Cyclic release of carbon dioxide accompanied by abdominal telescoping movements in forager ants of Formica polyctena (Hymenoptera, Formicidae)

Abstract.  Discontinuous gas exchange and abdominal telescoping movements were investigated in intact forager ants of Formica polyctena Förster. For simultaneous recording of discontinuous gas exchange and abdominal movements, an electrolytic differential microrespirometer was combined with an infrared-optical device using an infrared-sensor diode commonly applied as a cardiograph in insect studies. The air in the insect chamber was saturated with water vapour, and an ant was contacted with a sliver of wet filter paper. Accordingly, the ants used in the experiments were regarded as being hydrated. The enforced immobility of the ant in the respirometry chamber (0.15 mL volume) induced continuous struggling during the first hours of measurement but, after 3–4 h, the activity periods alternated with quiescent periods when regular cycles of discontinuous gas exchange (8.97 mHz) were displayed. After remaining in the chamber for a day, the ants showed such cycles (8.15 mHz) without any interruption by periods of activity. The cyclic release of carbon dioxide (burst) was accompanied by a bout of telescoping movements of the abdominal segments (rapid contractions and slow relaxations), which were interpreted as active ventilation. The irregular and rare abdominal contractions, recorded during the interburst periods on the first day of measurements, were regarded as a symptom of stress because these disappeared on the second day. In approximately 20% of foragers, the telescoping movements during the interburst periods were characterized by very rapid (0.09 s) protractions and slow retractions of the abdominal segments, obviously acting as inspiration movements. The results do not support the hypothesis that discontinuous gas exchange is an adaptation for conserving water in ants.