Timbal muscle physiology in the endothermic cicada Tibicen winnemanna (Homoptera: Cicadidae).

The operative muscle temperature and contraction kinetics are described for the endothermic cicada Tibicen winnemanna (Davis). Measurements of timbal muscle temperature in the field demonstrate that timbal muscle temperature is elevated above ambient temperature during activity. Timbal muscle temperature increases as the acoustic output progresses from a 'warm-up' buzz (27.9-29.7 degrees C) to full song production (36.3-39.5 degrees C). Mean muscle-ambient temperature difference increases from 5.8 degrees C in buzzing animals to 13.1 degrees C in animals producing a full calling song. Twitch rise time and onset to 50% relaxation time decrease while tension production increases with increasing temperature to 40 degrees C. Mean force production at 20 degrees C was determined to be 0.22+/-0.06 N/cm(2). The characteristics of T. winnemanna muscle are similar to those reported in other cicada species. Analysis of the songs produced by animals with one timbal destroyed and the sounds produced by mechanical manipulation suggest that the timbals alternately contract and relax in the sequence IN(1)-IN(2)-OUT(1)-OUT(2). Measurements of the inferred period of muscle contraction from song recordings and the contraction kinetics of isolated timbal muscles measured in the laboratory show that the temperature of the timbal muscle must be elevated in order for the cicada to be able to produce the calling song.