Patterning mechanisms in the body trunk and the appendages of Drosophila.

During evolution, many animal groups have developed specialised outgrowths of the body wall, limbs or appendages. The type of appendage depends on the identity of the segment where they appear, indicating that the Hox genes contribute to appendage specification. Moreover, work carried out principally in Drosophila has identified the gene products and the mechanisms involved in pattern formation in the appendages. In this essay, we compare the morphogenetic processes in the appendages and the body wall; the function of the Hox genes and the response to the signalling molecules involved in local patterning. We speculate that, although the basic mechanisms are similar, there are significant differences in the manner the body trunk and appendages respond to them.     

调控进化与形态多样性

揭示导致生物体形态和结构多样性产生的原因和机制, 是进化生物学研究的重要内容。进化发育生物学的研究表明, 许多复杂的形态结构及其多样性, 都是通过对古老调控网络的修饰或改造来完成的。也就是说, 生物体形态和结构的多样化并不是像以前认为的是由基因编码区的变化造成的, 而更多的是取决于基因的调控进化。作为控制基因表达的关键组分, 基因调控区的顺式调控元件通过与特定反式作用因子结合, 精细调控基因表达的时、空和量。因此, 调控元件的获得、丢失、修饰或者改变都能引起基因表达模式的变化, 是形态和结构多样性产生的主要原因。本文结合近年来国际上在基因的调控进化方面所取得的进展, 总结了真核生物中基因调控的方式和特点, 阐述了调控进化的基本式样, 揭示了调控进化在生物进化(特别是形态和结构多样化)中的作用。     

The importance of mechanisms for the evolution of cooperation

Studies aimed at explaining the evolution of phenotypic traits have often solely focused on fitness considerations, ignoring underlying mechanisms. In recent years, there has been an increasing call for integrating mechanistic perspectives in evolutionary considerations, but it is not clear whether and how mechanisms affect the course and outcome of evolution. To study this, we compare four mechanistic implementations of two well-studied models for the evolution of cooperation, the Iterated Prisoner''s Dilemma (IPD) game and the Iterated Snowdrift (ISD) game. Behavioural strategies are either implemented by a 1 : 1 genotype–phenotype mapping or by a simple neural network. Moreover, we consider two different scenarios for the effect of mutations. The same set of strategies is feasible in all four implementations, but the probability that a given strategy arises owing to mutation is largely dependent on the behavioural and genetic architecture. Our individual-based simulations show that this has major implications for the evolutionary outcome. In the ISD, different evolutionarily stable strategies are predominant in the four implementations, while in the IPD each implementation creates a characteristic dynamical pattern. As a consequence, the evolved average level of cooperation is also strongly dependent on the underlying mechanism. We argue that our findings are of general relevance for the evolution of social behaviour, pleading for the integration of a mechanistic perspective in models of social evolution.     

Variations in the sequences of BMP2 imply different mechanisms for the evolution of morphological diversity in vertebrates

Bone morphogenetic protein 2 (BMP2) plays an important role in skeletogenesis, osteoblastic differentiation and limb patterning. Its protein coding region consists of the signal peptide, the pro-domain (that regulates post-translational control of synthesis) and the mature domain (that carries out gene function). This gene has been considered previously to be conserved. By re-analyzing the coding region of BMP2 in 31 species of vertebrates, we found that the mature domain region is indeed conserved in mammals, but not among non-mammalian taxa. Moreover, compared to the mature domain, the signal peptide and pro-domain have experienced dramatic variation in all vertebrates. Six amino acid sites in the pro-domain were identified to be under diversifying Darwinian selection in mammals. These results indicate that the signal peptide and pro-domain of BMP2 may be involved in skeletal poly-morphology during mammal evolution and the mature domain may also contribute to this function in non-mammals. This supports the hypothesis that morphological variations in mammals result mainly from a change in post-translational control of synthesis, whereas in non-mammals they result mainly from gene functional change.     

