Bee Lineages Research Articles

Not all male bees posses thirteen antennal segments: New megachilid species from the Afro-Arabian and Afrotropical regions (Apoidea: Anthidiini: Pseudoanthidium) with deviant numbers of segments

Male bees (Apoidea) typically possess antennae with 13 articles, with only a few exceptions reported, none of which are from the Megachilidae family. In this study, we describe two new species of the megachilid tribe Anthidiini that display an unusual characteristic – their males have only 12 antennal segments. We attributed these species, Pseudoanthidium omanicum sp. nov. from the Arabian Peninsula, and P. ethiopicum sp. nov. from Ethiopia, to the subgenus Pseudoanthidium (Mesanthidiellum), previously known only from Sub-Saharan Africa. Notably, the male of a third species in this subgenus, P. (Mesanthidiellum) sakaniense (Cockerell, 1936) was also found to have only 12 antennal segments. Further investigation revealed that males with antennae with 12 articles are also present in the closely related subgenus Pseudoanthidium (Branthidium), suggesting that this phenomenon may be more widespread yet often overlooked. A broader review indicates that deviations from the typical 13 antennal articles are known in 10 genera of bees and account for less than 0.5% of all bee species. We conclude that this trait has evolved independently across different bee lineages. However, the specific function of a reduced number of antennal articles remains elusive. http://www.zoobank.org/urn:lsid:zoobank.org:pub:56B808FB-E4F2-46A9-9B54-850AF83263D0

Further revisions to the Palaearctic Andrena fauna (Hymenoptera: Andrenidae).

