Sea Snake Research Articles

Preclinical efficacy of Australian antivenoms against the venom of the small-eyed snake, Micropechis ikaheka, from Papua New Guinea: An antivenomics and neutralization study

There is no specific antivenom for the treatment of envenoming by the small-eyed snake, Micropechis ikaheka, a dangerous fossorial species endemic to Papua New Guinea, Irian Jaya (West Papua) and neighbouring islands. This study evaluated one marine (sea snake) and four terrestrial (tiger snake, brown snake, black snake and polyvalent) antivenoms, manufactured in Australia by bioCSL Limited, for their ability to immunoreact ('antivenomic' analysis) and neutralize enzymatic and toxic activities of M. ikaheka venom. All antivenoms neutralized lethality of the venom and attenuated, dose-dependently, myotoxic activity. The polyvalent antivenom also neutralized cardiotoxic activity. In contrast, antivenoms were ineffective in the neutralization of phospholipase A₂ (PLA₂) and anticoagulant activities. Antivenomics outcomes were in concordance with neutralization tests, for chromatographic peaks corresponding to α-neurotoxins of the three finger family, responsible for lethality, were quantitatively retained in the immunoaffinity columns, whereas peaks corresponding to PLA₂s were immunocaptured only to a partial extent. The ability of antivenoms to neutralize lethal, i.e. neurotoxic, and myotoxic activities of M. ikaheka venom, which represent the most relevant clinical manifestations of envenoming, suggests that these antivenoms may provide paraspecific protection in humans, although the poor neutralization of PLA₂ supports the need for well-designed clinical studies to not only determine which antivenoms are most appropriate for treatment of M. ikaheka envenoming, but to also fully describe the syndrome of envenoming caused by this beautiful, but lethal species. Snakebite by the small-eyed snake, Micropechis ikaheka, in Papua New Guinea can be life-threatening. The predominant clinical features in this envenoming are neurotoxicity and systemic myotoxicity. Although it accounts for only a small proportion of snakebites on the mainland, 40% of snakebites on Karkar Island are attributed to bites by the Ikaheka snake. However, no specific antivenom is available for the treatment of M. ikaheka envenoming in Papua New Guinea. This study evaluated a panel of Australian bioCSL antivenoms for their paraspecific immunoreaction and neutralization of the toxic activities of M. ikaheka venom. All antivenoms exhibited strong immunorecognition of α-neurotoxins of the 3FTx family and neutralized the lethal, i.e. neurotoxic, and myotoxic activities of M. ikaheka venom. However, these antivenoms exhibited poor neutralization of PLA₂ and anticoagulant activities. This study suggests that the Australian antivenoms may provide paraspecific protection against M. ikaheka venom in humans, a hypothesis that demands studies aimed at assessing whether these antivenoms neutralize neurotoxicity and myotoxicity in the clinical setting.

Pelagic sea snakes dehydrate at sea

Secondarily marine vertebrates are thought to live independently of fresh water. Here, we demonstrate a paradigm shift for the widely distributed pelagic sea snake, Hydrophis (Pelamis) platurus, which dehydrates at sea and spends a significant part of its life in a dehydrated state corresponding to seasonal drought. Snakes that are captured following prolonged periods without rainfall have lower body water content, lower body condition and increased tendencies to drink fresh water than do snakes that are captured following seasonal periods of high rainfall. These animals do not drink seawater and must rehydrate by drinking from a freshwater lens that forms on the ocean surface during heavy precipitation. The new data based on field studies indicate unequivocally that this marine vertebrate dehydrates at sea where individuals may live in a dehydrated state for possibly six to seven months at a time. This information provides new insights for understanding water requirements of sea snakes, reasons for recent declines and extinctions of sea snakes and more accurate prediction for how changing patterns of precipitation might affect these and other secondarily marine vertebrates living in tropical oceans.

