Antioxidant defence system, a highly conserved biochemical mechanism, protects organisms from harmful effects of reactive oxygen species (ROS), a by-product of metabolism. Both invertebrates and vertebrates are unable to modify environmental physical factors such as photoperiod, temperature, salinity, humidity, oxygen content, and food availability as per their requirement. Therefore, they have evolved mechanisms to modulate their metabolic pathways to cope their physiology with changing environmental challenges for survival. Antioxidant defences are one of such biochemical mechanisms. At low concentration, ROS regulates several physiological processes, whereas at higher concentration they are toxic to organisms because they impair cellular functions by oxidizing biomolecules. Seasonal changes in antioxidant defences make species able to maintain their correct ROS titre to take various physiological functions such as hibernation, aestivation, migration, and reproduction against changing environmental physical parameters. In this paper, we have compiled information available in the literature on seasonal variation in antioxidant defence system in various species of invertebrates and vertebrates. The primary objective was to understand the relationship between varied biological phenomena seen in different animal species and conserved antioxidant defence system with respect to seasons.
Types of seasons and their duration may vary from one ecological region to another and influence the physiology of the inhabiting flora and fauna [
Metabolism is a direct reflection of cellular respiration where molecular oxygen is tetraelectronically reduced to water in electron transport chain of mitochondria to generate ATP to meet their energy requirement [
There are several reports in literature which have clearly demonstrated alterations in concentrations of various pollutants in air and water with respect to seasons [
Being highly reactive and nonspecific in nature, ROS usually oxidize biomolecules such as lipids, carbohydrates, proteins, and DNA and, thereby, impair normal cellular functions. A shift in balance between oxidants to antioxidants in favour of oxidants is termed as “oxidative stress.” Oxidative stress is considered as cause or effects of several pathophysiological conditions, diseases, and aging processes [
Antioxidant defence system comprises both enzymatic and nonenzymatic components. Enzymatic system contains a cascade of enzymes which are together known as antioxidant enzymes (AOE). Antioxidant enzymes are ubiquitous and highly conserved in their catalytic nature. Some of them are present in multiple forms. The first member of this cascade is superoxide dismutase (SOD) which dismutates
Schematic representation of cellular production of ROS, their impact on biomolecules, and their metabolism by antioxidant enzymes. SOD, superoxide dismutase; CAT, catalase; GPX, glutathione peroxidase; GR, glutathione reductase;
Animals have developed various physiological strategies such as hibernation, aestivation, and migration because they do not have control over the physical components of the environment such as food availability, temperature, and day length [
The central focus of this mini review is to compile pieces of information available in literature on various parameters related to ROS and antioxidant defences in some vertebrates and invertebrates of different phyla with respect to seasons under one platform. Since components of antioxidant defence system are highly conservative, it will be interesting to find out how different species manipulate their antioxidant defences to adjust themselves to seasons.
Metabolic activities and mitochondrial functions of invertebrates are regulated by several components of seasons such as photoperiod, temperature, humidity, and food availability [
However, the major limitation in the use of antioxidant molecules or OS parameters as biomarkers to monitor environmental pollution is the lack of basic information on their seasonal variation. It is essential to ascertain the normal seasonal changes in antioxidant defence parameters before using them to monitor environment contamination. The lack of systematic information on the responses of antioxidant defences and OS markers of species to pollutants makes it difficult to use them as biomarkers to assess pollution.
Annelids (phylum Annelida) include ringworms, earthworms, and leeches. Annelids have adapted to various ecological zones which span aquatic (both marine and freshwater environments) to terrestrial environment. Seasonal variation of antioxidant defence system in species of this phylum is scanty.
