Evolution of the Mammalian Neck from Developmental,Morpho-Functional,and Paleontological Perspectives

The mammalian neck adopts a variety of postures during daily life and generates numerous head trajectories. Despite its functional diversity, the neck is constrained to seven cervical vertebrae in (almost) all mammals. Given this low number, an unexpectedly high degree of modularity of the mammalian neck has more recently been uncovered. This work aims to review neck modularity in mammals from a developmental, morpho-functional, and paleontological perspective and how high functional diversity evolved in the mammalian neck after the occurrence of meristic limitations. The fixed number of cervical vertebrae and the developmental modularity of the mammalian neck are closely linked to anterior Hox genes expression and strong developmental integration between the neck and other body regions. In addition, basic neck biomechanics promote morpho-functional modularity due to preferred motion axes in the cranio-cervical and cervico-thoracic junction. These developmental and biomechanical determinants result in the characteristic and highly conserved shape variation among the vertebrae that delimits morphological modules. The step-wise acquisition of these unique cervical traits can be traced in the fossil record. The increasing functional specialization of neck modules, however, did not evolve all at once but started much earlier in the upper than in the lower neck. Overall, the strongly conserved modularity in the mammalian neck represents an evolutionary trade-off between the meristic constraints and functional diversity. Although a morpho-functional partition of the neck is common among amniotes, the degree of modularity and the way neck disparity is realized is unique in mammals.

     

The Subadult Plumage of Male Purple Martins: Variability,Female Mimicry and Recent Evolution

Like a number of other passerine birds year-old male purple martins, Progne subis, often breed in a ♀-like plumage. We have examined delayed plumage maturation in martins by testing assumptions and predictions derived from two hypotheses advanced to explain their appearance and behavior: the sexual selection hypothesis and the female mimicry hypothesis. First, we examine the success of subadults of different appearance 1) in dominance interactions with adults and with other subadults and 2) at entering colonies with different numbers of adults. Second, we compare the mating success of subadults of different appearance. Finally, we examine predictions from the female mimicry hypothesis concerning the appearance of subadults with regard to geographic variation in colony size and with regard to historical changes in colony size in Eastern North America.     

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

Recent phylogenetic analyses imply a distant relationship and long separated evolution of two-toed sloths (Choloepus) and three-toed sloths (Bradypus). No known fossil sloth is interpreted to have been suspensory. As a consequence, the suspensory posture and locomotion of the extant genera likely evolved convergently in both lineages, forming a new framework for the analysis of functional aspects of the locomotor apparatus of extant tree sloths. The suspensory posture and locomotion has altered functional demands from the phylogenetically plesiomorphic non-suspensory pronograde situation. Here, anatomical traits that have been argued to be of adaptive significance for quadrupedal suspensory locomotion are reviewed and the evolution of these traits is discussed in light of the new framework. Experimental data are largely limited to Choloepus, but help to deduce functional aspects of the anatomy in Bradypus as well. The most important adaptive traits are hands and feet modified into relatively rigid hook-like appendages, great mobility of all joints proximal to the midcarpal and transverse tarsal joints, relatively long arms with a relatively short scapula, a rounded thorax with a small diameter, a highly mobile sterno-clavicular articulation, and emphasis on powerful flexion in the proximal limb joints via advantageous lever arms. Despite these changes, patterns of limb kinematics remained conservative during the course of evolution in the lineages leading to extant tree sloths, and it is suggested here that this also applies to the pattern of neuromuscular control of limb movements during locomotion. Morphological ‘solutions’ to altered functional demands posed by inversed orientation of the body differ in the two genera of extant tree sloths, thereby corroborating the proposed diphyly. Convergent evolution in tree sloths may be attributed to functional constraints posed by fossorial adaptations in early Xenarthra that canalized sloths to adopt a suspensory posture and locomotion in the arboreal habitat.     

植物内生菌研究新进展

虽然早在 10 0多年前人们就已发现在健康植物组织的内部也有微生物存在,这类微生物在文献中后来被称为植物内生菌（ｅｎｄｏｐｈｙｔｅ）,但由于内生菌生活在没有外在感染症状的健康植物组织内部,其存在和作用长期以来一直为人们所忽视。自 2 0世纪 30年代发现造成畜牧业重大损失的牲畜中毒是由于食用了感染内生真菌的牧草,内生菌的研究才得以广泛深入地开展起来［1］。植物内生菌几乎存在于所有目前已研究过的植物中,分布广,种类多。研究表明,感染内生菌的植物宿主往往具有生长快速、抗逆境、抗病害、抗动物危害等优势,比未感染植…     

Epaxial Musculature in Armadillos,Sloths, and Opossums: Functional Significance and Implications for the Evolution of Back Muscles in the Xenarthra