CO2 concentrating mechanisms in cyanobacteria: molecular components,their diversity and evolution

Cyanobacteria have evolved an extremely effective single-cell CO(2) concentrating mechanism (CCM). Recent molecular, biochemical and physiological studies have significantly extended current knowledge about the genes and protein components of this system and how they operate to elevate CO(2) around Rubisco during photosynthesis. The CCM components include at least four modes of active inorganic carbon uptake, including two bicarbonate transporters and two CO(2) uptake systems associated with the operation of specialized NDH-1 complexes. All these uptake systems serve to accumulate HCO(3)(-) in the cytosol of the cell, which is subsequently used by the Rubisco-containing carboxysome protein micro-compartment within the cell to elevate CO(2) around Rubisco. A specialized carbonic anhydrase is also generally present in this compartment. The recent availability of at least nine cyanobacterial genomes has made it possible to begin to undertake comparative genomics of the CCM in cyanobacteria. Analyses have revealed a number of surprising findings. Firstly, cyanobacteria have evolved two types of carboxysomes, correlated with the form of Rubisco present (Form 1A and 1B). Secondly, the two HCO(3)(-) and CO(2) transport systems are distributed variably, with some cyanobacteria (Prochlorococcus marinus species) appearing to lack CO(2) uptake systems entirely. Finally, there are multiple carbonic anhydrases in many cyanobacteria, but, surprisingly, several cyanobacterial genomes appear to lack any identifiable CA genes. A pathway for the evolution of CCM components is suggested.     

The origin and evolution of appendages

Current awareness of gene expression patterns and developmental mechanisms involved in the outgrowth and patterning of animal appendages contributes to our understanding of the origin and evolution of these body parts. Nevertheless, this vision needs to be complemented by a new adequate comparative framework, in the context of a factorial notion of homology. It may even be profitable to categorize as appendages also gut diverticula, body ingrowths and 'virtual appendages' such as the eye spots on butterfly wings. Another unwarranted framework is the Cartesian co-ordinate system onto which the appendages are currently described and where it is supposed that one patterning system exists for each separate Cartesian axis. It may be justified, instead, to look for correspondences between the appendages and the main body axis of the same animal, as the latter might be the source of the growth and patterning mechanisms which gave rise to the former. This hypothesis of axis paramorphisms is contrasted with the current hypothesis of gene co-option. Recapitulationism is a common fault in current Evo-Devo perspectives concerning the origin of the appendages, in that the evolutionary origin of appendages is often expected to be the same as one of the key mechanisms involved in the ontogenetic inception of appendage formation. This unwarranted perspective is also evident in the current debate on the nature of the default arthropod appendage. Most likely, a default arthropod appendage never did exist, as the first appendages probably developed along the trunk of an animal already patterned extensively along the antero-posterior body axis.     

Axonal terminals of sensory neurons and their morphological diversity

The application of electron microscopy to defining the fine structural characteristics of axon terminals and synapses was followed by a half century of intensive exploration of the molecular concomitants of synaptic activity. The summer of 2003 marks the 50th anniversary of the earliest accounts of synapses by Palay and Palade. Prompted by recent findings of specialization in the fine structure of nociceptor terminals that lack contacts remotely resembling a synapse, we present a survey of arrangements, contacts and axoplasmic contents of peripheral sensory axon terminals. The morphological principles underlying the variety of small, clear, spherical vesicles, mitochondrial aggregation, the membrane thickenings associated with sensory terminals and the organelles or inclusions associated with the site of transduction apparently do not conform to a simple parsimonious rule. It is also evident that the terminal of the central branch of bifurcated sensory axons differs structurally from its distal counterparts. This brief illustrated account addresses some important unresolved problems in the functional interpretation of the diverse morphological features exhibited in both synaptic and non-synaptic sensory axon terminals with the aim of identifying and emphasizing some key questions amenable to resolution with contemporary morphological and physiological techniques.     

Major clades of parmelioid lichens (Parmeliaceae, Ascomycota) and the evolution of their morphological and chemical diversity

Parmelioid lichens comprise about 1500 species and have a worldwide distribution. Numerous species are widely distributed and well known, including important bioindicators for atmospheric pollution. The phylogeny and classification of parmelioid lichens has been a matter of debate for several decades. Previous studies using molecular data have helped to establish hypotheses of the phylogeny of certain clades within this group. In this study, we infer the phylogeny of major clades of parmelioid lichens using DNA sequence data from two nuclear loci and one mitochondrial locus from 145 specimens (117 species) that represent the morphological and chemical diversity in these taxa. Parmelioid lichens are not monophyletic; however, a core group is strongly supported as monophyletic, excluding Arctoparmelia and Melanelia s. str., and including Parmeliopsis and Parmelaria. Within this group, seven well-supported clades are found, but the relationships among them remain unresolved. Stochastic mapping on a MC/MCMC tree sampling was employed to infer the evolution of two morphological and two chemical traits believed to be important for the evolutionary success of these lichens, and have also been used as major characters for classification. The results suggest that these characters have been gained and lost multiple times during the diversification of parmelioid lichens.     