Molluscs (phylum Mollusca) encompass a large number of species that spread from aquatic to terrestrial ecosystem. Impacts of tidal heights on activities of antioxidant enzymes in gills and digestive glands of
It was reported that DNA strand fragmentation was elevated in tissues of
Antioxidant defence system in oyster (
Lack of water, humidity, and food in a specific season leads to metabolic depression in snails. In summer, they undergo aestivation, whereas in winter they undergo hibernation. After arrival of suitable environment conditions, the animal arouse from the metabolic depression. In general, aestivation followed by arousal is accompanied by a transient elevation in oxygen consumption leading to elevated ROS production [
Due to the sedentary nature, sessile-filter feeding, wide geographical distribution, and abundant availability,
Most arthropod species are land dwellers and few are aquatic in nature. Niyogi et al. [
A study on different antioxidant enzymes in honey bee (
All species of the phylum are marine dwellers. A seasonal variation in feed intake under constant temperature and natural photoperiod was noticed in green sea urchin [
Taken together, the above discussion reveals that invertebrates adapt different strategies to regulate their antioxidant defences in response to seasonal factors depending on ecological demands/environment.
Season-related changes in antioxidant defence parameters in case of vertebrates indicate a composite reflection of impacts of several biotic and abiotic factors. Biotic factors mainly include migration, reproduction, metabolic status, and age of animals, while abiotic factors are mainly temperature, photoperiod, salinity, oxygen content, food availability, and so forth.
Literature reveals that most of the studies related to seasonal variation of antioxidant defences in fish are investigated with respect to pollutants present in water. A decrease in GSH content and an increase in GR activity in hepatopancreas of kill fish population (
A comparative study on seasonal variation in antioxidant defence parameters and OS indices in tissues of four species of fish (
Although amphibians are very important group used for study as bioindicators of environmental pollutions, seasonal studies related to antioxidant defences were limited to few species. An elaborate investigation has noticed the occurrence of seasonal fluctuation of antioxidant proteins in liver tissues of
Not much information is available on free radical metabolism in reptiles in general and snakes and crocodiles in particular with reference to seasons. Reptiles are poikilotherms. External environmental factors have profound impacts on metabolism of reptiles in general and free radical metabolism in particular. Reptiles have adapted to various ecological niches which span from completely dry atmosphere of desert to submerged aquatic habitat and some of them make long distance movement. Though there are few reports on free radical metabolism in reptiles, not much information is available in relation to seasonal variation. In this regard, crocodiles deserve special attention because submerged habitat had made crocodiles with more tolerance to hypoxia, since hypoxia is directly related to redox metabolism; crocodiles are an excellent model to establish relationship between hypoxia and OS.
A preliminary study from Hermes-Lima’s laboratory [
Birds are homeotherms. Some reports indicate occurrence of seasonal variation in their antioxidant defence system and OS status. Habitat and photoperiodism may be responsible for the observed seasonal variation of OS metabolism in their tissues. Poor habitat due to unavailability of food may induce intensive foraging activity which may increase generation of ROS in birds. In case of Seychelles warblers (
Mammals inhabiting temperate zone usually exhibit seasonal changes in their morphology, behavior, and physiology in order to cope with changing environment. Therefore, they can exhibit seasonal variation in their antioxidant defence system and OS status. Photoperiod has been shown to affect lipid droplets and LPx in bank vole [
In the present review an attempt is made to summarize information available in the literature on seasonal changes in antioxidant defence system and OS markers in invertebrates as well as in vertebrates. It is inferred that seasonal variation in antioxidant defence system may be an evolutionary strategy by animals for different adaptations against various physical aspects of environment. Also a far-fetched implication of changes in seasonal factors on global food chain cannot be denied as larval or embryonic forms of invertebrates constitute first line of primary productivity. It is apparent that various cues of seasons may regulate metabolic functions in tissues through appropriate receptors which in turn decide ROS and antioxidant defences in tissues and, thereby, govern various physiological activities in the animals (Figure
A schematic figure showing how seasonal factors affect various physiological functions through reactive oxygen species.
The authors declare that there are no competing interests regarding the publication of this paper.
The authors are grateful to Department of Biotechnology, Govt. of India, for funding.