The genus Andrena is the second largest genus of bees, and is undergoing a period of concentrated study that has resulted in the description or recognition of almost 200 additional species during the last decade. This process is far from complete, and substantial revisions are required even in well-studied regions; this present work contributes to this ongoing process. The following new synonymies are reported (senior name first): Andrena (Chrysandrena) fulvago (Christ, 1791) = A. (Chrysandrena) colonialis Morawitz, 1886 syn. nov., Andrena (Cnemidandrena) jagnobensis Morawitz, 1893 = A. (Cnemidandrena) nigriceps ssp. pamirensis Alfken, 1931 syn. nov., Andrena (Hoplandrena) romankovae Osytshnjuk, 1995 = A. (Hoplandrena) fagopyri Xu & Tadauchi, 2005 syn. nov., Andrena (Melanapis) fuscosa Erichson, 1835 = A. cussariensis kohatensis Cockerell, 1917 syn. nov., Andrena (Melandrena) flavipes Panzer, 1799 = A. bentoni Cockerell, 1917 syn. nov. and A. incanescens Cockerell, 1923 syn. nov., Andrena (Melandrena) marmora Nurse, 1904 = A. chionospila Cockerell, 1917 syn. nov. and A. pullipennis Alfken, 1931 syn. nov., Andrena (Melandrena) sibirica Morawitz, 1888 = A. phaneroleuca Cockerell, 1929 syn. nov., Andrena (Micrandrena) alfkenella Perkins, 1914 = A. (Micrandrena) caneibia Strand, 1915 syn. nov., Andrena (Micrandrena) minutuloides Perkins, 1914 = A. (Micrandrena) corssubalpina Theunert, 2007 syn. nov., Andrena (Micrandrena) saxonica Stöckhert, 1935 = A. (Micrandrena) warnckei Gusenleitner & Schwarz, 2000 syn. nov., Andrena (Notandrena) trimarginata (Radoszkowski, 1886) = A. (Notandrena) zostera Warncke, 1975 syn. nov., Andrena (Taeniandrena) afzeliella (Kirby, 1802) = A. heteropoda Cockerell, 1922 syn. nov., and Andrena (Ulandrena) crecca Warncke, 1965 = A. (Ulandrena) resoluta Warncke, 1973 syn. nov. A lectotype is designated for A. (incertae sedis) meripes Friese, 1922 which is recognised as the senior synonym of A. (Tarsandrena) palliata Wood, 2023 syn. nov. A neotype is created for A. (Ulandrena) abbreviata Dours, 1873 and A. abbreviata ssp. osychniukae Osytshnjuk, 1977 syn. nov. is synonymised with it. Andrena carinata Morawitz, 1877 is considered a nomen dubium. Andrena (incertae sedis) splendula Osytshnjuk, 1984 spec. resurr. is returned to species status as distinct from A. kurdistanica Engel, 2005 (=A. minor Warncke nec. Radoszkowski). Lectotypes are designated for A. (Andrena) rogenhoferi Morawitz, 1872, A. (Avandrena) melaleuca Friese, 1922, A. (Chlorandrena) orienticola Strand, 1915 stat. nov., A. (Euandrena) rufula Schmiedeknecht, 1884, A. (Leucandrena) favosa Morawitz, 1872, A. (Melandrena) ovinella Friese, 1914, and A. (Taeniandrena) callopyrrha Cockerell, 1929. Andrena (Avandrena) caligata Warncke, 1974 stat. nov., A. (Avandrena) eureka Warncke, 1974 stat. nov., A. (Avandrena) liturata Warncke, 1974 stat. nov., A. (Avandrena) gavia Warncke, 1974 stat. nov., A. (Micrandrena) pelagica Warncke, 1975 stat. nov., A. (Micrandrena) pillichi Noskiewicz, 1939 stat. rev., and A. (Truncandrena) donata Warncke, 1967 stat. nov. are elevated or returned to species status. The unknown female of A. (Euandrena) hermonella Scheuchl & Pisanty, 2016 is described. Andrena (Euandrena) allosa ssp. canigica Warncke, 1975 is placed in combination with Andrena (Euandrena) pileata ssp. canigica comb. nov. The following twenty-six new species are described: A. (incertae sedis) risha spec. nov. from Algeria, A. (Avandrena) collisa spec. nov. from Cyprus, A. (Aciandrena) elbensis spec. nov. from Egypt, A. (Graecandrena) balticola spec. nov. from Estonia, A. (Micrandrena) lediveleci spec. nov. and A. (Ulandrena) incustodita spec. nov. from Greece (Crete), A. (Euandrena) coronula spec. nov., A. (Euandrena) lustrum spec. nov., A. (Taeniandrena) perpetua spec. nov., A. (incertae sedis) tehranica spec. nov. from Iran, A. (incertae sedis) contraria spec. nov. from Mongolia, A. (incertae sedis) tenasserima spec. nov. from Myanmar and Thailand, A. (incertae sedis) dacia spec. nov. from Romania, A. (Avandrena) melacanoides spec. nov. from Spain, A. (Avandrena) baldocki spec. nov. from Spain and Portugal, A. (incertae sedis) concisura spec. nov. from Tajikistan, A. (Aciandrena) equus spec. nov., A. (Aciandrena) karahisara spec. nov., A. (Euandrena) eosphora spec. nov., A. (Euandrena) ridicula spec. nov., A. (Simandrena) michezi spec. nov., A. (incertae sedis) hakkariensis spec. nov., A. (incertae sedis) perforata spec. nov. from Turkey, A. (Euandrena) semota spec. nov., from Turkey and Iraq, A. (Graecandrena) volkoides spec. nov. from Turkey, Syria, Israel and the West Bank, and Jordan, and A. (Troandrena) namaka spec. nov. from Pakistan. Though the focus of much recent taxonomic attention, the Middle East continues to produce many undescribed Andrena species, in line with its suspected point of origin and centre of diversity for this massive bee genus.

Allele Frequencies of Genetic Variants Associated with Varroa Drone Brood Resistance (DBR) in Apis mellifera Subspecies across the European Continent.

Implementation of marker-assisted selection (MAS) in modern beekeeping would improve sustainability, especially in breeding programs aiming for resilience against the parasitic mite Varroa destructor. Selecting honey bee colonies for natural resistance traits, such as brood-intrinsic suppression of varroa mite reproduction, reduces the use of chemical acaricides while respecting local adaptation. In 2019, eight genomic variants associated with varroa non-reproduction in drone brood were discovered in a single colony from the Amsterdam Water Dune population in the Netherlands. Recently, a new study tested the applicability of these eight genetic variants for the same phenotype on a population-wide scale in Flanders, Belgium. As the properties of some variants varied between the two studies, one hypothesized that the difference in genetic ancestry of the sampled colonies may underly these contribution shifts. In order to frame this, we determined the allele frequencies of the eight genetic variants in more than 360 Apis mellifera colonies across the European continent and found that variant type allele frequencies of these variants are primarily related to the A. mellifera subspecies or phylogenetic honey bee lineage. Our results confirm that population-specific genetic markers should always be evaluated in a new population prior to using them in MAS programs.

