Wing serial homologs and the origin and evolution of the insect wing

The origin and evolution of insect wings has been the subject of extensive debate. The issue has remained controversial largely because of the absence of definitive fossil evidence or direct developmental evidence of homology between wings and a putative wing origin. Recent identification of wing serial homologs (WSHs) has provided researchers with a potential strategy for identifying WSHs in other species. Future comparative developmental analyses between wings and WSHs may clarify the important steps underlying the evolution of insect wings.     

Resilin in dragonfly and damselfly wings and its implications for wing flexibility

Although there is mounting evidence that passive mechanical dynamics of insect wings play an integral role in insect flight, our understanding of the structural details underlying insect wing flexibility remains incomplete. Here, we use comparative morphological and mechanical techniques to illuminate the function and diversity of two mechanisms within Odonata wings presumed to affect dynamic wing deformations: flexible resilin vein‐joints and cuticular spikes. Mechanical tests show that joints with more resilin have lower rotational stiffness and deform more in response to a load applied to an intact wing. Morphological studies of 12 species of Odonata reveal that resilin joints and cuticular spikes are widespread taxonomically, yet both traits display a striking degree of morphological and functional diversity that follows taxonomically distinct patterns. Interestingly, damselfly wings (suborder Zygoptera) are mainly characterized by vein‐joints that are double‐sided (containing resilin both dorsally and ventrally), whereas dragonfly wings (suborder Epiprocta) are largely characterized by single‐sided vein‐joints (containing resilin either ventrally or dorsally, but not both). The functional significance and diversity of resilin joints and cuticular spikes could yield insight into the evolutionary relationship between form and function of wings, as well as revealing basic principles of insect wing mechanical design. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

The control of wing kinematics by two steering muscles of the blowfly (Calliphora vicina)

We used a combination of high speed video and electrophysiological recordings to investigate the relationship between wing kinematics and the firing patterns of the first (b1) and second (b2) basalar muscles of tethered flying blowflies (Calliphora vicina). The b1 typically fires once during every wing stroke near the time of the dorsal stroke reversal. The b2 fires either intermittently or in bursts that may be elicited by a visual turning stimulus. Sustained activation of the b1 at rates near wing beat frequency appears necessary for the tonic maintenance of stroke amplitude. In addition, advances in the phase of b1 activation were correlated with both increased wing protraction during the down-stroke and increased stroke amplitude. Similar kinematic alterations were correlated with b2 spikes, and consequently, both muscles may function in the control of turns toward the contralateral side. The effects of the two muscles were evident within a single stroke period and decayed quickly. Kinematic changes correlated with b1 phase shifts were graded, suggesting a role in compensatory course stabilization. In contrast, b2 spikes were correlated with all-or-none changes in the wing stroke, a characteristic consistent with a role in mediating rapid turns towards or away from objects.Abbreviations b1 first basalar muscle - b2 second basalar muscle - PWP pleural wing process - RS radial stop - S wing span · - angle between the stroke plane and the longitudinal body axis - stroke amplitude - stroke elevation - L wing length - b1 phase of b1 activation - b2 phase of b2 activation - stroke deviation     

The origin and early evolution of birds

Birds evolved from and are phylogenetically recognized as members of the theropod dinosaurs; their first known member is the Late Jurassic Archaeopteryx, now represented by seven skeletons and a feather, and their closest known non-avian relatives are the dromaeosaurid theropods such as Deinonychus. Bird flight is widely thought to have evolved from the trees down, but Archaeopteryx and its outgroups show no obvious arboreal or tree-climbing characters, and its wing planform and wing loading do not resemble those of gliders. The ancestors of birds were bipedal, terrestrial, agile, cursorial and carnivorous or omnivorous. Apart from a perching foot and some skeletal fusions, a great many characters that are usually considered ‘avian’ (e.g. the furcula, the elongated forearm, the laterally flexing wrist and apparently feathers) evolved in non-avian theropods for reasons unrelated to birds or to flight. Soon after Archaeopteryx, avian features such as the pygostyle, fusion of the carpometacarpus, and elongated curved pedal claws with a reversed, fully descended and opposable hallux, indicate improved flying ability and arboreal habits. In the further evolution of birds, characters related to the flight apparatus phylogenetically preceded those related to the rest of the skeleton and skull. Mesozoic birds are more diverse and numerous than thought previously and the most diverse known group of Cretaceous birds, the Enantiornithes, was not even recognized until 1981. The vast majority of Mesozoic bird groups have no Tertiary records: Enantiornithes, Hesperornithiformes, Ichthyornithiformes and several other lineages disappeared by the end of the Cretaceous. By that time, a few Linnean ‘Orders’ of extant birds had appeared, but none of these taxa belongs to extant ‘families’, and it is not until the Paleocene or (in most cases) the Eocene that the majority of extant bird ‘Orders’ are known in the fossil record. There is no evidence for a major or mass extinction of birds at the end of the Cretaceous, nor for a sudden ‘bottleneck’ in diversity that fostered the early Tertiary origination of living bird ‘Orders’.     

