• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 117
  • 74
  • 35
  • 21
  • 20
  • 4
  • 3
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 363
  • 181
  • 71
  • 49
  • 48
  • 40
  • 34
  • 32
  • 27
  • 27
  • 26
  • 24
  • 24
  • 23
  • 23
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Chondrocranial Evolution in Rana Tadpoles: Integrating Form, Function, Ontogeny, and Phylogeny

Larson, Peter 04 December 2003 (has links)
No description available.
92

Molecular Phylogenetics and Geometric Morphometrics Reveal Possible Cryptic Species Within the Solitary Bees Melissodes agilis and M. trinodis (Hymenoptera: Apidae)

Roch, Justin C. 01 September 2023 (has links) (PDF)
Recent concerns of declining bee populations have highlighted the importance of monitoring wild bees, but bee community assessments are hampered by species complexes that are difficult to identify. Bees in the genus Melissodes are often considered challenging to identify to species, with two widespread North American species, M. agilis Cresson and M. trinodis Robertson, being particularly difficult due to similar morphology, geographic ranges, and preferred floral hosts. These two species exhibit characteristics of cryptic species complexes, raising the possibility that our current understanding of their taxonomy is incomplete. We conducted a study to clarify the species boundaries within this complex, and to test if geometric morphometrics could be used to differentiate its member taxa. We sequenced fragments of the mitochondrial COI gene from 112 M. agilis/trinodis specimens, and integrated them into a phylogeny based on published reference sequences of over 70 Melissodes species. We additionally landmarked forewing venation for 102 of these specimens, tested if forewing morphometrics was associated with sex and phylogenetic clade, and tested if forewing morphometrics could accurately assign specimens to their proper clade and sex. Phylogenetic reconstructions resulted in nearly all specimens being assigned to three primary clades, with one clade containing reference sequences for M. agilis and M. trinodis, and two clades appearing to be undetermined cryptic taxa. Forewing morphometrics differed between clades and sexes, and was able to assign specimens to their proper clade or sex with over 80% accuracy, although accuracy of classification to clade declined to between 33-93% after cross-validation. Our results suggest the existence of cryptic diversity within M. agilis and M. trinodis, and indicate that forewing morphometrics can characterize some of this diversity. M. agilis and M. trinodis may comprise a complex of 3-5 cryptic species, but whether these are described or undescribed species is unknown. Also unclear is the degree to which the potential cryptic species contribute to the economically important sunflower pollination services currently considered to be conducted by M. agilis and M. trinodis. We encourage additional study of this complex to determine the nature of this cryptic diversity and resolve the taxonomic questions this study has raised.
93

Warped Ideas: Geometric Morphometrics as a Complementary Technique for Studying Gastropod Shell Morphology

Yousif, Mariam 10 1900 (has links)
<p>Geometric morphometrics (GM) provides a complementary method for studying morphology. Snails have been analyzed in the field of morphometrics since the 1960s because their shells serve to record information about their life histories and environmental habitats. In this thesis, we present an annotated bibliography for advancements in GM, using applications to snail shells as a representative case study. We categorize 30 publications into four fields, morphology, ecology, taxonomy and evolution, and show that developments have been unequal among them. We conclude by predicting that GM applications on snail shells will increase, especially in hybrid fields, such as, ecotoxicology, which currently are underrepresented. As a demonstration, we describe an experiment wherein we applied GM as a complementary morphological method to study the garden snail species Cepea nemoralis in an organophosphatepesticide, ecotoxicological setting. We conclude by showing that GM reveals subtle morphological differences among treatment groups with no relation to pesticide dosage.</p> / Master of Science (MSc)
94

