Depredación sobre el erizo diadema aff. antillarum en blanquizales de las Islas Canarias

Experimental studies were carried out to determine the effects of predation on populations of the sea urchin Diadema aff. antillarum in barren grounds at the Canary Islands. The studied urchin populations were dominated by small to medium sized individuals (24-38 mm) and were variable in space. Tethering experiments showed that predation rates on D. aff. antillarum were very low and no differences were found between sites. Predation was found to be most intense on juveniles ( 40 mm were not preyed upon whatsoever. We have experimentally demonstrated that there is an absolute predator ‘escape size’ of around 40 mm for D. aff. antillarum individuals in barren grounds. Predation rates obtained for juveniles show that a sufficient number may escape predation and sustain the adult population, maintaining the urchin barren habitat. Recruitment and topographic complexity, rather than predation, seem to determine the structure of urchin populations in barren grounds. We conclude that predation in fished barren grounds of the Canarian Archipelago is not of sufficient magnitude to substantially alter dense urchin populations and cause community-level effects.Se realizaron unos estudios experimentales para valorar el efecto de la depredación sobre las poblaciones del erizo Diadema aff. antillarum, en zonas de blanquizales de las islas Canarias. Las poblaciones de erizos aparecieron dominadas por erizos de tallas pequeñas a medianas (24-38 mm) y resultaron variables en el espacio. Los experimentos de atado mostraron que D. aff. antillarum soporta una presión de depredación muy baja y no se encontraron diferencias entre las estaciones de estudio. La tasa de depredación fue más intensa sobre juveniles (< 20 mm) y adultos de entre 20-30 mm, rango de talla en el que la mayoría de los individuos dejan de tener comportamiento críptico. Los erizos de más de 40 mm de diámetro no fueron depredados en ningún caso. Demostramos experimentalmente la existencia de una talla de escape de D. aff. antillarum frente a la depredación en zonas de blanquizal en torno a los 40 mm. La tasa de depredación obtenida para juveniles indica que un número suficiente debe escapar de la depredación, manteniendo las poblaciones adultas y los blanquizales. Las tasas de reclutamiento y la complejidad topográfica, más que el nivel de depredación, parecen determinar la estructura de las poblaciones de erizos en los blanquizales. Concluimos que la depredación en los fondos rocosos sobreexplotados de las islas Canarias no tiene la magnitud suficiente para alterar substancialmente las densas poblaciones de erizos y causar efectos sobre la comunidad

Diferentes efectos de la protección frente al marisqueo en las poblaciones de dos especies de lapas en una reserva marina de reciente creación

This study aimed to evaluate the effects of protection from extractive activities on the population structure of two limpets of commercial interest, Patella ulyssiponensis and Patella candei crenata. We evaluated the status of these populations in La Palma Marine Protected Area (MPA), Canary Islands, and in comparable unprotected areas in the lower intertidal zone of the same island. We showed that the density of P. ulyssiponensis depended greatly on the level of protection, whereas the effects of protection on the density of P. candei crenata were less clear and only differences between sites were found. These results are probably linked to the different habitat affinities of the two species studied and demonstrate the need to tailor conservation strategies in MPAs to individual species for appropriate management of local shellfish resources.Este estudio tiene por objetivo evaluar el efecto de la protección frente a actividades extractivas sobre la estructura poblacional de las especies de lapas de interés marisquero, Patella ulyssiponensis y Patella candei crenata. Para ello, se evaluó el estado de sus poblaciones en el intermareal inferior de localidades situadas tanto dentro de la Reserva Marina de La Palma (islas Canarias) como en zonas no protegidas de características similares. Se observó que la densidad de P. ulyssiponensis depende en gran medida del nivel de protección, mientras que en el caso de P. candei crenata el efecto de la protección sobre la densidad no fue tan claro, observándose diferencias sólo entre localidades. Estos resultados probablemente se relacionan con las distintas afinidades de hábitat entre las especies estudiadas, lo que indica la necesidad de proteger áreas más heterogéneas que incluyan una variedad de hábitat adecuada para la diversidad de especies de una región, asegurando una correcta regulación y conservación de los recursos marisqueros

Annual reversible plasticity of feeding structures: cyclical changes of jaw allometry in a sea urchin

A wide variety of organisms show morphologically plastic responses to environmental stressors but in general these changes are not reversible. Though less common, reversible morphological structures are shown by a range of species in response to changes in predators, competitors, or food. Theoretical analysis indicates that reversible plasticity increases fitness if organisms are long-lived relative to the frequency of changes in the stressor and morphological changes are rapid. Many sea urchin species show differences in the sizes of jaws (demi-pyramids) of the feeding apparatus, Aristotle's lantern, relative to over-all body size, and these differences have been correlated with available food. The question addressed here is whether reversible changes of relative jaw size occur in the field as available food changes with season. Monthly samples of the North American Pacific coast sea urchin Strongylocentrotus purpuratus were collected from Gregory Point on the Oregon (USA) coast and showed an annual cycle of relative jaw size together with a linear trend from 2007 to 2009. Strongylocentrotus purpuratus is a long-lived species and under field conditions individuals experience multiple episodes of changes in food resources both seasonally and from year-to-year. Their rapid and reversible jaw plasticity fits well with theoretical expectations.Keywords: Fitness, Strongylocentrotus purpuratus, Morphology, Oregon, Reaction norm, Aristotle's lanternKeywords: Fitness, Strongylocentrotus purpuratus, Morphology, Oregon, Reaction norm, Aristotle's lanternKeywords: Fitness, Strongylocentrotus purpuratus, Morphology, Oregon, Reaction norm, Aristotle's lanternKeywords: Fitness, Strongylocentrotus purpuratus, Morphology, Oregon, Reaction norm, Aristotle's lanter