Patterning of the branched head appendages in Schistocerca americana and Tribolium castaneum

Much of our understanding of arthropod limb development comes from studies on the leg imaginal disc of Drosophila melanogaster. The fly limb is a relatively simple unbranched (uniramous) structure extending out from the body wall. The molecular basis for this outgrowth involves the overlap of two signaling molecules, Decapentaplegic (Dpp) and Wingless (Wg), to create a single domain of distal outgrowth, clearly depicted by the expression of the Distal-less gene (Dll). The expression of wg and dpp during the development of other arthropod thoracic limbs indicates that these pathways might be conserved across arthropods for uniramous limb development. The appendages of crustaceans and the gnathal appendages of insects, however, exhibit a diverse array of morphologies, ranging from those with no distal elements, such as the mandible, to appendages with multiple distal elements. Examples of the latter group include branched appendages or those that possess multiple lobes; such complex morphologies are seen for many crustacean limbs as well as the maxillary and labial appendages of many insects. It is unclear how, if at all, the known patterning genes for making a uniramous limb might be deployed to generate these diverse appendage forms. Experiments in Drosophila have shown that by forcing ectopic overlaps of Wg and Dpp signaling it is possible to generate artificially branched legs. To test whether naturally branched appendages form in a similar manner, we detailed the expression patterns of wg, dpp, and Dll in the development of the branched gnathal appendages of the grasshopper, Schistocerca americana, and the flour beetle, Tribolium castaneum. We find that the branches of the gnathal appendages are not specified through the redeployment of the Wg-Dpp system for distal outgrowth, but our comparative studies do suggest a role for Dpp in forming furrows between tissues.     

The spermatozoon of Eurasian murine rodents: Its morphological diversity and evolution

The murine rodents are the most speciose subfamily of mammals. Here the morphology of the spermatozoon, as determined by scanning and transmission electron microscopy of representative species from four Eurasian clades, is described. Much interspecific variability in all components of the spermatozoon was found to occur, although most species have a bilaterally flattened sperm head with a single apical hook of variable length and orientation. Ultrastructural observations indicate that this apical hook invariably contains a nuclear projection as well as a large extension of the subacrosomal cytoskeleton, as a perforatorium rostrally, and a complex asymmetrical acrosomal extension. These spermatozoa also have relatively long tails that are attached to the lower concave surface of the sperm head. Uniquely, in species in the Apodemus clade, the apical hook is orientated caudally. In a few species a highly derived sperm head morphotype that does not contain an apical hook is present. These sperm heads vary in morphology from being globular in two species of Bandicota, to bilaterally flattened and paddle-shaped in Tokudaia and Micromys. In spermatozoa of the latter two genera the subacrosomal cytoskeleton, which is less extensive than in species with a hooked sperm head, forms an apical extension, but that is not the case in Bandicota. In all species where the sperm head lacks an apical hook the acrosome is more symmetrical. The sperm tail is much shorter in these species, with attachment to the head occurring on the ventral surface in Tokudaia and basal in Micromys and the two species of Bandicota. As the sperm head morphotype with a complex apical hook is present in all the major clades of murine rodents, it is likely to be a plesiomorphic character within each of these clades, with the nonhooked sperm heads, which vary greatly in structure between species of the different lineages, probably being independently derived. The ultrastructural organization of the sperm head of Bandicota, but not those of Micromys or Tokudaia, suggest divergence in some of the morphological events associated with sperm-egg interaction at the time of fertilization.     

The evolution of morphological diversity in continental assemblages of passerine birds

Understanding geographic variation in the species richness and lineage composition of regional biotas is a long‐standing goal in ecology. Why do some evolutionary lineages proliferate while others do not, and how do new colonists fit into an established fauna? Here, we analyze the morphological structure of assemblages of passerine birds in four biogeographic regions to examine the relative influence of colonization history and niche‐based processes on continental communities of passerine birds. Using morphological traits related to habitat choice, foraging technique, and movement, we quantify the morphological spaces occupied by different groups of passerine birds. We further quantify morphological overlap between groups by multivariate discriminant analysis and null model analyses of trait dispersion. Finally, we use subclade disparity through time to assess the temporal component of morphological evolution. We find mixed support for the prediction, based on priority, that first colonizers constrain subsequent colonizers. Indeed, our results show that the assembly of continental communities is idiosyncratic with regards to the diversification of new clades and the filling of morphospace.     

