Density dependence and environmental factors affect population stability of an agricultural pest and its specialist parasitoid

Host–parasitoid dynamics are intrinsically unstable unless the risk of parasitism is sufficiently heterogeneous among hosts. Spatial aggregation of parasitoids can contribute to this heterogeneity, stabilising host–parasitoid population dynamics and thereby reducing pest outbreaks. We examined the spatial distribution of mango gall fly (Procontarinia matteiana, Kiefer and Cecconi), a non-native pest of South African mango orchards, which is controlled by a single parasitoid (Chrysonotomyia pulcherrima, Kerrich). We assessed whether spatial aggregation of parasitoids is associated with proximity to natural vegetation and/or to host density-dependent and host density-independent factors at three spatial scales. We found evidence for higher parasitism rates near natural vegetation at the field scale, and inverse host-density dependent and density-independent parasitoid aggregation at both the leaf scale and field scale. Therefore, we conclude that natural vegetation plays a role in promoting stabilising aggregation of parasitoids, possibly through provision of non-host resources (nectar, pollen), in this system.     

Rapid thermal adaptation in photosymbionts of reef‐building corals

Climate warming is occurring at a rate not experienced by life on Earth for 10 s of millions of years, and it is unknown whether the coral‐dinoflagellate (Symbiodinium spp.) symbiosis can evolve fast enough to ensure coral reef persistence. Coral thermal tolerance is partly dependent on the Symbiodinium hosted. Therefore, directed laboratory evolution in Symbiodinium has been proposed as a strategy to enhance coral holobiont thermal tolerance. Using a reciprocal transplant design, we show that the upper temperature tolerance and temperature tolerance range of Symbiodinium C1 increased after ~80 asexual generations (2.5 years) of laboratory thermal selection. Relative to wild‐type cells, selected cells showed superior photophysiological performance and growth rate at 31°C in vitro, and performed no worse at 27°C; they also had lower levels of extracellular reactive oxygen species (exROS). In contrast, wild‐type cells were unable to photosynthesise or grow at 31°C and produced up to 17 times more exROS. In symbiosis, the increased thermal tolerance acquired ex hospite was less apparent. In recruits of two of three species tested, those harbouring selected cells showed no difference in growth between the 27 and 31°C treatments, and a trend of positive growth at both temperatures. Recruits that were inoculated with wild‐type cells, however, showed a significant difference in growth rates between the 27 and 31°C treatments, with a negative growth trend at 31°C. There were no significant differences in the rate and severity of bleaching in coral recruits harbouring wild‐type or selected cells. Our findings highlight the need for additional Symbiodinium genotypes to be tested with this assisted evolution approach. Deciphering the genetic basis of enhanced thermal tolerance in Symbiodinium and the cause behind its limited transference to the coral holobiont in this genotype of Symbiodinium C1 are important next steps for developing methods that aim to increase coral bleaching tolerance.     

Structure of a ganglioside with Cad blood group antigen activity

The Cad antigen is a rare erythrocyte blood group antigen expressed on both sialoglycoprotein and ganglioside structures. It is related both serologically and biochemically to the Sda blood group antigen expressed on over 90% of Caucasian erythrocytes. We reported previously that Cad erythrocytes contain a novel ganglioside that binds Helix pomatia lectin and inhibits human anti-Sda antibody. We have now purified the Cad ganglioside and determined its structure. The ganglioside contained Glc-Gal-GlcNAc-GalNAc-NeuAc in a molar ratio of 1.00:1.94:0.95:0.93:1.05. Its chromatographic mobility was between that of GM1 and GD3. After treatment with beta-hexosaminidase (human placenta Hex A), the product migrated with 2-3-sialosylparagloboside (IV3NeuAcnLc4OseCer), it no longer bound H. pomatia lectin, and it acquired the ability to bind an antibody to sialosylparagloboside. Treatment of this material with neuraminidase (Vibrio cholerae) yielded a product with the mobility of paragloboside (nLc4OseCer) that bound monoclonal antibody 1B2, which is specific for terminal N-acetyllactosaminyl structures. Treatment of the Cad ganglioside with Arthrobacter ureafaciens neuraminidase yielded a product reactive with monoclonal antibody 2D4, which is specific for terminal GalNAc beta (1-4)Gal structures. These data provide strong evidence that the Cad ganglioside structure is GalNAc beta (1-4)[NeuAc alpha (2-3)]Gal beta (1-3)Gal beta (1-4)GlcCer. 1H NMR analysis also supports the conclusion that the terminal GalNAc is linked beta (1-4) to Gal. High-performance thin-layer chromatographic ganglioside patterns from three blood group Cad individuals showed a direct correlation between the quantity of Cad ganglioside and the strength of Cad antigen expression on the erythrocytes, as measured by hemagglutination.(ABSTRACT TRUNCATED AT 250 WORDS)     

