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Costs and benefits of Daphnia defense against Chaoborus in nature

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To estimate costs and benefits of antipredator defenses in the ChaoborusDaphnia system, we employed lake enclosures wherein controls (C) had no predators, the predation (P) treatment had freely swimming Chaoborus, and the kairomone (K) treatment predators were sequestered in a mesh tube apart from the Daphnia. Population growth (r) of two Daphnia pulex clones, one responsive (RC) and the other nonresponsive (NRC) to Chaoborus kairomone, was estimated for each predator treatment. Cost of defense was calculated as r(C,RC) – r(K,RC). Benefit was calculated as r(P,RC) – r(P,NRC). Antipredator defenses of Daphnia towards Chaoborus kairomone led to a 32% reduction in population growth in nature. The benefit of the defense, however, was a short-term 68% enhanced population growth by a responsive over a nonresponsive clone in the presence of the actual predation threat. The benefit of the defense exceeded the cost, but cost was nevertheless substantial. Our results verify that the in situ effects of Chaoborus on Daphnia involve direct and indirect impacts.

Afin d'évaluer les coûts et les bénéfices des défenses contre les prédateurs dans le système ChaoborusDaphnia, nous avons utilisé une série d'enclos lacustres: les enclos témoins (C) ne contenaient aucun prédateur, les enclos de prédation (P) avaient des Chaoborus en nage libre et les enclos de kairomone (K) contenaient des Chaoborus enfermés dans des tubes de grillage séparément des Daphnia. Nous avons mesuré la croissance de la population (r) chez deux clones de Daphnia pulex, l'un (RC) sensible et l'autre insensible (NRC) à la kairomone de Chaoborus. Les coûts de la défense sont représentés par r(C,RC) – r(K, RC) et les bénéfices par r(P,RC) – r(P,NRC). Les défenses contre les prédateurs de Daphnia en réaction à la kairomne de Chaoborus entraînent une réduction de 32 % de la croissance de la population en nature. Les bénéfices de la défense sont, par ailleurs, une croissance additionnelle à court terme de la population de l'ordre de 68 % chez le clone sensible, par rapport au clone insensible, en présence d'une menace réelle de prédation. Les bénéfices de la défense dépassent les coûts, bien que ces derniers soient importants. Nos résultats confirment que les effets in situ de Chaoborus sur Daphnia impliquent des impacts directs et indirects. [Traduit par la Rédaction]

Document Type: Research Article

Publication date: June 1, 2005

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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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