Morphological Discontinuities Research Articles

Characterization of Ferroelectric SrBi2Ta2 O 9 Thin Films Prepared from Alkoxide Solutions

thin films prepared by chemical liquid deposition using alkoxide precursor solutions, followed by annealing at various temperatures, were characterized with a focus on the correlation between composition, microstructure, and ferroelectric properties. P-E hysteresis loops of the films exhibited well‐defined shapes at temperatures above 700°C, and the leakage current decreased with increasing annealing temperature, except for a film annealed at 4750°C. The crystal growth proceeded and ferroelectric properties of the films improved with increasing annealing temperature, whereas a large leakage current was observed for the film annealed at 750°C. Quantitative X‐ray photoelectron specroscopic analysis and high‐resolution transmission electron microscopic observation indicated the presence of a substantial amount of metallic bismuth in all films, predominantly in microcrystallite regions and on film surfaces, including the inner surface of cavities. The atomic fraction of metallic bismuth increased upon slight argon etching; however, the total bismuth content was significantly reduced. The metallic bismuth was amorphous and detected as vibrating spherical particles measuring approximately 5 nm under electron irradiation. The discontinuity in morphology, such as cavities at the interface between large single‐crystal grains and microcrystallite regions, was most remarkable in the film annealed at 750°C. The condensation of metallic bismuth at the cavities is believed to increase the leakage current when the path formed by cavities penetrates through the film. © 1999 The Electrochemical Society. All rights reserved.

The arrested gravel front: stable gravel-sand transitions in rivers Part 1: Simplified analytical solution

Most rivers exhibit a tendency for the characteristic size of'the bed material to become finer in the downstream direction. In addition, most river sediments also exhibit a paucity of material in the pea gravel range. Because of this paucity the transition in the downstream direction from a gravel-bed stream to a sand-bed stream is usually rather abrupt, and is often marked by a discontinuity in bed slope and stream morphology as well. If the front marking the gravel-sand transition is not to prograde continuously in the direction of the point at which base level is established, e.g. the ocean, then some mechanism must operate to arrest it in place. Here two such mechanisms are examined; abrasion of gravel and basin subsidence (or alternatively base level rise). It is found that either one or a combination of the two can act to stabilize the spatial location of the gravel-sand transition. The present paper is devoted to a simplified analytical solution to the problem that renders the structure of the formulation relatively transparent. A complete numerical solution that more realistically describes the field manifestation is presented in a companion paper.

Morphological variation of Emoia murphyi (Lacertilia: Scincidae) on islands of the southwest Pacific

We examined variation in measurements and scalation of 114 specimens of Murphy's tree skink Emoia murphyi from five island groups of the southwest Pacific. In the largest sample (Niuafo'ou) males were significantly longer than females. Populations from Futuna, Samoa, Niuafo'ou, Vava'u and Ha'apai showed little morphological divergence, and there were no geographic trends in scalation. We conclude that the various populations are conspecific. The lack of morphological discontinuity suggests that the lizards dispersed between the far‐flung island groups recently, and makes more likely the possibility that Polynesian seafaring rather than natural spread was the agent of dispersal. The source population—whether within or beyond the known distribution of E. murphyi—is at present indeterminate.