Reproductive inefficiency and increased behavioral variation are associated with large group size in the orchid bee, Euglossa dilemma

Orchid bees are the only corbiculate bee lineage that is not obligately eusocial. However, multiple species of orchid bee show facultative sociality, with reproductive division of labor and a social hierarchy effectively enforced by oophagy. Orchid bee species differ in the degree of reproductive skew in social groups, as well as the rigidity of social roles. In the orchid bee Euglossa dilemma, previous observation of social groups of two or three individuals found that reproductive skew was complete, with one clear dominant individual that ate and replaced each subordinate laid egg. Here, we compare patterns of egg laying and egg-replacement between typical social nests of 2–3 individuals and larger social nests of 4–5 individuals. We find a striking difference in the reproductive behavior of colonies of varying group size; larger nests exhibit more reproductive inefficiency and conflict over the dominant social position, characterized by repeated oophagy and slower egg replacement. Our findings are consistent with the hypothesis that group size in E. dilemma may be limited by the ability of dominant bees to keep up with egg replacement. We discuss the possible causes and consequences of observed behavioral variation and its implications for understanding social behavior in orchid bees.

Pollen diet diversity across bee lineages varies with lifestyle rather than colony size.

The shift to a pollen diet and the evolution of more highly organized societies, i.e., eusocial, were key milestones in bee diversification over their evolutionary history, culminating in a high dependence on feeding broods with a large variety of floral resources. Here, we hypothesized that obligatory eusocial bees have a wider diet diversity than their relatives with solitary lifestyles, and this would be related to colony size. To test both hypotheses, we surveyed diet breadth data (palynological analysis) based on the Shannon-Wiener index (H') for 85 bee taxa. We also obtained colony size for 47 eusocial bee species. These data were examined using phylogenetic comparative methods. The results support the generalist strategy as a derived trait for the bee taxa evaluated here. The dietary diversity of eusocial bees (H': 2.1, on average) was 67.5% higher than that of noneusocial bees (H': 1.21, on average). There was, however, no relationship between diet breadth and colony size, indicating that smaller colonies can harvest a pollen variety as diverse as larger colonies. Taken together, these results provide new insights into the impact of lifestyle on the diversity of collected pollen. Furthermore, this work sheds light on an advantage of living in more highly structured societies irrespective of the size of the colony.

Lessons from assembling UCEs: A comparison of common methods and the case of Clavinomia (Halictidae).

Sequence data assembly is a foundational step in high-throughput sequencing, with untold consequences for downstream analyses. Despite this, few studies have interrogated the many methods for assembling phylogenomic UCE data for their comparative efficacy, or for how outputs may be impacted. We study this by comparing the most commonly used assembly methods for UCEs in the under-studied bee lineage Nomiinae and a representative sampling of relatives. Data for 63 UCE-only and 75 mixed taxa were assembled with five methods, including ABySS, HybPiper, SPAdes, Trinity and Velvet, and then benchmarked for their relative performance in terms of locus capture parameters and phylogenetic reconstruction. Unexpectedly, Trinity and Velvet trailed the other methods in terms of locus capture and DNA matrix density, whereas SPAdes performed favourably in most assessed metrics. In comparison with SPAdes, the guided-assembly approach HybPiper generally recovered the highest quality loci but in lower numbers. Based on our results, we formally move Clavinomia to Dieunomiini and render Epinomia once more a subgenus of Dieunomia. We strongly advise that future studies more closely examine the influence of assembly approach on their results, or, minimally, use better-performing assembly methods such as SPAdes or HybPiper. In this way, we can move forward with phylogenomic studies in a more standardized, comparable manner.

Elevated rates of dietary generalization in eusocial lineages of the secondarily herbivorous bees

