Mori Tsukasa, Machida Kazumasa, Kudou Yuki, Kimishima Masaya, Sassa Kaito, Goto-Inoue Naoko, Minei Ryuhei, Ogura Atsushi, Kobayashi Yui, Kamiya Kentaro, Nakaya Daiki, Yamamoto Naoyuki, Kashiwagi Akihiko, Kashiwagi Keiko
Nihon University College of Bioresource Sciences, Fujisawa, Japan.
Department of Computer Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama, Japan.
Front Physiol. 2023 Jun 6;14:1178869. doi: 10.3389/fphys.2023.1178869. eCollection 2023.
Organisms adapt to changes in their environment to survive. The emergence of predators is an example of environmental change, and organisms try to change their external phenotypic systems and physiological mechanisms to adapt to such changes. In general, prey exhibit different phenotypes to predators owing to historically long-term prey-predator interactions. However, when presented with a novel predator, the extent and rate of phenotypic plasticity in prey are largely unknown. Therefore, exploring the physiological adaptive response of organisms to novel predators is a crucial topic in physiology and evolutionary biology. Counterintuitively, tadpoles do not exhibit distinct external phenotypes when exposed to new predation threats. Accordingly, we examined the brains of tadpoles to understand their response to novel predation pressure in the absence of apparent external morphological adaptations. Principal component analysis of fifteen external morphological parameters showed that each external morphological site varied nonlinearly with predator exposure time. However, the overall percentage change in principal components during the predation threat (24 h) was shown to significantly ( < 0.05) alter tadpole morphology compared with that during control or 5-day out treatment (5 days of exposure to predation followed by 5 days of no exposure). However, the adaptive strategy of the altered sites was unknown because the changes were not specific to a particular site but were rather nonlinear in various sites. Therefore, RNA-seq, metabolomic, Ingenuity Pathway Analysis, and Kyoto Encyclopedia of Genes and Genomes analyses were performed on the entire brain to investigate physiological changes in the brain, finding that glycolysis-driven ATP production was enhanced and -oxidation and the tricarboxylic acid cycle were downregulated in response to predation stress. Superoxide dismutase was upregulated after 6 h of exposure to new predation pressure, and radical production was reduced. Hemoglobin was also increased in the brain, forming oxyhemoglobin, which is known to scavenge hydroxyl radicals in the midbrain and hindbrain. These suggest that tadpoles do not develop external morphological adaptations that are positively correlated with predation pressure, such as tail elongation, in response to novel predators; however, they improve their brain functionality when exposed to a novel predator.
生物体通过适应环境变化来生存。捕食者的出现是环境变化的一个例子，生物体试图改变其外部表型系统和生理机制以适应这种变化。一般来说，由于长期的捕食者 - 猎物相互作用，猎物对捕食者表现出不同的表型。然而，当面对新的捕食者时，猎物表型可塑性的程度和速率在很大程度上是未知的。因此，探索生物体对新捕食者的生理适应性反应是生理学和进化生物学中的一个关键课题。与直觉相反，蝌蚪在面临新的捕食威胁时不会表现出明显的外部表型。因此，我们检查了蝌蚪的大脑，以了解它们在没有明显外部形态适应的情况下对新捕食压力的反应。对十五个外部形态参数进行主成分分析表明，每个外部形态部位随捕食者暴露时间呈非线性变化。然而，与对照或5天移出处理（暴露于捕食5天，随后5天不暴露）相比，捕食威胁期间（24小时）主成分的总体百分比变化显示出显著（<0.05）改变了蝌蚪形态。然而，改变部位的适应策略是未知的，因为这些变化并非特定于某个特定部位，而是在各个部位呈非线性变化。因此，对整个大脑进行了RNA测序、代谢组学、通路分析和京都基因与基因组百科全书分析，以研究大脑中的生理变化，发现糖酵解驱动的ATP产生增强，而β-氧化和三羧酸循环在捕食应激反应中下调。暴露于新的捕食压力6小时后，超氧化物歧化酶上调，自由基产生减少。大脑中的血红蛋白也增加，形成氧合血红蛋白，已知其可清除中脑和后脑的羟基自由基。这些表明，蝌蚪在面对新的捕食者时不会发展出与捕食压力呈正相关的外部形态适应，如尾巴伸长；然而，它们在接触新捕食者时会改善大脑功能。
