PubMed/MEDLINE is a large database in biomedicine, and the Google search engine eventually stores the entire published peer-reviewed and other articles, while AGRICOLA contains about 6 million records associated with agriculture and allied sciences. It is to be noted that Pila sp is exclusively available in cultivated lands and grasslands, so it is included in the AGRICOLA database. The aforementioned factors played a role in our decision to use the above databases. Of the entire papers available in all the above databases on molluscs, only peer-reviewed literature published in English on “Pila globosa” was screened in relation to various search terms. Search terms such as “ecotoxic”, “physiological responses”, “abiotic and biotic stressors”, “heavy metals”, “organophosphorus”, “carbamate”, “butachlor”, “adaptation” “energy expenditure”, “fat metabolism”, “dormant period”, “desiccation”, “oxidative stress”, “respiratory” and “antioxidant enzymes”, “carbohydrate metabolism” “biological macromolecules”, “neurotransmitter enzymes”, “acetylcholinesterase” along with “Pila globosa” or “P. globosa” were searched ion the two databases electronically.

The entire published peer-reviewed articles in the English language in books, journals, periodicals, and various authentic reputed webpages from 1952 to July of 2022 on “Pila globosa” in relation to the search terms in PubMed/MEDLINE, AGRICOLA, and Google search engine with above search terms were screened in the review article. Articles not containing any of the above terms were not included in the review. Articles matching within the subject area of the Pila sp. Were included in the review, whereas any axillary article in which the above term(s) is merely used was excluded from the review. Since <50 and 10 articles were published on the snail P. globosa in PubMed/MEDLINE and AGRICOLA, respectively, all the articles were included in the study while the articles were filtered in the Google search engine. All the data from the published papers were independently extracted unbiasedly, irrespective of the geographical region. Published literature from all geographical area was selected for screening.

In order to streamline the entire review process securely and to ensure the reliability and consistency of this mollusc species, we have covered various aspects such as the economic importance, species origin, morpho-anatomical adaptive features, cellular, organ-specific, metabolic, behavioral adaptations against the biotic and abiotic stressors of the species Pila sp. Also, we have elegantly reviewed the effects of the specific chemicals and pollutants on its studied biochemical and molecular pathways. The role of this organism in its ecosystem as a disease carrier and ecologic relation with other co-habitants has also been reviewed for its better exploitation. It will extend the existing understanding of the link between enzymatic and pathophysiological activities or responses in lower animals and P. globosa, in particular. The objective of this article was to systematically review information to elucidate for the first time the ecotoxic responses, such as redox regulatory activities, neurotransmitter enzyme levels, and responses to heavy metal exposure of this snail. As a result, it can be helpful for its conservation in general and environmental ecotoxic and environmental chemistry studies in particular.

Once the authors were convinced of the peer-reviewed articles on this species, altogether, 41 and 10 articles were obtained from the PubMed and AGRICOLA databases, respectively on the species, P. globosa were analyzed in the study, and the total articles published on P. globosa in Google search engine along with any additional mentioned search terms were filtered to 80 number and some of them were repetitions among all databases. The subject area of each article was extracted and categorized to describe the economic importance and other life cycle aspects of this species in relation to various environmental factors, which could be natural or anthropogenic in nature. However, the number of peer-reviewed articles on P. globosa indicates scanty studies on this species, starting from physiological responses to life history trade-off, and it was emphatically analyzed in the present review.

The blood (hemocyanin) and the heart constitute the circulatory system in P. globosa, and this system, especially the heartbeat, is modulated by a small change in the surrounding environment (Panda et al., 2021a; 2021b). The hemocyte contributes to 5 physiological events such as wound and shell repair, nutrition, transport, excretion, and immunology in univalve organisms (Panda et al., 2021a; 2021b). Mahilini and Rajendran (2008) identified granulocyte I in P. globosa as the smaller and younger hemocytes with a 5.28 µm diameter. They characterized larger hemocytes into granulocytes II and III with diameters of 16.5 and 22.46 µm, respectively. They differentiated two granulocytes based on the staining property having a centrally and eccentrically located nucleus with heavy cytoplasm. However, more studies are still needed to understand the role of different hemocytes in relation to the immune system and detoxification in P. globosa.