BackgroundWithin the Hymenoptera, bees are notable for their relationship with flowering plants, being almost entirely dependent on plant pollen and nectar. Though functionally herbivorous, as a result of their role as pollinators, bees have received comparatively little attention as models for insect herbivory. Bees often display dietary specialization, but quantitative comparison against other herbivorous insects has not previously been conducted.ResultsIn the most comprehensive analysis to date for 860 bee species, dietary specialization amounted to 50.1% of studied species collecting pollen from between 1 and 2 botanical families with a relatively long tail of dietary generalists, with 11.1% of species collecting from more than 10 botanical families. This distribution deviated from the truncated Pareto distribution of dietary breadth seen in other herbivorous insect lineages. However, this deviation was predominantly due to eusocial bee lineages, which show a range of dietary breadths that conformed to a normal distribution, while solitary bees show a typical truncated distribution not strongly different from other herbivorous insects. We hypothesize that the relatively low level of dietary specialization in bees as a whole reflects the relaxation of the constraints typically observed in herbivorous insects with a comparatively reduced importance of plant chemistry and comparatively increased importance of phenology and foraging efficiency. The long flight periods of eusocial bees that are necessary to allow overlapping generations both allows and necessitates the use of multiple flowering resources, whereas solitary bees with short flight periods have more limited access to varied resources within a constrained activity period.ConclusionsCollectively, solitary bees show slightly lower specialization compared to other herbivorous insects, possibly due to their balanced relationship with plants, rather than direct antagonism such as seen in the direct consumption of plant tissues. An additional factor may be the mediocre diversity of bees at low latitudes combined with low levels of dietary specialization, whereas these areas typically display a high rate of specialization by herbivorous insects in general. Though the most important factors structuring dietary specialization in bees appear to differ from many other herbivorous insects, solitary bees show a surprisingly similar overall pattern of dietary specialization.

Prevalent bee venom genes evolved before the aculeate stinger and eusociality

BackgroundVenoms, which have evolved numerous times in animals, are ideal models of convergent trait evolution. However, detailed genomic studies of toxin-encoding genes exist for only a few animal groups. The hyper-diverse hymenopteran insects are the most speciose venomous clade, but investigation of the origin of their venom genes has been largely neglected.ResultsUtilizing a combination of genomic and proteo-transcriptomic data, we investigated the origin of 11 toxin genes in 29 published and 3 new hymenopteran genomes and compiled an up-to-date list of prevalent bee venom proteins. Observed patterns indicate that bee venom genes predominantly originate through single gene co-option with gene duplication contributing to subsequent diversification.ConclusionsMost Hymenoptera venom genes are shared by all members of the clade and only melittin and the new venom protein family anthophilin1 appear unique to the bee lineage. Most venom proteins thus predate the mega-radiation of hymenopterans and the evolution of the aculeate stinger.

Biogeography: The origin and spread of bee lineages

Where and when bees originated and how they dispersed and diversified across ancient continents has remained ambiguous. A new study that combines phylogenetics with fossil data reconstructs the origin and diversification of bees across geological time and space.

The evolutionary history of bees in time and space

Bees are the most significant pollinators of flowering plants. This partnership began ca. 120 million years ago, but the uncertainty of how and when bees spread across the planet has greatly obscured investigations of this key mutualism. We present a novel analysis of bee biogeography using extensive new genomic and fossil data to demonstrate that bees originated in Western Gondwana (Africa and South America). Bees likely originated in the Early Cretaceous, shortly before the breakup of Western Gondwana, and the early evolution of any major bee lineage is associated with either the South American or African land masses. Subsequently, bees colonized northern continents via a complex history of vicariance and dispersal. The notable early absences from large landmasses, particularly in Australia and India, have important implications for understanding the assembly of local floras and diverse modes of pollination. How bees spread around the world from their hypothesized Southern Hemisphere origin parallels the histories of numerous flowering plant clades, providing an essential step to studying the evolution of angiosperm pollination syndromes in space and time.

Mite non-reproduction, recapping behavior, and hygienic behavior (freeze-kill method) linked to Varroa destructor infestation levels in selected Apis mellifera colonies.

The genetic selection of honey bees (Apis mellifera) possessing specific social hygienic behaviors offers the beekeeping industry the possibility of controlling the Varroa destructor parasite and thus reducing its dependence on acaricides. However, the links between these behavioral traits are not yet well defined, which limits genetic progress in breeding programs. We measured the following behavioral varroa resistance traits: freeze-kill brood (FKB) and pin-kill brood (PKB) assays, varroa-sensitive hygiene (VSH), pupae removal, mite non-reproduction (MNR), and recapping activity. We found 2 negative and significant relationships: 1) between the recapping of cells infested with varroa and the total number of recapped cells, and 2) between the recapping of cells infested with varroa and VSH. We also selected the best predictive model of varroa infestation levels using the "step-wise" approach based on the Akaike information criterion. Our model revealed that MNR and FKB were significantly related to the varroa population levels, with a negative relationship; recapping was significantly related to mite infestation levels, with a positive relationship. Thus, a higher MNR or FKB score was linked to lower levels of mite infestation in colonies on August 14 (prior to fall infestation treatments); a higher recapping activity was linked to a higher level of mite infestation. Recapping behavior could be a useful trait to aid the selection of varroa-resistant bee lineages.

