Group Size buffers against energetic stress in honeybee workers (Apis mellifera)

Individuals of the Western honeybee species, Apis mellifera, live in large groups of thousands of worker bees, a queen, and a few drones. Workers interact frequently with related individuals while performing various tasks. Although it is well understood why and under which conditions sociality can evolve, the consequences for individuals living in permanent groups are less well understood. As individuals of solitary species become stressed when kept at high density, it might be the opposite in obligate social species. Here, I use an experimental laboratory set-up to study the effect of varying group sizes on the magnitude and within-group variance of stress responses towards energetic and heat stress. While only a weak difference was found in the magnitude of an energetic stress response as a function of group size, the within-group variance showed a statistically significant positive relationship with group size for the glucose/trehalose ratio, a marker for energetic stress. The heat stress marker, hsp70AB gene expression, did not show any relationship to group size. Individuals of obligate social species seem to benefit from adaptations to permanent group living, e.g., buffering against stress, especially at a higher density of individuals. The consequences of infections and immune system activation in isolated individuals are discussed

Molecular genetic analysis of reproductive dominance hierarchies in the honeybee colony (Apis mellifera L.)

Soziale Insekten sind durch eine reproduktive Arbeitsteilung charakterisiert. Damit verbunden ist die Ausprägung von morphologisch unterschiedlichen Kasten (Arbeiterinnen, Königinnen). Besonders deutlich ist die Kastendifferenzierung bei der Honigbiene Apis mellifera L. Man geht davon aus, dass die Kastendifferenzierung durch die unterschiedliche Fütterung der Larven hervorgerufen wird, also einem rein umweltbedingten Einfluss. Die funktionell sterilen Arbeiterinnen sind teilweise in der Lage ihre Ovarien zu entwickeln und parthenogenetisch Eier zu legen. In Anwesenheit der Königin ist dies jedoch nicht der Fall, da die Königin durch eine Vielzahl von Pheromonen die Ovarentwicklung der Arbeiterinnen unterdrückt. Des weiteren kannibalisieren Arbeiterinnen von anderen Arbeiterinnen gelegte Eier ("worker policing"). Reproduktiv aktive Arbeiterinnen entwickeln aus der Sicht ihrer Physiologie und des Verhaltens recht königinnenähnliche Merkmale. Besonders stark ausgeprägt sind diese Merkmale bei Arbeiterinnen der Kap Honigbiene, A. m. capensis Esch. Arbeiterinnen dieser in Südafrika beheimateten Subspezies der westlichen Honigbiene können sehr schnell ihre Ovarien entwickeln, produzieren sehr königinnenähnliche Pheromone und sind in der Lage parthenogenetisch diploide (weibliche) Nachkommen zu erzeugen (= Thelytokie). Durch gezielte Kreuzungsexperimente konnte die genetische Grundlage der unterschiedlichen Parthenogenesetypen analysiert werden. Ein einzelnes Gen (theytoky, th) verursacht die thelytoke Parthenogenese, wenn die Arbeiterinnen homozygot an diesem Locus sind. Durch Bioassays mit Arbeiterinnen unterschiedlicher Parthenogenesetypen konnte demonstriert werden, dass andere Merkmale der reproduktiven Dominanz (Pheromonproduktion, Ovarentwicklung) ebenfalls durch das th-Gen (pleiotrop) beeinflusst werden. Das Gen konnte mit Hilfe von über 500 Mikrosatelliten Markern im Genom kartiert werden. Es befindet sich auf Chromosom 13. Neun Kandidatengene wurden identifiziert, von denen eines ein Transkriptionsfaktor (grainy head, grh) ist. Da der allelische Zustand des th-Gens einen starken Einfluss auf die Ausprägung von königinnenähnlichen Merkmalen hat, scheint es doch eine genetische Komponente in der Kastendetermination zu geben.Social insects are characterised by a reproductive division of labour. Associated with is the establishment of morphological differing castes (workers, queens). In honeybees, Apis mellifera L., the caste differentiation is most obvious. Caste determination is achieved by differential larval nutrition, a strict environmental factor. Workers are functionally sterile and are able to develop their ovaries and parthenogentically lay eggs. This does not occur in presence of the queen, since queens suppress the ovarial development of workers by a suite of pheromones. Moreover, workers cannibalise worker-laid eggs (worker policing). Reproductive workers develop queen-like phenotypes with respect to physiology and behaviour. These traits are expressed to a high extent in workers of the Cape honeybee, A. m. capensis Esch. Workers of this South African subspecies of the Western honeybee may develop their ovaries rapidly, produce queen-like pheromonal secretions and are able to parthenogenetically lay diploid (female) offspring (= thelytoky). By means of crossing experiments the genetic basis of differing types of parthenogenesis were analysed. A single gene (thelytoky, th) causes thelytokous parthenogenesis, when workers are homozygous for this gene. Using workers of displaying different types of parthenogenesis in bioassays it was shown, that other characters of reproductive dominance (production of pheromones, ovarial development) are affected by the th-gene via pleiotropy. This gene was mapped in the genome using more than 500 microsatellite markers. The gene is located on chromosome 13. Nine candidate genes were identified, one of them a transcription factor (grainy head, grh). Since the allelic condition at the th-gene is crucial for the expression of queen-like characters it seems that there is a strong genetic component in caste determination.von Hans Michael Georg Lattorf