Insect duets: underlying mechanisms and their evolution

Abstract. Duetting between the sexes in insects involves the use of airborne acoustic signals, substrate vibration and bioluminescence. Unlike avian duets, in which females may initiate the interaction, among insects the duet starts with the male, and the female usually provides a brief reply. Insect duets are characterized by low variance in the reply latency of the female (the time between a key element in the male call and the onset of the female's response). Duetting is reviewed principally in Orthoptera but also in Plecoptera, Hemiptera, Neuroptera and bioluminescence in the Coleoptera. The mechanisms of the duet are examined first, followed by evolution and the associated change in searching strategies of each sex. As defined, the duet has distinct temporal characteristics and these are compared with acoustic interactions among males in those species that exhibit male–male synchrony and alternation. For insects, the key element of a duet for species' recognition is low variance in the reply latency of females. In cases in which the male's initiating signal is extremely short, reply latencies become indicators of species' recognition. However, in those species in which the initiating male call is under selection through female choice, the male call is predictably longer and occasionally more complex. Under these circumstances, reply latencies often increase, creating an opportunity for alternative male tactics. When alternative tactics exist in nature, males may decrease the intensity of their call, insert a trigger pulse that signals to the female the end of its complex call, or males may even add a masking signal that obscures the competing signal.     

Phylogenetic relationships and morphological diversity in Darwin's finches and their relatives

Despite the importance of Darwin's finches to the development of evolutionary theory, the origin of the group has only recently been examined using a rigorous, phylogenetic methodology that includes many potential outgroups. Knowing the evolutionary relationships of Darwin's finches to other birds is important for understanding the context from which this adaptive radiation arose. Here we show that analysis of mitochondrial DNA sequence data from the cytochrome b gene confirm that Darwin's finches are monophyletic. In addition, many taxa previously proposed as the sister taxon to Darwin's finches can be excluded as their closest living relative. Darwin's finches are part of a well-supported monophyletic group of species, all of which build a domed nest. All but two of the non-Darwin's finches included in this clade occur on Caribbean islands and most are Caribbean endemics. These close relatives of Darwin's finches show a diversity of bill types and feeding behaviors similar to that observed among Darwin's finches themselves. Recent studies have shown that adaptive evolution in Darwin's finches occurred relatively quickly. Our data show that among the relatives of Darwin's finches, the evolution of bill diversity was also rapid and extensive.     

Molecular diversity of spider venom

Spider venom, a factor that has played a decisive role in the evolution of one of the most successful groups of living organisms, is reviewed. Unique molecular diversity of venom components including substances of variable structure (from simple low molecular weight compounds to large multidomain proteins) with different functions is considered. Special attention is given to the structure, properties, and biosynthesis of toxins of polypeptide nature.     

更新世中期中国古人类演化区域连续性与多样性的化石证据

以往,在东亚大陆发现的更新世中期人类化石被分别归入直立人和古老型智人。这种分类的主要依据是化石形态特征以及年代。魏敦瑞对周口店第一地点人类化石研究描述的一些头骨、下颌骨和牙齿特征通常被作为判定直立人的标准。根据这些化石的年代分布,一般将30万年前的中更新世晚期作为划分直立人与古老型智人的大致年代界限。近20年来,在非洲、欧洲和东亚新发现了一些更新世中期人类化石,目前古人类学界对中国更新世中期人类化石特征及演化有了与以往不同的认识。最近对大荔、许家窑、盘县大洞、许昌、华龙洞等人类化石的研究显示,近30万年以来东亚大陆人类演化呈现复杂的多样性,将这一时期人类全部归入古老型智人难以准确反映更新世中期中国古人类演化模式及规律。本文结合近年中国更新世中期人类演化研究进展,选择部分具有演化及分类价值的形态特征,分析这些特征在更新世中期中国古人类化石的表现特点。在此基础上,对更新世中期中国古人类演化模式做了尝试性探讨。本研究发现,周口店、和县、沂源、南京等中更新世早期人类化石呈现有较多的区域性特征,形态特征表现相对稳定;而大荔、金牛山、许家窑、许昌、华龙洞、马坝、盘县大洞等中更新世晚期人类在化石形态特征表现复杂多样,变异范围大。此外,在这一时期人类化石上发现较多与生存活动、健康、环境适应有关的证据。根据这些发现,作者认为中国中更新世早期组人类演化以形态连续性为主;进入中更新世晚期,中国古人类演化区域性特征减弱,演化模式以多样性为主。一系列新的化石发现和研究证据提示中更新世晚期东亚大陆可能生存有不同的古人类成员。根据目前掌握的化石形态和年代证据,大约30万年前是中国更新世中期演化变化关键时间节点。     