Reaction of a sea snake (Hydrophis major) to contact with a sea anemone

Reaction of a sea snake (Hydrophis major) to contact with a sea anemone

Protected species use of a coastal marine migratory corridor connecting marine protected areas

The establishment of protected corridors linking the breeding and foraging grounds of many migratory species remains deficient, particularly in the world’s oceans. For example, Australia has recently established a network of Commonwealth Marine Reserves, supplementing existing State reserves, to protect a wide range of resident and migratory marine species; however, the routes used by mobile species to access these sites are often unknown. The flatback marine turtle (Natator depressus) is endemic to the continental shelf of Australia, yet information is not available about how this species uses the marine area. We used a geospatial approach to delineate a coastal corridor from 73 adult female flatback postnesting migratory tracks from four rookeries along the north-west coast of Australia. A core corridor of 1,150 km length and 30,800 km2 area was defined, of which 52 % fell within 11 reserves, leaving 48 % (of equivalent size to several Commonwealth Reserves) of the corridor outside of the reserve network. Despite limited data being available for other marine wildlife in this region, humpback whale migratory tracks overlapped with 96 % of the core corridor, while the tracks of three other species overlapped by 5–10 % (blue whales, olive ridley turtles, whale sharks). The overlap in the distribution ranges of at least 20 other marine vertebrates (dugong, cetaceans, marine turtles, sea snakes, crocodiles, sharks) with the corridor also imply potential use. In conclusion, this study provides valuable information towards proposing new locations requiring protection, as well as identifying high-priority network linkages between existing marine protected areas.

Distribution of sea snakes in the Great Barrier Reef Marine Park: observations from 10 yrs of baited remote underwater video station (BRUVS) sampling

The distributions of three species of sea snake (olive sea snake: Aipysurus laevis, spine-bellied sea snake: Lapemis curtus, and ornate sea snake: Hydrophis ocellatus) were estimated over 14° of latitude within the Great Barrier Reef Marine Park (GBRMP) using data from baited remote underwater video stations (BRUVS). A total of 2,471 deployments of BRUVS were made in a range of locations, in sites open and closed to trawl fishing. Sightings of sea snakes were analysed alongside six spatial factors [depth, relative distance across (longitude) and along (latitude) the GBRMP, proximity to land, proximity to the nearest reef, and habitat complexity] to determine the factors that most strongly influenced the distribution and abundance of sea snakes. The results showed a strong latitudinal effect on the distribution of all three sea snake species, with the highest densities and diversities occurring in central and southern GBRMP locations, while the northern Great Barrier Reef was relatively depauperate in terms of both occurrence and diversity. Shallow inshore areas were identified as key habitats for A. laevis and L. curtus, whereas deeper offshore habitats were most important for H. ocellatus. No significant difference was found in the mean number of snakes sighted per hour between sites open and closed to trawling. There was a high degree of congruence in the distribution of sea snakes estimated from the BRUVS data and results from previous trawl and underwater visual surveys, demonstrating the utility of BRUVS to estimate distribution and relative abundance in these species of sea snake at broad spatial scales in a non-extractive manner.

Two color morphs of the pelagic yellow-bellied sea snake, Pelamis platura, from different locations of Costa Rica: Snake venomics, toxicity, and neutralization by antivenom

