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Eight garter snakes, Thamnophis elegans, were collected in northern New Mexico during July and August. The snakes were kept in an environmental chamber and were entrained to a 141 (0630-2030 h) / 10D (2030-0630 h) cycle for five weeks at 25 C. Ventilation was monitored with a head/body plethysmograph. Pulmonary oxygen uptake was measured by open-system respirometry. Heart rate was recorded with electrodes implanted subcutaneously, bi-lateral to the heart. Ventilation, oxygen uptake and heart rate were measured simultaneously at 25+-1 C. All measurements were recorded continuously for 48-96 hours. As well as investigating the diurnal rhythms of ventilation, oxygen uptake and heart rate under a 141/ 10D regime, a continuous darkness regime (24D), was also investigated. T. elegans exhibited a pronounced diurnal rhythm in pulmonary oxygen uptake (v02). During 14L, V02 was 0.98 ml STPD x kg -1 x min -1 and decreased to 0.90 ml STPD x kg -1 x min -1 during 10D. The decrease in V02 was statistically significant. Since the diurnal rhythm persisted during 24D, it was considered endogenous. Heart rate (HR) did not exhibit a diurnal rhythm, however during 24D heart rates were lower overall. Ventilatory movements were basically biphasic, but occasionally a triphasic pattern was apparent. This triphasic pattern consisted of: expiration, inspiration, breath-hold and a small (0.1-0.4 ml) second inspiration. This type of ventilatory movement has not been described for other reptiles. Breathing frequency (f) during 14L was 2.2 breaths x min-1 and decreased to 1.5 breaths x min-1 during 10D. During the night there was a pronounced increase in apneas greater than two minutes (x = 8.1 min; range = 2-34 min). These long apneic periods were accompanied by a pronounced bradycardia. Tidal volume (vt) was 16.4 ml x kg -1 during 14L and did not change during 10D. Minute ventilation (VE) during 14L was 33.5 ml BTPS x kg -1 and decreased to 20.5 ml BTPS x kg -1 x min-1 during 10D. The diurnal changes in breathing frequency and minute ventilation persisted during 24D, thus were considered endogenous rhythms. The distinct changes in ventilator patterns, during the night, were postulated to be a characteristic of a “sleeping” state. The decrease in minute ventilation was not matched by a proportional decrease in pulmonary oxygen uptake, thus resulting in a pronounced diurnal rhythm in air convection requirement (VE/V02). Air convection requirement is usually associated with a 10C increase in temperature. As a result of the data is postulated that regulation of ventilation during the “waking” state is different from regulation during the “sleeping” state.



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UNM Biology Department

First Committee Member (Chair)

Marvin LeRoy Riedesel

Second Committee Member

Stephen C. Wood

Third Committee Member


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