Natural Sciences

The orientation of the fibers in the dermis of the tiger salamander, Ambystoma tigrinum, undergoes a dramatic repatterning at metamorphosis. The pre-metamorphic, larval dermis is a tight layer composed of crossed fibers that wind helically around the trunk. This condition is retained by neotenic adults which do not undergo metamorphosis. In contrast, the neotenic adults which do not undergo metamorphosis. In contrast, the metamorphosed adult dermis consists of a superficial, loose network of fibers invested with large multicellular glands--the stratum spongiosum--and a deeper tight layer of fibers--the stratum densum. However, unlike the crossed fibers of the pre-metamorphic dermis, there is no preferred orientation to the fibers in either layer of the post-metamorphic dermis. In order to evaluate whether these two distinctly different fiber patterns are constructed from biochemically similar fibers, the collagen types present in the pre- and post-metamorphic dermis were determined using SDS-polyacrylamide gel electrophoresis. Type I collagen is the predominant collagen of the dermis and the same major collagen types are present for all individuals, whether pre- or post-metamorphic. Thus, the major types of collagen that compose the dermal fibers do not change during metamorphic repatterning of the dermis.

... The “Amigas de la Naturaleza,” from Camilo Domínguez High School, Mariscal Sucre, were our ever-trusty field companions. ... John Lynch from Universidad Nacional de Colombia and Diego Cisneros from the Universidad San Francisco de Quito (USFQ) also helped confirm ...

Many animal connective tissues are composite materials formed into sheaths containing regularly organized collagen fibres in a crossed, fabric-like array. From a few simple assumption about the interactions between fibres, we construct a model for the effect of such a fabric-like construction on the Poisson's ratio of connective tissue sheaths. Surprisingly, the model predicts high Poisson's ratios (often greater than 1.0) Mdashespecially high given the value of 0.5 that is usually used for primarily aqueous biological tissues (based on assumptions of incompressibility and anisotropy). However, virtually all empirical attempts to measure Poisson's ratio in animal connective tissue sheaths (including our own experiments on salamander skin) reveal similarly high Poisson's ratios. The model also predicts that Poisson's ratio will increase with increasing strain, at a rate dependent on the initial angle of the crossed fibres relative to the direction of strain. Since the Poisson's ratio of a material is directly correlated with the material's stiffness, such strain-dependent changes in Poisson's ratio have important implications for the stiffness properties of connective tissue sheaths. Given the structural support role of connective tissues, stiffness is assumed to be one of their most important qualities, and several examples of how our model might predict the stiffness qualities within the walls of cylinders formed from helically wound crossed fibre sheaths (such as mammalian annular ligament and nematode cuticle) are given.

The grapevine genetic transformation programs have relayed on the use of solid media-based somatic embryogenesis. To reach a high throughput of candidate gene evaluation in 'Thompson Seedless', a semi-automatic system allowing viable transformation of explants was designed. An intermediate procedure using liquid media and agitated flasks was first characterized, leading to reduction in the biomass duplication time of pro-embryogenic (PE) cells from 30 d in dishes to 14 d. The oxygen transfer coefficient value in this system was 213h(-1) at 120rpm and 25 degrees C with a 16/8-h (light/darkness) photoperiod. The scaling-up to the air-lift bioreactor decreased the biomass duplication time of PE cells up to 5.3 d post-inoculation (pi) and an average volumetric productivity of 1.6g/(dxL). Although slight browning was seen in the explants during the phase of 8-14 d pi, no losses in their viability and regenerative capability were observed. Cultured cells showed normal elongation in the transition from heart- to the torpedo-shape and finally to advanced developmental stages, with radicle emergence and whole plant generation. Agrobacterium-mediated transformation of cells was efficiently incorporated after this multiplication process by use of conventional procedures in dishes, allowing the generation of transgenic plantlets confirmed by PCR.

ABSTRACT: The objective of this study was to manufacture a shortening using chemical interesterification (IT) of tallow–sun-flower oil blends to replace fish oil in the present formulation, which is now in short supply in Chile. The significant variables of the IT process were obtained by 24-1 ...

Herbivory and nutrient enrichment are drivers of benthic dynamics of coral reef macroalgae; however, their impact may vary seasonally. In this study we evaluated the effects of herbivore pressure, nutrient availability and potential propagule supply on seasonal recruitment and succession of macroalgal communities on a Florida coral reef. Recruitment tiles, replaced every three months, and succession tiles, kept in the field for nine months, were established in an ongoing factorial nutrient enrichment-herbivore exclusion experiment. The ongoing experiment had already created very different algal communities across the different herbivory and nutrient treatments. We tracked algal recruitment, species richness, and species abundance through time. Our results show seasonal variation in the effect of herbivory and nutrient availability on recruitment of coral reef macroalgae. In the spring, when there was higher macroalgal species richness and abundance of recruits, herbivory appeared to have more control on macroalgal community structure than did nutrients. In contrast, there was no effect of either herbivory or nutrient enrichment on macroalgal communities on recruitment tiles in cooler seasons. The abundance of recruits on tiles was positively correlated with the abundance of algal in the ongoing, established experiment, suggesting that propagule abundance is likely a strong influence on algal recruitment and early succession. Results of the present study suggest that abundant herbivorous fishes control recruitment and succession of macroalgae, particularly in the warm season when macroalgal growth is higher. However, herbivory appears less impactful on algal recruitment and community dynamics in cooler seasons. Ultimately, our data suggest that the timing of coral mortality (e.g., summer vs. winter mortality) and freeing of benthic space may strongly influence the dynamics of algae that colonize open space.

