Comparative analyses of mitogenomes in the social bees with insights into evolution of long inverted repeats in the Meliponini

The insect mitogenome is typically a compact circular molecule with highly conserved gene contents.Nonetheless,mitogenome structural variations have been reported in specific taxa,and gene rearrangements,usually the tRNAs,occur in different lineages.Because synapomorphies of mitogenome organizations can provide information for phylogenetic inferences,comparative analyses of mitogenomes have been given increasing attention.However,most studies use a very few species to represent the whole genus,tribe,family,or even order,overlooking potential variations at lower taxonomic levels,which might lead to some incorrect inferences.To provide new insights into mitogenome organizations and their implications for phylogenetic inference,this study conducted comparative analyses for mitogenomes of three social bee tribes(Meliponini,Bombini,and Apini)based on the phylogenetic framework with denser taxonomic sampling at the species and population levels.Comparative analyses revealed that mitogenomes of Apini and Bombini are the typical type,while those of Meliponini show diverse variations in mitogenome sizes and organizations.Large inverted repeats(IRs)cause significant gene rearrangements of protein coding genes(PCGs)and rRNAs in Indo-Malay/Australian stingless bee species.Molecular evolution analyses showed that the lineage with IRs have lower dN/dS ratios for PCGs than lineages without IRs,indicating potential effects of IRs on the evolution of mitochondrial genes.The finding of IRs and different patterns of gene rearrangements suggested that Meliponini is a hotspot in mitogenome evolution.Unlike conserved PCGs and rRNAs whose rearrangements were found only in the mentioned lineages within Meliponini,tRNA rearrangements are common across all three tribes of social bees,and are significant even at the species level,indicating that comprehensive sampling is needed to fully understand the patterns of tRNA rearrangements,and their implications for phylogenetic inference.

Numerical investigation of the cavitation dynamic parameters in a Francis turbine draft tube with columnar vortex rope

The cavitation developed in the Francis turbine draft tube is known to be a source of the hydraulic instability,especially under the conditions with columnar cavitation vortex rope occurring in the draft tube.The hydraulic system will suffer from the risk of the self-excitation and the high pressure pulsations because of the dynamic features of the complex cavitation vortex rope.The links between the cavitation dynamic characteristics and the hydraulic system stability are important for an accurate system instability prediction.For this purpose,the cavitating flows in a Francis turbine operating under the overload conditions are simulated by using the Zwart-Gerber-Belamri(ZGB)cavitation model.The cavitation dynamic parameters in different cavitation development stages and the evolutions under various overload conditions are analyzed and compared in this paper.It is shown that the cavitation dynamic parameters,including the cavitation compliance,the mass flow gain factor and the wave speed,can well represent the cavitation characteristics with the vortex rope evolution.The predicted cavitation dynamic parameters are in a reasonable agreement with other available results,with an obvious dependency on the loads.The results obtained in this study are relevant to the system stability analysis.

Seed dispersal by hornets:An unusual insect-plant mutualism

Vespicochory, seed dispersal by hornets, is a rare seed dispersal mechanism in angiosperms and, to date, there are few records of this phenomenon.Through field investigations and behavioral assays conducted in four populations of Stemona tuberosa from 2011–2016, we demonstrate that hornets are the primary seed dispersers of S. tuberosa and play an important role in "long-distance" seed dispersal in this species. Furthermore, some ant species act as secondary dispersers and may transport the seeds to safe sites.Hornets and ants provide complementary seed dispersal at different spatial scales. This unique example of insect-plant mutualism may be an underestimated but important strategy to ensure "long-distance" seed dispersal in other myrmecochorous plants.

Study of the formation and dynamic characteristics of the vortex in the pump sump by CFD and experiment

The formation mechanism and the dynamic characteristics of the floor-attached vortex(FAV)in the pump sump are analyzed,with the velocity gradient as the key factor.The FAV is shown to be formed when the velocity gradient in the singular point area reaches a certain strength.The evolution of the FAV is accompanied by the energy accumulation and dissipation in the vortex area.The generated FAV is in the form of the vortex pair at the initial stage,with opposite directions of rotation.The vortex with the same rotating direction as the impeller is strong because the rotational kinetic energy is easy to accumulate.The circumferential velocity of the FAV first increases and then decreases with the radius of the vortex core,indicating the FAV is a kind of forced vortex.The radius with the largest velocity gradient is the radius of the vortex core.

Numerical study of the natural frequency and mode shape of prototype Francis turbine runner

The prediction of the dynamic behavior of the structure is a key to ensure the safe and stable operation of the unit.In this paper,the acoustic fluid-structure coupling method is used to study the natural frequency and the mode shape of the prototype Francis turbine runner.With an added mass,the natural frequency of the runner in the water is reduced.The added mass force mc is reduced under the cavitation,resulting in an increase of the natural frequency,but it is still much lower than the frequency in the air.As the order number of the runner mode increases,the added mass force increases,and the frequency reduction rate increases.From 0ND to 4ND,the nodal lines on the upper crown of the runner gradually disappear,and the mode shape becomes more complex.The modal displacement D*in the circumferential direction of the runner and the outlet edge of the blade are selected to compare the structural mode shapes under different operating conditions.The results show that the amplitude of D*in the circumferential direction of the runner gradually increases from the upper crown to the lower band of the runner,and the curve assumes a symmetrical distribution of sinusoidal waves,whose number is twice of that of the nodal lines of the runner.The D*value changes are caused by the added mass in the water,and it will further change under the cavitation conditions.It means that the vibration form of the structure has changed.These will cause damages to the runner under the resonance conditions at different positions and in different degrees.