白头鹎的体温调节与蒸发失水

Thermoregulation and Evaporative Water Loss in Chinese Bulbuls Pycnonotus sinensis

采用开放式呼吸测定仪和数字式温度测量仪,在环境温度为5.0~35.0℃范围内,测定8只白头鹎（Pycnonotus sinensis）的体温、代谢产热和蒸发失水（EWL）,并计算其热传导等生理生态特征。结果表明,白头鹎的热中性区为25.0~32.0℃;基础代谢率（BMR）为（3.67±0.03）ml/（g·h）,是体重预期值的64%。平均最小热传导为（0.15±0.00）ml/（g·h·℃）,是体重预期值的124%。蒸发失水与产热的比率（EWL/RMR）在5.0~35.0℃时随着环境温度的升高而升高,在35℃时达到峰值,为0.20±0.01。代谢水和蒸发失水的比率（MWP/EWL）随环境温度上升而下降,在16.4℃时,MWP/EWL为1。这些结果表明,白头鹎具有较低的基础代谢率和高的热传导,蒸发失水在体温调节中占有重要的地位。

Basal metabolic rate（ BMR） is thought to be a major hub of physiological mechanisms connecting life history characteristics. Evaporative water loss（ EWL） is a physiological indicator used to measure water relations in interor intra-specific studies of birds. In this study,we examined body temperature（ Tb）,resting metabolic rate（ RMR） and EWL at ambient temperatures（ Ta） between 5 and 35℃ in summer-acclimatized Chinese bulbul（ Pycnonotus sinensis） captured in Wenzhou,in July 2011. Eight animals were transported to the laboratory and caged for 1 week（ 50 cm × 30 cm × 20 cm） outdoors under natural photoperiod and temperature. Birds’ metabolic rates were measured with an open-circuit respirometry system（ AEI technologies S-3A / I,USA）. Birds were exposed to stable temperatures between 5 and 35℃ for at least 1 h prior to measuring oxygen consumption which was recorded at 20-second intervals. Most birds were tested only once per day with at least two days between tests. A few birds were measured more than once per day. These birds wereallowed to equilibrate at the new test temperature for 1 h before the next measurement was made. Every bird was tested at all nine temperatures. Food was removed from the birds’ cages 4 h before each measurement period to minimize the heat increment associated with feeding. A‘U’tube（ containing silica gel） was connected in series behind the respiratory chamber and weighed（ ± 0. 1 mg）. The amount of evaporative water lost by each bird was absorbed by the silica gel and could therefore be measured by reweighing the U tube at the end of the measurement. Statistics analysis was performed using the SPSS statistical package（ version 13. 0 for windows）.The effect of ambient temperature on body temperature,resting metabolic rate,evaporative water loss,thermal conductance,metabolic water production / evaporative water loss and dry thermal conductance were analyzed using repeated measures ANOVA or ANCOVA with body mass as a covariate. Results were reported as Mean ±SE and P 〈 0. 05 was considered statistically significant. We found that mean body temperature was 40. 7 ±0. 1℃（ Fig. 1a）. The thermal neutral zone（ TNZ） was 25. 0- 32. 0℃ and basal metabolic rate was 3. 67 ±0. 03 ml /（ g·h）（ Fig. 1b）. Below the lower critical temperature of the thermal neutral zone,resting metabolic rate increased linearly with decreasing ambient temperature according to the relationship： RMR= 5. 296- 0. 068 Ta. Evaporative water lost increased with ambient temperature according to the relationship： Log LEW= 1. 563 ＋0. 021 Ta（ Fig. 1c）,which exceeded metabolic water production at Ta〉 16. 4℃. Thermal conductance was stable from 5 to 20℃,and average thermal conductance within this temperature range was 0. 15 ± 0. 00 ml /（ g·h·℃）（ Fig. 1d）. Dry thermal conductance was also stable from 5 to 20℃,and average dry thermal conductance within this temperature range was 0. 14 ± 0. 00 ml /（ g · h ·℃）（ Fig. 1e）. The ratio of evaporative water loss to metabolic rate（ EWL / RMR） was affected significantly by ambient temperature.Between 5 and 35℃,EWL / RMR was positively correlated with ambient temperature and EWL / RMR increased linearly with increasing temperature（ Fig. 1f）. Metabolic water production / evaporative water loss（ MWP /EWL） was also affected significantly by ambient temperature. MWP / EWL decreased exponentially with increasing temperature（ Fig. 1g）. Chinese bulbuls had a low level of BMR and a high level of thermal conductance,compared with the predicted values based on their body masses,and it also had wide thermal neutral zone. The high evaporative water loss / resting metabolic and metabolic water production / evaporative water loss ratios in the Chinese bulbul suggest that EWL plays an important role in thermoregulation.