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First published online May 24, 2005
Journal of Experimental Biology 208, 2165-2175 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01614

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Effects of hypoxia acclimation on morpho-physiological traits over three generations of Daphnia magna

M. D. Seidl, R. J. Paul and R. Pirow^*

Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Hindenburgplatz 55, 48143 Münster, Germany

^* Author for correspondence (e-mail: pirow{at}uni-muenster.de)

Accepted 22 March 2005

The mechanisms, dynamics and effects of hypoxia acclimation were studied in the water flea Daphnia magna over three successive generations (parental, first and second filial generation: P, F₁ and F₂). The P generation was raised under normoxic conditions at 20°C and became exposed to environmental hypoxia (10-19% air saturation) at maturity. Their progenies (F₁ and F₂) experienced hypoxia from birth onwards. Controls were kept under normoxic conditions. Individuals were successively sampled in a 3-day interval from each acclimation group to determine morpho-physiological parameters relevant in oxygen transport and regulation. Hypoxia acclimation induced adjustments at the haemoglobin (Hb) and metabolic level (within 3 days) but none at the systemic level. The convective performance and oxygen-sensitive control of the ventilatory and circulatory systems were the same in both acclimation groups. The Hb concentration and oxygen affinity increased by 266% and 32%, respectively. The 22% decrease in mass-specific oxygen consumption rate reduced the energy allocation to somatic growth without greatly affecting reproduction. The onset and duration of hypoxic exposure during ontogenesis have had a significant influence on Hb oxygen affinity and body size. Transgenerational effects of hypoxia acclimation could not be observed. The adjustments at the Hb and metabolic levels in combination with the smaller body size, which is advantageous to diffusive oxygen transport, reduced the critical ambient oxygen tension by approximately 50%.

Key words: Crustacea, Branchiopoda, Daphnia magna, acclimation, circulation, growth, hypoxia, haemoglobin, NADH, oxygen transport, respiration, ventilation

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