Ultrastructure of the larval eye of the scorpionfly Panorpa dubia (mecoptera: Panorpidae) with implications for the evolutionary origin of holometabolous larvae

The evolutionary origin of holometabolous larvae is a long‐standing and controversial issue. The Mecoptera are unique in Holometabola for their larvae possessing a pair of compound eyes instead of stemmata. The ultrastructure of the larval eyes of the scorpionfly Panorpa dubia Chou and Wang, 1981 was investigated using transmission electron microscopy. Each ommatidium possesses a cornea, a tetrapartite eucone crystalline cone, eight retinula cells, two primary pigment cells, and an undetermined number of secondary pigment cells. The rhabdomeres of the eight retinula cells form a centrally‐fused, tiered rhabdom of four distal and four proximal retinula cells. The rhabdomeres of the four distal retinula cells extend distally into a funnel shape around the basal surface of the crystalline cone. Based on the similarity of the larval eyes of Panorpidae to the eyes of the hemimetabolous insects and the difference from the stemmata of the holometabolous larvae, the evolutionary origin of the holometabolous larvae is briefly discussed. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Detailed analysis of the prothoracic tissues transforming into wings in the Cephalothorax mutants of the Tribolium beetle

Despite the immense importance of the wing in the evolution and successful radiation of the insect lineages, the origin of this critical structure remains a hotly-debated mystery. Two possible tissues have been identified as an evolutionary origin of wings; the lateral expansion of the dorsal body wall (tergal edge) and structures related to an ancestral proximal leg segment (pleural tissues). Through studying wing-related tissues in the red flour beetle, Tribolium castaneum, we have previously presented evidence in support of a dual origin of insect wings, a third hypothesis proposing that wings evolved from a combination of both tergal and pleural tissues. One key finding came from the investigation of a Cephalothorax (Cx) mutant, in which the ectopic wing characteristic to this mutant was found to be formed from both tergal and pleural contributions. However, the degree of contribution of the two tissues to the wing remains elusive. Here, we took advantage of multiple Cx alleles available in Tribolium, and produced a variety of degrees and types of ectopic wing tissues in their prothoracic segments. Through detailed phenotypic scoring of the Cx phenotypes based on nine categories of mutant traits, along with comprehensive morphological analysis of the ectopic wing tissues, we found that (i) ectopic wing tissues can be formed at various locations in the prothorax, even internally, (ii) the lateral external ectopic wing tissues have tergal origin, while the internal and posterior external ectopic wing tissues appear to be of pleural origin, and (iii) the ectopic wing tissues of both tergal and pleural origin are capable of transforming into wing surface tissues. Collectively, these outcomes suggest that the evolutionary contribution of each tissue to a complete wing may be more complex than the simple binary view that is typically invoked by a dual origin model (i.e. the wing blade from the tergal contribution + musculature and articulation from the pleural contribution).     

