摘要:

SummaryIn animals, adaptive radiation at the level of species is based to a large extent upon adaptations to survival in different climates, as well as to the occupation of different ecological niches in similar communities. In plants, adaptive radiation at the species level, as well as the origin of higher categories, depends to a large extent upon diversification of the methods of reproduction, both pollination and seed dispersal, as well as seed germination and the establishment of seedlings. With respect to the latter, evolutionary success depends to a large extent upon solution of three often conflicting problems: protection of the developing seed, dispersal to a new but similar location; and germination with sufficient seedling vigor to survive competition. In plants, the origin of higher categories is not associated with the appearance of distinctive characters that never serve to distinguish species. Evolutionary progress, here regarded as an increase in the amount and diversity of DNA‐coded information, is based upon the bias in favor of mutations that increase rather than reduce the amount of genetic information already present.

ISSN:0040-0262    

DOI:10.2307/1218529

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryBorn over 200 years ago the science of anthecology (pollination ecology) has developed new concepts in the last 50 years using quantified information from studies of insect sense perception and behavior. Flower‐insect coadaptation is considered a continuing process in which changing interrelationships establish and remove reproductive barriers in breeding systems at the vital link of pollen transport. Convergent evolution is apparently reflected in the development of similar pollination mechanisms in unrelated plant taxa through pollinator sharing, floral mimicry, and synchronous anthesis of sympatric species. Reproductive isolation of plant taxa is suggested in diversity and versatility of pollinator behavior, unsynchronized anthesis, and functional as well as structural differences in pollination mechanisms. Contributions of anthecology to systematics are primarily useful for a fuller understanding of the origin of taxonomic entities and secondarily in defining criteria for their establishment.

ISSN:0040-0262    

DOI:10.2307/1218530

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryPolyploidy played a significant role in the origin and evolution of many plant species. The primary phylogenetic effect of polyploidy is to stabilize selected hybrid genotypes. It also provides a mechanism by which daughter and parental populations become immediately isolated from each other. Isolation, however, is rarely complete, and introgression commonly takes place across partially sterile hybrids. Polyploidy also buffers genotypes against the shock of absorbing foreign genomes, making hybridization possible between species that are otherwise genetically isolated from each other. Traditional taxonomy can usually not adequately indicate the extent of variability that characterize polyploid complexes.

ISSN:0040-0262    

DOI:10.2307/1218531

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryPhenotypic variation is as poorly understood as it is ubiquitous. Many biologists hold simplistic and even contradictory views of the relation between genic diversity and phenotypic variation. The correlation of electrophoretically detectable enzyme polymorphisms and morphological variation in island populations of lizards is described. A model explaining the different levels of genetic‐phenetic variation among the populations is suggested by a multiple regression analysis. The principal conclusions are that gene flow between habitats significantly elevates variation, and isolation by distance results in a variation asymptote.

ISSN:0040-0262    

DOI:10.2307/1218532

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryAn outline of evolutionary developmental and genetic mechanisms and relations as evidenced by the comparative study of amino acid sequences, mainly of eukaryotic cytochromesc.

ISSN:0040-0262    

DOI:10.2307/1218533

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryRecent investigations on gene variation as revealed by electrophoresis of proteins show that in mice, man andDrosophila, 30–40% of the loci are polymorphic and 7–12% of the loci are in a heterozygous state in an individual. Populations ofD. pseudoobscurafrom ecological margins are as heterozygous as those in the center and the allele frequencies are very similar in all the populations except in Bogota, Colombia, which is a complete isolate from the main body of the species. The Bogota population ofD. pseudoobscurahas reduced genetic variation and when Bogota females are mated to males of various populations from the United States and Guatemala, the F1males are sterile and the F1females are fertile. The reciprocal cross produces fertile hybrids of both sexes. Founder effect and lack of gene flow from other populations is a very important aspect of speciation. When two closely related sibling speciesD. pseudoobscuraandD. persimilisare compared for genetic changes at 24 homologous loci, it is found that no locus is monomorphic or polymorphic for entirely different alleles, however, at several polymorphic loci, the two species have unique alleles in addition to the similar alleles.

ISSN:0040-0262    

DOI:10.2307/1218534

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryCertain structural changes have occurred repeatedly in the evolution of flowering plants. Evidence for these evolutionary trends is often in the form of character gradients or morphoclines, within which the direction of change can be inferred from paleobotanical, geographical, or ecological circumstances. No trends are more firmly established than those involving microscopic characters of the secondary xylem, trends for which the ancestral condition is known from fossil evidence. Recently, trends in the evolution of angiospermous pollen grains have also been convincingly demonstrated from the fossil record. Since postulated evolutionary trends in floral structure cannot be verified in the same manner, floral anatomy has always been a controversial subject. Despite the controversy, the anatomical investigation of flowers benefits systematics in at least two ways: by revealing characters of potential taxonomic value and, when floral vascular bundles of related taxa are united in varying degree, by indicating the direction of evolutionary change.

ISSN:0040-0262    

DOI:10.2307/1218535

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryThe study of functional anatomy, biological roles of features, and adaptations is not a practical starting point for establishing a classification but the concepts derived from such studies may be powerful tools in solving difficult taxonomic problems. They also serve to modify or corroborate classifications and to make them biologically meaningful. The functional approach may be used at any taxonomic level. The biological species definition provides an important base line for comparison with other categories. Functional anatomy may play a role in ranking taxa into a hierarchy through its contribution to recognition of key adaptations, adaptive radiation, parallel evolution, convergent evolution, determining the direction of evolution, and determining the most closely related group. Ultimately we may understand the hierarchy of adaptations that forms the basis for natural groupings of organisms.

ISSN:0040-0262    

DOI:10.2307/1218536

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummaryA brief outline is given of the principal types of multivariate statistical techniques which have found use in taxonomy. Techniques such as correlation, principal components, canonical correlation, and factor analyses are described for problems dealing with analysis of covariation within a single sample. Techniques such as canonical variate, cluster, multidimensional scaling, and network analyses are described for dealing with analyses of among sample variation. The purpose of this account is to give an intuitive understanding of what the various techniques have to offer to research in taxonomy.

ISSN:0040-0262    

DOI:10.2307/1218537

出版商:Wiley    

年代:2019

数据来源: WILEY

摘要:

SummarySympatric congeneric species of flowering plants are precluded from freely exchanging genes by reproductive barriers which are operative prior to pollination, between pollination and fertilization and after fertilization. The barriers may be the by‐products of divergent evolution, or may have been selected for their ability to reduce hybridization and disruptive gene flow, or competition for similar elements of the pollinator fauna. Autogamy and hybrid floral isolation are included in a classification of reproductive isolating barriers. The origin of reproductive barriers is discussed in light of new information and insight on pollinator behavior and perception, the S‐gene complex, pollen‐tube competition, and population level selection. It is suggested that reproductive barriers are not inherent properties of species, but reside in the interface between species, and arise from the incongruities in the reproductive formats of species paired in nature or by the systematist.

ISSN:0040-0262    

DOI:10.2307/1218538

出版商:Wiley    

年代:2019

数据来源: WILEY