Sea Urchin Spines as a Model-System for Permeable, Light-Weight Ceramics with Graceful Failure Behavior. Part I. Mechanical Behavior of Sea Urchin Spines under Compression

The spines of pencil and lance urchins Heterocentrotus mammillatus and Phyllacanthus imperialis were studied as a modelof light-weight material with high impact resistance.The complex and variable skeleton construction ("stereom") of body andspines of sea urchins consists of highly porous Mg-bearing calcium carbonate.This basically brittle material with pronouncedsingle-crystal cleavage does not fracture by spontaneous catastrophic device failure but by graceful failure over the range of tensof millimeter of bulk compression instead.This was observed in bulk compression tests and blunt indentation experiments onregular,infiltrated and latex coated sea urchin spine segments.Microstructural characterization was carried out using X-raycomputer tomography,optical and scanning electron microscopy.The behavior is interpreted to result from the hierarchicstructure of sea urchin spines from the rnacroscale down to the nanoscale.Guidelines derived from this study see ceramics withlayered porosity as a possible biomimetic construction for appropriate applications.     

追溯山茱萸科植物的性状进化和生物地理学历史——方法选择的影响?

This study compares results on reconstructing the ancestral state of characters and ancestral areas of distribution in Cornaceae to gain insights into the impact of using different analytical methods. Ancestral character state reconstructions were compared among three methods (parsimony, maximum likelihood, and stochastic character mapping) using MESQUITE and a full Bayesian method in BAYESTRAITS and inferences of ancestral area distribution were compared between the parsimony-based dispersal-vicariance analysis (DIVA) and a newly developed maximum likelihood (ML) method. Results indicated that among the six inflorescence and fruit characters examined, "perfect" binary characters (no homoplasy, no polymorphism within terminals, and no missing data) are little affected by choice of method, while homoplasious characters and missing data are sensitive to methods used. Ancestral areas at deep nodes of the phylogeny are substantially different between DIVA and ML and strikingly different between analyses including and excluding fossils at three deepest nodes. These results, while raising caution in making conclusions on trait evolution and historical biogeography using conventional methods, demonstrate a limitation in our current understanding of character evolution and biogeography. The biogeographic history favored by the ML analyses including fossils suggested the origin and early radiation of Cornus likely occurred in the late Cretaceous and earliest Tertiary in Europe and intercontinental disjunctions in three lineages involved movements across the North Atlantic Land Bridge (BLB) in the early and mid Tertiary. This result is congruent with the role of NALB for post-Eocene migration and in connecting tropical floras in North America and Africa, and in eastern Asia and South America. However, alternative hypotheses with an origin in eastern Asia and early Trans-Beringia migrations of the genus cannot be ruled out.     

离子通道递质受体大家族:每种受体所特有的变构调制中心在神经药理学中的重要性

美国飞迪亚-乔治城神经科学研究所所长、美国科学院院士E.Costa博士,1989年1月10日来北京接受北京医科大学授予名誉教授衔。Costa教授在该仪式上所作的报告指出了当前神经递质研究的新方向,具有重要的学术意义。特予介绍,以飨读者。     

1 生物动能学导言

1.1 生物学中的能流和物流地球上能量的基本来源是太阳的电磁幅射。高等植物、藻类和兰绿细菌利用这一幅射的可见和近短红外成分,驱动伴随分子氧释放的二氧化碳(光合自养生长)的还原同化作用     

Sieve element occlusion provides resistance against Aphis gossypii in TGR-1551 melons

Feeding behavior and plant response to feeding were studied for the aphid Aphis gossypii Glover on susceptible and resistant melons(cv.Iroquois and TGR-1551,respectively).Average phloem phase bout duration on TGR-1551 was<7% of the duration on Iroquois.Sixty-seven percent of aphids on TGR-1551 never produced a phloem phase that attained ingestion(EPG waveform E2)in contrast to only 7% of aphids on Iroquois.Average bout duration of waveform E2(scored as zero if phloem phase did not attain E2)on TGR-1551 was<3% of the duration on Iroquois.Conversely,average bout duration of EPG waveform El(sieve element salivation)was 2.8 times greater on TGR-1551 than on Iroquois.In a second experiment,liquid nitrogen was used to rapidly cryofix leaves and aphids within a few minutes after the aphids penetrated a sieve element.Phloem near the penetration site was then examined by confocal laser scanning microscopy.Ninety-six percent of penetrated sieve elements were occluded by protein in TGR-1551 in contrast to only 28% in Iroquois.Usually in TGR-1551,occlusion was also observed in nearby nonpenetrated sieve elements.Next,a calcium channel blocker,trivalent lanthanum,was used to prevent phloem occlusion in TGR-1551,and A.gossypii feeding behavior and the plants phloem response were compared between lanthanum-treated and control TGR-1551.Lanthanum treatment eliminated the sieve element protein occlusion response and the aphids readily ingested phloem sap from treated plants.This study provides strong evidence that phloem occlusion is a mechanism for resistance against A.gossypii in TGR-1551.     

