Meeting Abstract
While traditionally insect gas exchange is thought of as primarily diffusive, it has become increasingly clear that advective flow, sometimes uni-directional as in birds, supplements diffusion in most insects. Depending on the species and physiological conditions, gas exchange in insects can be mostly diffusive, tidally advective, or uni-directionally advective either in the forward or backwards direction, but the mechanisms and consequences of such variation are poorly understood. We measured CO2 emission rates and unidirectional flow for adult Zophobas morio, the giant mealworm beetle, using a latex membrane to separate the mesothoracic spiracles and the subelytral abdominal spiracles into two separate respirometry chambers. In these beetles, the abdominal spiracles open into the subelytral space, so inhalation from this space is likely to increase the humidity of inhaled air. 90 percent of the animals displayed strongly unidirectional flow, with significantly more CO2 being emitted in one direction, and such patterns were usually consistent over 24 h of measurement. However, whether the flow was forward or backward 90 percent of the recordings displayed unidirectionality. Females expelled most CO2 via the mesothoracic spiracles, while males expelled most CO2 via the abdominal spiracles, suggesting that morphological or physiological differences associated with sex affect direction of flow. Removal of the elytra was associated with increased CO2 output via the mesothoracic spiracles, suggesting that alteration of subelytral conditions or desiccation (higher in animals with elytra removed) affect the direction of flow. These findings suggest that the direction of unidirectional flow is under physiological control, possibly in response to water balance or to reflect tissue-level variation in metabolism. This research was funded by NSF IOS 1558052.
