Department of Endangered Species Management, Wildlife Institute of India, Dehradun, India.
Wildlife Conservation Trust, Mumbai, India.
J Therm Biol. 2023 Feb;112:103468. doi: 10.1016/j.jtherbio.2023.103468. Epub 2023 Jan 7.
Incubation temperature in nests of oviparous reptiles affects reproductive success indicators, including hatching time and success, offspring size, fitness, and behaviour. The female king cobra builds an above ground nest to incubate and protect its eggs. However, it is not clear how thermal regimes inside king cobra nests respond to external environmental temperature regimes, especially in subtropical regions that witness high diel and seasonal temperature fluctuations. To better understand the relationship between inside nest temperatures and hatching outcomes for this snake, we monitored the thermal regimes of 25 natural king cobra nests in the subtropical forests of the Western Himalayas in Uttarakhand state, northern India. We hypothesized that inside nest temperatures would be higher than outside (ambient) temperatures and that thermal regimes inside nests would affect hatching success and hatchling size. Internal and external temperatures at nest sites were measured every hour until hatching, via automatic data loggers. We then calculated hatching success of eggs and measured hatchling length and weight. Mean inside nest temperatures were consistently higher by about 3.0 °C than outside environmental temperatures. External temperature reduced with increasing elevation of nest sites and was the best determinant of inside nest temperature, which had a smaller range of variability. Physical characteristics of nests (size and leaf materials used) did not influence nest temperature significantly, but nest size was positively related to clutch size. Mean inside nest temperature was the best predictor of hatching success. Average daily minimum nest temperature, which indicates a possible lower threshold for thermal tolerance by eggs, was also correlated positively with hatching success. Mean daily maximum temperature was a significant predictor of mean length of hatchlings, but not of mean hatchling weight. Our study provides unequivocal evidence for the critical thermal benefits of king cobra nests for increased reproductive success, in subtropical environments with lower and sharply fluctuating temperature regimes.
卵生爬行动物巢中的孵化温度会影响繁殖成功指标，包括孵化时间和成功率、后代大小、适应性和行为。眼镜王蛇的雌性会建造一个地上巢穴来孵化和保护其卵。然而，目前尚不清楚眼镜王蛇巢内的热环境如何对外部环境温度模式做出响应，尤其是在亚热带地区，那里存在着高昼夜和季节性温度波动。为了更好地了解这种蛇的巢内温度与孵化结果之间的关系，我们监测了印度北部北阿坎德邦喜马拉雅山西部亚热带森林中 25 个自然眼镜王蛇巢的热环境。我们假设巢内温度会高于外部（环境）温度，并且巢内的热环境会影响孵化成功率和幼体大小。通过自动数据记录器，我们每小时测量一次巢内和巢外的温度，直到孵化为止。然后，我们计算了卵的孵化成功率，并测量了幼体的长度和重量。巢内的平均温度始终比外部环境温度高约 3.0°C。外部温度随巢址海拔的升高而降低，是巢内温度的最佳决定因素，其变化范围较小。巢的物理特征（大小和使用的叶片材料）对巢温的影响不显著，但巢的大小与卵的数量呈正相关。巢内平均温度是孵化成功率的最佳预测因子。平均每日最低巢温，它可能表示卵对热容忍度的下限，也与孵化成功率呈正相关。日平均最高温度是幼体平均长度的重要预测因子，但不是幼体平均重量的预测因子。我们的研究为眼镜王蛇巢在较低和波动剧烈的亚热带环境中提高繁殖成功率提供了明确的证据，证明了其对温度的重要益处。
