75.5 Saturday, Jan. 5 The mechanism of tracheal collapse in beetles: a multi-linked system PENDAR, H*; SOCHA, JJ; Virginia Tech; Virginia Tech email@example.com
Many insects are known to augment their respiration via rhythmic tracheal compression and reinflation. A significant decrease in the volume of tracheal tubes during compression displaces air out of the body and likely mixes air within the tracheal system, thereby enhancing gas exchange. In carabid and tenebrionid beetles, compression of tracheae occurs mostly in the head and thorax, and only some tracheae collapse in the abdomen. Different mechanisms have been suggested to explain tracheal collapse, including collapse by contraction of surrounding muscles, abdominal or thoracic pumping, auto-ventilation by leg or wing movement, and hemolymph transport. None of these hypotheses have been investigated in detail, and the mechanism of tube collapse in most insect taxa remains unknown. To determine the mechanism of collapse in beetles, we have been probing multiple physiological processes that are correlated with tube collapse to explore possible mechanical linkages in the system. Although previous work has used synchrotron x-ray imaging to observe tracheal compression, we have been able to take advantage of small locations of transparent cuticle in the thorax, abdomen, and legs to observe compression within the lab. Additionally, we use synchronous measurements of movement, pressure, and CO2 to quantify internal and external processes while tracheae collapse. These measurements have revealed the relationship of collapse with abdominal pumping, hemolymph pressure, gut movement, and CO2 release. Simultaneous pressure pulses of different magnitude throughout the body suggest that the abdominal pump helps to produce pressure, which is mediated by gut movements and regional compartmentalization. This research demonstrates how the use of multiple coordinated processes can result in collapse of tracheal tubes and the augmentation of gas exchange. Support: NSF 0938047 (JJS).