High levels of arbuscular mycorrhizal fungus colonization on Medicago truncatula reduces plant suitability as a host for pea aphids (Acyrthosiphon pisum)

This study sheds light on a poorly understood area in insect-plant-microbe interactions,focusing on aphid probing and feeding behavior on plants with varying levels of arbuscular mycorrhizal(AM)fungus root colonization.It investigates a commonly occurring interaction of three species:pea aphid Acyrthosiphon pisum,barrel medic Medicago truncatula,and the AM fungus Rhizophagus irregularis,examining whether aphid-feeding behavior changes when insects feed on plants at different levels of AM fungus colonization(42% and 84% root length colonized).Aphid probing and feeding behavior was monitored throughout 8 h of recording using the electrical penetration graph(EPG)technique,also,foliar nutrient content and plant growth were measured.Summarizing,aphids took longer to reach their 1st sustained phloem ingestion on the 84% AM plants than on the 42% AM plants or on controls.Less aphids showed phloem ingestion on the 84% AM plants relative to the 42% AM plants.Shoots of the 84% AM plants had higher percent carbon(43.7%)relative to controls(40.5%),and the 84% AM plants had reduced percent nitrogen(5.3%)relative to the 42% AM plants(6%).In conclusion,EPG and foliar nutrient data support the hypothesis that modifications in plant anatomy(e.g.,thicker leaves),and poor food quality(reduced nitrogen)in the 84% AM plants contribute to reduced aphid success in locating phloem and ultimately to differences in phloem sap ingestion.This work suggests that M.truncatula plants benefit from AM symbiosis not only because of increased nutrient uptake but also because of reduced susceptibility to aphids.     

Diapause affects cuticular hydrocarbon composition and mating behavior of both sexes in Drosophila montana

Envipnmental cues,mainly photoperiod and temperature,are known to control female adult reproductive diapause in several insect species.Diapause enhances female survival during adverse conditions and postpones progeny production to the favorable season.Male diapause(a reversible inability to inseminate receptive females)has been studied much less than female diapause.However,if the males maximized their chances to fertilize females while minimizing their energy expenditure,they would be expected to be in diapause at the same time as females.We investigated Drosophila montana male mating bchavior under short-day conditions that induce diapause in females and found the males to be reproductively inactive.We also found that males reared under long-day conditions(reproducing individuals)court reproducing postdiapause fermales,but not diapausing ones.The diapausing fies of both sexes had more long-chain and less short-chain hydrocarbons on their cuticle than the reproducing ones,which presumably increase their survival under stressful conditions,but at the same time decrease their attractiveness.Our study shows that the mating behavior of females and males is well coordinated during and afier overwintering and it also gives support to the dual role of insect cuticular hydrocarbons in adaptation and mate choice.     

Aphid populations showing differential levels of virulence on Capsicum accessions

The green peach aphid,Myzus persicae,is one of the most threatening pests in pepper cultivation and growers would benefit from resistant varietices.Previously,we identified two Capsicum acessions as susceptible and three as resistant to M.persicae using an aphid population originating from the Netherlands(NL).Later on we identified an aphid population originating from a diferent gcographical region(Switserland,SW)that was virulent on all tested Capsicum acessions.The objeetive of the current work is to describe in detail diferent aspects of the interaction between two aphid populations and two sclected Capsicum acessions(one that was susceptible[PB2013046]and one that was resistant[PB2013071]to population NL),including biochemical processes involved.Electrical penetration graph(EPG)recordings showed similar feeding activities for both aphid populations on PB2013046.On acession PB2013071 the aphid population sw was able to devote significantly more time to phloem ingestion than population NL.We also studied plant defense response and found that plants of acession PB2013046 could not induce an accumulation of reactive oxygen species and callose formation after infestation with either aphid population.However,plants of PB2013071 induced a stronger defense response after infestation by population NL than after infestation by population SW.Based on these results,population SW of M.persicae seems to have overcome the resistance of PB2013071 that prevented feeding of aphids from NL population.The potential mechanism by which SW population overcomes the resistance is discussed.