Life Sciences Commons^™

Xenopus Laevis As A Model Organism, David C. Cannatella, Rafael O. De Sá

Biology Faculty Publications

Model organisms are often assumed to be representative of some more inclusive taxon of which the species is a part. This assumption leads to mistaken generalizations about the evolutionary and comparative significance of the data gathered. This paper reviews com? parative and evolutionary studies of Xenopus laevis and its relatives. Phylogenetic analysis of data from DNA sequences and morphology indicate that Xenopus is monophyletic and that Silurana is its sister group. The most basal lineages of Pipidae diverged prior to the breakup of Gondwana. The bizarre morphology of Xenopus is in part due to changes in the mode of meta? …

An Evaluation Of Hands-On Instruction As A Method To Improve Observation Skills In Second Grade Students, Lydia Rogers

Master's Theses

A hands-on assessment tool for testing second-grade students' ability to discriminate physical attributes (size, shape, color, texture, pattern, edge, part-to-whole, and type) of mollusk shells was developed, pretested, and administered to 48 second-grade students at Maybeury Elementary School, Henrico County, Virginia. Treatment group students (n = 24) attended five afterschool, activitybased classes in which close observation of object a~tributes was taught. The classes included the same discriminations as did the assessment test but used different materials. Control and test group students were retested. Neither paired t test nor question-by-question analysis showed a significant improvement in the test group's score. Presence …

Ribosomal Dna And The Phylogeny Of Frogs, David M. Hills, Loren K. Ammerman, Michael T. Dixon, Rafael O. De Sá

Biology Faculty Publications

Phylogenetic analysis of 1656 aligned sites in the 28S ribosomal RNA gene of frogs supports some of the recently recognized higher groups of anurans but provides counter-support for others. The 28S rDNA data support the monophyly of the recently recognized Pipanura (me- sobatrachians plus neobatrachians), which in turn indicates paraphyly of archaeobatrachians. Me- sobatrachians (pelobatoids plus pipoids), which are either considered paraphyletic or weakly sup- ported as monophyletic in morphological analyses, also receive support as a monophyletic group from the 28S rDNA data. Hyloidea (=Bufonoidea), which is widely recognized but lacks morphological support, receives some molecular support as being monophyletic. …

Relationships Of Epidermal Morphology And Breeding Behaviors In Pebble Nest-Building Minnows (Pisces: Cyprinidae), William R. Mcguire

Master's Theses

Abstrad The objective of this study was to determine if epidermal morphology corresponds with reproductive behavior in cyprinid fishes. Representative species of nest-building fishes (Nocomds leptocephalus, Semotilus atromeculatus, exoglossum maxillingua) and non nest-building fishes (Campostoma anomaulm and Clinostomus funduloides) were studied. Light and scanning electron microscopy were used to examine epidermal morphology and keratin distribution of skins from the snout, cheek, mandible, anterior dorso-lateral trunk, and caudal peduncle of breeding males of nest-building species and were compared to those in non nest-building cyprinid species. Previous frame-by-frame analysis of video tapes of reproductive activities of each species and literature accounts were …

Wood Anatomy Of Amanoa (Euphorbiaceae), W. John Hayden, Mark P. Simmons, Linda J. Swanson

Biology Faculty Publications

Wood anatomy of 29 specimens of seven species of Amanoa from tropical Africa, South America, and the Caribbean is described. The wood is diffuse-porous with most vessels in short radical multiples. Vessel elements are notably long, have simple perforation plates and small, alternative intervessel pits; tyloses are present in heartwood. Libriform wood fibres bear thick walls. Axial parenchyma distribution is diffuse and diffuse-in-aggregates. Chambered crystalliferous axial parenchyma is common. Rays are heterocellular, narrow, and very tall. The species examined, all from moist lowland forests, have similar wood structure. Wood of Amanoa resembles that of other primitive Euphorbiaceae.

Morfología Y Moléculas: Bases Complementarias De La Sistemática Moderna, Rafael O. De Sá, David M. Hillis

Biology Faculty Publications

RESUMEN

El auge de las técnicas moleculares en las últimas dos décadas ha traído nuevos enfoques en los estudios sistemáticos. Aquí presentaremos una revisión del uso, las aplicaciones, y los problemas de las principales metodologías de trabajo. Cada una de estas técnicas es aplicable a algunos problemas e inapropiada para otros, y es importante entender las suposiciones y limitaciones de cada técnica. Concluimos que el uso combinado de los enfoques morfológicos y moleculares otorga mejor resolución a los problemas sistemáticos.

ABSTRACT

The development of molecular techniques during the last two decades has brought new approaches to the analysis of systematic …