigona , and Plebeia ). Nectar transfer occurred in all species and for > 99% of foragers. Multiple transfer, in which a forager unloads nectar to more than one receiver, occurred but at a lower level than in Apis . In M. beecheii , multiple transfer was associated strongly with putative recruitment dances.
3. The data provide some support for the hypothesis that task partitioning is favoured by large colony size, in that the Meliponini never have small colonies because colonies are swarm founded. This ensures that colonies are always large enough to prevent delays in finding a transfer partner imposing high costs. Further tests of this hypothesis are suggested.
4. Viewed in a phylogenetic context, the most parsimonious interpretation is that nectar transfer evolved once in the clade (Apini + Meliponini).     

Phylogenetic analysis of the corbiculate Apinae based on morphology of the sting apparatus (Hymenoptera: Apidae)

This study aimed to test the various competing hypotheses regarding the relationships among the four tribes of corbiculate apine bees (Euglossini “orchid bees”, Bombini “bumble bees”, Meliponini “stingless bees”, and Apini “honey bees”) with a completely new set of previously unstudied morphological characters derived from the sting apparatus. The result was one most parsimonious tree of 49 steps, CI = 89, RI = 93 that is perfectly congruent with most studies based on morphological and combined morphological/molecular data, i.e., Euglossini + (Bombini + (Meliponini + Apini)), supporting a well accepted scenario of social evolution for these bees. This data matrix was then combined with other published matrices for this group in order to perform simultaneous analyses. The problem of how to best combine the multiple matrices that did not use the same exemplars was investigated. © The Willi Hennig Society 2007.     

Non-linear benefits and the evolution of eusociality in the hymenoptera

A general model for examining the evolution of social behavior is developed which does not require that benefits received be linear functions of the number of social donors encountered. The subsocial route for the evolution of eusociality in haplodiploid organisms is then examined within the context of this model Non-linearities render conditions for frequency independent fixation or loss of sister helping alleles more stringent than expected from models based on the assumption of linear benefits. In particular, both stable polymorphisms and frequency dependent selective thresholds for sister helping behaviour may commonly obtain.     

Phylogenetic utility of the major opsin in bees (Hymenoptera: Apoidea): a reassessment

Major opsin (LW Rh) DNA sequence has been reported to provide useful data for resolving phylogenetic relationships among tribes of corbiculate bees based on analyses of 502 bp of coding sequence. However, the corbiculate tribes are believed to be of Cretaceous age, and strong support for insect clades of this age from small data sets of nucleotide sequence data has rarely been demonstrated. To more critically assess opsin's phylogenetic utility we generated an expanded LW Rh data set by sequencing the same gene fragment from 52 additional bee species from 24 tribes and all six extant bee families. Analyses of this data set failed to provide substantial support for monophyly of corbiculate bees, for relationships among corbiculate tribes, or for most other well-established higher-level relationships among long-tongued bees. However, monophyly of nearly all genera and tribes is strongly supported, indicating that LW Rh provides useful phylogenetic signal at lower taxonomic levels. When our expanded LW Rh data set is combined with a morphological and behavioral data set for corbiculate bees, the results unambiguously support the traditional phylogeny of the corbiculate bee tribes: (Euglossini + (Bombini + (Meliponini + Apini))). This implies a single origin of advanced eusocial behavior among bees rather than dual origins, as proposed by several recent studies.     

A conceptual model for the origin of worker behaviour and adaptation of eusociality

In a model based on the wasp family Vespidae, the origin of worker behaviour, which constitutes the eusociality threshold, is not based on relatedness, therefore the origin of eusociality does not depend on inclusive fitness, and workers at the eusociality threshold are not altruistic. Instead, incipient workers and queens behave selfishly and are subject to direct natural selection. Beyond the eusociality threshold, relatedness enables 'soft inheritance' as the framework for initial adaptations of eusociality. At the threshold of irreversibility, queen and worker castes become fixed in advanced eusociality. Transitions from solitary to facultative, facultative to primitive, and primitive to advanced eusociality occur via exaptation, phenotypic accommodation and genetic assimilation. Multilevel selection characterizes the solitary to highly eusocial transition, but components of multilevel selection vary across levels of eusociality. Roles of behavioural flexibility and developmental plasticity in the evolutionary process equal or exceed those of genotype.     