Nowadays, much attention has been paid to selecting preferable controlling agents for a heartbeat in the natural population. Lal and Agarwal (1968a) standardized a medium containing saline solution for sustaining the P. globosa heart by adjusting the composition of different ions such as NaCl, KCl, CaCl₂, MgCl₂.6H₂O, MgCl₂.7H₂O, Na₂HPO₄.12H₂O at 3.17, 0.373, 0.85, 0.254, 0.028, and 0.063 g, respectively in one liter of distilled water and finally, introduced glucose into it as the source of energy. The chemical agent 5-hydroxytryptamine (5-HT), a neuro-hormone, is found in tissues of apple snail I and is responsible for controlling the heartbeat of P. globosa as it increases the heartbeat, which is prevented by Lysergic Acid Diethylamide (LSD) as stated previously. Later on, it was found that LSD rather increases the heartbeat as it mimics 5-hydroxytryptamine, although the bromine derivative of LSD (10⁻⁷ to 10⁻⁸ g/ml) sometimes elevates the threshold of 5-HT. The chemical 5-hydroxytryptamine (5-HT) is a derived product from one of the essential amino acids, L-tryptophan; it is required for brain development and is influenced by the environment in many organisms (Booij et al., 2015). Therefore, the management of this molecule for the regulation of the circulatory system is crucial under varying environmental conditions; however, additional research on this aspect of P. globosa is anticipated. Alkaloid reserpine also has the same effect of increasing amplitude but decreasing heartbeat frequency (Lal and Agarwal 1968b). Therefore, LSD and alkaloids can be used as possible heart rhythm controllers in the future by providing the threshold amount of doses in P. globosa in particular.

Although varieties of hemocytes in apple snails have been discovered, the role of these cells in the immune system is yet to be revealed. Similarly, LSD and alkaloids, along with 5-HT, can control the heart rhythm in gastropods in general and in P. globosa in particular. So, the immunological responses indicate that other biochemical mechanisms must be affected in this snail under various ecotoxic conditions, including heavy metal exposure.

Organophosphate is the organophosphorus compound and is mostly used as insecticide in general. An organophosphate compound phorate inhibits the hydrolytic activity of acetylcholinesterase by 175%–325% by forming phosphorylated enzyme complexes, and this effect was largely found to be time-dependent but not dose-dependent. Similarly, another organophosphate, phosphorothioates, also inhibits acetylcholinesterase activity by forming an oxygen analog (Singh and Agarwal 1978). The effects of pesticides such as formothion and trichlorfon on the acetylcholine activity of P. globosa are shown to be time-dependent, similar to phorate. For instance, formothion takes 55 min longer than trichlorfon to achieve maximal effectiveness. Therefore, different organophosphates impact differently in a time or dose-dependent manner on P. globosa, which illustrates the mechanism of the effects of organophosphates.

Some organophosphates exert toxicity selectively under different conditions. For instance, a high concentration of two pesticides, formothion, and trichlorfon, blocks the activity of acetylcholinesterase on excitatory receptors only by 130% and 64%, respectively. It indicates the selective action of organophosphates on two different types of acetylcholine receptors (Singh and Agarwal, 1979). Similarly, carboxy esterase in the hepatopancreas of P. globosa is sensitive to organophosphates such as methyl parathion and fenitrothion (Aparna et al., 2010). The above information suggests the selective active action of organophosphates and is recommended in P. globosa as possible biomarker of organophosphate toxicity.

Carbamate, another class of insecticides, is nearly similar to the structure as well as the mechanism of organophosphates. Metcalf (1971) proposed that carbamate compounds having N-methyl and N, N -dimethyl groups show anti-acetylcholinesterase activity. However, aldicarb 107%–289% inhibits acetylcholinesterase activity though it does not contain either of the above chemical groups (Singh and Agarwal 1979). It is found that P. globosa is more susceptible to the toxicity of carbamate, such as mexacarbate, in comparison to that carbaryl and aldicarb (Singh and Agarwal 1981). The above studies found that P. globosa is susceptible to carbamates as this compound targets the major neuromuscular enzyme acetylcholinesterase, thus elevating the level and duration of acetylcholine enzyme action.

