形态性状、分子性状与同源性

“同源性（homology）”是生物学中最基本的概念之一。近年来,随着分子生物学、生物信息学、发育生物学以及进化发育遗传学等学科的快速发展,同源性一词在形态性状的比较、核苷酸和氨基酸序列的分析以及探讨形态性状进化的分子机制等方面都有广泛应用。然而,由于不同的研究者对同源性概念的理解有所不同,在实际应用中难免会出现不恰当使用“同源性”一词并得出错误结论的情况。本文从不同的角度介绍了如何对同源性进行判断以及影响同源性判断的因素。并指出正确理解同源性这一概念的含义,以及通过综合各方面的证据对同源性进行推断对于揭示基因型和表型的进化以及二者之间的关系非常重要。     

形态性状、分子性状与同源性

“同源性(homology)”是生物学中最基本的概念之一。近年来, 随着分子生物学、生物信息学、发育生物学以及进化发育遗传学等学科的快速发展, 同源性一词在形态性状的比较、核苷酸和氨基酸序列的分析以及探讨形态性状进化的分子机制等方面都有广泛应用。然而, 由于不同的研究者对同源性概念的理解有所不同, 在实际应用中难免会出现不恰当使用“同源性”一词并得出错误结论的情况。本文从不同的角度介绍了如何对同源性进行判断以及影响同源性判断的因素。并指出正确理解同源性这一概念的含义, 以及通过综合各方面的证据对同源性进行推断对于揭示基因型和表型的进化以及二者之间的关系非常重要。     

Series of Pollen Morphology and Phylogeny of Angiosperms

Studies on angiosperm phylogeny have taken the characters of pollen grains into special account since good documentation on modern and fossil pollen morphology has become available. The diversified pollen types within angiosperms obey a limited number of evolutionary laws, and the successiformy and breviary are the most important morphological series. The successiformy is a evolutionary succession of pollen types: tricolpate-pericolpate-periporate, which is linked to spherical pollen grains. The terminal form of successiformy, periporate types, might have been derived through a different process. viz. the spiralization of apertures. The breviary consists of a series of tricolpate-oblate to tricolporate-triporate pollen types, which includes markedly oblate form and angular-aperturate pollen grains with a particularly short polar axis. The series of successiformy is found in taxa of the order Centrospermales and some taxa of the Rosidae and Asteridae, while the breviary is widespread in many Rosidae and Amentiferae. These morphological series have been otherwise proved in regard to the evolutionary direc-tions by the reliable fossil data.     

Molecules and Morphology,Phylogenetics and Genetics

Various explanations can be offered for the incongruence between phylogenetic hypotheses resulting from morphological and molecular data sets. Of these, the possibility that incongruence may result from the mutation of major morphogenetic genes leading to dramatic morphological divergence unaccompanied by equivalent change of the phylogenetic marker molecule(s) used is discussed in detail. As evidence for this hypothesis, several examples for such incongruence are surveyed. It seems possible that in many cases the genetic basis of the morphological characters responsible for the incongruence found may be simple, and that the genes involved may be homologous to genes known from mutant systems. It is suggested that: 1. the systematic documentation of incongruence between molecular and morphological phylogenies may help to assess the frequency of evolutionary change through the mutation of major morphogenetic genes, and that 2. the identification of major morphological characters distinguishing closely related taxa with mutant phenotypes known from mutant systems eventually may allow an experimental approach to the problem of evolutionary change resulting from major genes. Natural taxa suspected to be the result of such processes could be changed morphologically through transformation with the relevant genes.     

Evolution of Starfishes: Morphology, Molecules, Development, and Paleobiology. Introduction to the Symposium

Among starfishes, fascinating life cycles and complex morphologicalpatterns have evolved within a familiar but unusual basic bodyplan. In spite of these rich complexities, available phylogeneticinterpretations conflict, and the history of this importantgroup remains uncertain. The symposium brought together currentperspectives on phylogeny, the implications of certain poorlyknown aspects of asteroid morphology, and consideration of significantevents that preceded the diversification of extant asteroidgroups in the Mesozoic. It has become axiomatic in modern organismal biology that stronglysupported phylogenetic reconstructions are crucial to the understandingof biological pattern and progress. Although asteroids exhibitcomplex morphologies, life cycles, and behaviors that indicatetheir status as ideal model organisms in the study of marineinvertebrates, their evolutionary history remains obscure. Thisis in part due to a lack of treatment by researchers but alsoin part due to inherent limitations of the available data. In the following pages, the state of inquiry into the studyof relationships among starfishes is arranged in three sections:the nature of the fossil record (an introduction to modern starfishes),taxa and morphology, and phylogenetic interpretations.     