Geographical variation in abdominal colour pattern in Criorhina pachymera (Egger, 1858) (Diptera: Syrphidae)

The bee-mimicking hoverfly species Criorhina pachymera shows pronounced geographical variation in abdominal colour pattern. Based on 218 records from 22 European countries, we describe six abdomen forms divided over two main groups. Group A in western, northern and central parts of Europe contains abdomen forms A1–A3 with slender pollinose bands on the third and fourth tergite. Group B in south-eastern Europe contains forms B1–B3 with broad pollinose bands. These groups are separated by the Alps and the Carpathians, such as the separation of the original distributions of the two main postglacial recolonization lineages of honey bees in Europe. As these honey bee groups differ by the width of the pollinose bands on the third to fifth tergite, Batesian mimicry can explain the group distribution of C. pachymera with slender or broad pollinose bands. The different forms of C. pachymera in both groups are categorised by the extent of orange colouration on the second and third tergite. The darkest form A1, has a widespread distribution in Europe. Intermediate bright forms A2 and A3 occur predominantly in a belt along the southern margin of the group A distribution and in Sweden. Dark form B1 and intermediate bright form B2 occur on the Balkan peninsula and in neighbouring regions. The brightest form B3, is found in Italy, Switzerland (Ticino) and Greece. There is an average increase in the extent of orange colouration on the second and third tergite with decreasing geographical latitude, making temperature a likely additional cause for the described abdominal colour variation.

Geographical variation in abdominal colour pattern in Criorhina pachymera (Egger, 1858) (Diptera: Syrphidae)

The bee-mimicking hoverfly species Criorhina pachymera shows pronounced geographical variation in abdominal colour pattern. Based on 218 records from 22 European countries, we describe six abdomen forms divided over two main groups. Group A in western, northern and central parts of Europe contains abdomen forms A1–A3 with slender pollinose bands on the third and fourth tergite. Group B in south-eastern Europe contains forms B1–B3 with broad pollinose bands. These groups are separated by the Alps and the Carpathians, such as the separation of the original distributions of the two main postglacial recolonization lineages of honey bees in Europe. As these honey bee groups differ by the width of the pollinose bands on the third to fifth tergite, Batesian mimicry can explain the group distribution of C. pachymera with slender or broad pollinose bands. The different forms of C. pachymera in both groups are categorised by the extent of orange colouration on the second and third tergite. The darkest form A1, has a widespread distribution in Europe. Intermediate bright forms A2 and A3 occur predominantly in a belt along the southern margin of the group A distribution and in Sweden. Dark form B1 and intermediate bright form B2 occur on the Balkan peninsula and in neighbouring regions. The brightest form B3, is found in Italy, Switzerland (Ticino) and Greece. There is an average increase in the extent of orange colouration on the second and third tergite with decreasing geographical latitude, making temperature a likely additional cause for the described abdominal colour variation.

Prospects, challenges and perspectives in harnessing natural selection to solve the 'varroa problem' of honey bees.

Honey bees, Apis mellifera, of European origin are major pollinators of crops and wild flora. Their endemic and exported populations are threatened by a variety of abiotic and biotic factors. Among the latter, the ectoparasitic mite Varroa destructor is the most important single cause behind colony mortality. The selection of mite resistance in honey bee populations has been deemed a more sustainable solution to its control than varroacidal treatments. Because natural selection has led to the survival of some European and African honey bee populations to V. destructor infestations, harnessing its principles has recently been highlighted as a more efficient way to provide honey bee lineages that survive infestations when compared with conventional selection on resistance traits against the parasite. However, the challenges and drawbacks of harnessing natural selection to solve the varroa problem have only been minimally addressed. We argue that failing to consider these issues could lead to counterproductive results, such as increased mite virulence, loss of genetic diversity reducing host resilience, population collapses or poor acceptance by beekeepers. Therefore, it appears timely to evaluate the prospects for the success of such programmes and the qualities of the populations obtained. After reviewing the approaches proposed in the literature and their outcomes, we consider their advantages and drawbacks and propose perspectives to overcome their limitations. In these considerations, we not only reflect on the theoretical aspects of host-parasite relationships but also on the currently largely neglected practical constraints, that is, the requirements for productive beekeeping, conservation or rewilding objectives. To optimize natural selection-based programmes towards these objectives, we suggest designs based on a combination of nature-driven phenotypic differentiation and human-directed selection of traits. Such a dual strategy aims at allowing field-realistic evolutionary approaches towards the survival of V. destructor infestations and the improvement of honey bee health.