Reproductive Biology of the Cape Honeybee: A Critique of Beekman et al: A critique of "Asexually Produced Cape Honeybee Queens (Apis mellifera capensis) Reproduce Sexually,” authors: Madeleine Beekman, Michael H. Allsopp, Julianne Lim, Frances Goudie, and Benjamin P. Oldroyd. Journal of Heredity. 2011:102(5):562-566

Laying workers of the Cape honeybee parthenogenetically produce female offspring, whereas queens typically produce males. Beekman et al. confirm this observation, which has repeatedly been reported over the last 100 years including the notion that natural selection should favor asexual reproduction in Apis mellifera capensis. They attempt to support their arguments with an exceptionally surprising finding that A. m. capensis queens can parthenogenetically produce diploid homozygous queen offspring (homozygous diploid individuals develop into diploid males in the honeybee). Beekman et al. suggest that these homozygous queens are not viable because they did not find any homozygous individuals beyond the third larval instar. Even if this were true, such a lethal trait should be quickly eliminated by natural selection. The identification of sex (both with molecular and morphological markers) is possible but notoriously difficult in honeybees at the early larval stages. Ploidy is however a reliable indicator, and we therefore suggest that these "homozygous” larvae found in queen cells are actually drones reared from unfertilized eggs, a phenomenon well known by honeybee queen breeder

The genomes of two key bumblebee species with primitive eusocial organization

Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation

Pollination and Pesticides in runner beans in Poland – a commentary on Kot et al. (2023) in Agriculture 13: 2138

Pollination of crop plants is highly valued as it contributes to productivity in terms of quality and quantity. Globally, pollination is valued at more than USD 500 billion. The primary pollinators are insects and amongst them, bees. The Western honeybee (Apis mellifera) is a very generalist pollinator that is managed. Honeybees contribute up to 50% of the pollination of various crop plants. Pollinators are at risk due to land-use/land-cover changes and agricultural pesticide input.In a recently published study, research on honeybees in runner bean (Phaseolus coccineus L.) in Poland is presented. In one part of the study, the actual foraging of honeybees in beans is recorded, along with the time of day, abundance and time spent on flowers. The second part of the study investigated several apiaries concerning the potential poisoning of bees by means of pesticide exposure. The authors recorded the fitness of colonies, flight activity, behaviour, productivity and pesticide residues in bees.The manuscript, unfortunately, has several scientific flaws that are outlined in this commentary. These flaws, particularly those related to experimental planning and data collection and analysis, have the potential to compromise the conservation of pollinators. The misguidance in the implementation of measures to protect pollinators and pollination services is a cause for concern and should motivate us to address these issues

Paternity skew in seven species of honeybees (Hymenoptera: Apidae: Apis)

Honeybees (Apis) show an extremely polyandrous mating system. In general honeybee queens mate with at least ten drones. The reproductive success of the drones is usually biased giving rise to speculations of a first or last male advantage. Especially for A. andreniformis and A. florea a first male advantage was hypothesized due to the peculiar anatomy of their male genitalia. We reanalyzed data from the literature by using a sample size calibration method to survey the differences and similarities in paternity skew among species in the genus Apis. The paternity skew among seven honeybee species differed significantly, particularly due to the rare patrilines. The sorting algorithm, i.e. the ranking of the patrilines, had, however, a considerable effect on the paternity skew pattern. The frequent patrilines appeared to be similarly distributed in all tested species. As a consequence the proposed first male advantage in the dwarf honeybees is not supported by empirical data

Genetic underpinnings of division of labor in the honeybee (Apis mellifera)

Honeybees have been studied for centuries, starting with Aristotle, who wrote the first book about bee breeding. More than 2000 years later, the honeybee entered the genomic era as the first social insect whose genome was sequenced, leading to significant insight into the molecular mechanisms underlying social behavior. In addition, gene expression studies and knockdown using RNAi have extended the understanding of social interactions. Much of the work has focused on caste determination – the mechanism that results in reproductive division of labor, division of labor within the worker caste, and worker reproduction – an essential process underlying eusociality. Here we review the molecular factors involved in caste determination and the differential regulation of caste-specific genes. Recent findings suggest that division of labor is influenced by a small number of loci showing high levels of pleiotropy, suggesting that changes in a small number of genes lead to large changes in the phenotype.German Research Foundation DFG (grants Mo 373/26-2 and Mo 373/30-1) to R.F.A.M. and the Federal Ministry for Education and Research BMBF (FKZ: 0315126) to H.M.G.L.http://www.journals.elsevier.com/trends-in-geneticshb201