The yellow-bellied sea snake, Pelamis platura, is the most broadly distributed snake species. Despite being endowed with a highly lethal venom, a proteomic analysis of its toxin composition was unavailable. The venoms of specimens collected in Golfo de Papagayo and Golfo Dulce (Costa Rica), where two distinctive color morphs occur, were chromatographically compared. The latter inhabits a fjord-like gulf where the transit of oceanic sea snakes into and from the basin is restricted, thus possibly affecting gene flow. RP-HPLC evidenced a conserved venom protein profile in both populations, despite their divergent color phenotypes. Following a trend observed in other sea snakes, P. platura venom is relatively simple, being composed of proteins of the three-finger toxin (3FTx), phospholipase A2 (PLA2), cysteine-rich secretory protein (CRISP), 5'-nucleotidase, and metalloproteinase families. The first three groups represent 49.9%, 32.9%, and 9.1% of total venom protein, respectively. The most abundant component (~26%) is pelamitoxin (P62388), a short-chain 3FTx, followed by a major basic PLA2 (~20%) and a group of three isoforms of CRISPs (~9%). Whereas isolated pelamitoxin was highly lethal to mice, neither the PLA2 nor the CRISP fraction caused death. However, the PLA2 rapidly increased plasma creatine kinase activity after intramuscular injection, indicating its myotoxic action. Differing from myotoxic PLA2s of viperids, this PLA2 was not cytolytic to murine myogenic cells in vitro, suggesting possible differences in its mechanism of action. The median lethal dose (LD50) estimates for P. platura crude venom in mice and in three species of fishes did not differ significantly. The sea snake antivenom manufactured by CSL Ltd. (Australia), which uses Enhydrina schistosa as immunogen, cross-recognized the three major components of P. platura venom and, accordingly, neutralized the lethal activity of crude venom and pelamitoxin, therefore being of potential usefulness in the treatment of envenomations by this species. Integrative analyses of animal venoms that combine the power of proteomics (venomics) with the characterization of their functional and immunological properties are significantly expanding knowledge on these remarkable bioweapons, both from a basic and a medical perspective. Costa Rica harbors a unique population of the yellow-bellied sea snake, Pelamis platura, that is restricted to a fjord-like gulf (Golfo Dulce). This population differs markedly from oceanic populations found elsewhere along the Pacific coast of this country, by presenting a patternless bright yellow coloration, instead of the typical bicolored or tricolored pattern of this species. It has been suggested that the dominance of this yellow-morph in Golfo Dulce might reflect gene flow restrictions, caused by the oceanographic conditions at this location. The present study demonstrates that the remarkable phenotypic variation between the two color morphs inhabiting Golfo Dulce and Golfo de Papagayo, respectively, is not associated with differences in the expression of venom components, as shown by their conserved RP-HPLC profiles. Proteomic analysis revealed the relatively simple toxin composition of P. platura venom, which contains three predominant types of proteins: three-finger toxins (protein abundance: 49.9%), phospholipases A2 (32.9%), and cysteine-rich secretory proteins (9.1%), together with few minor components. Further, the involvement of these most abundant proteins in the toxic effects of the venom, and their cross-recognition and neutralization by a sea snake antivenom produced against the venom of Enhydrina schistosa, were analyzed.

Fine arrangement of photoreceptors in retina and mode of vision in beaked sea snake, Enhydrina schistosa (Daudin, 1803) (Reptilia: Hydrophiidae)

The role of eyes was discussed in the beaked sea snake (Enhydrina schistosa) living in the open sea. Fine scanning electron microscope (SEM) images of the cellular arrangement were taken based on histological preparations of the retina. The retina possesses the usual layers of the vertebrate eye and is composed of only cone photosensitive cells lacking rods. Ophidian double cones were not found in the cell composition. Measurements of cone densities and dimensions showed their density in the ventral quadrant was more than that in the dorsal, temporal and nasal quadrants. The ventral specialized retina could be corresponding to surveillance of aerial predators. The presence of three-layered spectacle, single-type, large and dispersed photosensitive cells was evidence of the low visual capability of the eyes in E. schistosa.

Pelagic sea snakes dehydrate at sea (860.19)

Secondarily marine vertebrates are thought to live independently of fresh water. However, some species of sea snakes require sources of fresh water even though they possess extrarenal salt glands. Here we tested the hypothesis, and demonstrate, that the only pelagic sea snake, Pelamis platurus, dehydrates at sea and spends a significant part of its life in a dehydrated state corresponding to seasonal drought. Snakes that are captured following prolonged periods without rainfall have lower body water content, lower body condition, and increased tendencies to drink fresh water than do snakes captured following seasonal periods of high rainfall. These snakes do not drink seawater. Snakes at sea presumably rehydrate by drinking from a freshwater lens that forms on the ocean surface during large rainfall events. These new data for spontaneous and voluntary drinking of fresh water, as well as the status of hydration and body condition, indicate unequivocally that this exclusively marine vertebrate dehydrates at sea and potentially remains in negative water balance for 6‐7 months at a time.Grant Funding Source: Supported by the U.S. National Science Foundation grant IOS‐0926802 to HBL

