Molecular determinants of caste differentiation in the highly eusocial honeybee Apis mellifera

Abstract Background In honeybees, differential feeding of female larvae promotes the occurrence of two different phenotypes, a queen and a worker, from identical genotypes, through incremental alterations, which affect general growth, and character state alterations that result in the presence or absence of specific structures. Although previous studies revealed a link between incremental alterations and differential expression of physiometabolic genes, the molecular changes accompanying character state alterations remain unknown. Results By using cDNA microarray analyses of >6,000 Apis mellifera ESTs, we found 240 differentially expressed genes (DEGs) between developing queens and workers. Many genes recorded as up-regulated in prospective workers appear to be unique to A. mellifera, suggesting that the workers' developmental pathway involves the participation of novel genes. Workers up-regulate more developmental genes than queens, whereas queens up-regulate a greater proportion of physiometabolic genes, including genes coding for metabolic enzymes and genes whose products are known to regulate the rate of mass-transforming processes and the general growth of the organism (e.g., tor). Many DEGs are likely to be involved in processes favoring the development of caste-biased structures, like brain, legs and ovaries, as well as genes that code for cytoskeleton constituents. Treatment of developing worker larvae with juvenile hormone (JH) revealed 52 JH responsive genes, specifically during the critical period of caste development. Using Gibbs sampling and Expectation Maximization algorithms, we discovered eight overrepresented cis-elements from four gene groups. Graph theory and complex networks concepts were adopted to attain powerful graphical representations of the interrelation between cis-elements and genes and objectively quantify the degree of relationship between these entities. Conclusion We suggest that clusters of functionally related DEGs are co-regulated during caste development in honeybees. This network of interactions is activated by nutrition-driven stimuli in early larval stages. Our data are consistent with the hypothesis that JH is a key component of the developmental determination of queen-like characters. Finally, we propose a conceptual model of caste differentiation in A. mellifera based on gene-regulatory networks.

“What Happens When Pollinators Get Sick? Behavioral Impacts of Honeybee Viruses”

Like all organisms on the planet, honeybees (Apis mellifera) are susceptible to infection with a wide variety of viruses. These viruses may produce infections with no visible symptoms or may have devastating consequences on both the individual bee and the entire hive. Deformed Wing Virus, a member of the Iflavirus group of viruses, has an RNA genome and has had a particularly important impact on bee health. It can be spread between bees in a several ways – bees can infect each other during feeding or grooming activities, drones can pass the virus to the queen during mating and queens can lay infected eggs. The primary and most devastating way that these viruses are transmitted within and between hives involves a parasitic mite, an animal known ominously as Varroa destructor. The talk will discuss the effect that viruses have on the health and behavior of honeybees and will outline the collaborative research activities of Drs. Evans and Pizzorno over the last 7 years.

Spinal cord injury causes sustained disruption of the blood-testis barrier in the rat.

There is a high incidence of infertility in males following traumatic spinal cord injury (SCI). Quality of semen is frequently poor in these patients, but the pathophysiological mechanism(s) causing this are not known. Blood-testis barrier (BTB) integrity following SCI has not previously been examined. The objective of this study was to characterize the effects of spinal contusion injury on the BTB in the rat. 63 adult, male Sprague Dawley rats received SCI (n = 28), laminectomy only (n = 7) or served as uninjured, age-matched controls (n = 28). Using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), BTB permeability to the vascular contrast agent gadopentate dimeglumine (Gd) was assessed at either 72 hours-, or 10 months post-SCI. DCE-MRI data revealed that BTB permeability to Gd was greater than controls at both 72 h and 10 mo post-SCI. Histological evaluation of testis tissue showed increased BTB permeability to immunoglobulin G at both 72 hours- and 10 months post-SCI, compared to age-matched sham-operated and uninjured controls. Tight junctional integrity within the seminiferous epithelium was assessed; at 72 hours post-SCI, decreased expression of the tight junction protein occludin was observed. Presence of inflammation in the testes was also examined. High expression of the proinflammatory cytokine interleukin-1 beta was detected in testis tissue. CD68(+) immune cell infiltrate and mast cells were also detected within the seminiferous epithelium of both acute and chronic SCI groups but not in controls. In addition, extensive germ cell apoptosis was observed at 72 h post-SCI. Based on these results, we conclude that SCI is followed by compromised BTB integrity by as early as 72 hours post-injury in rats and is accompanied by a substantial immune response within the testis. Furthermore, our results indicate that the BTB remains compromised and testis immune cell infiltration persists for months after the initial injury.

