CARBOHYDRATE AND CALLING - DEPLETION OF MUSCLE GLYCOGEN AND THE CHORUSING DYNAMICS OF THE NEOTROPICAL TREEFROG HYLA-MICROCEPHALA

Chorusing males of the neotropical treefrog Hyla microcephala call in distinct bouts punctuated by periods of silence, a pattern known as un ison bout singing. Schwartz (1991) previously tested and refuted the h ypotheses that males periodically stop calling either because of a fem ale preference for males that call cyclically, or because high ambient noise levels inhibit vocal activity. Males of H. microcephala are voc ally responsive to the calls of other males, and during calling bouts their rate of note production can exceed 10,000 per hour. In natural c horuses females preferentially pair with males that call at the higher rates. Because females can pair with males over many hours, males may stop calling periodically to save energy so they can continue to call for the entire period that females are available. We directly tested this energy conservation hypothesis by collecting samples of males ear ly in the evening just after chorusing commenced and later when chorus ing had ended for the night. Trunk muscles (internal and external obli que), which are responsible for the airflow associated with note produ ction, were dissected, frozen, and their glycogen content measured. Da ta on calling behavior were obtained for late-evening samples. Individ ual calling behavior was not correlated with a male's final glycogen l evel. In addition, many males ended their calling before glycogen rese rves were exhausted, indicating that factors other than energy can det ermine when males finally stop chorusing. However, the biochemical ass ays supported the energy conservation hypothesis. Unless chorusing was punctuated by pauses, most males would have been unable to sustain hi gh rates of calling for an entire evening without exhausting glycogen reserves in their trunk muscles. Because the time females pair with ma les is probably unpredictable to males, the ability to call for long p eriods may improve a male's chances of mating.