The feeding activity of herbivorous fishes and their impact on coral reefs with different levels of anthropogenic degradation. The feeding activity of three herbivorous fishes (Sparisoma viride, Scarus iserti and Acanthurus coeruleus) and its impact on two coral reefs were studied during the dry (February) and rainy (August) seasons of 2006 in Cuba. One of the reef stations is at the " Acuario " dive point in the Guanahacabibes National Park, and is relatively pristine. The second one is located at the north coast of Havana City facing the Instituto de oceanología (IdO) and is subject to pollution and fishing pressures. Herbivore fish composition was analized, and foraging intensity was measured for all Acanthurid and Scarid species, by counting fish bites in 1 m 2 during five minute intervals (25 replicates). Concurrently, species foraging intensity was measured for juvenile, intermediate, and adult phases, counting fish bites during 10 minutes intervals (10 replicates). Algal consumption rate was estimated using a coefficent of consumed biomass per bite, for each size class. The algal cover was sampled at 20 m linear transects with four replicates at each site. Food items were assessed sampling algae at the observed bitten substrates. Compared to Acuario, herbivores in IdO showed lower species richness and higher density of small size fishes, but large-sized parrotfish was almost absent due to intense fishing. The highest bite rate was observed for the smallest fish size, but net consumption rate was three times greater for medium and great size fishes, which were more abundant in the protected area. Algal cover was lower in Acuario, while in IdO it was very high, and coral cover was very low. In both locations epiphytic algae were the preferred food. These results support generalizations referring to the importance of great size herbivores fishes in controlling excesive algal proliferation on coral reefs. Rev. Biol. Trop. 57 (3): 687-697. Epub 2009 September 30.

Resumen Se propone un sistema de escalas de clasificación y puntaje de bioindicadores de de condición del bentos y de la ictiofauna de arrecifes coralinos de la metodología AGRRA (Atlantic and Gulf Rapid Reef Assessment), con algunos márgenes de variación más amplios que los aplicados en la Región del Arrecife Mesoamericano por otros autores. Por esa razón puede ser aplicable tanto en Cuba como en el Gran Caribe. Las escalas tienen cinco categorías de condición de los indicadores a los que corresponden puntajes del 1 al 5, respectivamente. La mayoría de los indicadores tiene en sus intervalos una progresión geométrica de base 2. En los restantes, la escala de intervalos se basó en el criterio de los autores. Las escalas se basaron en los abundantes datos de AGRRA disponibles de Cuba y del Gran Caribe. Esta propuesta es una herramienta complementaria o alternativa a la aplicación actual de promedios regionales de los indicadores AGRRA como valores de referencia de condición del bentos y de la ictiofauna en arrecifes coralinos. Tiene la ventaja de que a diferencia de los promedios regionales las escalas no varían con el tiempo. Abstract A system of scales is proposed for the classification and scoring of bioindicators of AGRRA (Atlantic and Gulf Rapid Reef Assessment) methodology, for both benthic and ichthyofaunal conditions in coral reefs, with some wider variation limits than those applied by other authors in the Mesoamerican Reef Region. For that reason it can be applied in Cuba as well as in the wider Caribbean. The scales bear five condition categories consistent with scores of 1 to 5, respectively. Most indicators have a base-2 geometrical progression in their intervals. In the remaining indicators, the scales of intervals are based upon author's criterion. Scales are based on the abundant AGRRA data available from Cuba and the Wider Caribbean. This proposal is a complementary or alternative tool to the current application of regional averages of AGRRA indicators, as reference values of benthic and ichtyofaunal conditions in coral reefs. The proposal has the advantage that, unlike regional averages, the scales do not vary in time.

Composition and structure of fishes communities was evaluated in San Antonio's Bank, an area to be declared Outstanding Natural Element by the National Protected Areas System. Visual censuses were carried out in 5 stations using the AGRRA methodologies (4 stations) and Brock (1 station), located in the northwest area of the Bank. The indexes of diversity, evenness, species richness, frequency-abundance, density and biomass were considered, as well as the structure strophic. A total of 93 species were recorded in the area. Species such as Stegastes partitus, Clepticus parrae, the complex Coryphopterus personatus /hyalinus and Chromis cyanea were abundant. The composition for sizes was dominated by small individuals (Class <5 cm total longitude), due to the homogeneity of the bottom. The Serranidae, Carangidae, Lutjanidae and Kyphosidae families, representing more than 75% of total biomass. The structure strophic was dominated by the benthophagous (83% of the observed species) and inside this group, the omnivorous ones (51%), they were the most abundant, the herbivores presented low densities. The synthetic indexes showed similar values to those reported to the south of Guanahacabibes; both places present a similar bottom structure and are not exposed to antropics impacts. The bank is a difficult access area and its geographical location restricts all kind of fishing. Lack of refuge constitutes a handicap for big fish communities’ establishment.