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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



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  		Fig. 1. Experimental schedule. Time of birth (circles) and subsequent period of life of each generation (P, F1, F2: parental, first and second filial generation, respectively; horizontal arrows). Broken lines indicate the juvenile period. White and black lines, arrows and circles indicate normoxic and hypoxic culturing conditions, respectively. Vertical ticks mark the times at which individuals were sampled from the respective generations.

 


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  		Fig. 2. Whole-animal oxygen consumption rate (O2; A-C) relative to carapace length (Lc), and age-dependence of clutch size (D-F) and carapace length (Lc; G-I) of normoxia-acclimated (open circles) and hypoxia-acclimated animals (filled triangles). P, parental generation; F1, first filial generation; F2, second filial generation. Each data point refers to a single measurement (A-C) or represents the mean ± S.D. of 8-15 animals (D-I).

 


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  		Fig. 3. Summary of the physiological characteristics of normoxia-acclimated (open circles) and hypoxia-acclimated animals (filled triangles). The data of the three generations (P, F1 and F2) were pooled and given as means ± S.D. Also shown are the physiological responses (A-E) to decreasing ambient oxygen partial pressures (PO2amb) or oxygen equilibrium curves (F) of haemolymph samples. Sigmoid curves in E and F were fitted to the data using the Hill equation. Broken lines represent critical PO2amb values, which indicate a deflection point on the response curve of a physiological parameter (Pc,O, Pc,N, Pc,A, Pc,H, PHP,) or the half-saturation oxygen tension of Hb (P50). For clarity, the critical values are given only for normoxia-acclimated animals.

 


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  		Fig. 4. Summary of the morphological and physiological characteristics of normoxia-acclimated (open circles) and hypoxia-acclimated animals (filled triangles) of the three generations (P, F1 and F2). Values are means ± S.D. The numbers of measurements on different animals per data point were 5-6 (A-C,L) and 10-12 (D-K,M,N), respectively. Asterisks indicate significant differences between the two acclimation groups within one generation (*P<0.05).

 


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  		Fig. 5. Relation between logarithmically transformed stroke volume (lnVS, VS in nl) and carapace length (ln Lc, Lc in mm) of normoxia-acclimated (open circles) and hypoxia-acclimated animals (filled triangles) of all generations (P, F1 and F2). The broken and solid lines represent linear regression lines for the data of the former (lnVS=-0.178+2.734lnLc, r2=0.81, N=36) and the latter groups (lnVS=-0.0454+2.588lnLc, r2=0.80, N=33), respectively.

 


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  		Fig. 6. Time course of selected physiological parameters of normoxia-acclimated (open circles) and hypoxia-acclimated animals (filled triangles) of the P generation. The start of hypoxic incubation is indicated by vertical broken lines. Each data point represents one measurement (B) or shows the mean of two measurements (A,C,D) on different animals. [Hb], haem-based haemoglobin concentration; Pc,N, Pc,A, critical PO2amb values (see Fig. 3B,C); O2, mass-specific oxygen consumption rate.

 


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  		Fig. 7. Summary of all physiological parameters which showed a dependency on carapace length. Open circles represent the data of all normoxia-acclimated animals with dashed lines indicating significant linear dependencies. The data of hypoxia-acclimated animals are given separately for the P generation (filled circles) and the F1 and F2 generation (filled triangles). The data of both filial generations were used for linear regression analysis with solid lines indicating significant linear dependencies. Other details as in Fig. 4.

 

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© The Company of Biologists Ltd 2005