Significance Of Morphological Variation Research Articles

Prevalence, distribution, and prognostic significance of morphological variants of neuroendocrine tumors of the gastrointestinal tract - a multicenter study.

The incidence and prevalence of neuroendocrine neoplasms (NENs) in many organs are increasing. Although such NENs have similar grades, they may exhibit quite different behaviors. In this multicenter study, we aimed to investigate the prevalence and distribution of different morphological NEN variants in the non-pancreatic gastrointestinal (GI) tract and determine whether they can guide prognosis prediction. Two hundred and fifty-six patients diagnosed with NENs originating from the GI tract from 7 different centers were included in the study. In 89 (36.6%) cases, different morphological variants were detected. When the variants were grouped according to their aggressiveness as described in the literature, a statistically significant relationship between aggressiveness and the variables organ and age was found ( p < 0.05). The oncocytic variant was found to metastasize more than the other aggressive types (42.9%). The paraganglioma-like variant was found to have a smaller size, lower proliferation index, and a more benign clinical course. This study demonstrated that well-differentiated GI neuroendocrine tumors (GI-NETs) have considerable morphological diversity. Generally, case reports of rare morphological variants of GI-NETs are available in the literature. We believe that our study contributes to a better understanding of the prevalence, localization, and significance of morphological variations in GI-NETs.

On the morphology, systematics and phylogeny of Noteroclada (Noterocladaceae, Marchantiophyta)

Noteroclada Taylor ex Hook. & Wilson has long been recognized as a unique leafy taxon having affinities to the north temperate, simple thalloid liverwort genus, Pellia Raddi. Although a suite of diagnostic characters clearly separate it from Fossombronia Raddi and other leafy, anacrogynous taxa, considerable confusion regarding its identity exists in historical treatments. There are unresolved questions in regards to the extent and significance of morphological variation within the genus, the number of species that should be recognized, the geographic range that it occupies and its position in liverwort phylogeny. Morphological, experimental and molecular techniques are employed to address these questions. These studies show that there are two forms of perennating tubers, which are geographically partitioned, that plants are always monoicous, that sporophytes are enclosed by a shoot calyptra and Fossombronia-like caulocalyx and that sporeling ontogeny is different from that of Pellia. Molecular analyses show some genetic variation within Noteroclada, but both morphological and molecular data support the recognition of but a single species, N. confluens Taylor ex Hook. & Wilson. It is confirmed that there are no reliable specimens of Noteroclada from Africa, Australasia or the Kerguelen sector and that the genus has two centers of distribution in Latin America, with disjunct populations in the Falkland Islands, South Georgia, Tristan da Cunha and Gough Island. Significant ontogenetic differences between Noteroclada and Pellia support their placement in separate monogeneric families of the Pelliales.

Kiik-Koba 2 and Neandertal axillary border ontogeny

The significance of morphological variation in the axillary border among Pleistocene and recent humans has been considered for nearly a century, with the high frequency of the dorsal sulcus pattern in the Neandertal lineage receiving particular attention. Although usually considered an epigenetic trait, or phylogenetic marker, the variation has also been related to functional demands on the shoulder region. The Kiik-Koba 2 infant Neandertal scapula, as one of the developmentally youngest ones known, exhibits a smooth ventral surface, a ventral displacement of the lateral margin, a prominent dorsal bar, and a dorsolateral sulcus along the border. This configuration is best seen as an incipient dorsal sulcus pattern, and given the young age-at-death of Kiik-Koba 2, supports the epigenetic trait interpretation of the morphological variation.

On the Significance of Acheulean Biface Variability in Southern Britain

The significance of morphological variation in Acheulean bifaces has been a central issue in Palaeolithic research for well over a century. For much of that period interpretation has been dominated by culture-historical models and it is only in the past 20 years that other explanatory factors have received adequate attention. This paper examines the combined role of several of these factors – namely raw materials, reduction intensity, and function – on biface variability in the British Isles, with special reference to the two major shaped-based ‘tradition’ devised by Roe (1967; 1968). First-hand examination of bifaces from 19 assemblages suggests that final biface shape depends largely on the dimensions of the original raw materials and the technofunctional strategies designed to deal with them. Through these observations a new model is generated and tested. This suggests that the patterning in the British Acheulean simply reflects the nature of the resources available at a site and the hominid procurement and technological strategies used to exploit them. According to this model, well-worked ovates with all-round edges were preferentially produced wherever raw materials were large and robust enough to frequently support intensive reduction procedures, usually when obtained from primary flint sources. Assemblages characterised by partially-edged, moderately-reduced pointed forms were only manufactured when smaller, narrower blanks, that imposed restrictions on human technological actions regarding the location and extent of working, were exploited. Such blanks were usually obtained from a secondary flint source, such as river gravel. Thus, Roe's pointed and ovate ‘traditions’ are seen not as the products of different biface making populations, but as the same broad populations coping with the exigencies of a heterogeneous environment, using different resources in an adaptive, flexible manner.