基因及其顺式调控元件在动物表型进化中的作用

顺式调控假说是当前进化发育生物学中重要的理论之一, 该假说认为顺式调控元件的进化是调控外表性状进化的主要遗传机制。然而越来越多的实验结果表明, 仅靠顺式调控假说远不足以解释复杂的进化发育过程, 其他因素也会导致表型的进化, 如：与顺式调控元件相联基因的蛋白序列改变; 基因及染色体组复制; 蛋白结构域与顺式调控元件的灵活性等。文章回顾了近年来顺式调控元件以及与顺式调控元件相联基因的进化发育研究, 探讨了进化发育生物学研究的新方法与新思路。     

The evolution of segmentation of centipede trunk and appendages

The segmentation of centipedes is interpreted in the light of a biphasic model of segmentation (holomeric plus meromeric). The mid-body anomaly (e.g. in the alternating short and long terga, or in the sequence of segments with and without spiracles) is regarded as due to an early patterning of the embryo, occurring before the onset of meromeric segmentation and affecting a level within the fourth eosegment of the trunk. Comparisons with the Diplopoda suggest that genital structures such as millipede gonopods did probably develop originally at this spot, whose position remained marked even after the transition from a putatively progoneate to the current opisthogoneate condition of centipedes, perhaps following gene duplication and divergence of expression patterns of the paralogues. A new lower limit for the number of leg-bearing segments [27, in a male specimen of Schendylops oligopus (Pereira, Minelli & Barbieri,1995)] is established for Geophilomorpha. Coevolutionary trends involving the segmentation of the trunk, the segmentation of the appendages (especially the antennae), the postembryonic developmental schedule and the presence or absence of regeneration ability supports a recent view of the appendages as evolutionarily divergent duplicates of the main body axis.     

Characterization of mouse sialyltransferase genes: their evolution and diversity

Sialic acids are negatively charged acidic sugars, and sialylglycoconjugates often play important roles in various biological phenomena. Sialyltransferases are involved in the synthesis of sialylglycoconjugates, and 20 members of the mammalian sialyltransferase family have been identified to date. These sialyltransferases are grouped into four families according to the carbohydrate linkages they synthesize: beta-galactoside alpha2,3-sialyltransferases (ST3Gal I-VI), beta-galactoside alpha2,6-sialyltransferases (ST6Gal I and II), GalNAc alpha2,6-sialyltransferases (ST6GalNAc I-VI), and alpha2,8-sialyltransferases (ST8Sia I-VI). Analysis of the amino acid sequence similarities, substrate specificities, and gene structures of mouse sialyltransferases has revealed that they can be further divided into seven subfamilies. The genomic structural resemblance of members of the same subfamily suggests that they arose from a common ancestral gene through gene duplication events. These multiple sialyltransferase genes are needed for fine control of the expression of sialylglycoconjugates, resulting in a variety of developmental stage- and tissue-specific glycosylation patterns.     

The origin,patterning and evolution of insect appendages

The appendages of the adult fruit fly and other insects and Arthropods develop from secondary embryonic fields that form after the primary anterior/posterior and dorsal/ventral axes of the embryo have been determined. In Drosophila, the position and fate of the different fields formed within each segment are determined by genes acting along both embryonic axes, within individual segments, and within specific fields. Since the major architectural differences between most Arthropod classes and orders involve variations in the number, type and morphology of body appendages, the elucidation of the embryology and molecular genetics of the origin and patterning of insect limb fields may help to facilitate an understanding of both the mechanism of appendage formation and some of the major steps in the morphological evolution of the Arthropods. In this review, we will discuss recent studies that have advanced our understanding of both the origin and patterning of Drosophila leg and wing secondary fields. These results provide fresh insights into potentially general mechanisms of how body parts develop and evolve.