Locomotor kinematics of turtles moving in shallow water environments

Mazouchova, Nicole January 2019 (has links)
Locomotion, moving around in our complex world is as crucial to many animals as finding food, shelter or a mate. The intricate interplay between the brain, nerves, muscles, tendons and bones allows for a variety of gaits. Animal movement has been studied in many environments like water, land or air, often focusing on one habitat alone. These studies were crucial in establishing the principles of animal locomotion, but don’t always reflect the intricate lifestyle of an animal. More often then not, animals will encounter different surface structures (such as grass, sand, soil, forest debris) or even interact between different habitats, such as at the water-land interface. Fewer studies have focused on understanding how movement changes when physical conditions vary. A turtle swimming in a dense, buoyancy-dominated water habitat transitioning to a walking on gravity-dominated terrestrial habitat is poorly understood and may open insight into new locomotor strategies. Turtles are an interesting study subject to study water-land transitions, as their spines are fused to their carapace, isolating any movement generation to their limbs only. In this thesis, I chose different size red-eared slider (Trachemys scripta elegans) turtles to investigate their locomotion during discreet water depth, as well as during shallow water locomotion and investigated whether bone shape can be predictive of the environment they live in. / Biology
95

Intraclonal Morphological Plasticity within the Myzus persicae (Sulzer) Complex Related to Host Plant and Temperature

Marie, Joan 25 August 2004 (has links)
Blackman (1987) used life cycle and morphology to separate Myzus nicotianae Blackman, a tobacco-feeding species of aphid, from Myzus persicae (Sulzer). In the present study, the first objective was to investigate the influence of temperature and host plant on the morphology of M. nicotianae and M. persicae. The second objective was to assess Blackman's 1987 key to Myzus for separating tobacco and non-tobacco originating morphs under different environmental conditions. Four host plants were used: tobacco, turnip, pepper, and okra, and three temperatures, 15°C, 20°C, and 25°C. The intraclonal plasticity of two tobacco collected morphs and one turnip collected morph was investigated in relation to these combinations of host and temperature in a 4 x 3 x 3 factorial experimental design. Fifth generation mature apterous aphids were mounted on slides and 10 different morphological structures utilized in morphometric analysis were measured. Data support a morphologically distinct, host-adapted tobacco race but not a separate tobacco-feeding species of M. persicae. The key developed by Blackman (1987) did not discriminate between the tobacco and non-tobacco originating clones but the canonical variates generated from the analysis successfully separated the tobacco and non-tobacco groups. Other studies have used many different clones to investigate the possible distinctions between M. persicae and M. nicotianae; the objective here was to see how much morphological perturbation may be induced within a clone by rearing at different temperatures and on different host plants. Temperature and host plant had substantial influences on the morphology of these aphids. The physiological interactions of temperature-host plant-aphid morphology are very complex yet controlling only for temperature and host plant was sufficient to group specimens according to these independent variables with remarkable accuracy using the linear discriminant functions generated with these data. Percent of aphids in which rearing temperature was correctly identified using linear discriminant functions generated for temperature classes was 87%, 63%, and 64% for 15°C, 20°C, and 25°C, respectively. Random designations would be 33%. Correct identification of host plant was 65%, 45%, 47%, and 48% successful for tobacco, turnip, pepper, and okra, respectively. Random designations for host plant would be 25%. Canonical variates produced clusters by host, temperature, morph, and combinations of these independent variables with varying degrees of discreteness. CV1 by CV2 for host plants gave a very distinct cluster for tobacco and also separate groupings for aphids reared on turnip and pepper. Aphids from the host plant okra were scattered quite widely across the CV1 by CV2 graph. CV1 by CV2 for temperature conditions showed a tight cluster for aphids from 15°C and still distinct though less closely grouped clusters for both 20°C and 25°C rearing temperatures. CV1 by CV2 for the three morphs gave substantial overlap for the two tobacco originating morphs and a more separate cluster for the morph originally collected from turnip. / Master of Science
96

Etude tridimensionnelle de la partie postérieure de la base du crâne chez le fœtus : applications à la détermination de l'âge en anthropologie médico-légale