New Information and Reappraisals Concerning Some Alien and Indigenous Snake Records from the Federated States of Micronesia and the Mariana Islands

New information is presented on old records of four species of snakes from four different islands in Micronesia. A record of Dendrelaphis caudolineatus from Saipan is reexamined and the specimen reidentified as D. philippinensis, and a snake from Pohnpei previously recorded only as an unidentified species of Dendrelaphis is identified as D. punctulatus striolatus. We also provide supplementary data on circumstances surrounding records of a brown tree snake, Boiga irregularis, from Chuuk, and a yellow-bellied sea snake, Hydrophis platurus (Pelamis platura), from Kosrae.

Coastal Nurseries and Their Importance for Conservation of Sea Kraits

Destruction and pollution of coral reefs threaten these marine biodiversity hot stops which shelter more than two thirds of sea snake species. Notably, in many coral reef ecosystems of the Western Pacific Ocean, large populations of sea kraits (amphibious sea snakes) have drastically declined during the past three decades. Protecting remaining healthy populations is thus essential. In New Caledonia, coral reefs shelter numerous sea krait colonies spread throughout an immense lagoon (24,000 km2). Sea kraits feed on coral fish but lay their eggs on land. However, ecological information on reproduction and juveniles is extremely fragmentary, precluding protection of key habitats for reproduction. Our 10 years mark recapture study on Yellow sea kraits (L. saintgironsi >8,700 individuals marked) revealed that most neonates aggregate in highly localized coastal sites, where they feed and grow during several months before dispersal. Hundreds of females emigrate seasonally from remote populations (>50 km away) to lay their eggs in these coastal nurseries, and then return home. Protecting these nurseries is a priority to maintain recruitment rate, and to retain sea krait populations in the future.

Venomous snakes of Costa Rica: Biological and medical implications of their venom proteomic profiles analyzed through the strategy of snake venomics

In spite of its small territory of ~50,000km(2), Costa Rica harbors a remarkably rich biodiversity. Its herpetofauna includes 138 species of snakes, of which sixteen pit vipers (family Viperidae, subfamily Crotalinae), five coral snakes (family Elapidae, subfamily Elapinae), and one sea snake (Family Elapidae, subfamily Hydrophiinae) pose potential hazards to human and animal health. In recent years, knowledge on the composition of snake venoms has expanded dramatically thanks to the development of increasingly fast and sensitive analytical techniques in mass spectrometry and separation science applied to protein characterization. Among several analytical strategies to determine the overall protein/peptide composition of snake venoms, the methodology known as 'snake venomics' has proven particularly well suited and informative, by providing not only a catalog of protein types/families present in a venom, but also a semi-quantitative estimation of their relative abundances. Through a collaborative research initiative between Instituto de Biomedicina de Valencia (IBV) and Instituto Clodomiro Picado (ICP), this strategy has been applied to the study of venoms of Costa Rican snakes, aiming to obtain a deeper knowledge on their composition, geographic and ontogenic variations, relationships to taxonomy, correlation with toxic activities, and discovery of novel components. The proteomic profiles of venoms from sixteen out of the 22 species within the Viperidae and Elapidae families found in Costa Rica have been reported so far, and an integrative view of these studies is hereby presented. In line with other venomic projects by research groups focusing on a wide variety of snakes around the world, these studies contribute to a deeper understanding of the biochemical basis for the diverse toxic profiles evolved by venomous snakes. In addition, these studies provide opportunities to identify novel molecules of potential pharmacological interest. Furthermore, the establishment of venom proteomic profiles offers a fundamental platform to assess the detailed immunorecognition of individual proteins/peptides by therapeutic or experimental antivenoms, an evolving methodology for which the term 'antivenomics' was coined (as described in an accompanying paper in this special issue). Venoms represent an adaptive trait and an example of both divergent and convergent evolution. A deep understanding of the composition of venoms and of the principles governing the evolution of venomous systems is of applied importance for exploring the enormous potential of venoms as sources of chemical and pharmacological novelty but also to fight the consequences of snakebite envenomings. Key to this is the identification of evolutionary and ecological trends at different taxonomical levels. However, the evolution of venomous species and their venoms do not always follow the same course, and the identification of structural and functional convergences and divergences among venoms is often unpredictable by a phylogenetic hypothesis. Snake venomics is a proteomic-centered strategy to deconstruct the complex molecular phenotypes the venom proteomes. The proteomic profiles of venoms from sixteen out of the 22 venomous species within the Viperidae and Elapidae families found in Costa Rica have been completed so far. An integrative view of their venom composition, including the identification of geographic and ontogenic variations, is hereby presented. Venom proteomic profiles offer a fundamental platform to assess the detailed immunorecognition of individual venom components by therapeutic or experimental antivenoms. This aspect is reviewed in the companion paper. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

