Abstract
Survival under stress, such as exposure to hypoxia, anoxia, freezing, dehydration, air exposure of water breathing organisms, and estivation, is commonly associated to enhanced endogenous antioxidants, a phenomenon coined “preparation for oxidative stress” (POS). The regulation of free radical metabolism seems to be crucial under these selective pressures, since this response is widespread among animals. A hypothesis of how POS works at the molecular level was recently proposed and relies on two main processes: increased reactive species production under hypoxia, and activation of redox-sensitive transcription factors and signaling pathways, increasing the expression of antioxidants. The present paper brings together the current knowledge on POS and considers its future directions. Data indicate the presence of POS in 83 animal species (71.6% among investigated species), distributed in eight animal phyla. Three main research challenges on POS are presented: (i) to identify the molecular mechanism(s) that mediate/induce POS, (ii) to identify the evolutionary origins of POS in animals, and (iii) to determine the presence of POS in natural environments. We firstly discuss the need of evidence for increased RS production in hypoxic conditions that underlie the POS response. Secondly, we discuss the phylogenetic origins of POS back 700 million years, by identifying POS-positive responses in cnidarians. Finally, we present the first reports of the POS adaptation strategy in the wild. The investigation of these research trends and challenges may prove useful to understand the evolution of animal redox adaptations and how they adapt to increasing stressful environments on Earth.
Highlights
Animals are naturally submitted to environmental stresses that act as selective pressures leading to fixation of many behavioral, physiological, and biochemical adaptations
Several biochemical adaptations, including metabolic depression, use of anaerobic pathways, epigenetic modifications, and changes in redox metabolism are conserved among many animal species that tolerate low oxygen stress (Staples and Buck, 2009; Storey and Storey, 2012; Biggar and Storey, 2015; Storey, 2015)
Further investigations showed that many other animal species, from cnidarians to vertebrates, enhance their endogenous antioxidants when exposed to different low oxygen stress conditions (Welker et al, 2013; Moreira et al, 2016)
Summary
Animals are naturally submitted to environmental stresses that act as selective pressures leading to fixation of many behavioral, physiological, and biochemical adaptations. One situation that many animals endure is the periodic reduction in oxygen availability, which can last from hours to days/weeks. This occurs in animals during several natural events, including exposure to hypoxic/anoxic environments, exposure to freezing, or severe dehydration (which resemble ischemia), air exposure of water breathing organisms and estivation. These conditions are termed as “low oxygen stress” (Hermes-Lima et al, 2015)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have