Abiotic conditions in cephalopod ( Sepia officinalis ) eggs: embryonic development at low pH and high p CO 2
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Abiotic conditions in cephalopod (Sepia officinalis) eggs: embryonic development at low pH and high pCO2 Magdalena A. Gutowska Æ Frank Melzner
Received: 18 September 2008 / Accepted: 18 November 2008 / Published online: 9 December 2008 Ó Springer-Verlag 2008
Abstract Low pO2 values have been measured in the perivitelline fluids (PVF) of marine animal eggs on several occasions, especially towards the end of development, when embryonic oxygen consumption is at its peak and the egg case acts as a massive barrier to diffusion. Several authors have therefore suggested that oxygen availability is the key factor leading to hatching. However, there have been no measurements of PVF pCO2 so far. This is surprising, as elevated pCO2 could also constitute a major abiotic stressor for the developing embryo. As a first attempt to fill this gap in knowledge, we measured pO2, pCO2 and pH in the PVF of late cephalopod (Sepia officinalis) eggs. We found linear relationships between embryo wet mass and pO2, pCO2 and pH. pO2 declined from [12 kPa to less than 5 kPa, while pCO2 increased from 0.13 to 0.41 kPa. In the absence of active accumulation of bicarbonate in the PVF, pH decreased from 7.7 to 7.2. Our study supports the idea that oxygen becomes limiting in cephalopod eggs towards the end of development; however, pCO2 and pH shift to levels that have caused significant physiological disturbances in other
Communicated by U. Sommer.
Electronic supplementary material The online version of this article (doi:10.1007/s00227-008-1096-7) contains supplementary material, which is available to authorized users. M. A. Gutowska (&) Marine Animal Physiology, Alfred-Wegener-Institute for Polar- and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany e-mail: [email protected] F. Melzner Biological Oceanography, IFM-GEOMAR Leibniz Institute of Marine Sciences, Hohenbergstrasse 2, 24105 Kiel, Germany
marine ectothermic animals. Future research needs to address the physiological adaptations that enable the embryo to cope with the adverse abiotic conditions in their egg environment.
Introduction Designed to protect embryonic stages from predation, egg capsules also can provide severe physiological challenges to their inhabitants, as the egg wall represents a barrier to diffusion of gases. Previous work has demonstrated that oxygen diffusion coefficients ðKO2 Þ of marine animal egg capsules are typically 10–20% that of pure water (e.g., Brante 2006). In molluscs (as in all other developing embryos), oxygen consumption rates rise dramatically during development (e.g., Cronin and Seymour 2000; Brante 2006). Thus, in order to enable rising oxygen fluxes by means of diffusion, many molluscan eggs swell during development, leading to enhanced surface areas and reduced egg wall thicknesses (e.g., Kress 1972; Cronin and Seymour 2000), and consequently increased oxygen conductances (Seymour 1994). In addition, embryos inhabiting fluid filled capsules often produce convective currents that prevent the formation of
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