CYCLIC CO2RELEASE IN DIAPAUSING AGAPEMA PUPAE

Abstract

1. Forcing a few of the spiracles of the Agapema pupa to remain open abolishes the alternate retention and release ("burst") of CO2 and greatly augments water loss. The effects are reversed by sealing the inactivated spiracles.2. Pupae exposed to N2 after a normal CO2 burst has been produced release an additional volume of CO2 twice that of the original burst. The first cycle after such a "purge" is nearly twice as long as normal. These results further implicate the spiracles in CO2 retention and favor the idea that accumulation of CO2 triggers the burst.3. A statistical analysis of successive cycles within individual pupae indicates that burst volume tends to be constant, and comparison of individuals in a population shows significant inverse relations between metabolic rate and cycle length, and possibly between burst volume and cycle length. The significance of these findings is discussed in relation to the triggering of CO2 release and the rationale of the cycle.4. Mechanical disturbances may also trigger CO2 bursts.5. The effects of temperature and ambient Po2 on interburst CO2 release rate are interpreted in terms of spiracular response to O2.6. The transition from cyclic to continuous CO2 release is discussed in relation to triggering and to spiracular involvement.7. The prominence of CO2 in triggering bursts and of the apparent control of the spiracles by O2 during interburst; the lack of clear functional relation between interburst release rate, burst volume and cycle length; and the lack of special association between burst volume and either preceding or succeeding cycle length, make it difficult to interpret the burst cycle in terms of simple CO2 regulation, in which the spiracles act as safety valves to prevent undue accumulation of CO2. It is suggested that the CO2 release cycle may be a secondary consequence of minimization of transpiratory water loss.8. Though the spiracles are intimately involved in CO2 retention and release it is shown theoretically that regulation of valve area per se cannot achieve appreciable CO2 retention without interfering with O2 uptake. Further analysis in terms of gas diffusion gradients will be discussed elsewhere.