Herbicides are generally used to control plants, but these compounds can target non-specific organisms non-selectively. Butachlor, an herbicide, affects non-target species like P. globosa, in which it decreases 54.79% and 96.08% in acetylcholinesterase activity and butyryl-cholinesterase enzymes, respectively (Rajyalakshmi et al., 1996). However, the activity gradually increased up to 82%, possibly due to either operating any degradation mechanism or increasing the activity of both enzymes as a compensatory mechanism. Many other apple snails are found to be non-specifically susceptible to many herbicides (Panda et al., 2021a; 2021b). The above information indicates that P. globosa is susceptible to herbicides such as butachlor.

Calcium in the form of calcium chloride may present several significant health hazards depending on the specific circumstances. Exposure to calcium chloride causes activation of the glycolytic pathway and ATP hydrolysis as well as increases in the glucose level in P. globosa. Elevating the activity of the above enzymes helps in a 13.99% increment of succinate dehydrogenase activity through oxidative metabolism in P. globosa (Rao and Kumar 1982). Therefore, calcium chloride also alters physiological activities by targeting respiratory enzymes.

The amount of research that has been done on how heavy metals affect the metabolic and physiological responses of the snail P. globosa is quite limited. Therefore, special attention is needed to document the metals available in the environment, particularly in soil and water. Since this snail scrawls on the land, absorption of heavy metals into its body and their effects are expected. In the interest of its conservation, it has been tried to analyze the environmental physiology of P. globosa in the current article.

It is inferred that the decreased carbohydrate and protein contents are crucial in the dormant period in P. globosa. Acetylcholinesterase enzyme is the most susceptible enzyme to respond against pollutants. The decreased activities of respiratory enzymes are found to be vital in the dormant period. Heavy metal reduces the activity of enzymes involved in amino acid metabolism. The above can be reliably studied under pollution or environmental stress using P. globosa as a model organism.

The gastropod P. globosa can be considered as a threat to higher animals due to its parasitic activities, and it also acts as a host for many parasites. Freshwater snails, including P. globosa, are used as intermediate hosts for many parasites, especially by trematodes (Nakao and Sasaki, 2021; Wiroonpan et al., 2021). In turn, they can become a big threat to other higher organisms, including humans. A common trematode, Diplodiscus species, occasionally uses P. globosa as its intermediate host (Anjaneyulu 1967; Afaq-Husain and Shameel 2021; Hu et al., 2021), so there is a possibility for transmission to other higher trophic levels, including human beings. This is observed in some parts of India where the foot muscle of Pila is consumed as food. Metacercariae of trematode Pseudodiplodiscoides pilai reside in the esophagus of P. globosa while they mature in the stomach of this snail (Murty 1973). A trematode, P. pilai resembles Diplodiscus, Catadiscus, and Pseudodiplodiscus in having a single testis but varies in the structure of oral sucker and ventral sucker uses P. globosa as host (Murty 1970). Therefore, the involvement of this apple snail as an intermediate host suggests that it should be boiled enough before using this snail as a diet (Figure 5).

The snail P. globosa also acts as an intermediate host for many microorganisms. For example, it acts as a host for probiotic microorganisms, Pichia kudriavzevii, which can deplete the cholesterol level by performing various adaptive mechanisms. One mechanism includes 86.30% higher action of bile salt hydrolase and 20.29% inhibition of enzymatic activity by the generation of 3-hydroxy-3-methylglutaryl and absorbing cholesterol (Kathade et al., 2020). Bacteria like Aeromonas, Pseudomonas, Escherichia, and Listeria cause disease in the shell of P. globosa characterized by the formation of the blister in the periostracum of it, which later disconnects the underlying calcified layer (Ajesh and Sreejith 2014). The above information suggests the possible transmission of these microorganisms from P. globosa to higher organisms.