Sastre, Julien 05 December 2011 (has links)
La morphométrie géométrique permet la visualisation dynamique 3D de la base du crâne et une prévision de leurs variations liées à la croissance. Le but de ce travail est de proposer des méthodes fiables et précises pour estimer l’âge fœtal et caractériser un stade de développement par sa conformation osseuse. Les os temporal, occipital et sphénoïde de 33 fœtus âgés de la 19ème à la 24ème semaine d’aménorrhée (S.A.) ont été reconstruits en 3D et 44 landmarks ont été positionnés. L’étude par morphométrie géométrique a permis de déterminer les maxima de variation morphologique, ainsi que d’étudier les trajectoires ontogénétiques. Les formules établies permettent l’estimation de l’âge à ±2,44 semaines. Les points de césure classiquement utilisés en anthropologie ont été confirmés. Nous avons établi une chronologie des conformations entre la 19ème, la 27ème et la 41ème S.A. L’os sphénoïde et occipital présentent un rythme de croissance commun alors que l’os temporal diffère. Nous avons confirmé ces structures anatomiques comme étant des critères indirects de maturation permettant d’estimer l’âge. / Geometric morphometric techniques allow the 3D visualization of the skull base and a forecast of their related growth variations. The aim of this work is to provide reliable and accurate methods to estimate fetal age and stage of development characterized by bone conformation. The temporal bone, occipital and sphenoid in 33 fetuses aged from the 19th to the 24th week of amenorrhea (W.A) were reconstructed in 3D and 44 landmarks were positioned. Geometric morphometrics was used to determine the maxima of morphological variation and ontogenetic trajectories. The established formulas allow the estimation of age at ±2.44 weeks. Hyphenation points conventionally used in anthropology have been confirmed. We have established a chronology of the conformations between 19th, 27th and 41st WA. The sphenoid and the occipital bone have a common growth rate, while the temporal bone differs. We confirmed these anatomical structures as indirect criteria of maturation to estimate age.
97

Genital variation in moths—evolutionary and systematic perspectives

Mutanen, M. (Marko) 10 May 2006 (has links)
Abstract genital characteristics have peculiar morphological patterns. They show great divergence between species. At the same time, they are assumed to vary little within species by taxonomists who frequently use genital features to delimit species. I studied moth (Lepidoptera) genital size and shape variation within and between species. I also tested hypotheses proposed to explain rapid genital diversification among species. Studies were carried out using traditional distance measurement morphometrics and modern geometric morphometrics. Several moth species were analyzed. d that genital structures show variation that in closely related species may show structural overlap. More surprisingly, the amount of variation in internal genitalia was equal to non-genital traits. These and some other findings are against the predictions of the lock-and-key hypothesis, which suggests that genital differences form a mechanical isolation system between species. Meanwhile, the findings are in good accordance with the various mechanisms of the sexual selection hypothesis. I found that external genital traits express varying amounts of variability. However, both external and internal genitalia consistently show small variation in size so that large individuals have disproportionately small genitalia and vice versa. This finding is consistent with the lock-and-key theory, but also with the cryptic female choice hypothesis. In conclusion, the results suggest that sexual selection plays a major role in genital diversification, but the exact mechanism remained unclear in this study. Some structures in moth genitalia strongly suggest that sexual conflict is present as well. It is possible that several mechanisms of sexual selection are in action simultaneously. dings have implications to insect taxonomy. Genital characters, although often useful, should not be considered superior to other characters because they may vary considerably within species. I have shown that subjective visual evaluation of genital characteristics and a priori assumption of their low variability may easily lead to unsound taxonomic conclusions. Sophisticated morphometric tools are very useful and objective in delimiting sibling species. Geometric morphometrics is particularly useful since it helps to evaluate limits of variation. There are, however, no theoretical grounds to assume that genitalia are not subject to intraspecific geographic variation. Such variation was detected in this study as well. Geographic relationships should therefore be taken into consideration more frequently when delimiting populations into different species.
98

Variação morfológica e molecular das populações de Mesoclemmys vanderhaegei (Testudines: Chelidae) / Morphological and molecular variation of the Mesoclemmys vanderhaegei populations (Testudines: Chelidae)

