The Cooloola sedgefrog ( Litoria cooloolensis ) is one of a number of frog species endemic to the coastal sandy lowlands of east Australia exhibiting remarkable tolerance to dilute waters of low pH (< pH 3.5). To investigate the physiological and morphological underpinnings of acid tolerance in L. cooloolensis larvae, we compared Na + balance, uptake and efflux rates, and gill and skin morphology in larvae reared in circum-neutral (pH 6.5) and pH 3.5 water. We hypothesised that L. cooloolensis larvae would be more resistant to ionregulatory disturbance and epithelial damage at low pH relative to acid-sensitive species. Net Na + flux rates were not significantly different from zero in L. cooloolensis larvae reared at pH 3.5 and in acid-naïve animals maintained in pH 6.5 water. Animals reared at pH 6.5 and acutely exposed to pH 3.5, however, exhibited a net loss of Na + due to inhibition of Na + uptake. In contrast, L. cooloolensis larvae reared at pH 3.5 maintained Na + balance at pH 3.5 and did not exhibit inhibition of Na + uptake at this pH. Investigation of Na + transport kinetics and the morphology of the gills and integument suggests tolerance of L. cooloolensis larvae to low pH may be attributed to a high capacity for branchial Na + uptake, increased tight junction length and elevated mucus production at the gills and integument. These factors confer resistance to acid damage and disruption of ionic homeostasis which would otherwise result in the death of amphibian larvae exposed to waters of pH 4.0 and less.

中文翻译：

---

嗜酸性两栖动物 Litoria cooloolensis 幼虫极端耐酸的生理和形态相关性

Cooloola sedgefrog ( Litoria cooloolensis ) 是澳大利亚东部沿海沙质低地特有的多种青蛙物种之一，对低 pH (< pH 3.5) 的稀释水域表现出显着的耐受性。为了研究 L.cooloolensis 幼虫耐酸的生理学和形态学基础，我们比较了在环中性 (pH 6.5) 和 pH 3.5 水中饲养的幼虫的 Na + 平衡、吸收和流出率以及鳃和皮肤形态。我们假设 L.cooloolensis 幼虫在低 pH 值下比对酸敏感的物种更能抵抗离子调节干扰和上皮损伤。在 pH 3.5 饲养的 L.cooloolensis 幼虫和维持在 pH 6.5 水中的酸幼虫中，净 Na + 通量率与零没有显着差异。在 pH 6.5 下饲养并急性暴露于 pH 3.5 的动物，然而，由于抑制 Na + 摄取，表现出 Na + 的净损失。相比之下，在 pH 3.5 下饲养的 L.cooloolensis 幼虫在 pH 3.5 下保持 Na + 平衡，并且在该 pH 下没有表现出对 Na + 吸收的抑制。对 Na + 转运动力学以及鳃和外皮形态的研究表明，L.cooloolensis 幼虫对低 pH 的耐受性可能归因于鳃吸收 Na + 的能力高、紧密连接长度增加以及鳃和外皮处粘液产量增加. 这些因素赋予对酸损伤和离子稳态破坏的抵抗力，否则会导致暴露于 pH 4.0 及更低的水的两栖动物幼虫死亡。5 并且在该 pH 值下没有表现出对 Na + 吸收的抑制。对 Na + 转运动力学以及鳃和外皮形态的研究表明，L.cooloolensis 幼虫对低 pH 的耐受性可能归因于鳃吸收 Na + 的能力高、紧密连接长度增加以及鳃和外皮处粘液产量增加. 这些因素赋予对酸损伤和离子稳态破坏的抵抗力，否则会导致暴露于 pH 4.0 及更低的水的两栖动物幼虫死亡。5 并且在该 pH 值下没有表现出对 Na + 吸收的抑制。对 Na + 转运动力学以及鳃和外皮形态的研究表明，L.cooloolensis 幼虫对低 pH 的耐受性可能归因于鳃吸收 Na + 的能力高、紧密连接长度增加以及鳃和外皮处粘液产量增加. 这些因素赋予对酸损伤和离子稳态破坏的抵抗力，否则会导致暴露于 pH 4.0 及更低的水的两栖动物幼虫死亡。增加紧密连接长度并增加鳃和外皮处的粘液产生。这些因素赋予对酸损伤和离子稳态破坏的抵抗力，否则会导致暴露于 pH 4.0 及更低的水的两栖动物幼虫死亡。增加紧密连接长度并增加鳃和外皮处的粘液产生。这些因素赋予对酸损伤和离子稳态破坏的抵抗力，否则会导致暴露于 pH 4.0 及更低的水的两栖动物幼虫死亡。