A Method for Analysis of Protein in Individual Amoebae

SYNOPSIS The microelectrophoresis technic of Hydén and Lange has been adapted for analysis of the proteins of individual Amoeba proteus, A. dubia , and Pelomyxa carolinensis. The method has the sensitivity required for analyzing electrophoretic mobilities of the proteins of these 3 species and is reproducible. The possibility of using this technic to differentiate amoeba species according to their protein composition is discussed.     

Sound Producing Mechanisms in Recent Reptiles: Review and Comment

Reptiles produce sound by three categories of devices: thoseinvolving massive air expulsions or movements, those involvingmodulations of intermittent air movements through a modifiedglottis, and those involving rubbing or vibration of the integument.Each ocours in numerous species and there is good evidence ofmultiple origins. Most of the devices are used as predator deterrents,but there are a few cases of sound being used as an intraspecificcommunicating device. The various structures are here discussed.One may ask the general question whether the distribution ofreptilian sensory modalities may not have forced this rathermiscellaneous distribution of signalling devices.     

The Synthesis of Hyaluronic Acid by Ectoderm During Early Organogenesis in the Chick Embryo

This study demonstrates that the dorsal ectoderm of the stage 14 chick embryo synthesizes hyaluronic acid. About 49 to 52% of the H³ glucosamine-labeled glycosaminoglycan that is synthesized by explanted ectoderm can be identified as hyaluronic acid on the basis of its susceptibility to Streptomyces hyaluronidase or isolation of chondroitinase ABC digestion products. In addition, autoradiographic evidence shows that the ectoderm, unlike adjacent tissues like epithelial somites or neural tube, incorporates glucosamine into hyaluronidase-sensitive material which becomes largely extracellular and localized in the subectodermal cell-free space. Ultrastructural evidence shows that there is a fine fibrillar matrix between the ectodermal cells and in the subectodermal spaces when tannic acid is included in the primary fixative. This material resembles authentic hyaluronate, similarly fixed, and is absent when tannic acid is omitted from the fixative or when embryos have been previously treated in ovo with Streptomyces hyaluronidase. The concomitant reduction in the intercellular and subectodermal cell-free spaces after in ovo treatment with Streptomyces hyaluronidase supports the hypothesis that the dorsal ectoderm plays a morphogenetic role by contributing hyaluronate to the forming extracellular spaces. It is proposed that ectodermally derived hyaluronate might influence the morphogenesis of subjacent tissues such as the dermatome and neural crest.     

Evolution on a volcanic conveyor belt: using phylogeographic reconstructions and K–Ar-based ages of the Hawaiian Islands to estimate molecular evolutionary rates

The Hawaiian Islands form as the Pacific Plate moves over a 'hot spot' in the earth's mantle where magma extrudes through the crust to build huge shield volcanos. The islands subside and erode as the plate carries them to the north-west, eventually to become coral atolls and seamounts. Thus islands are ordered linearly by age, with the oldest islands in the north-west (e.g. Kauai at 5.1 Ma) and the youngest in the south-east (e.g. Hawaii at 0.43 Ma). K–Ar estimates of the date of an island's formation provide a maximum age for the taxa inhabiting the island. These ages can be used to calibrate rates of molecular change under the following assumptions: (i) K–Ar dates are accurate; (ii) tree topologies show that derivation of taxa parallels the timing of island formation; (iii) populations do not colonize long after island emergence; (iv) the coalescent point for sister taxa does not greatly predate the formation of the colonized younger island; (v) saturation effects and (vi) among-lineage rate variation are minimal or correctable; and (vii) unbiased standard errors of distances and regressions can be estimated from multiple pairwise comparisons. We use the approach to obtain overall corrected rate calibrations for: (i) part of the mitochondrial cytochrome b gene in Hawaiian drepanidines (0.016 sequence divergence/Myr); (ii) the Yp1 gene in Hawaiian Drosophila (0.019/Myr Kambysellis et al. 1995 ); and (iii) parts of the mitochondrial 12S and 16S rRNA and tRNA^val in Laupala crickets (0.024–0.102/Myr, Shaw 1996 ). We discuss the reliability of the estimates given the assumptions (i–vii) above and contrast the results with previous calibrations of Adh in Hawaiian Drosophila and chloroplast DNA in lobeliods.     

Centennial‐scale changes to the aquatic vegetation structure of a shallow eutrophic lake and implications for restoration

1. We investigate long‐term (>200 years) changes to the composition and spatial structure of macrophyte communities in a shallow, eutrophic lake (Barton Broad, eastern England) and consider the implications for lake restoration. 2. Historical macrophyte data were assembled from a variety of sources: existing plant databases, museum herbaria, journal articles, old photographs and eyewitness accounts. Additionally, two types of sediment core sample were analysed for plant macro‐remains and pollen; bulk basal samples from multiple core sites analysed to provide information on ‘pre‐disturbance’ macrophyte communities and two whole cores analysed to determine historical change. 3. Prior to the late 1800s, macrophyte communities were diverse and included a multilayered mosaic of short‐stature submerged taxa and taller submerged and floating‐leaved species. With the progression of eutrophication after around 1900, the former community was displaced by the latter. Diversity was maintained, however, since an encroaching Schoenoplectus–nymphaeid swamp generated extensive patches of low‐energy habitat affording refugia for several macrophytes otherwise unable to withstand the hydraulic forces associated with open water conditions. When this swamp vegetation disappeared in the 1950s, many of the ‘dependent’ aquatic macrophytes also declined leaving behind a sparse, species‐poor community (as today) resilient to both eutrophication and turbulent open waters. 4. The combination of historical and palaeolimnological data sources offers considerable benefits for reconstructing past changes to the aquatic vegetation of lakes and for setting restoration goals. In this respect, our study suggests that successful restoration might often be better judged by reinstatement of the characteristic structure of plant communities than the fine detail of species lists; when nutrients are low and the structure is right, the right species will follow.     