Advanced eusociality, kin selection and male haploidy

Abstract  The generation-long primacy of kin selection in explaining the evolution of advanced eusociality in social insects has been challenged in recent papers. Does this challenge succeed? I consider three questions: is kin selection still the unchallengeable explanation for the evolution of eusociality; is the male haploidy of Hymenoptera important in this explanation; and, a subsidiary question of why are there no male workers in Hymenoptera? I briefly trace the origins of kin selection back to Darwin and then consider the explanations of mutualism, group selection, parental manipulation, and kin selection and its variant 'green beard' alleles. I stress that in the kin selection equation, however written, relatedness is deeply intertwined with ecology so that both are essential. Kin selection does remain unchallengeable but, for some, the role of male haploidy has lost favour recently despite several modelling efforts all finding that it favours the evolution of eusociality. Sex allocation is deep at the heart of the evolution of hymenopteran advanced eusociality, indicating the interacting roles of population genetics and general biology. Modellers have also found no reason for a lack of male workers, so that a biological superiority of females for this role is indicated for social Hymenoptera.     

The antiquity and evolutionary history of social behavior in bees

A long-standing controversy in bee social evolution concerns whether highly eusocial behavior has evolved once or twice within the corbiculate Apidae. Corbiculate bees include the highly eusocial honey bees and stingless bees, the primitively eusocial bumble bees, and the predominantly solitary or communal orchid bees. Here we use a model-based approach to reconstruct the evolutionary history of eusociality and date the antiquity of eusocial behavior in apid bees, using a recent molecular phylogeny of the Apidae. We conclude that eusociality evolved once in the common ancestor of the corbiculate Apidae, advanced eusociality evolved independently in the honey and stingless bees, and that eusociality was lost in the orchid bees. Fossil-calibrated divergence time estimates reveal that eusociality first evolved at least 87 Mya (78 to 95 Mya) in the corbiculates, much earlier than in other groups of bees with less complex social behavior. These results provide a robust new evolutionary framework for studies of the organization and genetic basis of social behavior in honey bees and their relatives.     

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.     

A molecular phylogeny of the Old World stingless bees (Hymenoptera: Apidae: Meliponini) and the non-monophyly of the large genus Trigona

Abstract.  We examined the inter- and infrageneric relationships of Old World Meliponini with a near-complete sampling of supra-specific taxa. DNA sequences for the taxa were collected from four genes (mitochondrial 16S rRNA, nuclear long-wavelength rhodopsin copy 1 (opsin), elongation factor-1α copy F2 and arginine kinase). Additional sampling of New World taxa indicated that Trigona sensu lato is not monophyletic: Trigona from the Indo-Malayan/Australasian Regions forms a large clade distantly related to the Neotropical Trigona . A separate clade comprises the Afrotropical meliponines, and includes the 'minute' species found in the Afrotropical, Indo-Malayan and Australasian Regions. The Neotropical genus Melipona , by contrast with previous investigations, is not the sister lineage to the remaining stingless bees, but falls within the strongly supported Neotropical clade. These results constitute the framework for a revised classification and ongoing biological investigations of Meliponini. A single taxonomic change, Heterotrigona bakeri stat.n. , is proposed on the basis of sequence divergence.     

Multiple origins of eusociality among sponge-dwelling shrimps (Synalpheus)

Abstract.— As the most extreme expression of apparent altruism in nature, eusociality has long posed a central paradox for behavioral and evolutionary ecology. Because eusociality has arisen rarely among animals, understanding the selective pressures important in early stages of its evolution remains elusive. Employing a historical approach to this problem, we used morphology and DNA sequences to reconstruct the phylogeny of 13 species of sponge-dwelling shrimps ( Synalpheus ) with colony organization ranging from asocial pair-bonding through eusociality. We then used phylogenetically independent contrasts to test whether sociality was associated with evidence of enhanced competitive ability, as suggested by hypotheses invoking an advantage of cooperation in crowded habitats. The molecular, morphological, and combined data each strongly supported three independent origins of monogynous, multigenerational (eusocial) colony organization within this genus. Phylogenetically independent contrasts confirmed that highly social taxa, with strong reproductive skew, have significantly higher relative abundance within the host sponge than do less social taxa, a result that was robust to uncertainty in tree topology and varying models of character change. A similar tendency for highly social species to share their sponge with fewer congener species was suggestive, but not significant. Because unoccupied habitat appears to be limiting for many sponge-dwelling shrimp species, these data are consistent with hypotheses that cooperative social groups enjoy a competitive advantage over less organized groups or individuals, where independent establishment is difficult, and that enemy pressure is of central importance in the evolution of animal sociality.     

