Center for Marine Biotechnology and Biomedicine and Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
Integr Comp Biol. 2013 Aug;53(2):248-57. doi: 10.1093/icb/ict034. Epub 2013 Apr 25.
The Japanese mudskipper (Periophthalmus modestus), an amphibious fish that possesses many respiratory and locomotive specializations for sojourns onto land, was used as a model to study how changing atmospheric oxygen concentrations during the middle and late Paleozoic Era (400-250 million years ago) may have influenced the emergence and subsequent radiation of the first tetrapods. The effects of different atmospheric oxygen concentrations (hyperoxia = 35%, normoxia = 21%, and hypoxia = 7% O2) on terrestrial performance were tested during exercise on a terrestrial treadmill and during recovery from exhaustive exercise. Endurance and elevated post-exercise oxygen consumption (EPOC; the immediate O2 debt repaid post-exercise) correlated with atmospheric oxygen concentration indicating that when additional oxygen is available P. modestus can increase oxygen utilization both during and following exercise. The time required post-exercise for mudskippers to return to a resting metabolic rate did not differ between treatments. However, in normoxia, oxygen consumption increased above hyperoxic values 13-20 h post-exercise suggesting a delayed repayment of the incurred oxygen debt. Finally, following exercise, ventilatory movements associated with buccopharyngeal aerial respiration returned to their rest-like pattern more quickly at higher concentrations of oxygen. Taken together, the results of this study show that P. modestus can exercise longer and recover quicker under higher oxygen concentrations. Similarities between P. modestus and early tetrapods suggest that increasing atmospheric oxygen levels during the middle and late Paleozoic allowed for elevated aerobic capacity and improved terrestrial performance, and likely led to an accelerated diversification and expansion of vertebrate life into the terrestrial biosphere.
日本弹涂鱼（Periophthalmus modestus）是一种具有许多呼吸和运动特化功能的两栖鱼类，可以在陆地上短暂停留。本研究以弹涂鱼为模型，探讨古生代中晚期（4 亿至 2.5 亿年前）大气氧气浓度变化如何影响第一批四足动物的出现和随后的辐射。通过在陆地跑步机上运动和从剧烈运动中恢复来测试不同大气氧浓度（高氧=35%、常氧=21%和低氧=7%O2）对陆地性能的影响。耐力和剧烈运动后耗氧量（EPOC；运动后立即偿还的 O2 债务）与大气氧浓度相关，表明当有更多氧气时，弹涂鱼可以在运动中和运动后增加氧气利用。剧烈运动后，弹涂鱼恢复到静息代谢率所需的时间在不同处理之间没有差异。然而，在常氧下，运动后 13-20 小时，耗氧量高于高氧值，表明氧气债务偿还延迟。最后，运动后，与口咽空气呼吸相关的呼吸运动在氧气浓度较高时更快地恢复到休息状态。总之，这项研究的结果表明，弹涂鱼在较高氧气浓度下可以更长时间地运动和更快地恢复。弹涂鱼和早期四足动物之间的相似性表明，古生代中晚期大气氧气水平的增加允许提高有氧能力和改善陆地性能，并可能导致脊椎动物生命向陆地生物圈的加速多样化和扩张。
