Department of Zoology, Mizoram University, Aizawl, Mizoram 796004, India.
Department of Zoology, Mizoram University, Aizawl, Mizoram 796004, India.
J Photochem Photobiol B. 2019 Feb;191:44-51. doi: 10.1016/j.jphotobiol.2018.12.005. Epub 2018 Dec 14.
Seasonality is represented as an initiation-termination-reinitiation of any physiological processes. Photoperiod is the most predictable environmental cue which organism use to time their daily physiology and seasonal functions. In natural light environmental conditions, day and night components change in terms of duration, intensity and spectrum of light available. In many vertebrate species, daytime light intensity and spectrum of light play a critical role in gonadal recrudescence-regression cycle. In tropical conditions, many amphibian species show a clear relationship between reproduction and seasonal distribution of rainfall. In temperate conditions, reproduction is usually centered during spring and summer seasons when environmental conditions are favorable. Poikilotherms are highly sensitive to change in environmental temperature and their physiology and metabolic activities depend on environmental temperature. How environmental factors (light and temperature) influence, the reproduction of terai tree frog (Polypedates teraiensis) is not known. We hypothesized that light acts as a proximate factor but the temperature is the ultimate factor for reproduction of terai tree frog. Three experiments were performed. In experiment one, we studied the annual reproductive cycle under natural environmental conditions. Beginning from the month of March till October 2016, we procured adult frogs (male and female) in the middle of each month. Monthly observations were recorded for body weight and gonadal weight and GSI was calculated. We found the annual change in body mass, gonadal weight and GSI in both male and female with high gonadal weight and GSI values from March to June. These results suggest that terai tree frog is seasonal breeders, and their breeding corresponds with long days. In experiment two we addressed the effects of light duration, light intensity and light spectrum on gonadal growth regression cycle. We observed that long days promote gonadal growth regression cycle. However, after achieving critical daylength there is no additive effect of light duration. Further, light intensity and spectrum have limited role in gonadal growth regression cycle of this species. In experiment three we tested the role of temperature on body weight and testicular growth under stimulatory photoperiod (12 L:12D). Group one was exposed to high temperature (34 ± 2 °C), while group two was exposed to low temperature (22 ± 2 °C). We found that low temperature promotes testicular recrudescence under laboratory conditions. Altogether our study suggests both photoperiod and temperature are involved in the regulation of seasonal breeding in tree frog. Findings from the above study could be used for captive breeding of amphibians and may be helpful in amphibian conservation programmes.
季节性表现为任何生理过程的开始-结束-重新开始。光周期是生物体用来计时日常生理和季节性功能的最可预测的环境线索。在自然光环境条件下，昼夜成分在持续时间、强度和可用光的光谱方面发生变化。在许多脊椎动物物种中，白天的光强度和光谱对性腺的恢复-退化周期起着关键作用。在热带条件下，许多两栖动物物种的繁殖与降雨的季节性分布之间存在明显的关系。在温带条件下，繁殖通常集中在春季和夏季，当环境条件有利时。变温动物对环境温度的变化非常敏感，它们的生理和代谢活动取决于环境温度。环境因素（光照和温度）如何影响热带树蛙（Polypedates teraiensis）的繁殖尚不清楚。我们假设光照是一个近因因素，但温度是热带树蛙繁殖的最终因素。进行了三项实验。在实验一中，我们在自然环境条件下研究了年度繁殖周期。从 2016 年 3 月到 10 月，我们每个月在中间采集成年青蛙（雄性和雌性）。每月记录体重和性腺重量，并计算 GSI。我们发现，雄性和雌性的体重、性腺重量和 GSI 都有年度变化，从 3 月到 6 月，性腺重量和 GSI 值较高。这些结果表明，热带树蛙是季节性繁殖者，它们的繁殖与长日照相吻合。在实验二中，我们研究了光持续时间、光强度和光光谱对性腺生长退化周期的影响。我们发现，长日照促进了性腺生长退化周期。然而，在达到临界日长后，光持续时间没有附加效应。此外，光强度和光谱对该物种的性腺生长退化周期的作用有限。在实验三中，我们在刺激光周期（12L：12D）下测试了温度对体重和睾丸生长的作用。第一组暴露在高温（34±2°C）下，而第二组暴露在低温（22±2°C）下。我们发现，在实验室条件下，低温促进了睾丸的重新发育。总之，我们的研究表明，光周期和温度都参与了树蛙季节性繁殖的调节。这项研究的结果可用于两栖动物的圈养繁殖，并可能有助于两栖动物保护计划。