High rates of hybridisation reveal fragile reproductive barriers between endangered Australian sea snakes

The viviparous sea snakes include 62 ecologically diverse species, many of which are of very recent evolutionary origin and have overlapping distributions. Peak sea snake diversity and endemism is recorded from the isolated emergent reefs of the Timor Sea in Northwest Australia. However, nine species have disappeared from Ashmore, the largest of these reefs, over the last 15years, including two critically endangered Aipysurus species that have also disappeared from neighbouring Hibernia Reef. A third Timor Sea endemic, Aipysurusfuscus, is now known only from Scott and Hibernia reefs, where it coexists with closely related and locally abundant Aipysuruslaevis. We analysed microsatellite markers for A. fuscus and A. laevis sampled across four Timor Sea reefs to assess evidence for recent inter-specific gene flow and historical introgression. Our data fit an Isolation–Migration model, which showed significant and asymmetrical levels of gene flow following species divergence, and highest rates of introgression from the large A. laevis population into the much smaller A. fuscus population. Population assignment analyses recovered two ancestral clusters that broadly corresponded to morphological species designations, but revealed high frequencies of hybrids on all four reefs and individuals of pure A. fuscus ancestry only at Scott and (historically) Ashmore. Most unexpectedly, 95% of snakes sampled at Hibernia were hybrids that resembled A. laevis in phenotype, revealing a collapse of reproductive barriers (‘reverse speciation’) at this reef. These results have dire implications for the conservation status of A. fuscus, and highlight the fragility of reproductive barriers in a recent marine radiation.

Food Habits and Distribution of the Lake Taal Sea Snake(Hydrophis semperi Garman 1881) and the Sympatric Little File Snake(Acrochordus granulatus Schneider 1799) in Lake Taal, Philippines

Our knowledge about the food habits of sea snakes and how it is associated with their distribution has seen much development through its description across a number of species available through published literature except for the key threatened species such as Hydrophis semperi. This paper aims to describe the food habits of H. semperi through gut content and stable isotope analyses. We also compared data with the Little File Snake, Acrochordus granulatus, sympatric with H. semperi. Recorded captures of H. semperi suggest that the sea snake tends to occur in the littoral zones and the shallower portions of the limnetic zone. Gut content analysis of H. semperi have shown that gobies and eels are primary prey items. Halfbeaks (Family Hemiramphidae) were recorded as one of the Lake Taal Sea Snake's prey items which is considered as a new prey record for sea snakes. These extracted gut contents are confirmed to be the temporal food preference of H. semperi given our detected stable isotope signatures. It appears that A. granulatus and H. semperi share common prey items suggesting possible diet overlap and resource competition. This study reports the first account of the endemic Lake Taal Sea Snake's distribution and food habits which poses implications towards its conservation as it occurs in a restricted ecosystem that has undergone considerable habitat alteration.