Morphology and biogeography of Gephyrocapsa coccoliths in Holocene sediments

Morphological analysis of 70 globally distributed Holocene sediment assemblages of the calcareous marine phytoplankton genus Gephyrocapsa (Prymnesiophyta) displays significant correlations between the measured morphological parameters and environmental gradients. By extrapolating these essential findings, paleoecological and evolutionary interpretations can be obtained for the Pleistocene period. Measurements of various morphometric parameters of 3600 coccoliths showed that the morphologically most distinct features arc bridge angle and placolith length. Bridge angle ranged from 120 ° to 3 ° and placolith length from 6.2 μm to 0.9 μm. The combination of the mean bridge angle and the mean length of each sediment assemblage (Holocene) leads to six morphological groups which characterise different environments and geographic areas: Equatorial associations have a mean bridge angle larger than 56 ° and a mean size between 3.1 μm and 3.9 μm. The temperature range of these associations is 25 °C to 29.5 °C mean sea surface temperature (MSST). Abbreviation GE: Gephyrocapsa Equatorial. Subtropical central water-mass associations have a mean bridge angle between 27 ° and 56 ° and a mean length larger than 3.1 μm. These associations are only found in oligotrophic central gyre regions with a MSST between 22 °C and 25 °C. Abbreviation GO: Gephyrocapsa Oligotrophic. Transitional associations have a mean bridge angle between 27 ° and 56 ° and a mean length between 2.4 μm and 3.1 μm. These associations are only found in areas with a mean SST between 19 °C and 20 °C. Abbreviation GT: Gephyrocapsa Transitional. Transitional to subarctic cold associations have a mean bridge angle less than 27 ° and a mean length larger than 2.4 μm. These associations are found in moderately productive regions with a mean SST lower than 21 °C. Abbreviation GC: Gephyrocapsa Cold. Moderately productive temperate associations have a mean bridge angle larger than 56 ° and a mean length larger than 3.9 μm. These associations are dominant in upwelling regions, but also occur in non-upwelling areas. Their temperature range is 18 °C to 23 °C. The relative abundance of these associations within the Gephyrocapsa complex in individual samples decreases with increasing distance from the coast. Abbreviation: GL Gephyrocapsa Larger. Associations consisting of small placoliths with a mean bridge angle between 20 ° and 50 ° and a mean length less than 2.4 μm show no well defined environmental or geographic preference. Such forms seem to be frequent near islands and coasts (neritic) in tropical to subtropical regions. Abbreviation: GM: Gephyrocapsa Minute. The observed morphological discontinuities along the environmental gradients are suggestive of distinct and possibly genetically isolated species populations. In individual assemblages, however, considerable morphological variability is observed and characteristic morphological traits show gradual change along environmental gradients. These features could be expected, if a single, globally homogeneous genotypic species Gephyrocapsa oceanica should show high phenotypic plasticity. Future morphological analysis of plankton samples from various areas and taken at various seasons are expected to confirm the conclusion of environmental dependence of Gephyrocapsa morphology drawn from this analysis.

Fault mechanisms and tectonic implication of the 1985-1987 earthquake sequence in south-western Ethiopia

Integrated inversions of short-period P, broadband P, and long-period P &s waves are done for fault mechanisms, focal depths, seismic moments, and source-time functions from the largest four earthquakes of the 1985 and 1987 earthquake sequence in south-western Ethiopia. These earthquakes had similar normal-faulting mechanisms. The general trends of the fault planes follow the Main Ethiopian Rift which is in agreement with foreshock-aftershock distribution, surface breaks and geology. Despite the morphological discontinuity of the Main Ethiopian Rift at its southern tip, the mode of deformation of the continental crust under study shows its extension southward. There are no significant strike-slip components trending NW–SE in all the mechanisms which would have been associated with the Aswa Fault Zone in southern Sudan or Anza Rift in northern Kenya. We also infer that the relatively broad fracture zone at the southern extreme of the Main Ethiopian Rift demonstrates the early stage of the break-up between the Nubia and Somalia plates in comparison with the Main Ethiopian Rift proper and the Afar Depression. The main shock of the sequence (Mw = 6.3) ruptured at a depth of 6.8 km, shallower than expected since the depth of earthquakes generally increase southward from the Afar Depression. The shallow depth of earthquake occurrence is supported by surface deformations with an overall trend in the direction of the Main Ethiopian Rift.

New Taxa of Consolea Lemaire (Cactaceae: Opuntioideae) from Cuba

The ranges ofConsolea nashii andC. moniliformis were found to extend from the Bahamas and Hispaniola, respectively, into Cuba. Two new subspecies are now recognized on the basis of morphological and geographical discontinuities of populations:Consolea nashii subsp.gibarensis from the coastal thickets between Manati and Maisi, northeastern Cuba, andC. moniliformis subsp.guantanamana from the cacti thorn-woodlands and thickets of Guantanamo and Santiago de Cuba Provinces, on the southern coast and adjacent dry plains of eastern Cuba. A key to the Cuban species ofConsolea is provided.