Convergence in Aerially Feeding Insectivorous Birds

An analysis of bill, forelimb and hindlimb skeletal morphology of four families of aerial foraging birds (apodids, caprimulgids, glareolids and hirundinids) and closest related families of non-aerial foragers (charadriids and parids) was made to investigate possible convergence for acrial feeding in groups with very different phylogenetic histories. The correlated evolution of foraging mode and skeletal morphology was studied using the phylogenetically independent contrasts method in order to test a prediction of convergent evolution, and to assess the adaptive significance of morphological variation. Results show the existence of an ecomorphological pattern relating the aerial feeding technique with short, wide and flat bills, and short legs and pclvcs. We demonstrate that to properly test convergent hypotheses the effect of 'common ancestry' must be taken into account, otherwise spurious relationships can be obtained. This study also shows that in spite of the ecomorphological pattern shared for aerial foragers, they are segregated in the morphological space. We suggest the existence of some design limitations (phylogenetic constraints) which make certain morphological responses more likely than others.

A morphometric analysis of the Thrips hawaiiensis (Morgan) species-group (Thysanoptera: Thripidae)

AbstractThe significance of morphological variation within the Thrips hawaiiensis (Morgan) species-group is examined. Multivariate analyses of four characters from 344 females and seven characters from 90 males show two distinct groups found throughout the Oriental, Pacific and American Regions, corresponding to T. hawaiiensis and T. florum Schmutz, and an intermediate group, exilicornis Hood, from Africa. The results are compared with previously published morphometric data concerning the separation of T. hawaiiensis and T. florum, and additional distinguishing characteristics are assessed. The distributions of the three forms as recognized in this study are summarized.

The significance of morphological variation in the finch species on Gough, Inaccessible and Nightingale Islands, South Atlantic Ocean

Uni‐ and multivariate analyses were made of nine morphological characters on three species of finches Nesospiza acunhae (Inaccessible, Nightingale), N. wilkinsi (Nightingale) and Rowettia goughensis (Gough). The results of the univariate analysis were used to test four predictions about morphological changes with altered competitive backgrounds. Finch species that occur alone on an island or on an island where other finch species are rare have longer characters and more variable character distributions.A multivariate analysis of six bill characters showed that the bill of Rowettia is more similar to that of acunhae than either is to wilkinsi. A multivariate analysis on wing length, tarsus length and hallux length shows that Rowettia is morphologically closer to wilkinsi than it is to acunhae. It is suggested that nothing is gained by treating the Gough I. finch as belonging to a monotypic genus.

A Comparative Study of the Cause and Significance of Morphological Variation in Adults and Pupae of Culicoides: A Factor Analysis and Multiple Regression Study

A Comparative Study of the Cause and Significance of Morphological Variation in Adults and Pupae of Culicoides: A Factor Analysis and Multiple Regression Study

Causes and Significance of Morphological Variation in Fishes

MANY ICHTHYOLOGISTS have tended to assume extreme positions as to whether observed differences between populations of a given species of fish are caused by genetic differences or merely by dissimilarities of environments. Early workers were inclined to regard differences, especially countable ones, as indicative of genetic divergence alone. Many of these forms were formally recognized as subspecies, or species (examples are cited in Jensen, 1944). The weight of thought swung the opposite direction after the discovery that characters could be altered through manipulation of the environment. Now ichthyologists commonly assume differences between populations of a species are environmentally induced unless a genetic basis can be demonstrated experimentally. The bulk of recent literature, however, is concerned primarily with the elucidation of the effect of environment on a given genetic stock. The problem of genetic divergence between populations of a fish species, or within a single population, has not received as much attention and evidence along these lines, therefore, is meager (but see Gordon, 1957). It is essential to the progress of systematic ichthyology, as well as to the planning of experiments on this problem, that the nature of morphological variation in fishes be properly understood. Since the early papers by Hubbs, only Taning (1952) has reviewed this subject. Taning stressed the role of the environment in determining meristic characters, and also fostered the misleading notion of daydegrees. The primary objective of the article at hand is to put forth arguments to support what is meant to be a more balanced point of view. Morphological clines, especially for those forms which have somewhat disjunct populations, are regarded as the consequences of environmental modifications coupled with adaptive genetic changes. In the course of writing the article it also became necessary to reconsider the problem of the production of variation in fishes, particularly, meristic variation.' As a result, a refinement of Hubbs's (1926) hypothesis has been developed to account for the genesis of meristic variation in the hope it may give direction to the design of future experiments.