The topological differences between visitation and pollen transport networks: a comparison in species rich communities of the Himalaya–Hengduan Mountains

Pollination networks are usually constructed and assessed by direct field observations which commonly assume that all flower visitors are true pollinators. However, this assumption is often invalid and the use of data based on mere visitors to flowers may lead to a misunderstanding of intrinsic pollination networks. Here, using a large dataset by both sampling floral visitors and analyzing their pollen loads, we constructed 32 networks pairs (visitation versus pollen transport) across one flowering season at four elevation sites in the Himalaya–Hengduan Mountains region. Pollen analysis was conducted to determine which flower visitors acted as potential pollinators (pollen vectors) or as cheaters (those not carrying pollen of the visited plants). We tested whether there were topological differences between visitation and pollen transport networks and whether different taxonomic groups of insect visitors differed in their ability to carry pollen of the visited plants. Our results indicated that there was a significantly higher degree of specialization at both the network and species levels in the pollen transport networks in contrast to the visitation networks. Modularity was lower but nestedness was higher in the visitation networks compared to the pollen transport networks. All the cheaters were identified as peripheral species and most of them contributed positively to the nested structure. This may explain in part the differences in modularity and nestedness between the two network types. Bees carried the highest proportion of pollen of the visited plants. This was followed by Coleoptera, other Hymenoptera and Diptera. Lepidoptera carried the lowest proportion of pollen of the visited plants. Our study shows that the construction of pollen transport networks could provide a more in‐depth understanding of plant–pollinator interactions. Moreover, it suggests that detecting and removing cheater interactions when studying the topology of other mutualistic networks might be also important.     

贵州剑河寒武系“清虚洞组”管状微体骨骼化石初步研究

华南寒武系地层中广泛富集微体骨骼化石,为解决某些疑难化石的亲缘关系及研究早期后生动物的演化提供了重要化石证据。在贵州剑河八郎"清虚洞组"中发现一些管状微体骨骼化石。经鉴定后主要有4属,分别为小钻孔螺Torellella、似软舌螺Hyolithellus、鞘状螺Coleoloides和表面具鳞片状管状化石Mongolitubulus squamifer。Mongolitubulus分布范围较为广泛,本文结合前人对该化石亲缘关系的探讨及剑河寒武系"清虚洞组"化石的特征,推测M.squamifer可能是高肌虫的装饰刺。     

Streptomycin-induced ribosome engineering complemented with fermentation optimization for enhanced production of 10-membered enediynes tiancimycin-A and tiancimycin-D

Tiancimycins (TNMs) are a group of 10-membered anthraquinone-fused enediynes, newly discovered from Streptomyces sp. CB03234. Among them, TNM-A and TNM-D have exhibited excellent antitumor performances and could be exploited as very promising warheads for the development of anticancer antibody-drug conjugates (ADCs). However, their low titers, especially TNM-D, have severely limited following progress. Therefore, the streptomycin-induced ribosome engineering was adopted in this work for strain improvement of CB03234, and a TNMs high producer S. sp. CB03234-S with the K43N mutation at 30S ribosomal protein S12 was successfully screened out. Subsequent media optimization revealed the essential effects of iodide and copper ion on the production of TNMs, while the substitution of nitrogen source could evidently promote the accumulation of TNM-D, and the ratio of produced TNM-A and TNM-D was responsive to the change of carbon and nitrogen ratio in the medium. Further amelioration of the pH control in scaled up 25 L fermentation increased the average titers of TNM-A and TNM-D up to 13.7 ± 0.3 and 19.2 ± 0.4 mg/L, respectively. The achieved over 45-fold titer improvement of TNM-A, and 109-fold total titer improvement of TNM-A and TNM-D enabled the efficient purification of over 200 mg of each target molecule from 25 L fermentation. Our efforts have demonstrated a practical strategy for titer improvement of anthraquinone-fused enediynes and set up a solid base for the pilot scale production and preclinical studies of TNMs to expedite the future development of anticancer ADC drugs.     

Mechanics of the Formation,Interaction, and Evolution of Membrane Tubular Structures

Membrane nanotubes, also known as membrane tethers, play important functional roles in many cellular processes, such as trafficking and signaling. Although considerable progresses have been made in understanding the physics regulating the mechanical behaviors of individual membrane nanotubes, relatively little is known about the formation of multiple membrane nanotubes due to the rapid occurring process involving strong cooperative effects and complex configurational transitions. By exerting a pair of external extraction upon two separate membrane regions, here, we combine molecular dynamics simulations and theoretical analysis to investigate how the membrane nanotube formation and pulling behaviors are regulated by the separation between the pulling forces and how the membrane protrusions interact with each other. As the force separation increases, different membrane configurations are observed, including an individual tubular protrusion, a relatively less deformed protrusion with two nanotubes on its top forming a V shape, a Y-shaped configuration through nanotube coalescence via a zipper-like mechanism, and two weakly interacting tubular protrusions. The energy profile as a function of the separation is determined. Moreover, the directional flow of lipid molecules accompanying the membrane shape transition is analyzed. Our results provide new, to our knowledge, insights at a molecular level into the interaction between membrane protrusions and help in understanding the formation and evolution of intra- and intercellular membrane tubular networks involved in numerous cell activities.     

Maternal obesity enhances oocyte chromosome abnormalities associated with aging

Obesity is increasing globally, and maternal obesity has adverse effects on pregnancy outcomes and the long-term health of offspring. Maternal obesity has been associated with pregnancy failure through impaired oogenesis and embryogenesis. However, whether maternal obesity causes chromosome abnormalities in oocytes has remained unclear. Here we show that chromosome abnormalities are increased in the oocytes of obese mice fed a high-fat diet and identify weakened sister-chromatid cohesion as the likely cause. Numbers of full-grown follicles retrieved from obese mice were the same as controls and the efficiency of in vitro oocyte maturation remained high. However, chromosome abnormalities presenting in both metaphase-I and metaphase-II were elevated, most prominently the premature separation of sister chromatids. Weakened sister-chromatid cohesion in oocytes from obese mice was manifested both as the terminalization of chiasmata in metaphase-I and as increased separation of sister centromeres in metaphase II. Obesity-associated abnormalities were elevated in older mice implying that maternal obesity exacerbates the deterioration of cohesion seen with advancing age.

     

Elevated temperature increased nitrification activity by stimulating AOB growth and activity in an acidic paddy soil

Plant and Soil - Cadmium (Cd) is the most widespread toxic heavy metal to plant growth. As the second leading oil crop, some genotypes of Brassica napus (B. napus) are potential Cd accumulators....