Warkentin K M
Department of Zoology, University of Texas, Austin, TX 78712, USA.
Physiol Biochem Zool. 2000 Sep-Oct;73(5):557-65. doi: 10.1086/317751.
I examined the effects of development, hatching, and oxygen availability on external gill loss in red-eyed tree frogs, Agalychnis callidryas. Under natural conditions, the arboreal embryos maintained large external gills until hatching, which occurred from 5-8 d after oviposition. At hatching, when tadpoles entered the water, external gills began to regress. In older hatchlings this process was extremely rapid. Gill circulation was lost on average within 16 min and sometimes within 5 min. Gills often regressed completely in under 2 h. Younger hatchlings reduced gill circulation, shortened and adducted their gills, then resumed normal circulation for some time after hatching; half had completely lost external gills within 24 h. Experimentally increasing the area of egg surface exposed to the air induced loss of external gills in unhatched embryos. Older hatchlings in hypoxic water without access to air maintained their external gills. This suggests that loss of external gills is a response to increased oxygen availability, rather than a response to hatching per se. Extended maintenance of external gills by large, late-hatching embryos may facilitate continued rapid development in closely packed eggs.
我研究了发育、孵化和氧气供应对红眼树蛙（红眼睛树蛙，Agalychnis callidryas）外鳃消失的影响。在自然条件下，树栖胚胎在孵化前一直保留着大的外鳃，孵化发生在产卵后5至8天。孵化时，蝌蚪进入水中，外鳃开始退化。在较大的幼体中，这个过程极其迅速。鳃循环平均在16分钟内消失，有时在5分钟内消失。鳃通常在2小时内完全退化。较小的幼体减少鳃循环，缩短并内收鳃，然后在孵化后一段时间恢复正常循环；一半在24小时内完全失去外鳃。实验性地增加暴露于空气中的卵表面面积会导致未孵化胚胎的外鳃消失。处于缺氧水中且无法接触空气的较大幼体保留了它们的外鳃。这表明外鳃的消失是对氧气供应增加的反应，而不是对孵化本身的反应。大型、孵化较晚的胚胎对外鳃的长期保留可能有助于紧密排列的卵中持续快速发育。