The antioxidant activities are influenced in response to various abiotic factors such as temperature, salinity, and pH in lower invertebrates (Paital and Chainy 2010; Paital and Chainy 2013a; Paital and Chainy 2013b; Pati et al., 2022). Exposure of untreated effluents released from tannery to P. globosa causes a 1.5 to 3.09 folds increase in antioxidant enzymes as well as 32 and 37% alleviation in carbohydrate and protein levels, respectively, in its different tissues (Bhattacharya et al., 2016). Along with that, comet assay reveals the damage of DNA that leads to genotoxicity (Bhattacharya et al., 2016). It indicates the elevation of antioxidant enzymes during unfavorable conditions, especially to generate oxidative stress, as elaborated in Table 3; Swarnakar et al., 1991. The catalytic potential (low K_m and high V_max) of aspartate and alanine aminotransferases are elevated by exposure to organophosphate malathion in vivo but do not change their activity in vitro. It indicates the role of the intracellular environment on the activity of these enzymes in P. globosa (Sahib and Rao 1988). Therefore, P. globosa can be used as a biomarker to assess the environment, especially the freshwater ecosystem, by determining the changes in antioxidant activities (Bal et al., 2021a, b). Few recent articles published also support this assumption, especially using the change in redox regulatory molecules as tissue and spatiotemporal specific (Panda et al., 2022a; 2022b).

The excretory pattern is crucial for every organism, and in P. globosa, it plays a major role during hibernation and aestivation. During aestivation, 62.6 and 75.3% lower expression of adenosine deaminase and AMP deaminase are observed, respectively, in its hepatopancreas. It happened due to a 43% decrease in the level of adenosine nucleotide and a lower energy state in the snail. It is because ATP is the activator for AMP deaminase during aestivation, and snail decreases 153% lower production of ammonia due to the depleted AMP deaminase activity (Figure 6). On the other hand, the activity of AMP deaminase is 87.4% elevated during the active period so that ammonia production is increased by 214% and it does not become a risk to snail in aquatic habitat. This event implies the transition of ammonotelism to uricotelism during the aestivation condition (Moorthy et al., 1982). Therefore, adenosine deaminase and AMP deaminase play an important role in converting excretory products from ammonia to uric acid, thus protecting the animal from ammonia toxicity and desiccation during dormant periods.

The metabolic activities also influence the alteration of excretory patterns during dormant periods. According to a report by Chaturvedi and Agarwal (1983), excretion of ammonia is restricted exclusively during active phases in the case of P. globosa due to the near absence of metabolic activity and preference for dry habitats during the dormant stages (Chaturvedi and Agarwal, 1983). During hibernation, this transition mode of the excretory system in P. globosa is transformed from ammonotelism to uricotelism. It could occur through Kreb’s cycle as ammonia is more toxic than uric acid, but the chance of elimination of this excretory product under the terrestrial mode of habituation becomes less feasible (Saxena 1956a). Moreover, uric acid acts as an excretory product that helps the animal conservation of water. Thus, the switching of excretory products is beneficial to this organism which prevents and saves the snail from desiccation and the toxic effects of ammonia during such dormant periods.

Many organs play crucial roles in accumulating excretory products during dormant periods. The hepatopancreas acts as the urea-generating site in P. globosa, probably due to the involvement of the ornithine cycle in it. During dormant stages, this metabolic waste cannot be excreted due to cease of excretion activities (Chaturvedi and Agrawal, 1979). About 97 and 138% elevated accumulation of uric acid in hepatopancreas and foot muscles, respectively, are documented during aestivation, which is analogous to such an event in insects (Athawale and Reddy 2000). Therefore, the foot muscle of P. globosa serves as a potential accumulation site during the dormant period. The membrane system of secretory cells of salivary glands in P. globosa is stretched during the active period to produce and store many secretory products. This metabolic process is ceased during aestivation, indicating the inactivation of the salivary gland during aestivation (Bhattacharyya et al., 2012). Therefore, the role of the hepatopancreas, foot muscle, and salivary gland is crucial in secreting and accumulating excretory products such as urea and uric acid by a few of the above-selected organs.

During aestivation, many biochemical activities are also altered to compensate for the effects of lowered metabolic responses during dormant phases (Figure 7). The activities of glucogenic aminotransferases such as aspartate aminotransferase and alanine aminotransferase found in the hepatopancreas of P. globosa are elevated during an active period in comparison to that of aestivation period. It indicates the cessation of these enzymes during aestivation, which slows down amino acid metabolism (Reddy et al., 1990). Injection of sterol obtained from the cerebral ganglia of aestivated snail to an active one causes the depletion of oxygen consumption in the latter case (Meenakshi 1956). It is corroborated by the data that during the starvation period, the activities of respiratory and mitochondrial enzymes in Pila, such as succinic dehydrogenase, cytochrome C oxidase, and glutamic dehydrogenase are 54%, 59%, and 62% decreased, respectively, due to the action of sterols (Raghupathiramireddy 1967). The absence of glucose content is also found in P. globosa during the dormant period (Saxena 1956a). It may be due to glucose conversion to glycogen or non-carbohydrate substances like fat. Thus, most of the physiological activities are halted to overcome the energy expenditure of this organism during the dormant period.