Snake bite poisoning: A neglected life-threatening occupational hazard

Snake bite poisoning: A neglected life-threatening occupational hazard

Combining in-trawl video with observer coverage improves understanding of protected and vulnerable species by-catch in trawl fisheries

Assessments of incidental wildlife mortality resulting from fishing rarely account for unobserved by-catch. We assessed by-catch of protected and vulnerable wildlife species in an Australian trawl fishery by comparing in-trawl video footage with data collected by an on-board observer. Data were obtained from 44 commercial trawls with two different by-catch reduction devices (BRDs). Eighty-six individuals from six major taxa (dolphins, sharks, rays, sea snakes, turtles and sygnathids) were documented from video analysis, including the endangered scalloped hammerhead shark (Sphyrna lewini) and the critically endangered green sawfish (Pristis zijsron). On the basis of the 2008–2009 fishing effort of 4149 trawls and scaling from these results, we estimated the annual catch of protected and vulnerable species (± 1 s.e.) at 8109 ± 910 individuals. Only 34% of by-catch was expelled through the BRDs. Independent observer data for the 44 trawls showed that 77% of the landed by-catch from these taxa were dead when discarded. The results indicate that unaccounted by-catch in trawl fisheries can be substantial, and that current methods of recording by-catch on-board vessels are likely to underestimate total fishing mortality. We recommend gear modifications and their validation through dedicated observer coverage, combined with in-trawl video camera deployments to improve current approaches to by-catch mitigation.

1P1-E05 圧電繊維複合材料を用いた生物模倣型ソフト水中ロボットの研究開発 : ウミヘビ型ロボットの試作(水中ロボット・メカトロニクス(2))

Aimming to design a soft robotic fish for more flexible and efficient fish-like motion by biomimetic method, we are developing a snake-like robot with body undulating propulsion using the piezoelectric fiber composite (PFC) as soft actuator by mimicking the sea snake. Due to the large deformation of flexible structure and complicated dynamics with fluid, the design method for soft fish robots has not been established, and we need to study it by considering the coupling between them. In this paper, the sea snake-like robot using PFC is developed by the analytical simulation with considering the coupling between flexible structure and fluid. The efficient body undulating propulsion based on meandering motion is realized successfully from the prototype, and its swimming efficiency is similar to the real sea snake's.

Enhydrina schistosa (Elapidae: Hydrophiinae) the most dangerous sea snake in Sri Lanka: Three case studies of severe envenoming

Sea snakes are highly venomous and inhabit tropical waters of the Indian and Pacific Oceans. Enhydrina schistosa is a common species of sea snake that lives in the coastal waters, lagoons, river mouths and estuaries from the Persian Gulf through Sri Lanka and to Southeast Asia. It is considered one of the most aggressive sea snakes in Sri Lanka where fishermen and people wading are at high risk. However, sea snake bites are rarely reported. In this report, we describe three cases where E. schistosa was the offending species. These three patients presented to two hospitals on the west coast of Sri Lanka within the course of 14 months from November 2011 with different degrees of severity of envenoming. The first patient was a 26-year-old fisherman who developed severe myalgia with very high creatine kinase (CK) levels lasting longer than 7 days. The second patient was a 32-year-old fisherman who developed gross myoglobinuria, high CK levels and hyperkalaemia. Both patients recovered and their electromyographic recordings showed myopathic features. The nerve conduction and neuromuscular transmission studies were normal in both patients suggesting primary myotoxic envenoming. The third patient was a 41-year-old man who trod on a sea snake in a river mouth and developed severe myalgia seven hours later. He had severe rhabdomyolysis and died three days later due to cardiovascular collapse. In conclusion, we confirm that E. schistosa is a deadly sea snake and its bite causes severe rhabdomyolysis.

