Cramp Rebecca L, Ohmer Michel E B, Franklin Craig E
School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Department of Biology, University of Mississippi, MS, 38677, USA.
Conserv Physiol. 2022 Jul 3;10(1):coac038. doi: 10.1093/conphys/coac038. eCollection 2022.
Levels of ultraviolet (UV) radiation have increased in many parts of the world due to the anthropogenic destruction of the ozone layer. UV radiation is a potent immunosuppressant and can increase the susceptibility of animal hosts to pathogens. UV radiation can directly alter immune function via immunosuppression and photoimmunotolerance; however, UV may also influence pathogen defences by affecting the distribution of energy resources among competing physiological processes. Both defence against UV damage and repair of incurred damage, as well as the maintenance of immune defences and responding to an immune challenge, are energetically expensive. These competing demands for finite energy resources could trade off against one another, resulting in sub-optimal performance in one or both processes. We examined the potential for a disease-related energy trade-off in green tree frog () larvae. Larvae were reared under high- or low-UV conditions for 12 weeks during which time we measured growth rates, metabolic rate and susceptibility to the amphibian fungal pathogen, (). We found that larvae exposed to high levels of UV radiation had higher rates of energy expenditure than those exposed to low UV levels; however, UV exposure did not affect growth rates or developmental timings. Larvae exposed to high UV radiation also experienced greater infection rates and carried a higher infection burden than those not exposed to elevated UV radiation. We propose that the increased energetic costs of responding to UV radiation were traded off against immune defences to protect larval growth rates. These findings have important implications for the aetiology of some -associated amphibian declines, particularly in montane environments where infections are most severe and where UV levels are highest.
由于臭氧层受到人为破坏，紫外线（UV）辐射水平在世界许多地区都有所上升。紫外线辐射是一种强效免疫抑制剂，会增加动物宿主对病原体的易感性。紫外线辐射可通过免疫抑制和光免疫耐受直接改变免疫功能；然而，紫外线也可能通过影响能量资源在相互竞争的生理过程中的分配来影响病原体防御。抵御紫外线损伤和修复已发生的损伤，以及维持免疫防御和应对免疫挑战，都需要消耗大量能量。对有限能量资源的这些相互竞争的需求可能会相互权衡，导致在这一个或两个过程中表现欠佳。我们研究了绿树蛙（）幼虫中与疾病相关的能量权衡的可能性。将幼虫在高紫外线或低紫外线条件下饲养12周，在此期间我们测量了生长速率、代谢率以及对两栖类真菌病原体（）的易感性。我们发现，暴露于高水平紫外线辐射的幼虫比暴露于低水平紫外线的幼虫能量消耗率更高；然而，紫外线暴露并未影响生长速率或发育时间。暴露于高紫外线辐射的幼虫也比未暴露于增强紫外线辐射的幼虫感染率更高，且感染负担更重。我们认为，应对紫外线辐射增加的能量成本是以牺牲免疫防御为代价的，以保护幼虫的生长速率。这些发现对于一些与相关的两栖动物数量下降的病因具有重要意义，特别是在山区环境中，感染最为严重且紫外线水平最高。