Geographical variation in the tropical cave cockroach Paratemnopteryx stonei Roth (Blattellidae) in North Queensland, Australia

Observations of cave dwelling organisms in both tropical and temperate caves often reveal morphological modifications, which may reflect various stages of adaptation to cave life. From April 1994 to June 1995 a number of adult Paratemnopteryx stonei were collected from 7 caves in tropical North Queensland to investigate the degree of geographical variation in such troglomorphies between cave populations. Results of morphometric analyses showed the occurrence of a morphological discontinuity between cave populations from the different geographic regions. The body dimensions particularly important in discriminating between each cave population were tegmen length (both sexes), and secondly, tegmen width and tarsus length for males and females respectively. Morphological differences between populations are discussed in relation to stages of adaptation to cave live.

Hybridisation, genomic constitution and generic delimitation in Elymus s. l. (Poaceae: Triticeae)

Intergeneric crosses were made between representatives of the genomically-defined generaElymus, Agropyron, Elytrigia, Pseudoroegneria, andThinopyrum. The genomic constitution ofElytrigia repens, the type species ofElytrigia, is shown to be SSH, a genomic combination otherwise found only inElymus. The S genome ofPseudoroegneria has almost always a dominant influence on the morphology of the taxa of which it is a component.Wang (1989) showed that the J genome inThinopyrum and the S genome have considerable homoeology, with a mean c-value of 0.35 in diploid SJ hybrids. A genetic coherence from S to SJe, Je, JeJb, and Jb can be expected, agreeing with the continuous morphologic variation pattern observed. Because of the absence of morphological discontinuities between the taxa,Pseudoroegneria (S),Elymus (SH, SY, sometimes with additional genomes),Elytrigia (SSH, SSHX), andThinopyrum (SJ, SJJ, J) are best treated as a single genus,Elymus, following the generic concept ofMelderis in Flora Europaea and Flora of Turkey. The basic genomic constituents ofElymus will then be the S and/or J genomes.Agropyron, with diploids, tetraploids, and hexaploids based on the P genome is morphologically distinct from other genera inTriticeae. In a few species ofElymus andPseudoroegneria, a P genome is an additional constituent. In these cases the P genome has a negligible morphological influence. Therefore, it seems reasonable to maintainAgropyron as a separate genus.

Studies in Cyperaceae in southern Africa 27: a contribution to knowledge of spikelet morphology in Epischoenus and the relationship of this genus to Schoenus

Spikelet morphology in the endemic, southern African genus Epischoenus C.B. Clarke is considered and new information is given. Some problems of interpretation are discussed. The relationship of Epischoenus to the older and larger genus Schoenus L., which is predominantly SE Asian and Australian, is further emphasized by the new information provided. The question arises as to whether Epischoenus is separable from Schoenus by definite morphological discontinuity, or whether it is primarily on continental location that generic limitation rests. Species delimitation in Epischoenus is unsatisfactory and in need of revision. Field study of living organisms from stage to stage of development is required, but made difficult by habitats.

The Species of the Early Carboniferous Fossil Plant Genus Genselia

Foliar compression plant fossils of highly variable pinnule shape and bipinnate organization, previously assigned to Triphyllopteris and reassigned to Genselia Knaus, are here assigned to four species, including Genselia lanceolata n.sp., based on a morphometric system of character delimitation. Triphyllopteris biloba Read is placed in synonymy with Genselia lescuriana, and Genselia latilobata (Read) Knaus is placed in synonymy with Genselia rarinervis Specimens were collected from the Lower Carboniferous Pocono and Price Formations of the Appalachian Basin of North America. Whole-frond reconstructions and emended species diagnoses are presented based on visual diagnostic characters and quantitatively determined ranges and patterns of variation. Specimens that are intermediate in appearance, and thereby unassignable to species by visual examination, were preliminarily grouped into subsets based on patterns of pinnule shape variation. These patterns were determined by measuring the length/width ratios of the basalmost and apicalmost pinnules for each pinna and then graphing their difference (within-pinna heteromorphy) against linear frond distance (pinna number). Final species assignments were determined by testing the conformity of these specimens to quantitatively defined ranges and patterns of variation. I expect that these delimitations based on morphological discontinuities will result in a more natural taxonomy than previously possible for this vaguely diagnosed form genus. Because specimens of Genselia exhibit highly intergradational character states, I considered it appropriate to test the null hypothesis that quantitative delimitations may be arbitrary partitions of a single highly variable taxon. This was tested by a one-way ANOVA and a Newman-Keuls Multiple Comparison Summary. This comparison tests whether partitioning into subsets having different means significantly reduces within-group variance. Subsets were identified in 12 out of 15 characters at a significance level of α = .05.