Concepciones de educadores y estudiantes normalistas sobre aprendizaje, enseñanza y evaluación de las matemáticas. Una propuesta de análisis

El presente documento muestra una propuesta de investigación que busca caracterizar las concepciones sobre el aprendizaje, la enseñanza y la evaluación de los aprendizajes que tienen los educadores y los próximos egresados del programa de Educación Secundaria con la especialidad en Matemáticas de algunas escuelas normales de los estados de Colima, Jalisco, Michoacán y Sinaloa, México. Se busca también identificar la posible correspondencia entre las concepciones de los educadores y sus estudiantes. La situación será abordada como un estudio exploratorio con enfoque cualitativo aplicándose el cuestionario compuesto por dilemas fundamentado en las teorías implícitas del aprendizaje (directa, interpretativa y constructiva)

Microplastics determination in gastrointestinal tracts of european sea bass (Dicentrarchus labrax) and gilt-head sea bream (Sparus aurata) from Tenerife (Canary Islands, Spain)

Microplastic pollution has an extremely widespread distribution, to the extent that microplastics could be ingested by aquatic organisms, including species of commercial importance for fisheries and aquaculture. In this work, the anthropogenic particles content of the gastrointestinal tracts of 86 individuals of cultivated European sea bass (Dicentrarchus labrax, n = 45) and gilt-head sea bream (Sparus aurata, n = 41) from Tenerife (Canary Islands, Spain) was determined. Samples were bought at local markets and directly transported to the laboratory. After the dissection of the fishes and digestion of the gastrointestinal tracts in 10% KOH (w/v) at 60◦C for 24 h, the digests were filtered (50 µm stainless-steel mesh) and visualized under a stereomicroscope, finding that most of the items were colourless (47.7% for Dicentrarchus labrax and 60.9% for Sparus aurata) and blue (35.3% vs. 24.8%) microfibers, with an average length of 1957 ± 1699 µm and 1988 ± 1853 µm, respectively. Moreover, 15.3% of the microfibres were analysed by Fourier transform infrared spec-troscopy, showing the prevalence of cellulosic fibres together with polyester, polyacrylonitrile, and poly(ether-urethane). This pattern (microplastics shapes, colours, sizes, and composition) clearly agrees with previous studies carried out in the Canary Islands region regarding the determination of microplastics in the marine environmen

Efficiency of artificial collectors for quantitative assessment of sea urchin settlement rates

Summary: We tested the suitability of three different kinds of artificial collectors designed for quantitative assessment of echinoid settlement rates: (1) nylon nets containing plastic biofilter balls, (2) vertical scrub brushes with vegetal bristles and (3) horizontal triangular mats of coconut fibre. We measured the collecting efficiency by counting the number of post-larvae of two sea urchin species (Paracentrotus lividus and Arbacia lixula) gathered by each collector and deployed in two geographic areas: Tenerife (Canary Islands, eastern Atlantic) and Tossa de Mar (Costa Brava, northwestern Mediterranean). The plastic biofilter ball collector proved to be the most efficient design, collecting more settlers of both sea urchin species under all assayed conditions and showing a higher reproducibility than the other two designs. We therefore suggest using plastic biofilter balls in future studies aimed at quantifying echinoid settlement rates

Spatial variability, structure and composition of crustose algal communities in Diadema africanum barrens

Crustose algal communities were studied in Diadema africanum urchin barrens around Tenerife (Canary Islands, NE Atlantic). A hierarchical nested sampling design was used to study patterns of community variability at different spatial scales (sectors, three sides of the island; sites within each sector, 5–10 km apart; stations within each site, 50–100 m apart). Although noncrustose species contributed the most to community richness, cover was dominated by crustose forms, like the coralline algae Hydrolithon farinosum, H. samoe¨nse, H. onkodes, Neogoniolithon orotavicum and N. hirtum, and the phaeophycean Pseudolithoderma adriaticum. The structure of these communities showed high spatial variability, and we found differences in the structure of urchin barrens when compared across different spatial scales. Multivariate analysis showed that variability in community structure was related to the five environmental variables studied (wave exposure, urchin density, substrate roughness, productivity and depth). Wave exposure was the variable that contributed most to community variability, followed by urchin density and substrate roughness. Productivity and depth had limited influence. The effects of these variables differed depending on the spatial scale; wave exposure and productivity were the main variables influencing community changes at the largest scale (between different sectors of the island), while D. africanum density, roughness and depth were the most influential at medium and small scales

Optimización de un modelo de trasplante intestinal heterotópico en ratas utilizando la combinación Sprague Dawley-Wistar para el estudio del proceso de rechazo celular agudo

El rechazo del injerto (RI) constituye una de las principales complicaciones pos-quirúrgicas en pacientes que reciben un trasplante intestinal (TI), ya que puede comprometer la vida del receptor y del órgano trasplantado. Por tal motivo, comprender de mejor manera la patogenia del rechazo intestinal y establecer estrategias para prevenirlo, diagnosticarlo de manera temprana y tratarlo representan un gran desafío en el área clínica y experimental. En este sentido, los modelos de TI en roedores constituyen una herramienta de gran utilidad para estudiar temas inherentes a este tipo de trasplante.Facultad de Ciencias Médica