A network for long-term ecological research in the United States

SUMMARY. 1. A network of seventeen long-term ecological research sites funded by the National Science Foundation (NSF) and spanning sites in arctic to tropical climates, low to high altitudes and wet to dry environments, provides evidence for the increasing popularity of sustained ecological research in the U.S.A.
2. The sites function as regional or national facilities for long-term research as well as for comparative and process studies by investigators from the operating institutions and by visiting researchers.
3. The aquatic habitats include a variety of lakes ponds, wetlands and a playa; montane, woodland, tundra and prairie streams; as well as salt marsh, estuary, ocean beach and inshore oceanic sites.     

Structure of Pentatrichomonas hominis (Davaine) as Revealed by Electron Microscopy*

SYNOPSIS. Fine structure of Pentatrichomonas hominis is described in the light of previous light microscopic findings. The relationships among kinetosomes #1-#4 and R are like those previously reported orhomonas gallinae, and the same is true of the rootlet filaments associated with the several kinetosomes. The kinetosome (I) of the independent flagellum is situated just behind the reflection of the sigmoid filaments of kinetosome #2 onto the pelta and parallels these filaments for a considerable distance. The peltaraxostylar junction consists of 3 layers: the capitulum of the axostyle (outer, the pelta (intermediate, and the sigmoid rootlets of kineto some #2 (inner). The pelta overlaps the axostylar capitulum to a variable extent. The parabasal body consists of elongate and flattened cisternae of smooth endoplasmic reticulum surrounded by numerous small vesicles. There are 2 typically cross-striated parabasal filaments, filament 2 probably contributing most, if not all, the material to the slender, periodic organelle that underlies the parabasal body and usually does not extend far beyond the posterior end of the nucleus. The periodic costa is paralleled by paracostal granules, but there are few, if any, paraxostylar granules. The ultrastructure of the costa appears to be a network of flattened hexagons, with a single fibril projecting thru each of the hexagonal areas. The major cross-striations are made up largely of densely-stained filaments which are occasionally cut in cross section. The undulating membrane consists of a cytoplasmic fold extending from the dorsal surface of the organism and of the attached part of the recurrent flagellum, which is closely applied to the fold. The segment of the membrane dorsal to the flagellum, presumably the “accessory filament,” contains the marginal lamella, a membrane folded upon itself and with periodicity virtually indistinguishable from that of the rootlet filament of kinetosome #1.     

Study of Dientamoeba fragilis Jepps & Dobell I. Electronmicroscopic Observations of the Binucleate Stages II. Taxonomic Position and Revision of the Genus*

Light- and electronmicroscopic observations on Dientamoeba fragilis strain A (Bi) 1 dealing primarily with the binucleate (arrested telophase) stages, predominant in all populations, revealed the microtubular nature of the extranuclear spindle which extends between the 2 polar complexes each adjacent to one of the nuclei. The spindle microtubules originate in paired, nonperiodic structures apparently homologous to the “atractophores” described from hypermastigotes. To the external surface of the atractophores are applied periodic elements, which extend laterally as the parabasal filaments. Extensive Golgi complexes overlie the filaments, these structures corresponding to the components of the parabasal apparatus known from trichomonads and hypermastigotes. The 2-layered structures, consisting of the atractophores and periodic layers, together with the proximal parts of the Golgi complex and the spindle microtubules constitute the polar complex. No kinetosome- or centriole-like organelles have been found in the polar complexes or elsewhere in the organism. The extranuclear spindle is composed of 2 microtubule bundles, each with ～30-40 microtubules. One of the bundles always appears at some distance from the nucleus; the other is juxtanuclear and is seen often to course within a groove of the nuclear envelope. A 3rd bundle of ～35-45 microtubules is seen on occasion to arise from the atractophores and to pass toward the nucleus at a wide angle to the other parts of the spindle. In some instances these microtubules traverse the nucleus within channels delimited by the nuclear envelope. The double-layered nuclear envelope contains numerous pores. Two morphologic types of rounded inclusions, one microbody-like, and the other with a more electron-translucent matrix, as well as digestive vacuoles containing rice starch, bacteria, and/or myelin configurations are distributed in the cytoplasm, which abounds also in glycogen granules. The fine structure of Dientamoeba is compared with those of trichomonads and of Entamoeba spp. The taxonomic position of Dientamoeba is discussed and emended; in view of its affinities, this genus is placed among trichomonads in the family Dientamoebidae Grassé, emend.