The carbohydrate metabolism and energy level are also altered in response to dormant periods in many ectotherms. A decrease in the level of ATPase activity during aestivation is found to be associated with an 80% increase in the ATP accumulation level in the snail as compared to the normal period. In turn, it lowers glycolytic activity by inhibiting phosphofructokinase enzyme through allosteric inhibition. It happens because the recovery event from aestivation is a process of energy expenditure, not energy saving (Raghupathiramireddy and Swami 1967). Similarly, the observed 34.7% and 70.6% decrease in glycogen and glucose levels, respectively, in ganglia (cerebral, pleuropedal, and visceral) of aestivated P. globosa indicates that carbohydrate is used as a source of energy during aestivation (Singh, 1976). However, the absence of glucose content in P. globosa by Saxena (1956b) may be due to the conversion of glucose to glycogen or non-carbohydrate substances like fat. However, fat may compensate for the lack of energy sources during dormant periods. This adaptive mechanism compensates for energy expenditure from carbohydrate sources during the dormant phases.

The role of fat is crucial during the dormant period. During aestivation, the iodine index or iodine absorption value mediated by ascorbic acid and fat is 81% elevated due to the increment of antioxidant enzymes in P. globosa (Krishnamoorthy 1968). Enzyme hydrolysis of methyl ester salicylate is increased, and olive and coconut oil are decreased during aestivation in P. globosa, indicating more hydrolysis of unsaturated fatty acid compared to saturated fatty acid during such periods (Krishnamoorthy and Brahmanandam 1970). Injection of sterol obtained from the cerebral ganglia of aestivated P. virens to an active one decreases oxygen consumption (Meenakshi 1956). The depletion of oxygen consumption suggests the 54%–62% inhibition of respiratory and mitochondrial enzyme activities due to the action of sterols during the starvation period (Raghupathiramireddy 1967). Therefore, sterol plays a crucial role during dormant periods by controlling oxygen consumption and respiratory and mitochondrial enzyme activities.

In P. globosa, energy cost is dependent on the surrounding habitat. The energy expenditure decreases when the water level lowers in the habitat. For example, about 14.7 kcal g⁻¹day⁻¹energy expenditure under the lower water level in its habitat is recorded in this species, while the value is found to rise to 67.4 kcal g⁻¹day⁻¹ when the water level rises (Haniffa 1980a). Similarly, the energy budget of P. globosa is 1.5–3 times elevated during starvation conditions, while absorption efficiency and conversion efficiency are influenced by both feeding and available food levels by 93=–76 and 6%–8%, respectively (Haniffa 1987). The energy in this snail is utilized or released via aerobic as well as anaerobic metabolic processes during the aestivation period (Haniffa 1978). Therefore, the energy expenditure is less in the organism during the dormant phases of its life, and the demanding value of energy is elevated during post-dormant periods and is mostly modulated changes in the habitats of P. globosa.

Interestingly, the energy source content varies between sexes, and the body pattern becomes favorable for females compared to males in P. globosa. The fat and carbohydrate content of P. globosa are found to be significantly higher, accounting for 7 and 36%, respectively, in larger females compared to that of the same-sized male counterpart (Nargis et al., 2012). It shows the female-biased higher energy source that may play a crucial role in the development of females. The growth rate and body weight of Plia sp. Have a negative correlation with each other, as studied by Haniffa (1980b). It has been calculated that its body growth rate is reduced by 14.13% when its body weight is increased and increased during achieving adult stages (Haniffa 1980b). It indicates the existing relation between energy expenditure and body pattern, especially with the body growth of this snail. The above information suggests a higher energy source requirement in females than males in P. globosa. Overall, P. globosa shows adaptative nature in response to abiotic stressors by altering redox regulation, excretory system, and metabolism such as carbohydrate, fat, and energy.