Network resilience of plant-bee interactions in the Eastern Afromontane Biodiversity Hotspot

Interaction network resilience can be defined as the ability of interacting organisms to maintain their functions, processes or populations after experiencing a disturbance. Studies on mutualistic interactions between plants and pollinators along environmental gradients are essential to understand the provision of ecosystem services and the mechanisms challenging their network resilience. However, it remains unknown to what level ecological changes along climatic gradients constrain the network resilience of mutualistic organisms, especially along elevation gradients. We surveyed bee species and recorded their interactions with plants throughout the four major seasons (i.e. long and short rainy, and long and short dry) on 50 study sites positioned along an elevation gradient (525 m to 2,530 m asl) in the Eastern Afromontane Biodiversity Hotspots in Kenya, East Africa. We calculated bee and plant network resilience using the network resilience parameter (βeff) and assessed changes in bee and plant network resilience along the elevation gradient using generalised additive models (gams). We quantified the effects of climate, bee and plant diversity, bee functional traits, network structure, and landscape configuration on bee and plant network resilience using a set of multi-model inference frameworks followed by structural equation models (SEM). We found that bee and plant species exhibited higher levels of network resilience at higher elevations. While bee network resilience increased linearly across the elevation gradient, plant network resilience increased exponentially from ∼1500 m and higher. Bee and plant network resilience increased in areas with reduced mean annual temperature (MAT) and decreased in areas with lower mean annual precipitation (MAP). Our SEM model showed that increasing temperatures indirectly influenced plant network resilience via network modularity and community assemblage of bees. We also found that MAP had a direct positive effect on plant diversity and network resilience, while the fragmentation of habitats reduced richness of plant communities and enhanced network modularity. In conclusion, we revealed that mutualistic networks showed higher network resilience at higher elevations. We also unveiled that climate and habitat fragmentation directly or indirectly influences the network resilience of plants and bees via the modulation of community assemblages and interaction networks. These influences are lower at higher elevations such that these systems seem better able to buffer against extinction cascades. We thus suggest that, management efforts should be geared at consolidating natural habitats. In contrast, restoration efforts should aim at mitigating climate change effects and harnessing the ability of mutualists to reconnect broken links to improve the network resilience and functioning of East-African montane ecosystems.journal articl

A selective sweep in a Varroa destructor resistant honeybee (Apis mellifera) population

The mite Varroa destructor is one of the most dangerous parasites of the Western honeybee (Apis mellifera) causing enormous colony losses worldwide. Various chemical treatments for the control of the Varroa mite are currently in use, which, however, lead to residues in bee products and often to resistance in mites. This facilitated the exploration of alternative treatment methods and breeding for mite resistant honeybees has been in focus for breeders in many parts of the world with variable results. Another approach has been applied to a honeybee population on Gotland (Sweden) that was exposed to natural selection and survived Varroa-infestation for more than 10 years without treatment. Eventually this population became resistant to the parasite by suppressing the reproduction of the mite. A previous QTL mapping study had identified a region on chromosome 7 with major loci contributing to the mite resistance. Here, a microsatellite scan of the significant candidate QTL regions was used to investigate potential footprints of selection in the original population by comparing the study population on Gotland before (2000) and after selection (2007). Genetic drift had caused an extreme loss of genetic diversity in the 2007 population for all genetic markers tested. In addition to this overall reduction of heterozygosity, two loci on chromosome 7 showed an even stronger and significant reduction in diversity than expected from genetic drift alone. Within the selective sweep eleven genes are annotated, one of them being a putative candidate to interfere with reduced mite reproduction. A glucose-methanol-choline oxidoreductase (GMCOX18) might be involved in changing volatiles emitted by bee larvae that might be essential to trigger oogenesis in Varroa.BEEDOC research network (EU FP7 to RFAM and IF, EU contract number: FP7-KBBE-2009-3 244956 CP-FP).http://www.elsevier.com/locate/meegidhb201

Comparative analyses of the major royal jelly protein gene cluster in three Apis species with long amplicon sequencing

The western honeybee, Apis mellifera is a prominent model organism in the field of sociogenomics and a recent upgrade substantially improved annotations of the reference genome. Nevertheless, genome assemblies based on short-sequencing reads suffer from problems in regions comprising e.g. multi-copy genes. We used single-molecule nanopore-based sequencing with extensive read-lengths to reconstruct the organization of the major royal jelly protein (mrjp) region in three species of the genus Apis. Long-amplicon sequencing provides evidence for lineage-specific evolutionary fates of Apis mrjps. Whereas the most basal species, A. florea, seems to encode ten mrjps, different patterns of gene loss and retention were observed for A. mellifera and A. dorsata. Furthermore, we show that a previously reported pseudogene in A. mellifera, mrjp2-like, is an assembly artefact arising from short read sequencing.The German Research Foundation (Deutsche Forschungsgemeinschaft - DFG, Grant MO 373/32-1 to RFAM).http://dnaresearch.oxfordjournals.orgam2017Zoology and Entomolog