Souza, Rodrigo Araujo de 12 September 2014 (has links)
Mesoclemmys vanderhaegei Bour, 1973 pertence à família Chelidae, que apresenta maior riqueza de espécies de Testudines no Brasil. Apesar de não se suspeitar do monofiletismo da família, há muitas dúvidas sobre as relações entre os táxons de Chelidae, com a possibilidade de vários grupos se revelarem parafiléticos. Mesoclemmys vanderhaegei tem uma ampla distribuição no centro-sul do continente sul-americano, havendo sido estudada mais especificamente sob uma temática ecológica. Seus aspectos taxonômicos e filogenéticos, porém, ainda necessitam de uma investigação mais detalhada, visto que o grupo pode representar um complexo de espécies. O presente trabalho visa, portanto, estudar as populações de M. vanderhaegei sob um ponto de vista taxonômico e filogenético, buscando identificar e caracterizar as populações através das divergências evolutivas que venham a ser reveladas, justificando assim um eventual desmembramento da espécie. Sendo assim, as populações de M. vanderhaegei foram investigadas por meio de técnicas de morfometria tradicional, morfometria geométrica, e uma filogenia molecular foi proposta para o gênero. Para a morfometria tradicional foram analisadas medidas lineares do plastrão, carapaça e cabeça; enquanto que para a morfometria geométria foram selecionados landmarks nos vértices dos escudos do casco e na linha média dorsal e ventral de cada espécime. Para o estudo de filogenia molecular, foram sequenciados três genes nucleares (RAG-2, R35 e c-mos), e dois mitocondriais (12S e NADH) de representantes da maioria das populações da espécie, e de todas as espécies do gênero. A análise discriminante tanto para os dados de medidas lineares quanto para os de landmarks separa a população do sul da Bacia do Paraguai (próxima à localidade tipo da espécie) das demais populações brasileiras. As análises morfométricas diferenciam outras duas populações: uma população composta por espécimes da Chapada dos Guimarães (MT), região de Cuiabá e um exemplar de Bonito (MS); enquanto a outra população é representada por espécimes de São João da Ponte (MG), na Bacia do São Francisco. A topologia resultante da análise de máxima verossimilhança aponta M. vanderhaegei como um grupo polifilético, com a possibilidade de ser dividida em quatro espécies: uma com os espécimes do sul da Bacia Amazônica; outra com os espécimes de Montes Claros (MG), na Bacia do São Francisco; uma terceira com os espécimes de São João da Lagoa e do interior de São Paulo (Bacia do Paraná, sub Bacia do Tietê); além daquela formada pelos espécimes próximos à localidade tipo. Sugere-se, portanto, (1) que a distribuição de Mesoclemmys vanderhaegei seja restringida ao norte da Argentina, Paraguai, e oeste do Mato Grosso do Sul até que novos estudos venham a elucidar o quanto a espécie adentra o território brasileiro; (2) que as populações da região da Chapada dos Guimarães e do interior de Minas Gerais sejam elevadas ao nível de espécie; (3) e que se façam novos estudos para elucidar a relação das populações da Bacia do Tocantins-Araguaia e Paraná com os outros grupos do complexo.! / Mesoclemmys vanderhaegei Bour, 1973 belongs to the family Chelidae, which presents the greatest variety of species of Testudines in Brazil. In spite of theories that suggest that the family might be monophyletic, there are still areas of doubt over the relationships between the taxa that belong to the Chelidae, and the possibility that various groups might prove to be paraphyletic. Mesoclemmys vanderhaegei has a large distribution range along the central and southern regions of the South American continent, and has been most specifically studied through an ecological perspective. A more detailed investigation of its taxonomic and phylogenetic characteristics is still both relevant and necessary, since the complex might represent multiple species. The present work aims, therefore, to study the populations of M. vanderhaegei from a phylogenetic and taxonomic perspective, looking to identify and characterize the populations in accordance with the evolutionary divergences that may be observed, thus justifying the subdivision of the complex into mutiple species. With this in mind, the populations of M. vanderhaegei were investigated using techniques of traditional and geometric morphometry, and a molecular phylogeny was proposed for the genus. The traditional morphometric data accounted for linear measurements of the plastron, carapace and head whilegeometric morphometric data were chosen as landmarks on the vertices of the scutes of the shells and on the dorsal and ventral midline of each specimen. Using samples of the majority of the populations of the species, and of all the species of the genus, three nuclear (RAG-2, R35 and c-mos) and two mitochondrial genes (12S and NADH) were sequenced for the study of the molecular phylogeny. Both the discriminant analysis of the linear measurements data and that of the landmarks separate the population found in the South of the Paraguay Basin (near the type locality of the species) from other Brazilian populations. The morphometric analyses show two other distinct populations: a population composed of specimens from Chapada dos Guimarães (MT), in the region of Cuiabá and one specimen from Bonito (MS); while the other population is represented by specimens taken from São João da Lagoa (MG), in the Basin of São Francisco. The resulting tree topology of theMaximum-Likelihood analysis derived from the molecular data suggests that M. vanderhaegei should be considered a polyphyletic group, that can be divided into four species: one species represented by the specimens from the South of the Amazonian Basin; another represented by the specimens from Montes Claros (MG), in the Basin of São Francisco; a third represented by the specimens from São João da Lagoa and the interior of São Paulo (Paraná Basin, sub Basin of the river Tietê); in addition to the one formed of the specimens close to the type locality. This would suggest, therefore, (1) that the distribution of Mesoclemmys vanderhaegei is restricted to the North of Argentina, Paraguay, and the West of Mato Grosso do Sul, until further studies are made to elucidate the extent to which the species has spread into Brazilian territory; (2) that the population of the Chapada dos Guimarães region and of the interior of Minas Gerais should be elevated to the category of species; (3) and that new studies must be carried out to determine the relationship between the populations of the Basin of Tocantins-Araguaia and Paraná with the other groups of the complex.!
99