Honey Bee Apis mellifera Parasites in the Absence of Nosema ceranae Fungi and Varroa destructor Mites

Few areas of the world have western honey bee (Apis mellifera) colonies that are free of invasive parasites Nosema ceranae (fungi) and Varroa destructor (mites). Particularly detrimental is V. destructor; in addition to feeding on host haemolymph, these mites are important vectors of several viruses that are further implicated as contributors to honey bee mortality around the world. Thus, the biogeography and attendant consequences of viral communities in the absence of V. destructor are of significant interest. The island of Newfoundland, Province of Newfoundland and Labrador, Canada, is free of V. destructor; the absence of N. ceranae has not been confirmed. Of 55 Newfoundland colonies inspected visually for their strength and six signs of disease, only K-wing had prevalence above 5% (40/55 colonies = 72.7%). Similar to an earlier study, screenings again confirmed the absence of V. destructor, small hive beetles Aethina tumida (Murray), tracheal mites Acarapis woodi (Rennie), and Tropilaelaps spp. ectoparasitic mites. Of a subset of 23 colonies screened molecularly for viruses, none had Israeli acute paralysis virus, Kashmir bee virus, or sacbrood virus. Sixteen of 23 colonies (70.0%) were positive for black queen cell virus, and 21 (91.3%) had some evidence for deformed wing virus. No N. ceranae was detected in molecular screens of 55 colonies, although it is possible extremely low intensity infections exist; the more familiar N. apis was found in 53 colonies (96.4%). Under these conditions, K-wing was associated (positively) with colony strength; however, viruses and N. apis were not. Furthermore, black queen cell virus was positively and negatively associated with K-wing and deformed wing virus, respectively. Newfoundland honey bee colonies are thus free of several invasive parasites that plague operations in other parts of the world, and they provide a unique research arena to study independent pathology of the parasites that are present.

The Honey Bee Pathosphere of Mongolia: European Viruses in Central Asia

Parasites and pathogens are apparent key factors for the detrimental health of managed European honey bee subspecies, Apis mellifera. Apicultural trade is arguably the main factor for the almost global distribution of most honey bee diseases, thereby increasing chances for multiple infestations/infections of regions, apiaries, colonies and even individual bees. This imposes difficulties to evaluate the effects of pathogens in isolation, thereby creating demand to survey remote areas. Here, we conducted the first comprehensive survey for 14 honey bee pathogens in Mongolia (N = 3 regions, N = 9 locations, N = 151 colonies), where honey bee colonies depend on humans to overwinter. In Mongolia, honey bees, Apis spp., are not native and colonies of European A. mellifera subspecies have been introduced ~60 years ago. Despite the high detection power and large sample size across Mongolian regions with beekeeping, the mite Acarapis woodi, the bacteria Melissococcus plutonius and Paenibacillus larvae, the microsporidian Nosema apis, Acute bee paralysis virus, Kashmir bee virus, Israeli acute paralysis virus and Lake Sinai virus strain 2 were not detected, suggesting that they are either very rare or absent. The mite Varroa destructor, Nosema ceranae and four viruses (Sacbrood virus, Black queen cell virus, Deformed wing virus (DWV) and Chronic bee paralysis virus) were found with different prevalence. Despite the positive correlation between the prevalence of V. destructor mites and DWV, some areas had only mites, but not DWV, which is most likely due to the exceptional isolation of apiaries (up to 600 km). Phylogenetic analyses of the detected viruses reveal their clustering and European origin, thereby supporting the role of trade for pathogen spread and the isolation of Mongolia from South-Asian countries. In conclusion, this survey reveals the distinctive honey bee pathosphere of Mongolia, which offers opportunities for exciting future research.

