溫度與UV-B交感效應對蝌蚪發育、形態與避敵行為的影響

Abstract

兩生類為可利用水域及陸域環境的外溫動物，對於棲息環境之變化極為敏感，近年研究已普遍顯示全球氣候變遷與兩生類之族群下降有密切關聯。過往針對溫度或UV-B分別如何影響兩生類之發育、形態及行為表現已有諸多研究，然而溫度和UV-B之間的交互作用卻較少被探討。本研究旨在探討全球暖化之下，溫度與UV-B的交互作用如何影響蝌蚪的發育與形態，並進一步了解其如何間接影響蝌蚪的避敵行為。實驗方法為自野外採集拉都希氏赤蛙 (Hylarana latouchii) 的卵團，隨機分成 4個實驗組(包含高低程度的溫度與UV-B)，記錄與分析蝌蚪從卵(G9)至Gosner 32 (G32)時期的發育與形態變化，並亦記錄與分析已成功發育到G32蝌蚪的游泳起速，以進行避敵行為測試。結果顯示高UV-B處理皆對蝌蚪大部份的特徵有顯著負面影響，包含增加死亡率及形態異常、減少壽命及蝌蚪整體大小 (包含全長、體長、體寬及尾肌寬) ，原因可能為長時間UV-B輻射造成DNA的累積損害；而高溫處理則只有顯著減少蝌蚪壽命與增加蝌蚪的尾肌寬。蝌蚪壽命的減少顯示輕微的溫度上升也可能對蝌蚪有直接的負面影響。另外，本研究亦發現溫度與UV-B之間具有交互作用，如高溫可調解高UV-B對蝌蚪成長的負面效果；而蝌蚪形態異常和損壞會間接降低游泳起速，這可能導致其被掠食者捕食的機率上升，也可能間接降低蝌蚪覓食效率。本研究發現在氣候暖化之下，UV-B輻射（相較於溫度）對兩生類的負面影響將更為顯著，而溫度在動物可耐受的範圍內逐步增加則可能有助於調解UV-B所造成形態上的損害。

Amphibians are ectotherms that reside in both aquatic and terrestrial systems which make them extremely sensitive to changes in their environment, and past research has shown that global climate change has contributed substantially to the recent global amphibian decline. Although there are plentiful research on the effects of temperature or UV-B radiation on amphibian development, morphology, and behaviour, respectively, there has been very little research on the interaction of high temperature and UV-B on amphibians. The aim of this study is to determine the interaction effects of high temperature and UV-B, under a global warming scenario, on tadpole development and morphology, as well as to determine how these effects would impact the predator avoidance behaviour of tadpoles. I examined the independent and interaction effects of temperature and UV-B on various developmental and morphological traits of the LaTouche's frog (Hylarana latouchii) by randomly distributing the egg masses into 4 different treatment groups in a 2 x 2 factorial combination of high and low temperature and UV-B. The developmental and morphological traits of the embryos/tadpoles were recorded and analyzed from Gosner stage 9 (G9) to Gosner stage 32 (G32). I also examined the predator avoidance response of tadpoles that have successfully reached G32 by measuring burst swimming speed. The results indicated that high UV-B had negatively affected the majority of tadpole traits including increased mortality and abnormalities, decreased longevity, and decreased tadpole overall size and width (including total length, body length, body width, and tail muscle width). This may be due to the DNA damage accumulated due to prolonged UV-B exposure. High temperature, on the other hand, had only decrease longevity and increased tail muscle width of tadpoles. The decrease in longevity revealed that slight increase in temperature may have a direct negative effect on tadpole development. Moreover, there was an interaction effect of temperature and UV-B. In this study, high temperature was ameliorating the negative effects that UV-B was exerting on tadpole. Also, morphological abnormality and damage did seem to carry over and significantly decreased burst swimming performance of tadpoles which may lead to increase in predation and decrease foraging capabilities. This study shows that under a global warming scenario, UV-B radiation is a much higher stressor to amphibian species than temperature and an incremental increase in temperature, within the species’ thermal range, may help ameliorate the morphological damages caused by UV-B.