Co-expression Gene Networks and Machine-learning Algorithms Unveil a Core Genetic Toolkit for Reproductive Division of Labour in Rudimentary Insect Societies.

The evolution of eusociality requires that individuals forgo some or all their own reproduction to assist the reproduction of others in their group, such as a primary egg-laying queen. A major open question is how genes and genetic pathways sculpt the evolution of eusociality, especially in rudimentary forms of sociality-those with smaller cooperative nests when compared with species such as honeybees that possess large societies. We lack comprehensive comparative studies examining shared patterns and processes across multiple social lineages. Here we examine the mechanisms of molecular convergence across two lineages of bees and wasps exhibiting such rudimentary societies. These societies consist of few individuals and their life histories range from facultative to obligately social. Using six species across four independent origins of sociality, we conduct a comparative meta-analysis of publicly available transcriptomes. Standard methods detected little similarity in patterns of differential gene expression in brain transcriptomes among reproductive and non-reproductive individuals across species. By contrast, both supervised machine learning and consensus co-expression network approaches uncovered sets of genes with conserved expression patterns among reproductive and non-reproductive phenotypes across species. These sets overlap substantially, and may comprise a shared genetic "toolkit" for sociality across the distantly related taxa of bees and wasps and independently evolved lineages of sociality. We also found many lineage-specific genes and co-expression modules associated with social phenotypes and possible signatures of shared life-history traits. These results reveal how taxon-specific molecular mechanisms complement a core toolkit of molecular processes in sculpting traits related to the evolution of eusociality.

A novel real-time PCR coupled with high resolution melting analysis as a simple and fast tool for the entomological authentication of honey by targeting Apis mellifera mitochondrial DNA

Honey is one of the foods easily adulterated worldwide. Recently, the analysis of honeybee DNA has been proposed as a useful tool to authenticate the entomological origin of honey. However, the methods proposed so far require more than one polymerase chain reaction (PCR) and the use of agarose gels, making the authentication process laborious and lengthy. In this work, a novel real-time PCR coupled with high-resolution melting (HRM) analysis of a 150 bp fragment of the cytochrome c oxidase I (COI) gene is proposed as a fast and simple tool to assess honey’s entomological origin by discriminating the mitochondrial DNA lineages of European honey bees (A, M and C lineages). In addition, the new tool allowed the differentiation of honeys produced by different mitotypes of C-lineage ancestry. The method showed high analytical performance and was able to successfully identify the entomological origin of honeys of known origin obtained from research apiaries/beekeepers. Therefore, it was applied to 44 commercial honeys from different countries. It confirmed the entomological authenticity of French PDO honeys that should be produced by the Corse ecotype A. m. mellifera. For the remaining honeys, the results were also in good agreement with the declared geographical origin. However, three honeys from Slovenia did not cluster with C2 mitotype A. m. carnica as expected, suggesting the mixture of honeys produced by honeybees of different mitotypes.

Social divergence: molecular pathways underlying castes and longevity in a facultatively eusocial small carpenter bee.

Unravelling the evolutionary origins of eusocial life is a longstanding endeavour in the field of evolutionary-developmental biology. Descended from solitary ancestors, eusocial insects such as honeybees have evolved ontogenetic division of labour in which short-lived workers perform age-associated tasks, while a long-lived queen produces brood. It is hypothesized that (i) eusocial caste systems evolved through the co-option of deeply conserved genes and (ii) longevity may be tied to oxidative damage mitigation capacity. To date, however, these hypotheses have been examined primarily among only obligately eusocial corbiculate bees. We present brain transcriptomic data from a Japanese small carpenter bee, Ceratina japonica (Apidae: Xylocopinae), which demonstrates both solitary and eusocial nesting in sympatry and lives 2 or more years in the wild. Our dataset captures gene expression patterns underlying first- and second-year solitary females, queens and workers, providing an unprecedented opportunity to explore the molecular mechanisms underlying caste-antecedent phenotypes in a long-lived and facultatively eusocial bee. We find that C. japonica's queens and workers are underpinned by divergent gene regulatory pathways, involving many differentially expressed genes well-conserved among other primitively eusocial bee lineages. We also find support for oxidative damage reduction as a proximate mechanism of longevity in C. japonica.

