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First published online January 31, 2007
Journal of Experimental Biology 210, 722-731 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02702
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Oxygen in egg masses: interactive effects of temperature, age, and egg-mass morphology on oxygen supply to embryos

Amy L. Moran1,* and H. Arthur Woods2

1 Department of Biological Sciences, Clemson University, Clemson, SC 29634 USA
2 Division of Biological Sciences, University of Montana, Missoula, MT 59812 USA


Figure 1
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  		Fig. 1. Egg masses of Tritonia diomedea. (A) Intact sections of egg masses at two stages. Left, a 2-day-old mass; right, a 2-week-old mass. The width of egg mass `rope' is approximately 3 mm. (B) Egg capsules within a 2-day-old egg mass. Egg capsules are ~800 µm across the longest dimension. (C) 2-day-old embryos removed from egg capsules. Embryos are approx. 90 µm across the longest dimension.

 

Figure 2
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  		Fig. 2. Tritonia diomedea; respiration measurements of early embryos at two temperatures. Each datum point shows the oxygen consumed in one single respiration chamber, plotted against the number of capsules in the chamber. Respiration of an individual capsule was estimated from the slope of the regression line at each temperature (orange circles, 21°C; b=863.1, r2=0.99; blue circles, 12°C; b=495.1, r2=0.95). Error was calculated as the s.e.m. of the slope (s.e.m. 21°C=201.6; s.e.m. 12°C=52.6). The non-zero intercepts are an unexplained but very common phenomenon in microrespiration measurements, and do not affect estimates of respiration rate derived from the slope; see discussion elsewhere (Marsh and Manahan, 1999Go).

 

Figure 3
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  		Fig. 3. Tritonia diomedea; metabolic rates of free embryos (filled circles) compared to embryos in egg capsules (open circles) at three stages of development. Each datum point ± s.e.m. was derived from a regression equation as shown in Fig. 2.

 

Figure 4
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  		Fig. 4. Tritonia diomedea; effect of temperature on metabolic rates at three developmental stages (blue circles=12°C; orange circles=21°C). (A) Direct measurements on embryos in egg capsules. Each datum point ± s.e.m. was derived from a regression equation as shown in Fig. 2. (B) Estimated per-embryo metabolic rates calculated by dividing the per-capsule rate by the number of embryos per capsule (the latter number was either directly counted or estimated from the mean number of embryos per capsule in other capsules from the same mass; see text).

 

Figure 5
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  		Fig. 5. Tritonia diomedea; oxygen distributions in intact sections of egg mass and in free embryo capsules at 12°C (blue circles) and 21°C (orange circles). Effects of temperature and configuration for early-cleavage stage embryos (left) and late-veliger stage embryos (right). Each point represents the mean ± s.d. of three measurements.

 

Figure 6
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  		Fig. 6. Dendraster excentricus; artificial egg masses. (A) Representative high- and low-embryo density artificial egg masses, constructed by casting newly fertilized D. excentricus into low-melting point agarose. Both masses are `medium diameter' masses, ~4 mm in diameter. (B) Radial profiles of oxygen through artificial masses of small, medium and large diameter, obtained using a Clark-style microelectrode. Arrows indicate position of midpoint.

 




© The Company of Biologists Ltd 2007