Intragenomic DNA sequence homologies in the chicken and other members of the classAves: DNA re-association under reduced stringency conditions

Summary We have investigated the intragenomic DNA sequence homologies of twelve species of birds representing five orders, and emphasizing Galliformes. This study differs in two important ways from the classical approaches taken in constructing and evaluating phylogenies based on DNA sequence similarities. Comparisons are made on the basis of sequence homologieswithin genomes of related birds, rather than between genomes. DNA is reassociated at 50°C in 0.5M phosphate buffer; these conditions allow formation and detection of duplexes containing more mismatch than would normally be permitted using more stringent conditions, affording an opportunity to observe more ancient sequence homologies. Thermal stability profiles of DNA duplexes formed under these conditions are the basis of comparison; three general patterns were observed. This approach emphasizes differences in sequence composition between genomes while the more traditional method of intergenomic tracer DNA hybridization at higher stringency emphasizes sequence similarities.No correlation was found between taxonomic position and intragenomic sequence composition, either within or between lineages. The thermal stability profiles of DNA duplexes formed within avian genomes did not reflect the biological similarities inferred from morphology, karyotype, and studies of interspecific hybridization. While all of the differences observed could have occurred over geological time, it was surprising that the genomes of the domestic chicken and the Red Jungle Fowl (Gallus gallus) differ in their sequence compositions. It appears that amplification/reduction events and/or positional changes occur rather often during evolution of a lineage.Abbreviations SDS sodium dodecyl sulphate - PB equimolar sodium phosphate buffer pH 6.8 - Cot concentration of DNA in moles of nucleotide per liter times the incubation time in seconds - Equiv. or Equivalent Cot Cot corrected for the monovalent cation concentration effect on re-association rate - HAP hydroxylapatite - Te_1/2 temperature at which one-half the DNA has eluted from HAP - SSC 0.15M sodium chloride-0.015M sodium citrate     

Genetic and biochemical implications of the endosymbiotic origin of the chloroplast

Summary The hypothesis stating that chloroplasts were derived from a photosynthetic procaryote is explored at a genetic and biochemical level. A transfer of genetic material from the endosymbiont to the nucleus of the host cell is proposed along with a corollary argument that the protein products of such transferred genes have remained specific to the chloroplast. This model provides an explanation for the presence of plastid-specific isozymes which are coded by nuclear DNA. It also suggests that the genome of the endosymbiont contributed the information necessary for the biosynthesis of carotenoids and the essential amino acids and the assimilation of nitrate-nitrogen and sulfate-sulfur. Animal cells lack these capabilities not because such were lost subsequent to the divergence of the plant and animal lines, but because animal cells did not become host to the appropriate symbionts. Additional implications of this thesis are discussed.     

Inter- and intra-genomic homology of the Brassica genomes: implications for their origin and evolution

In order to determine the homologous regions shared by the cultivated Brassica genomes, linkage maps of the diploid cultivated B. rapa (A genome, n = 10), B. nigra (B genome, n = 8) and B. oleracea (C genome, n = 9), were compared. We found intergenomic conserved regions but with extensitve reordering among the genomes. Eighteen linkage groups from all three species could be associated on the basis of homologous segments based on at least three common markers. Intragenomic homologous conservation was also observed for some of the chromosomes of the A, B and C genomes. A possible chromosome phylogenetic pathway based on an ancestral genome of at least five, and no more than seven chromosomes, was drawn from the chromosomal inter-relationships observed. These results demonstrate that extensive duplication and rearrangement have been involved in the formation of the Brassica genomes from a smaller ancestral genome.     

Gluteus maximus muscle function and the origin of hominid bipedality

Bipedality not only frees the hands for tool use but also enhances tool use by allowing use of the trunk for leverage in applying force and thus imparting greater final velocity to tools. Since the weight and acceleration of the trunk and forelimbs on the hindlimbs must be counteracted by muscles such as m. gluteus maximus that control pelvic and trunk movements, it is suggested that the large size of the cranial portion of the human gluteus maximus muscle and its unique attachment to the dorsal ilium (which is apparent in the Makapan australopithecine ilium) may have contributed to the effectiveness with which trunk movement was exploited in early hominid foraging activities. To test this hypothesis, the cranial portions of both right and left muscles were investigated in six human subjects with electromyography during throwing, clubbing, digging, and lifting. The muscles were found to be significantly recruited when the trunk is used in throwing and clubbing, initiating rotation of the pelvis and braking it as trunk rotation ceases and the forelimb accelerates. They stabilize the pelvis during digging and exhibit marked and prolonged activity when the trunk is maintained in partial flexion during lifting of heavy objects.     