Carbon isotopes as indicators of elephant diets and African environments

Stable carbon isotope ratios have been successfully used to assess modern animal diets and to reconstruct prehistoric diets of animals and humans (Vogel & van der Merwe, 1977; van der Merwe & Vogel, 1978; Burleigh & Brothwell, 1978; Vogel, 1978a; DeNiro & Epstein, 1978; Tieszen et al., 1979; Tieszen & Imbamba, 1980; Chisholm, Nelson & Schwarcz, 1982; Tauber, 1981). We have used ¹³C/¹²C ratio measurements of bone collagen to study the diets of African elephants in twelve wildlife refuges. These represent most of the habitats in which elephants live, including such diverse plant communities as primary rain forest, savanna woodland and desert. The δ¹³C values were found to have a simple linear relationship with tree density in most cases. When translated into relative amounts of dietary browse (C₃ plants) and graze (C₄ plants), the grass content is seen to be systematically under-represented, presumably due to inefficient metabolism. This does not affect the relationship between elephant diet and tree density, which has implications for the study of elephant-woodland interactions, and for reconstructions of past African environments.     

Biology of the stingless beePlebeia remota (Holmberg): observations and evolutionary implications

Summary The genusPlebeia has a special significance for the study of social evolution of stingless bees: morphologically primitive, its species display a wealth of behavioural evolution, especially with respect to the oviposition process. We comparePlebeia remota with the few other members of the genus studied so far.Related to its subtropical geographical range, brood production is seasonal (there is no brood in the colony in colder months), and adult workers occur as summer and winter bees. The nest is in tree cavities, and the involucrum is absent or restricted to the winter period. Brood cells are arranged in horizontal combs, and new cells are built completely synchronously. Each series consists of up to 50 cells, their number being mainly dependent on colony size. Construction speed is remarkably constant, allowing 4–6 batches per 24 hours. Cell building and provisioning are activities of a small group of specialized workers.The oviposition cycle follows the classical subdivisions for stingless bees. During the patrolling phase a worker may offer a trophic egg in a most remarkable way: while retreating backward from the queen she bends the abdomen under thorax and head, and lays an egg on the comb. This egg is eaten by the queen or a worker.The provisioning, oviposition and operculation of all cells occur simultaneously, each cell is provisioned by 4–9 workers. Localization of a cell by the queen may be facilitated by its characteristic guard, which defends the cell against the approaching queen. The degree of synchronization within a batch is very high: the duration per cell lasts 420–950 sec, the batch of up till 50 cells needs only 557–1160 sec. Operculation is done by a worker that was not involved in the previous steps.Males are generally produced by the queen. Several male producing cycles per year occur. In orphan colonies laying workers give rise to males, and in queenright colonies workers may occasionally reproduce as well.Division of labour follows the general pattern for stingless bees; however, cell building and provisioning are activities of a specialized group of workers.     

Diverse Brain Myeloid Expression Profiles Reveal Distinct Microglial Activation States and Aspects of Alzheimer’s Disease Not Evident in Mouse Models

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Substantial Metabolic Activity of Human Brown Adipose Tissue during Warm Conditions and Cold-Induced Lipolysis of Local Triglycerides

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Sensitivity of a two-dimensional biomorphoelastic model for post-burn contraction

We consider a two-dimensional biomorphoelastic model describing post-burn scar contraction. This model describes skin displacement and the development of the effective Eulerian strain in the tissue. Besides these mechanical components, signaling molecules, fibroblasts, myofibroblasts, and collagen also play a significant role in the model. We perform a sensitivity analysis for the independent parameters of the model and focus on the effects on features of the relative surface area and the total strain energy density. We conclude that the most sensitive parameters are the Poisson’s ratio, the equilibrium collagen concentration, the contraction inhibitor constant, and the myofibroblast apoptosis rate. Next to these insights, we perform a sensitivity analysis where the proliferation rates of fibroblasts and myofibroblasts are not the same. The impact of this model adaptation is significant.

     

Loss of Multi-Epitope Specificity in Memory CD4+ T Cell Responses to B. Pertussis with Age

Pertussis is still occurring in highly vaccinated populations, affecting individuals of all ages. Long-lived Th1 CD4⁺ T cells are essential for protective immunity against pertussis. For better understanding of the limited immunological memory to Bordetella pertussis, we used a panel of Pertactin and Pertussis toxin specific peptides to interrogate CD4⁺ T cell responses at the epitope level in a unique cohort of symptomatic pertussis patients of different ages, at various time intervals after infection. Our study showed that pertussis epitope-specific T cell responses contained Th1 and Th2 components irrespective of the epitope studied, time after infection, or age. In contrast, the breadth of the pertussis-directed CD4⁺ T cell response seemed dependent on age and closeness to infection. Multi-epitope specificity long-term after infection was lost in older age groups. Detailed knowledge on pertussis specific immune mechanisms and their insufficiencies is important for understanding resurgence of pertussis in highly vaccinated populations.