Age determination and sea-surface reconstruction of sediment cores from the Norwegian Sea

Polycystine radiolarians are used to reconstruct summer sea surface temperatures (SSSTs) for the Late Pleistocene-Holocene (600-13,400 14C years BP) in the Norwegian Sea. At 13,200 14C years BP, the SSST was close to the average Holocene SSST (~12°C). It then gradually dropped to 7.1°C in the Younger Dryas. Near the Younger Dryas-Holocene transition (~10,000 14C years BP), the SSST increased 5°C in about 530 years. Four abrupt cooling events, with temperature drops of up to 2.1°C, are recognized during the Holocene: at 9340, 7100 ("8200 calendar years event"), 6400 and 1650 14C years BP. Radiolarian SSSTs and the isotopic signal from the GISP2 ice core are strongly coupled, stressing the importance of the Norwegian Sea as a mediator of heat/precipitation exchange between the North Atlantic, the atmosphere, and the Greenland ice sheet. Radiolarian and diatom-derived SSSTs display similarities, with the former not showing the recently reported Holocene cooling trend.

Elevation lines of modelled ice sheet extension during last glacial maximum

A numerical ice-sheet model was used to reconstruct the Late Weichselian glaciation of the Eurasian High Arctic, between Franz Josef Land and Severnaya Zemlya. An ice sheet was developed over the entire Eurasian High Arctic so that ice flow from the central Barents and Kara seas toward the northern Russian Arctic could be accounted for. An inverse approach to modeling was utilized, where ice-sheet results were forced to be compatible with geological information indicating ice-free conditions over the Taymyr Peninsula during the Late Weichselian. The model indicates complete glaciation of the Barents and Kara seas and predicts a "maximum-sized" ice sheet for the Late Weichselian Russian High Arctic. In this scenario, full-glacial conditions are characterized by a 1500-m-thick ice mass over the Barents Sea, from which ice flowed to the north and west within several bathymetric troughs as large ice streams. In contrast to this reconstruction, a "minimum" model of glaciation involves restricted glaciation in the Kara Sea, where the ice thickness is only 300 m in the south and which is free of ice in the north across Severnaya Zemlya. Our maximum reconstruction is compatible with geological information that indicates complete glaciation of the Barents Sea. However, geological data from Severnaya Zemlya suggest our minimum model is more relevant further east. This, in turn, implies a strong paleoclimatic gradient to colder and drier conditions eastward across the Eurasian Arctic during the Late Weichselian.

(Table 1) Age determination of Cape Shpindler, Yugorski Peninsula, northwest Russia

Depositional environments, stratigraphic relations, and 35 new AMS 14C dates at Cape Shpindler, Yugorski Peninsula, help constrain the late Pleistocene glacial and environmental history of the southern Kara Sea region. Fifteen- to fifty-meter-high coastal exposures reveal a complex package of shallow marine, fluvial, glacial, and postglacial deposits, and are documented here in a 19-km-long cross-section and eight vertical sections. The shallow marine (Unit A), estuarine or prodeltaic (Unit B), and fluvio-deltaic (Unit C) deposits contain an interglacial molluscan fauna, yield radiocarbon dates greater than 40 ka, and may correspond with a regional sea-level highstand during the Eemian. These units are overlain by a diamicton (Unit D), and are pervasively deformed by folds and low- to high-angle faults into a stacked glaciotectonic accretionary complex. The diamicton (Unit D) is a subglacial till, and associated massive ground ice with deformed debris bands (Unit E) appears to be relict glacier ice. Glaciotectonic structures document both southward- and northward-directed glacier movement. Above the till and associated glaciotectonic horizons lies 0- to 11-m-thick postglacial deposits of peatland, eolian, fluvial, and primarily lacustrine origin (Unit F). The postglacial deposits yield radiocarbon ages of 12.8 to 0.8 ka. Thus, at least one regional glaciation is prominently represented in the stratigraphy, and occurred probably after the Eemian but before 12.8 ka. We infer that the bulk of the glacial record corresponds with southward advance by an early Weichselian Kara Sea Ice Sheet, in agreement with other recently documented, regional records from Yamal Peninsula and the Pechora Basin. The timing and source of northward-directed glacier ice are less well constrained. Across the broad expanse of the Eurasian Arctic, Quaternary stratigraphy is still sparsely documented. The new data from Cape Shpindler fill a spatial gap in paleoenvironmental research.