Convergent Loss of Prothoracicotropic Hormone, A Canonical Regulator of Development, in Social Bee Evolution.

The evolution of insect sociality has repeatedly involved changes in developmental events and their timing. Here, we propose the hypothesis that loss of a canonical regulator of moulting and metamorphosis, prothoracicotropic hormone (PTTH), and its receptor, Torso, is associated with the evolution of sociality in bees. Specifically, we posit that the increasing importance of social influences on early developmental timing in social bees has led to their decreased reliance on PTTH, which connects developmental timing with abiotic cues in solitary insects. At present, the evidence to support this hypothesis includes the absence of genes encoding PTTH and Torso from all fully-sequenced social bee genomes and its presence in all available genomes of solitary bees. Based on the bee phylogeny, the most parsimonious reconstruction of evolutionary events is that this hormone and its receptor have been lost multiple times, across independently social bee lineages. These gene losses shed light on possible molecular and cellular mechanisms that are associated with the evolution of social behavior in bees. We outline the available evidence for our hypothesis, and then contextualize it in light of what is known about developmental cues in social and solitary bees, and the multiple precedences of major developmental changes in social insects.

Admixture in Africanized honey bees (Apis mellifera) from Panamá to San Diego, California (U.S.A.).

The Africanized honey bee (AHB) is a New World amalgamation of several subspecies of the western honey bee (Apis mellifera), a diverse taxon historically grouped into four major biogeographic lineages: A (African), M (Western European), C (Eastern European), and O (Middle Eastern). In 1956, accidental release of experimentally bred “Africanized” hybrids from a research apiary in Sao Paulo, Brazil initiated a hybrid species expansion that now extends from northern Argentina to northern California (U.S.A.). Here, we assess nuclear admixture and mitochondrial ancestry in 60 bees from four countries (Panamá; Costa Rica, Mexico; U.S.A) across this expansive range to assess ancestry of AHB several decades following initial introduction and test the prediction that African ancestry decreases with increasing latitude. We find that AHB nuclear genomes from Central America and Mexico have predominately African genomes (76%–89%) with smaller contributions from Western and Eastern European lineages. Similarly, nearly all honey bees from Central America and Mexico possess mitochondrial ancestry from the African lineage with few individuals having European mitochondria. In contrast, AHB from San Diego (CA) shows markedly lower African ancestry (38%) with substantial genomic contributions from all four major honey bee lineages and mitochondrial ancestry from all four clades as well. Genetic diversity measures from all New World populations equal or exceed those of ancestral populations. Interestingly, the feral honey bee population of San Diego emerges as a reservoir of diverse admixture and high genetic diversity, making it a potentially rich source of genetic material for honey bee breeding.

Comparative morphology and evolution of the cranial musculature in bees (Hymenoptera: Apoidea)

Comparative morphological studies in bees are mostly restricted to the skeleton, and the musculature of bees has not been explored much from this perspective. Here we investigate the head extrinsic musculature under an evolutionary perspective. The musculature of 34 bee species belonging to six major lineages and 26 tribes plus two apoid wasps is described, illustrated, and compared. A standardized terminology for the extrinsic musculature is proposed and aligned with the Hymenoptera Anatomy Ontology (HAO). A total of 12 characters derived from the analysis were optimized onto a summary phylogenetic tree. The musculature was found to be conserved among the main bee lineages, and most variation was found in the proboscis; no modification was found in antennal muscles. Four characters are interpreted as synapomorphies for bees, one for the long-tongued bees, three for Halictinae, and one for Megachilinae. We also found that the Apinae clade of cleptoparasites is supported by some character state transformations and that stingless bees have a unique posterior fronto-pharyngeal muscle. Both sexes display similar morphology, except for having two fixed attachment points for the anterior cranio-mandibular muscle in the males of Andreninae. This study provides a foundation for future investigations on bee head musculature on various taxonomic levels.