Constraints on the wing morphology of pterosaurs

Animals that fly must be able to do so over a huge range of aerodynamic conditions, determined by weather, wind speed and the nature of their environment. No single parameter can be used to determine-let alone measure-optimum flight performance as it relates to wing shape. Reconstructing the wings of the extinct pterosaurs has therefore proved especially problematic: these Mesozoic flying reptiles had a soft-tissue membranous flight surface that is rarely preserved in the fossil record. Here, we review basic mechanical and aerodynamic constraints that influenced the wing shape of pterosaurs, and, building on this, present a series of theoretical modelling results. These results allow us to predict the most likely wing shapes that could have been employed by these ancient reptiles, and further show that a combination of anterior sweep and a reflexed proximal wing section provides an aerodynamically balanced and efficient theoretical pterosaur wing shape, with clear benefits for their flight stability.     

An atomic model of actin filaments cross-linked by fimbrin and its implications for bundle assembly and function

Actin bundles have profound effects on cellular shape, division, adhesion, motility, and signaling. Fimbrin belongs to a large family of actin-bundling proteins and is involved in the formation of tightly ordered cross-linked bundles in the brush border microvilli and in the stereocilia of inner ear hair cells. Polymorphism in these three-dimensional (3D) bundles has prevented the detailed structural characterization required for in-depth understanding of their morphogenesis and function. Here, we describe the structural characterization of two-dimensional arrays of actin cross-linked with human T-fimbrin. Structural information obtained by electron microscopy, x-ray crystallography, and homology modeling allowed us to build the first molecular model for the complete actin-fimbrin cross-link. The restriction of the arrays to two dimensions allowed us to deduce the spatial relationship between the components, the mode of fimbrin cross-linking, and the flexibility within the cross-link. The atomic model of the fimbrin cross-link, the cross-linking rules deduced from the arrays, and the hexagonal packing of actin bundles in situ were all combined to generate an atomic model for 3D actin-fimbrin bundles. Furthermore, the assembly of the actin-fimbrin arrays suggests coupling between actin polymerization, fimbrin binding, and crossbridge formation, presumably achieved by a feedback between conformational changes and changes in affinity.     

The origin of the animals and a ‘Savannah’ hypothesis for early bilaterian evolution

The earliest evolution of the animals remains a taxing biological problem, as all extant clades are highly derived and the fossil record is not usually considered to be helpful. The rise of the bilaterian animals recorded in the fossil record, commonly known as the ‘Cambrian explosion’, is one of the most significant moments in evolutionary history, and was an event that transformed first marine and then terrestrial environments. We review the phylogeny of early animals and other opisthokonts, and the affinities of the earliest large complex fossils, the so‐called ‘Ediacaran’ taxa. We conclude, based on a variety of lines of evidence, that their affinities most likely lie in various stem groups to large metazoan groupings; a new grouping, the Apoikozoa, is erected to encompass Metazoa and Choanoflagellata. The earliest reasonable fossil evidence for total‐group bilaterians comes from undisputed complex trace fossils that are younger than about 560 Ma, and these diversify greatly as the Ediacaran–Cambrian boundary is crossed a few million years later. It is generally considered that as the bilaterians diversified after this time, their burrowing behaviour destroyed the cyanobacterial mat‐dominated substrates that the enigmatic Ediacaran taxa were associated with, the so‐called ‘Cambrian substrate revolution’, leading to the loss of almost all Ediacara‐aspect diversity in the Cambrian. Why, though, did the energetically expensive and functionally complex burrowing mode of life so typical of later bilaterians arise? Here we propose a much more positive relationship between late‐Ediacaran ecologies and the rise of the bilaterians, with the largely static Ediacaran taxa acting as points of concentration of organic matter both above and below the sediment surface. The breaking of the uniformity of organic carbon availability would have signalled a decisive shift away from the essentially static and monotonous earlier Ediacaran world into the dynamic and burrowing world of the Cambrian. The Ediacaran biota thus played an enabling role in bilaterian evolution similar to that proposed for the Savannah environment for human evolution and bipedality. Rather than being obliterated by the rise of the bilaterians, the subtle remnants of Ediacara‐style taxa within the Cambrian suggest that they remained significant components of Phanerozoic communities, even though at some point their enabling role for bilaterian evolution was presumably taken over by bilaterians or other metazoans. Bilaterian evolution was thus an essentially benthic event that only later impacted the planktonic environment and the style of organic export to the sea floor.     