DNA and Morphology Unite Two Species and 10 Million Year Old Fossils

Species definition and delimitation is a non-trivial problem in evolutionary biology that is particularly problematic for fossil organisms. This is especially true when considering the continuity of past and present species, because species defined in the fossil record are not necessarily equivalent to species defined in the living fauna. Correctly assigned fossil species are critical for sensitive downstream analysis (e.g., diversification studies and molecular-clock calibration). The marine snail genus Alcithoe exemplifies many of the problems with species identification. The paucity of objective diagnostic characters, prevalence of morphological convergence between species and considerable variability within species that are observed in Alcithoe are typical of a broad range of fossilised organisms. Using a synthesis of molecular and morphometric approaches we show that two taxa currently recognised as distinct are morphological variants of a single species. Furthermore, we validate the fossil record for one of these morphotypes by finding a concordance between the palaeontological record and divergence time of the lineage inferred using molecular-clock analysis. This work demonstrates the utility of living species represented in the fossil record as candidates for molecular-clock calibration, as the veracity of fossil species assignment can be more rigorously tested.     

Molecular Data from the Chloroplast rpoC1 Gene Suggest a Deep and Distinct Dichotomy of Contemporary Spermatophytes into Two Monophyla: Gymnosperms (Including Gnetales) and Angiosperms

Partial sequences of the rpoC1 gene from two species of angiosperms and three species of gymnosperms (8330 base pairs) were determined and compared. The data obtained support the hypothesis that angiosperms and gymnosperms are monophyletic and none of the recent groups of the latter is sister to angiosperms. Received: 20 November 1998 / Accepted: 26 April 1999     

Angiosperms at the edge: Extremity,diversity, and phylogeny

A hallmark of flowering plants is their ability to invade some of the most extreme and dynamic habitats, including cold and dry biomes, to a far greater extent than other land plants. Recent work has provided insight to the phylogenetic distribution and evolutionary mechanisms which have enabled this success, yet needed is a synthesis of evolutionary perspectives with plant physiological traits, morphology, and genomic diversity. Linking these disparate components will not only lead to better understand the evolutionary parallelism and diversification of plants with these two strategies, but also to provide the framework needed for directing future research. We summarize the primary physiological and structural traits involved in response to cold- and drought stress, outline the phylogenetic distribution of these adaptations, and describe the recurring association of these changes with rapid diversification events that occurred in multiple lineages over the past 15 million years. Across these threefold facets of dry-cold correlation (traits, phylogeny, and time) we stress the contrast between (a) the amazing diversity of solutions flowering plants have developed in the face of extreme environments and (b) a broad correlation between cold and dry adaptations that in some cases may hint at deep common origins.     

Pollen, Mating and Paternity in Agamospermous Angiosperms

Abstract This review article deals with the male function in agamospermous plants, which is still not fully recognized. Of particular interest are mating and paternity problems. Pollen of agamospermous donors may influence female fitness in early mating phases by contributing the recognition substances or inducing spontaneous seed development. Various interactions between the sperm cell(s) and the female gametophyte at later phases may include (1) occasional double fertilization, (2) occasional syngamy, (3) pseudogamy, and (4) hemigamy. In the first two processes the offspring are sired normally. In pseudogamy, the offspring is maternal, the male contribution being restricted to endosperm paternity. In hemigamy, male function may include induction of the egg cell development only (maternal offspring), or the induction of the egg cell development as well as independent participation of the sperm cell in the offspring development leading to the formation of chimeras. It is concluded that the sperm may be a limiting resource in at least some agamospermous plants. Possible directions of future research are briefly outlined.     