Global stingless bee phylogeny supports ancient divergence,vicariance, and long distance dispersal

Stingless bees (Meliponini) are one of only two highly eusocial bees, the other being the well studied honey bee (Apini). Unlike Apini, with only 11 species in the single genus Apis, stingless bees are a large and diverse taxon comprising some 60 genera, many of which are poorly known. This is the first attempt to infer a phylogeny of the group that includes the world fauna and extensive molecular data. Understanding the evolutionary relationships of these bees would provide a basis for behavioural studies within an evolutionary framework, illuminating the origins of complex social behaviour, such as the employment of dance and sound to communicate the location of food or shelter. In addition to a global phylogeny, we also provide estimates of divergence times and ancestral biogeograhic distributions of the major groups. Bayesian and maximum likelihood analyses strongly support a principal division of Meliponini into Old and New World groups, with the Afrotropical+Indo‐Malay/Australian clades comprising the sister group to the large Neotropical clade. The meliponine crown clade is inferred to be of late Gondwanan origin (approximately 80 Mya), undergoing radiations in the Afrotropical and Indo‐Malayan/Australasian regions, approximately 50–60 Mya. In the New World, major diversifications occurred approximately 30–40 Mya. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 206–232.     

Phylogeny of the bees of the family Apidae based on larval characters with focus on the origin of cleptoparasitism (Hymenoptera: Apiformes)

Abstract.  Fifty-four genera of the bee family Apidae comprising almost all tribes were analysed based on 77 traditional and one new character of the mature larvae. Nine, especially cleptoparasitic species, were newly added. Analyses were performed by maximum parsimony and Bayesian inference. Trees inferred from the analysis of the complete dataset were rooted by taxa from the families Melittidae and Megachilidae. Unrooted trees inferred from the analysis of the partial dataset (excluding outgroup taxa) are also presented to preclude possible negative effects of the outgroup on the topology of the ingroup. Only the subfamily Nomadinae was statistically well supported. The monophyly of the subfamilies Xylocopinae and Apinae was not topologically recovered. The monophyly of the tribe Tetrapediini was supported, and this tribe was found to be related to xylocopine taxa. At the very least, larval morphology suggests that Tetrapedia is not a member of the subfamily Apinae. Our analyses support the monophyly of the Eucerine line (Emphorini, Eucerini, Exomalopsini, Tapinotaspidini) and of the Apine line (Anthophorini, Apini, Bombini, Centridini, Euglossini, Meliponini). All analyses support the monophyly of totally cleptoparasitic tribes of the subfamily Apinae. We named this group the Melectine line (Ericrocidini, Isepeolini, Melectini, Osirini, Protepeolini, Rhathymini). In previous studies all these cleptoparasitic tribes were considered independent evolutionary lineages. Our results suggest that their similarities with hosts in morphology and pattern are probably the result of convergence and host–parasite co-evolution than phylogenetic affinity. According to the present analysis, the cleptoparasitism has evolved independently only six times within the family Apidae.     

An overview of cytogenetics of the tribe Meliponini (Hymenoptera: Apidae)

The present study provides a comprehensive review of cytogenetic data on Meliponini and their chromosomal evolution. The compiled data show that only 104 species of stingless bees, representing 32 of the 54 living genera have been studied cytogenetically and that among these species, it is possible to recognize three main groups with n?=?9, 15 and 17, respectively. The first group comprises the species of the genus Melipona, whereas karyotypes with n?=?15 and n?=?17 have been detected in species from different genera. Karyotypes with n?=?17 are the most common among the Meliponini studied to date. Cytogenetic information on Meliponini also shows that although chromosome number, in general, is conserved among species of a certain genus, other aspects, such as chromosome morphology, quantity, distribution and composition of heterochromatin, may vary between them. This reinforces the fact that the variations observed in the karyotypes of different Meliponini groups cannot be explained by a single theory or a single type of structural change. In addition, we present a discussion about how these karyotype variations are related to the phylogenetic relationships among the different genera of this tribe.     