Patterns of modern human diversification: Implications for Amerindian origins

The study of modern human origins and the study of the origins of modern human diversity are intimately linked. The evolutionary models employed have implications both for interpreting the significance of morphological variation and evolutionary trends, and in terms of the processes that gave rise to such variation. Although controversial, available evidence is taken to indicate a single, recent origin of modern humans. This paper explores the process of differentiation of modern populations in Asia and argues for morphological discontinuities in the late Pleistocene populations in the region. The intensely studied population history of Eastern Asia suggests that the evolution of the Mongoloid population complex may result from a process of differentiations, expansions, and dispersals, resulting in the development of regional morphological patterns. The relatively late appearance of regional morphological differentiation, especially in Northeast Asia, opens the possibility of the earliest Amerindians not being a typical “Mongoloid” population. A more generalized Mongoloid morphology has been described for both North and South American Paleoindian remains. In this paper, the morphology of a robust, not typically Mongoloid, population in South America is investigated, and its implications for the homogeneity of Amerindians discussed. Since a derived, typically Mongoloid morphology cannot be attributed to the early Amerindian and Fueguian-Patagonian populations, it is argued either that the sinodont dental pattern was acquired in parallel in Asia and the Americas or that at least two migratory waves ancestral to Amerinds took place. © 1995 Wiley-Liss, Inc.

Systematics of Tree Mosses (Climacium: Musci): Genetic and Morphological Evidence

Three species of the moss genus Climacium are recorded from North America, but their systematic relationships have been unclear because of reports of morphological intergradation between them. Allopatric populations of C. americanum and C. dendroides appear to be morpholog- ically distinct, but the two species intergrade in a broad region of sympatry extending from Wis- consin to Massachusetts. We measured variation in two morphological traits and isozyme genotypes at 19 loci in 253 plants from six sites in New York state. The two species exhibited fixed allelic differences at three loci (Aco-i, Hex-i, and Me-i). Moreover, Nei's genetic identities between con- specific populations of the two species were substantially higher (mean = 0.980 and 0.988 for C. americanum and C. dendroides, respectively) than the mean genetic identity between the species (0.814). Levels of variation within populations were very low. The two species differed significantly in leaf cell length-width ratios and leaf auricle size, but there was substantial overlap between them. Our results indicate that C. americanum and C. dendroides are evolutionarily distinct, reproductively isolated species despite a lack of complete morphological discontinuity. We found no evidence that morphological intergradation is caused by interspecific hybridization.

Morphological variation among members of theStellaria longipes complex:S. longipes, S. longifolia, andS. porsildii (Caryophyllaceae)

Morphological relationships were investigated among diploidStellaria porsildii, polyploidS. longipes, and diploidS. longifolia. Canonical discriminant analysis, based on a priori assumptions to maximize differences among groups, showed thatS. longipes clusters equally distant between the two diploid species along an axis connecting the diploids' centroids, but it differs along an axis perpendicular to this axis. The intermediacy along the former axis is evidence thatS. longipes is an amphiploid derived fromS. longifolia andS. porsildii. The divergence along the latter axis may be attributable to adaptively valuable heterotic traits which were retained following amphidiploidization. The only morphological discontinuity occurred between the two diploids, whereas the morphological range ofS. longipes overlapped the range of both diploids forming a continuum. The lack of discrete clusters is likely due to hybridization and introgression withS. longifolia on one hand, and convergence of traits betweenS. longipes var.monantha andS. porsildii on the other. High a posteriori assignments in classificatory discriminant analysis supports the separation ofS. longipes var.monantha from otherS. longipes specimens. AlthoughS. longipes var.monantha grouped close toS. porsildii, the two groups separate based on leaf shape traits. Overall results support, firstly, the hypothesis thatS. porsildii is a diploid parent species which by hybridizing withS. longifolia gave rise to polyploidS. longipes. Secondly, results suggest thatS. longipes var.monantha converged morphologically towardsS. porsildii relatively recently due to ecological specialization, and merits distinction at least as a variety ofS. longipes.