Vývoj patra u pacientů s orofaciálními rozštěpy po primární sutuře rtu / Development of maxilla in patients with orofacial clefts after the primary cheiloplasty.

Hoffmannová, Eva January 2013 (has links)
The present study is concerned with development of maxilla, or moreprecisely palate,in course of first year of life in patients with unilateral cleft lip and palate (UCLP), before and after cheiloplasty. The metodology has it's center in processing of dental plaster casts of UCLP patients via classical and geometric morphometry. All the patients have been operated following same protocol in the neonatal period. The operation was conducted by the same surgeon Jiří Borský, M.D. in the teaching hospital Motol in Prague. In the trackedThe results suggest that the variability of shape was larger in cUCLP patients than in UCLP+M patients. Statistically significant differences in the palate shape were observed in both age categories within both defect categories. The variability of form (size and shape) was followed within each defect category and statistically significant differences between both age category was proven. In the light of average changes intha palate morphology, we tracked both anterior and posterior growth of both segments with increasing age in both defect categories. More distinctive aproximation of both segments, due to the pressure after the cheiloplasty and growth of both segments, was observed in cUCLP patients. Essencial influence of increasing gravity of the defect on changes...
100

Riziko hybridizace ohrožené třešně křovité (Prunus fruticosa) s pěstovanými zástupci rodu Prunus / Assessing the threat of hybridization between Prunus fruticosa and cultivated Prunus species

Musilová, Lenka January 2013 (has links)
Presented thesis evaluates the risk of ongoing hybridization (antropohybridization) in highly endangered Prunus fruticosa in the Czech Republic and selected adjacent countries. Absolute genome size analysis (estimated by flow cytometry) combined with both numeric and geometric morphometrics were used for evaluation of hybridization. Prunus fruticosa frequently hybridize with naturalized Prunus cerasus (emerging tetraploid hybrid Prunus ×eminens) and native Prunus avium (forming triploid hybrid Prunus ×mohacsyana). Discrimination between P. ×eminens and P. ×mohacsyana is difficult, when using leaf morphology characters only, so the occurrence of triploid hybrids was strongly underestimated in the Czech Republic (only tetraploid hybrids were reported). Both hybrids are surely differentiated using flow cytometry analysis (based on different ploidy level). The majority of analyzed populations is formed by either individuals of pure P. fruticosa or one of the mentioned hybrids. Only four populations were mixed. Continuous variability in absolute genome size was found in two of them, which may indicate hybrid swarm forming (incl. primary hybrids and backcrosses). Our findings can be considered only as indirect evidence for introgression, which needs to be confirmed by molecular markers (for example...

Page generated in 0.0256 seconds