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Temperature and diet effects on omnivorous fish performance: implications for the latitudinal diversity gradient in herbivorous fishes

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Herbivorous fishes show a clear latitudinal diversity gradient, making up a larger proportion of the fish species in a community in tropical waters than in temperate waters. One proposed mechanism that could drive this gradient is a physiological constraint due to temperature. One prediction based on this mechanism is that if herbivorous fishes could shift their diet to animal material, they would be better able to grow, survive, and reproduce in cold waters. We tested this prediction on the omnivore Girella nigricans under different temperature and diet regimes using RNA–DNA ratios as an indicator of performance. Fish had increased performance (100%) at low temperatures (12 °C) when their diet was supplemented with animal material. In contrast, at higher temperatures (17, 22, and 27 °C) fish showed no differences between diets. This indicates that omnivorous fishes could increase their performance at low temperatures by consuming more animal matter. This study supports the hypothesis that a relative increase in the nutritional value of plant material at warmer temperatures could drive the latitudinal diversity gradient in herbivorous fishes.

Les poissons herbivores se répartissent selon un gradient latitudinal de diversité, dans lequel ils représentent une proportion plus grande des poissons de la communauté dans eaux tropicales que dans les eaux tempérées. Un des mécanismes proposés pour expliquer ce gradient est une contrainte physiologique reliée à la température. Une des prédictions découlant de ce mécanisme est que, si les poissons herbivores pouvaient changer leur régime alimentaire pour augmenter le matériel animal, ils seraient mieux capables de croître, de survivre et de se reproduire dans les eaux froides. En utilisant les rapports ARN–ADN comme indicateurs de performance, nous avons testé cette prédiction chez l'omnivore Girella nigricans à différentes températures et sous divers régimes alimentaires. Les poissons ont une performance accrue (100 %) à basse température (12 °C) lorsque leur régime est additionné de matière animale. En revanche, aux températures plus élevées (17, 22 et 27 °C), il n'y a pas de différence chez les poissons, quel que soit le régime alimentaire. Cela indique que les poissons omnivores pourraient améliorer leur performance à basses températures en consommant plus de matière animale. Notre étude appuie l'hypothèse qui veut qu'une augmentation relative de la valeur nutritive de la matière végétale aux températures plus élevées pourrait expliquer le gradient latitudinal de diversité chez les poissons herbivores.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: June 29, 2007

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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