Systematic Relationships Within Gelsemium (Loganiaceae): Evidence from Isozymes and Cladistics

We used horizontal starch-gel electrophoresis to assess the degree of genetic diver- gence between four populations each of Gelsemium sempervirens and G. rankinii from the southeastern United States and to test the hypothesis that G. sempervirens is an autotetraploid derivative of G. rankinii. Levels of genetic variation in both taxa are somewhat higher than the mean for long-lived, woody perennials. There was no indication that the alleles of one species represent a subset of the variation present in the other nor was there any indication of tetrasomic expression in G. sempervirens. Moreover, chromosome counts from root tip squashes confirm that both species are diploid, with 2n = 16. There is, however, unusual mitotic behavior that may explain apparently erroneous counts of lower numbers by some previous workers, who also reported larger and fewer stomates in the presumably autotetraploid G. sempervirens. Sharp genetic differences between the two species (mean genetic identity, I = 0.48) parallel their morphological discontinuities in many characters, and there was no evidence of hybridization or introgression in regions of sympatry. A cladistic analysis using eight morphological characters supports the view that G. sempervirens and C. rankinii are sister species, more closely related to each other than either is to the third species in the genus, G. elegans from southeast Asia. Genetic evidence suggests that the lineage leading to G. rankinii and G. sempervirens split in the late Tertiary, about 3-3.5 million years ago. It is possible that G. rankinii adjusted to life in Coastal Plain swamps by loss of winged seeds, becoming adapted for dispersal by water, rather than wind.

Temporal craniometric changes from the Jomon to the Modern period in western Japan

Temporal changes in morphometric features of human cranial remains from the late Jomon period (1500 B.C.-300 B.C.) to the Modern period (1900-1950 A.D.) in western Japan are examined. The results of univariate and multivariate analysis indicate that the Yayoi people (300 B.C.-300 A.D.), characterized by high faces and tall stature, show morphological discontinuity with the earlier Jomon people, who exhibit lower faces and shorter stature. This discontinuity contrasts with the relatively continuous changes among populations after the Yayoi. Comparing these changes with those documented in the Kanto region of eastern Japan indicates there are significant regional differences in the degree and rate of transformation in certain cranial features, especially facial height, between the two regions. Differences in cranial shape between the two regions become apparent during the Yayoi period and these differences tend to diminish thereafter. The most plausible explanation for these observed changes is the introduction of new genes, coinciding with the arrival of new immigrants from the Asian continent in the northern Kyushu-Yamaguchi region at the beginning of the Yayoi period. Further testing of this hypothesis will be necessary before definitive conclusions can be reached regarding the appearance of modern Japanese.

The species concept and quaternary mammals

Quaternary palaeontologists must abandon the concept of fossil species (=chronospecies) and as far as possible adapt the concepts used at present by the neontologists to fossil materials. It is proposed to use an approach that consists of reversing the sequence of research procedures. This can be done by: (1) studying relevant recent populations in the entire present range of the species, (2) focussing attention on a full utilization of information concerning the variability of morphological traits used for palaeontological purposes in the recent species, (3) the taxonomic position of which should be defined on the basis of biochemical, genetic and ecological data and not exclusively on morphological discontinuities and finally (4) having acquired this knowledge to classify the fossil mammal samples.

Systematics of the Saguinus oedipus group of the bare-face tamarins: evidence from facial morphology.