Outbreeding and lack of temporal genetic structure in a drone congregation of the neotropical stingless bee Scaptotrigona mexicana

Drone aggregations are a widespread phenomenon in many stingless bee species (Meliponini), but the ultimate and proximate causes for their formation are still not well understood. One adaptive explanation for this phenomenon is the avoidance of inbreeding, which is especially detrimental for stingless bees due to the combined effects of the complementary sex-determining system and the small effective population size caused by eusociality and monandry. We analyzed the temporal genetic dynamics of a drone aggregation of the stingless bee Scaptotrigona mexicana with microsatellite markers over a time window of four weeks. We estimated the drones of the aggregation to originate from a total of 55 colonies using sibship re-construction. There was no detectable temporal genetic differentiation or sub-structuring in the aggregation. Most important, we could exclude all colonies in close proximity of the aggregation as origin of the drones in the aggregation, implicating that they originate from more distant colonies. We conclude that the diverse genetic composition and the distant origin of the drones of the S. mexicana drone congregation provides an effective mechanism to avoid mating among close relatives.     

Phylogeny of eusocial Lasioglossum reveals multiple losses of eusociality within a primitively eusocial clade of bees (Hymenoptera: Halictidae)

We performed a phylogenetic analysis of the species, species groups, and subgenera within the predominantly eusocial lineage of Lasioglossum (the Hemihalictus series) based on three protein coding genes: mitochondrial cytochrome oxidase I, nuclear elongation factor 1alpha and long-wavelength rhodopsin. The entire data set consisted of 3421 aligned nucleotide sites, 854 of which were parsimony informative. Analyses by equal weights parsimony, maximum likelihood, and Bayesian methods yielded good resolution among the 53 taxa/populations, with strong bootstrap support and high posterior probabilities for most nodes. There was no significant incongruence among genes, and parsimony, maximum likelihood, and Bayesian methods yielded congruent results. We mapped social behavior onto the resulting tree for 42 of the taxa/populations to infer the likely history of social evolution within Lasioglossum. Our results indicate that eusociality had a single origin within Lasioglossum. Within the predominantly eusocial clade, however, there have been multiple (six) reversals from eusociality to solitary nesting, social polymorphism, or social parasitism, suggesting that these reversals may be more common in primitively eusocial Hymenoptera than previously anticipated. Our results support the view that eusociality is hard to evolve but easily lost. This conclusion is potentially important for understanding the early evolution of the advanced eusocial insects, such as ants, termites, and corbiculate bees.     

The major opsin in bees (Insecta: Hymenoptera): A promising nuclear gene for higher level phylogenetics.

We report the phylogenetic utility of the nuclear gene encoding the long-wavelength opsin (LW Rh) for tribes of bees. Aligned nucleotide sequences were examined in multiple taxa from the four tribes comprising the corbiculate bees within the subfamily Apinae. Phylogenetic analyses of sequence variation in a 502-bp fragment (approx 40% of the coding region) strongly supported the monophyly of each of the four tribes, which are well established from previous studies of morphology and DNA. Trees estimated from parsimony and maximum likelihood analyses of LW Rh sequences show a strongly supported relationship between the tribes Meliponini and Bombini, a relationship that has been found uniformly in studies of other genes (28S, 16S, and cytochrome b). All of the tribal clades as well as relationships among the tribes are supported by high bootstrap values, suggesting the utility of LW Rh in estimating tribal and subfamily rank for these bees. The sequences exhibit minimal base composition bias. Both 1st + 2nd and 3rd position sites provide information for estimating a reliable tree topology. These results suggest that LW Rh, which has not been reported previously in studies of organismal phylogenetics, could provide important new data from the nuclear genome for phylogeny reconstruction.