WOODS, H.A.; Univ. of Texas at Austin: Interactive effects of temperature and oxygen on insect egg development

Most biological rates depend on temperature, but not always in the same way�e.g., metabolic rates usually are affected more strongly by temperature than are rates of transport by diffusion. In tissues, organs, or organisms supplied with oxygen primarily by diffusion, temperature fluctuations may therefore radically alter ratios of oxygen supply and demand. In particular, high temperatures should cause disproportionately high oxygen demand without equivalent increases in supply, leading to lower internal oxygen partial pressures and possibly inhibited function. I examined these predictions using eggs of the moth Manduca sexta. Like other insect eggs, those of M. sexta consist of metabolizing tissue (the embryo) surrounded by a diffusive barrier (the eggshell and yolk). In nature, eggs often experience diurnal temperature fluctuations of up to 30�C, so that even small differences in temperature coefficients of metabolism and gas transport may be important. Using time-lapse photography, I measured egg development rates in a factorial experiment with eight partial pressures of oxygen and three temperatures. Although eggs at the highest temperature developed fastest when the oxygen partial pressure was high, eggs at high temperature also were disproportionately sensitive to low oxygen partial pressures. In particular, compared to low-temperature (22 and 27�C) eggs, high-temperature eggs (32�C) required higher oxygen partial pressures to hatch, exhibited arrested development at earlier stages in low oxygen, and developed disproportionately slowly at low partial pressures. These results suggest that temperature affects partial pressures of oxygen within insect eggs and may bear on the design of insect eggshells.