Morphology,Molecules, and Monogenean Parasites: An Example of an Integrative Approach to Cichlid Biodiversity

The unparalleled biodiversity of Lake Tanganyika (Africa) has fascinated biologists for over a century; its unique cichlid communities are a preferred model for evolutionary research. Although species delineation is, in most cases, relatively straightforward, higher-order classifications were shown not to agree with monophyletic groups. Here, traditional morphological methods meet their limitations. A typical example are the tropheine cichlids currently belonging to Simochromis and Pseudosimochromis. The affiliations of these widespread and abundant cichlids are poorly understood. Molecular work suggested that genus and species boundaries should be revised. Moreover, previous morphological results indicated that intraspecific variation should be considered to delineate species in Lake Tanganyika cichlids. We review the genera Simochromis and Pseudosimochromis using an integrative approach. Besides a morphometric study and a barcoding approach, monogenean Cichlidogyrus (Platyhelminthes: Ancyrocephalidae) gill parasites, often highly species-specific, are used as complementary markers. Six new species are described. Cichlidogyrus raeymaekersi sp. nov., C. muterezii sp. nov. and C. banyankimbonai sp. nov. infect S. diagramma. Cichlidogyrus georgesmertensi sp. nov. was found on S. babaulti and S. pleurospilus, C. franswittei sp. nov. on both S. marginatus and P. curvifrons and C. frankwillemsi sp. nov. only on P. curvifrons. As relatedness between Cichlidogyrus species usually reflects relatedness between hosts, we considered Simochromis monotypic because the three Cichlidogyrus species found on S. diagramma belonged to a different morphotype than those found on the other Simochromis. The transfer of S. babaulti, S. marginatus, S. pleurospilus and S. margaretae to Pseudosimochromis was justified by the similarity of their Cichlidogyrus fauna and the intermediate morphology of S. margaretae. Finally parasite data also supported the synonymy between S. pleurospilus and S. babaulti, a species that contains a large amount of geographical morphological variation.     

Fossils, molecules, divergence times, and the origin of lissamphibians

A review of the paleontological literature shows that the early dates of appearance of Lissamphibia recently inferred from molecular data do not favor an origin of extant amphibians from temnospondyls, contrary to recent claims. A supertree is assembled using new Mesquite modules that allow extinct taxa to be incorporated into a time-calibrated phylogeny with a user-defined geological time scale. The supertree incorporates 223 extinct species of lissamphibians and has a highly significant stratigraphic fit. Some divergences can even be dated with sufficient precision to serve as calibration points in molecular divergence date analyses. Fourteen combinations of minimal branch length settings and 10 random resolutions for each polytomy give much more recent minimal origination times of lissamphibian taxa than recent studies based on a phylogenetic analyses of molecular sequences. Attempts to replicate recent molecular date estimates show that these estimates depend strongly on the choice of calibration points, on the dating method, and on the chosen model of evolution; for instance, the estimate for the date of the origin of Lissamphibia can lie between 351 and 266 Mya. This range of values is generally compatible with our time-calibrated supertree and indicates that there is no unbridgeable gap between dates obtained using the fossil record and those using molecular evidence, contrary to previous suggestions.     

Early Cretaceous Angiosperms of the Yanji Basin,Jilin Province

An assemblage of fossil plants was discovered in the Yanji Basin, Jitin Province, consisting mainly of pterid0Phytes, gymnosperms and a few angiosperms. The present paper deals with the angiosperms only; They are: Rogersia angunifolia, Saliciphyllum longifoliurn, Sapindopsis magnifolia, Sterculophyllurn eleganurn, ,Ficophyllum, "Sassafras", Ranunculophyllum pinnatisectum sp. nov., Clernatites lanceolatus sp. nov., and the fruits Carpolithus brookensis, Carpolithus sp. gymnosperm Sequoia as well, all angiosperms having the morphological features of early angiosperms. Most of them are similar to the elements of the Potomac Group in North America and to some extent approach the fossil plants of Neocomian in Mongolia. This assemblage is manifestly different from the Albian flora of Kolyma River (URSS) and Portugal of Europe because of belonging to different stages. Thus, the age of the Dalazi Formation of Yanji Basin is tentatively ascribed to Aptian. The characteristics of this assemblage indicate that the floras of Eurasia and North America had been closely related during the early Mid-Cretaceous and that the early angiosperms were widely distributed in the North Hemisphere. Judging from the characteristics of this assemblage and the deposition, the authors speculate that in Northeast China the climate was warm and humid during the early Mid-Cretaceous.     

The Relationship Between Adhesion Molecules and Neuronal Plasticity

1. It is presently widely assumed that structural reorganization of synaptic architectures subserves the functional gains that define certain neuronal plasticities.2. While target molecules thought to participate in such morphological dynamics are not well defined, growing evidence suggests a pivotal role for cell adhesion molecules.3. Herein, brief discussions are presented on (i) the history of how adhesion molecules became implicated in plasticity and memory processes, (ii) the general biology of some of the major classes of such molecules, and (iii) the future of the adhesion molecule/plasticity relationship.