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Respiratory airflow in a wingless dung beetle

Frances D. Duncan^1,* and Marcus J. Byrne²

¹ School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, South Africa
² Ecophysiological Studies Research Programme, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, Wits 2050, South Africa

View larger version (22K): [in a new window]   Fig. 1. A schematic representation of the position of the anterior and posterior spiracles in Circellium bacchus. The position of the tubes, which were attached to the ventral prothoracic suture and used to sample each mesothoracic spiracle separately, is shown.

View larger version (23K): [in a new window]   Fig. 2. The flow-through respirometry apparatus used to sample respiratory emissions individually from the mesothoracic spiracles of Circellium bacchus. A, anterior section of the respirometry chamber, P; posterior section of the respirometry chamber.

View larger version (19K): [in a new window]   Fig. 3. CO2 and O2 exchange of a Circellium bacchus (mass 8.153 g) from (A) the anterior mesothoracic spiracles, where the majority of exchange occurs, and (B) the posterior metathoracic and abdominal spiracles, which contribute less to respiratory exchange. The readings are from one individual and are matched in time. Negative values of O2 consumption are due to baseline drift.

View larger version (27K): [in a new window]   Fig. 5. Recordings of CO2 and O2 exchange of Circellium bacchus (mass 5.790 g) from the posterior and anterior spiracles when a gas mixture containing 30 % O2 was drawn over the elytral cavity (A). O2-enriched air entered through these spiracles because it could be seen to exit via the anterior mesothoracic pair of spiracles. When the 30 % O2-enriched air mixture was drawn over the anterior mesothoracic spiracles (B), no high-O2-content air was seen to leave via the posterior spiracles opening into the subelytral cavity. Comparison of Figs 3 and 5 reveals no change in the breathing pattern due to the elevated O2 concentration in the gas mixture.

View larger version (17K): [in a new window]   Fig. 4. The relationship between anterior and posterior CO2 emission rates during the discontinuous gas-exchange cycle (DGC) in Circellium bacchus (N=53 DGCs in six beetles, mean mass 7.427 g). The regression equations are: a=-0.022+0.891t, r2=0.98, P=0.001; p=0.022+0.109t, r2=0.4, P=0.001, where a is anterior spiracular CO2, p is posterior spiracular CO2 and t is total CO2. When the mean values for each beetle (N=6) are used, the regression equations are: a=-0.021+0.866t, r2=0.98, P=0.002; p=0.021+0.134t, r2=0.5, P=0.11.

View larger version (17K): [in a new window]   Fig. 6. Simultaneous recordings of CO2 and O2 exchange from the right and left mesothoracic spiracles of an individual Circellium bacchus (mass 8.455 g). The small amount of CO2 detected from left spiracle is probably due to slight cross-sampling of the right spiracle.