The systematics of the Saguinus oedipus group within the bare-face tamarins remains open to question. Hershkovitz (Living New World Monkeys (Platyrrhini), Vol.1. Chicago: University of Chicago Press, 1977) places the cotton-top and rufus-naped tamarins as subspecies of Saguinus oedipus (S. o. oedipus and S. o. geoffroyi, respectively). In contrast, several other authors have argued that these two taxa should be considered separate species (S. oedipus and S. geoffroyi). Phylogenetic relationships within the group are also disputed. Resolving these different interpretations has been difficult in part because no study of this group has included an objective measure of expected levels of specific vs. subspecific variation. We used facial measurements from 179 adult crania to address the systematics of this group and included a related species that is known to include multiple subspecies. Our sample included three taxa from the S. oedipus group of the bare-face tamarins (S. oedipus, S. geoffroyi, and S. leucopus) and six subspecies from the related hairy-face tamarin species S. fuscicollis. Comparisons to S. leucopus provided a relative measure of species-level differences. Analyses that included S. fuscicollis provided a measure of subspecific variation. There was no evidence of facial sexual dimorphism in any of these taxa. A variety of multivariate statistical analyses including discriminant function and cluster analysis suggest that S. oedipus and S. geoffroyi differ morphologically at a level consistent with species-level distinctions. The extent of differences between these taxa is large. The differences in their facial morphology was on the order of differences between S. oedipus or S. geoffroyi and S. leucopus rather than the extent of variation among S. fuscicollis subspecies. Furthermore, a comparison of collecting localities revealed that the variation we observed among S. oedipus and S. geoffroyi was not clinical but presented a large morphological discontinuity at the boundary between taxa. Our analyses also suggested that S. leucopus is more similar to S. oedipus than is either to S. geoffroyi. Finally, it may be that there are some distinct species within the S. fuscicollis group. However, this hypothesis, along with other phylogenetic relationships suggested by this study, will require more data and further study.

The Upper Permian articulate Phyllotheca australis from South Africa

The taxonomic position of two fossil articulates, which form an important element of the Permian Gondwana flora, is examined in the light of recent collections from South Africa. Vegetative and fertile axes, dispersed and attached sporangia, in-situ spores, isolated and attached whorls of leaves, rhizomes bearing roots and branches, naked axes and a permineralized axis are all assigned to Phyllotheca australis. The large numbers of axes with attached sporangia allow a reinterpretation of the fertile structure and the specific diagnosis is emended. Although it is recognized that the fossils assigned to this taxon may represent a species complex, there exist no clear morphological discontinuities between the material previously assigned to P. australis and P. indica from widely separated Gondwanan localities. Phyllotheca australis was common throughout Gondwana, and is a reliable index fossil of the Upper Permian.

An analysis of morphological variation in Senecio cymbalaria (Asteraceae)

Senecio cymbalaria Pursh is an arctic-alpine perennial that exhibits a broad range of morphological variation and occurs in four disjunct regions within North America. In this study, a morphological analysis of herbarium material is undertaken to determine whether the observed morphological variation is primarily attributable to morphological discontinuities among geographically isolated groups. Eighty individuals representing the total geographic range of the species were scored for 24 morphological characters and the data matrix subjected to principal components and cluster analyses. Individuals from the southern Rocky Mountains, previously recognized as Senecio conterminus, are separated from the remainder of S. cymbalaria in both analyses. Our results support recognition of two species, S. conterminus and S. cymbalaria. Although populations from the Gaspé and from Newfoundland form somewhat distinct clusters, neither can clearly be distinguished from populations of S. cymbalaria from Alaska, the Yukon, and Northwest Territories. Chromosome counts of 2n = 138 were obtained from two individuals from the Gaspé peninsula. Key words: biogeography, phenetics, Gulf of St. Lawrence, Senecio, disjunction, chromosome numbers.

The nature and origins of primate species

The living world has genetic discontinuity in it, and morphological discontinuity as well. Patterns of these discontinuities overlap to a large extent. When they do, species discrimination is unambiguous. But directly at the point of cladogenesis, there are parallel sets of processes occurring, which result in patterns that can be difficult to reconcile in a single term such as speciation. Primate “species,” living and extinct, exhibit various degrees of morphological discontinuity and genetic incompatibility, which implies that a single concept of speciation may be difficult to apply universally.