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First published online May 24, 2004
Journal of Experimental Biology 207, 2267-2276 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00991

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Temperature-dependent oxygen limitation in insect eggs

H. Arthur Woods^* and Ryan I. Hill

Section of Integrative Biology, University of Texas at Austin, Austin, TX 78712, USA

View larger version (15K): [in a new window]   Fig. 1. Effects of temperature and ambient oxygen partial pressure PO2 on development of eggs of Manduca sexta. Eggs were exposed to experimental conditions from within 6 h of oviposition until hatching. Ten eggs were exposed to each combination of factors (240 eggs total), and all treatments were started simultaneously. (A) Fraction hatching in each combination of temperature and oxygen. (B) Total development time from oviposition to hatching, including only those that actually hatched. In all cases, standard errors were so small that they are hidden by their respective symbol.

View larger version (18K): [in a new window]   Fig. 2. Carbon dioxide emission (mean ± S.E.M.) by batches of eggs (Manduca sexta) at different combinations of temperature and oxygen. See text for details.

View larger version (14K): [in a new window]   Fig. 3. Single batch of 40 eggs of Manduca sexta ramped from 16 to 48.5°C over 55 min (broken line is the temperature trace). Traces at all oxygen levels exhibited qualitatively similar patterns.

View larger version (22K): [in a new window]   Fig. 4. CO2 emission by batches of eggs of Manduca sexta, as a function of temperature. Eggs were ramped from 16 to 48.5°C over 55 min. Each color represents three batches of 40 eggs. Solid lines represent mean CO2 emission at 1°C increments, and broken lines indicate S.E.M.

View larger version (28K): [in a new window]   Fig. 5. Statistical analysis of data shown in Fig. 4. CO2 emission by each batch of eggs was fitted by the logistic curve (see text for details). (A) Fitted values of the coefficient K (filled diamonds) and calculated emission rates (µg mol–1 h–1) from the fitted model (coefficients given in Table 4) for temperatures of 16 (solid squares) and 38°C (open circles). K depends on ambient PO2 by the relationship: K=15.1+0.85PO2 (r2=0.71; F1,10=24.3, P<0.001). Calculated emission rates at 38°C depend on ambient PO2 by the relationship: CO2 (38°C)=15.4+0.65 PO2 (r2=0.70; F1,10=23.6, P<0.001). Calculated emission rates at 16°C were not significantly related to ambient oxygen (F1,10=0.05, P=0.82). (B) Residual variation about the model fitted to the emission trace from each batch of eggs.

View larger version (14K): [in a new window]   Fig. 6. Representative profile of radial oxygen partial pressure in an egg of Manduca sexta. The initial reading is from still water (temperature equilibrated and air saturated). The first arrow indicates electrode withdrawal into air, and the second indicates electrode penetration to just below the chorion. Each subsequent plateau represents a 100 µm increment, advancing past the central minimum PO2. The third arrow indicates where the electrode was withdrawn back into air and immediately placed back into still water. Inset: Stirring effect. The asterisk indicates when the air bubbles were turned off. All electrode calibration was done in still water after bubbles were turned off.

View larger version (22K): [in a new window]   Fig. 7. Radial oxygen profiles in eggs of Manduca sexta. A calibrated Clark-style microelectrode was advanced through a small hole in the egg chorion (egg surface=0 µm) and then in 100 µm increments. The two bottom traces are 3-day-old eggs (at 24 and 37°C, N=7 and 9, respectively), the middle two traces are freshly laid eggs (laid in previous 12 h, N=4 and 3 at low and high temperatures, respectively), and the top two traces are 2- and 3-day-old traces of dead eggs (killed by freezing in liquid N2 or in a –80°C freezer, N=2 and 4, respectively). Initial measurements were from still water (temperature equilibrated and air saturated). Values are means ± S.E.M. The dead 2-day-old eggs do not have error bars because N=2 eggs for this treatment.