Effect of stress on the ecophysiological response of the sand dollar Dendraster excentricus from northwestern Mexico

• Published in: Ciencias marinas Vol. 40; no. 2; pp. 133 - 147
• Main Authors: Olivares-Banuelos, Tatiana, Figueroa-Flores, Salvador, Carpizo-Ituarte, Eugenio
• Format: Journal Article
• Language: English; Spanish
• Published: 01.06.2014
• Subjects: Brackish; Dendraster excentricus; Marine; ISE, Mexico
• ISSN: 0185-3880
• DOI: 10.773/cm.v40i2.2360

In the Mexican Pacific, Dendraster excentricus, a common estuarine echinoderm, is subject to daily environmental variations in tidal fluxes. Little is known about its ecophysiological response when individuals are exposed to temperature and oxygen changes. This study evaluates their thermal stress response under normal and reduced oxygen conditions using the RNA/DNA ratio and hsp70 gene expression. We exposed sand dollars to different temperature and oxygen conditions. Three experimental temperatures were similar to the ones that organisms experience during one annual cycle and two were considered extreme. Reduced oxygen conditions were considered when levels dropped below 4 mg L super(-1). To estimate variations in the stress-induced RNA/DNA ratio, we determined the value for males and females during a daily cycle. We also analyzed the hsp70 expression. Under stress conditions, a significant decrease was observed in the RNA/DNA ratios. The lowest values were detected after 6 h under normoxic conditions and high temperatures seemed to induce a major effect on the RNA/DNA ratios during the first hour of stress. Analysis of the hsp70 expression showed significant differences. According to our results, thermal and reduced oxygen stress induces a reduction in the general metabolism of the organisms. These metabolic changes were observed by the decrease in the RNA/DNA ratios and expression levels of hsp70 (at high temperatures). We conclude that RNA/DNA ratios are a useful ecophysiological tool to evaluate the effect of particular stressors on the physiology of D. excentricus, and seem to be more sensitive to oxygen levels than to thermal stress, in contrast to the hsp70 expression, which was more sensitive to extreme temperatures.Original Abstract: En el Pacifico mexicano, Dendraster excentricus es un equinodermo comun en estuarios y esta sujeto a variaciones ambientales por el flujo de marea. Poco se conoce de su respuesta ecofisiologica cuando es expuesta a cambios de temperatura y oxigeno. Este estudio evalua su respuesta al estres termico en condiciones normales y de oxigeno reducido, utilizando como indicadores el indice de ARN/ADN y la expresion del gen hsp70. Se expusieron las galletas de mar a diferentes temperaturas y niveles de oxigeno. Tres de las temperaturas experimentales fueron comunes a las que los organismos experimentan durante un ciclo anual y dos de ellas se consideran extremas. Se consideraron condiciones de oxigeno reducido en niveles por debajo de 4 mg L super(-1). Para estimar las variaciones inducidas por estres en el indice de ARN/ADN, determinamos su valor en machos y hembras durante un ciclo diario. Ademas, analizamos la expresion del gen hsp70. En condiciones de estres, se observo un decremento significativo en los indices de ARN/ADN. Los valores mas bajos se detectaron despues de 6 h en condiciones normales de oxigeno y las temperaturas altas parecieron inducir un mayor efecto en los indices durante la primera hora de estres. El analisis de la expresion de hsp70 mostro diferencias significativas. Segun nuestros resultados, el estres termico y por oxigeno induce una reduccion general del metabolismo de los organismos. Estos cambios metabolicos se observaron en el decremento de los indices de ARN/ADN y en los niveles de la expresion de hsp70 (a altas temperaturas). Se concluye que los indices de ARN/ADN son una herramienta util para entender la respuesta ecofisiologica en D. excentricus y parecen mas sensibles a los niveles de oxigeno que al estres termico, en contraste con la expresion de hsp70 que resulto mas sensible a las temperaturas extremas.