Correspondence of function and phylogeny of ABC proteins based on an automated analysis of 20 model protein data sets

Using our BLAST-based procedure RiPE (Retrieval-induced Phylogeny Environment), which automates the evolutionary analysis of a protein family, we assembled a set of 1138 ABC protein components [adenosine triphosphate (ATP)-binding cassette and transmembrane domain] from the protein data sets of 20 model organisms and subjected them to phylogenetic and functional analysis. For maximum speed, we based the alignment directly on a homology search with a profile of all known human ABC proteins and used neighbor-joining tree estimation. All but 11 sequences from Homo sapiens, Arabidopsis thaliana, Drosophila melanogaster, and Saccharomyces cerevisiae were placed into the correct subtree/subfamily, reproducing published classifications of the individual organisms. By following a simple "function transfer rule", our comparative phylogenetic analysis successfully predicted the known function of human ABC proteins in 19 of 22 cases. Three functional predictions did not correspond, and 10 were novel. Predictions based on BLAST alone were inferior in five cases and superior in two. Bacterial sequences were placed close to the root of most subtrees. This placement coincides with domain architecture, suggesting an early diversification of the ABC family before the kingdoms split apart. Our approach can, in principle, be used to annotate any protein family of any organism included in the study.     

Larval morphology of Panorpodes kuandianensis (Insecta,Mecoptera, Panorpodidae) and its evolutionary implications

Larval characters play a significant role in evolutionary and systematic studies of holometabolous insects. However, Panorpodidae, a derived family of Mecoptera, are largely unknown in their immature stages to date. Here, the first instar larva of the short-faced scorpionfly Panorpodes kuandianensis Zhong, Zhang & Hua, 2011 is described and illustrated using light and scanning electron microscopy. The larva of Panorpodes is remarkable for the absence of compound eyes on the head and the presence of seven small unpaired proleg-like processes along the midventral line on abdominal segments II–VIII. The homology of these unpaired appendage-like processes, their ecological adaptation, and the evolutionary implications of some larval characters of Panorpodidae are discussed.     

Systematic classification of CDR-L3 in antibodies: implications of the light chain subtypes and the VL-VH interface

Antibody modeling is widely used for the analysis of antibody-antigen interactions and for the design of potent antibody drugs. The antibody combining site is composed of six complementarity determining regions (CDRs). The CDRs, except for CDR-H3, which is the most diverse CDR, form limited numbers of canonical structures, which can be identified from the amino acid sequences. A method to classify the CDR-H3 structure from its amino acid sequence was previously proposed. However, since those CDR structures were classified, many more antibody crystal structures have been determined. We performed systematic analyses of the CDR-L3 structures and found novel canonical structures, and we also classified a previously identified canonical structure into two subtypes. In addition, two differently defined canonical structures in the kappa and lambda subtypes were classified into the same canonical structure. We also identified a key residue in CDR-L3, which determines the conformation of CDR-H3. Several analyses of CDR-L3 loops longer than nine residues were performed. These new findings should be useful for structural modeling and are eventually expected to accelerate the design of antibody drugs.     

RHR转录因子家族起源、功能以及进化机制的研究进展

转录因子是一类能够通过与基因特异性序列进行结合,从而调控基因转录与表达的蛋白质,对细胞的生物学活性具有重要的调节作用。RHR (Rel-homology region,RHR)转录因子家族属于IF (immunoglobulin fold)转录因子超家族最主要的成员,其成员含有保守的Rel结构域和IPT (immunoglobulin-like fold)结构域。作为古老的转录因子家族,RHR家族成员随着物种演化,通过基因的复制、突变和沉默,不断分化出新型同源基因的同时也伴随着基因的丢失。自然选择导致了各家族成员不同的进化速率,并且在一些功能结构域上展现出了特殊的进化机制。然而,目前有关RHR家族起源和分化的综述比较少见。本文综述了RHR家族各成员的分布、分类、功能及家族进化等方面的研究成果,以期为研究整个转录因子家族的演化机制和物种之间的进化关系提供参考和新的思路。