To investigate the evolution of xenarthran epaxial muscles, fresh specimens of the North American Common long-nosed armadillo Dasypus novemcinctus and of a marsupial, the Virginia opossum Didelphis virginiana, were dissected. Data from one fixed specimen of a two-toed sloth Choloepus didactylus were also used for comparison, because it is a xenarthran exhibiting a highly derived locomotor mode. The opossum was used to represent a more generalized mammalian condition. Each of the three mammalian epaxial muscle groups, the iliocostalis, longissimus dorsi, and transversospinalis, was removed and its mass was determined. All data were corrected for body mass and length. Unpaired, one-tailed t-tests showed the average mass of the iliocostalis and transversospinalis of Dasypus to be significantly larger than the mass of the same muscles in Didelphis, whereas the average mass of the longissimus dorsi was not statistically different between the two species. In agreement with pronounced lateral bending and de-emphasized dorso-ventral flexion and extension, Choloepus also had a relatively large iliocostalis and small longissimus. Our limited data suggest that this condition was inherited from non-arboreal and probably digging early xenarthrans. We believe the relatively larger iliocostalis and transversospinalis muscles in Dasypus can be attributed to the need to provide vertical stabilization of the trunk and resist lateral reaction forces generated by digging. Thus, for Xenarthra it represents a synapomorphy linked to adaptations for fossoriality.     

Evolution of the Pedolateral Foot in Ground Sloths: Patterns of Change in the Astragalus

The rotation of the pes or pedolateral stance in the extinct ground sloths so the body weight of the animal is primarily supported by the fifth metatarsal and the calcaneum occurred independently at least three times and is present in the Megatheriidae, Nothrotheriidae, and Mylodontidae. In contrast, the pes in the Megalonychidae more closely resembles the primitive eutherian pattern. The pedolateral rotation of the pes thus represents an excellent example of parallel evolution in a closely related group of mammals. While the rotation of the foot occurs as a functional complex resulting in the modification of many bones in the pes, the astragalus is the one bone that shows the highest degree of departure from the primitive mammalian condition and the most distinctive changes in morphology. The morphological transition from a plantigrade foot as occurs in xenarthran anteaters and is essentially retained in the megalonychid sloths to the highly derived condition seen in the megathere, nothrothere, and mylodont sloths follows a similar pattern in all groups but there is still significant variation in the foot structure between the lineages. Despite these variations there are consistent patterns of change in the astragalus in all groups related to the progressive rotation of the pes and a change from dorso-plantar flexion and extension to a medio-lateral rotation of the pes relative to the tibia.     

绿脓杆菌外毒素A的最新研究进展

在免疫缺失、囊肿性纤维化、烧伤烫伤等患者的临床继发感染中,绿脓杆菌是引起感染的主要病原菌之一,其合成的细胞外毒性物质—绿脓杆菌外毒素A(PEA)被认为是引起感染的最关键内在机制。该文对中外学者们在PEA的结构、功能、提取和纯化方法、重组毒素、基因工程疫苗以及应用等方面的研究进行归纳总结,并对研究和应用中存在的问题加以分析,对预防和治疗绿脓菌感染、抗肿瘤、抗移植排斥和治疗自身免疫性疾病等具有重要而深远的意义。     

植物的基因对基因抗病性学说

植物的基因对基因抗病性学说促进了寄主与病原物相互作用分子机制研究的深入。介绍近几年来对Avr基因和R基因的特性,二之间的相互作用机制以及R基因信号传导途径等方面的研究进展。     

肝X受体的研究进展

肝X受体（liver Xreceptors,LXRs）作为一种氧化型固醇激活的核受体,调控胆固醇代谢过程中一些关键基因的表达,是机体的胆固醇代谢感受器。另外,LXRs还参与调节机体其他生理活动,包括脂肪形成、糖代谢、巨噬细胞的天然免疫和炎症反应等。因此,LXRs有望作为治疗动脉粥样硬化、高胆固醇血症、2型糖尿病等的药物靶点。     

低聚果糖的生物学效应及其安全性研究进展

作为一种应用最早和最为广泛的功能性低聚糖,低聚果糖具有调节肠道菌群、提高机体免疫功能、降低血脂和促进某些营养物质吸收的功能,且对人体无任何生理毒性.通过对其生物学效应与安全性等方面近年来的最新研究进展进行综述,以期推动低聚果糖的进一步深入研究开发和在食品上的广泛应用.     

蔗糖磷酸合成酶研究的新进展

蔗糖磷酸合成酶(sucrose phosphate synthase,SPS)是高等植物体内控制蔗糖合成的关键酶之一,它主要通过异构调节和磷酸化修饰在酶水平调节蔗糖合成。本文简要介绍SPS家族的成员、SPS蛋白上的3个磷酸化位点,以及SPS的生物学功能、SPS与磷酸蔗糖磷酸酶的关系等。     

microRNA及其应用研究进展

microRNA(miRNA)是在多种真核细胞和病毒中发现的一类内源性非编码单链RNA,长约22个核苷酸,在进化上具有高度的保守性。miRNA可以通过碱基互补与靶基因mRNA的特定位点结合,抑制该蛋白合成或诱导该mRNA降解,在生物体生长、发育和疾病发生等过程中发挥着重要的作用。我们简要叙述了miRNA的特点和作用机制,并对miRNA在基因表达调控、胚胎干细胞调控及免疫调节等方面的最新进展进行了综述。