Anguilliform fish reveal large scale contamination by mine trace elements in the coral reefs of New Caledonia

Due to intensive mining activity, increasing urbanization and industrialization, vast amounts of contaminants are discharged into the lagoon of New Caledonia, one of the largest continuous coral reef systems and a major biodiversity hotspot. The levels of 11 trace element concentrations were examined in the muscles of predator fish in the south-western lagoon (moray eels and congers). These species are sedentary, widespread, abundant, and they are easily collected using a sea snake sampling technique. We found the highest mean and maximal concentrations of different trace elements ever found in coral fish, notably regarding trace elements typical from mining activity (e.g., mean values for Cr and Ni, respectively: 5.53±6.99μgg−1 [max, 35.7μgg−1] and 2.84±3.38μgg−1 [max, 18.0μgg−1]). Results show that important trace element contamination extends throughout the lagoon to the barrier reef, following a concentration gradient from the oldest nickel factory (Nouméa).

Comparison of the osmoregulatory capabilities among three amphibious sea snakes (Laticauda spp.) in Taiwan

Abstract Background The three species of amphibious sea snakes (Laticauda semifasciata, L. laticaudata, and L. colubrina) in Taiwan were described as having different habitat affinities from terrestrial to marine. In this study, the osmoregulatory capabilities of three species were compared to test if their capabilities were associated with different habitat affinities. Results The sea snakes were transferred from a terrestrial environment to freshwater (FW) or seawater (SW) for 1 week, and then, Na+/K+-ATPase (NKA) activities of the salt gland (sublingual glands) and kidneys, the water content of the muscles, the body fluid osmolality, and Na+, Cl−, and K+ concentrations were measured. Results showed that the body fluid osmolality, Na+ and Cl− levels, and muscle water content of most marine species, L. semifasciata, remained relatively constant, and the NKA activity of its salt gland was approximately threefold higher than those of L. laticaudata and L. colubrina. In both L. semifasciata and L. laticaudata, NKA activities of the salt glands were higher in SW than in FW; however, no significant change was found in L. colubrina (the most terrestrial species). Conclusions This study suggests that the NKA activity of the sublingual gland is associated with salt excretion, and the three species possess different osmoregulatory strategies which are associated with their habitat affinities.

Dehydration and Drinking Behavior of the Marine File SnakeAcrochordus granulatus

Dehydration and drinking behaviors were investigated in the little file snake (Acrochordus granulatus) collected from marine populations in the Philippines and in Australia. File snakes dehydrate in seawater and do not drink seawater when dehydrated in air and offered seawater to drink. Dehydrated file snakes drink freshwater, and the threshold of dehydration for first drinking response is a deficit of -7.4% ± 2.73% (mean ± SD) of original body mass. The thirst mechanism in this species is more sensitive than that recently studied in sea snakes. The volume of water ingested increases with increasing dehydration. Mean plasma osmolality was 278.89 ± 33.17 mMol/kg, mean hematocrit was 59% ± 5.45%, and both decreased in snakes that drank freshwater following acclimation in seawater. Snakes always drank freshwater at the water's surface, testing water with tongue flicks between each swallowing of water. Some snakes ingested large volumes of freshwater, approaching 50% of body mass. Visual observations and measurements of osmolality in plasma and stomach fluids suggest that water is taken up from the gut and dilutes body fluids slowly over the course of 48 h or longer. Eighty percent of snakes that were collected during the dry season (following >4 mo of drought) in Australia drank freshwater immediately following their capture, indicating that snakes were dehydrated in their marine environment even when known to have been feeding at the time. Snakes kept in seawater maintained a higher state of body condition when freshwater was periodically available. These results support a growing conclusion that diverse taxa of marine snakes require environmental sources of freshwater to maintain water balance, contrary to earlier belief. Identifying the freshwater requirements of secondarily marine vertebrates is important for better understanding how they maintain water balance in marine habitats, especially with respect to conservation in changing environments.