MARE 494 Lecture 12

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Conservation and Ecology of Marine Reptiles MARE 494 Dr. Turner Summer 2007

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Class Reptilia Order Chelonia – marine turtles Order Squamata – marine snakes and iguanas Order Crocodilia – saltwater crocodile

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Order Squamata Family Elapidae - characterized by a hollow fixed front fang and neurotoxic venoms Elapids are divided into two subfamilies, Elapiinae and Laticaudinae – 61 species

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Order Squamata Snakes evolved from lizards ≈ 135 mya There are approximately 70 species of sea snakes living in our modern oceans They account for 86% of marine reptile species alive today

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Classically 5 major groups of “sea snakes” Hydrophiids - ‘true’ sea snakes – 54 species Laticaudids - sea kraits – 5 species Acrochordids - file snakes – 3 species Homalopsids - mangrove snakes – 9 species Natricids - salt marsh snakes – 3 species

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Hydrophiids - ‘true’ sea snakes The largest group of sea snakes Evolved from Australian terrestrial elapids that returned to the marine environment around 30 million years ago Have the same toxic venom and envenomation apparatus (they are proteroglyphs meaning they have fixed front fangs) as their terrestrial ancestors

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Hydrophiids - ‘true’ sea snakes Have exploited the viviparity that exists in some of their terrestrial ancestors, and have thus freed themselves entirely from the need to return to land to breed 54 species of hydrophiid sea snakes

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Laticaudids - sea kraits Comprise five species, four of which are marine Are strongly banded and commonly seen in large numbers on beaches in south east Asia and some Pacific Islands

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Laticaudids - sea kraits Sea kraits have also evolved from terrestrial elapids and are proteroglyphs and have highly toxic venom. However they are very placid and unlikely to bite unless provoked. Sea kraits are the only group of sea snakes that are oviparous (egg laying) and must return to land to breed.

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Acrochordids - file snakes Comprise three species One species is fully marine while the others live in estuaries and freshwater habitats Are not venomous & give birth to live young

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Homalopsids - mangrove snakes Confined almost entirely to estuarine environments Are nine species found primarily in tropical Asian waters and northern Australian waters Only three species are fully marine Homalopsids are venomous but they are rear-fanged

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Natricids - salt marsh snakes Confined to salt marsh environments Three species of marine natricids Confined to temperate & subtropical N. America Are not venomous Early stages of evolving marine adaptations

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Order Squamata Subfamily Hydrophiinae – Sea snakes & sea kraits Subfamily Elapinae – Cobras, coral snakes, terrestrial kraits

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Subfamily Hydrophiinae Subfamily Hydrophiinae – Sea snakes & sea kraits Sea kraits - amphibious (living on land and water), oviparous (returning to land to lay their eggs, have specialized ventral scales for crawling on land Sea Krait

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Subfamily Hydrophiinae Sea snakes – fully aquatic (never leaving the water ovoviviparous (bear their young in the water) lack specialized ventral scales Sea Snake

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Sea Kraits Sea Snakes

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Sea Krait Distribution Sea Snake Distribution

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Sea Snake Diets

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Sea Snake Diving Aerobic dives average 13 minutes & 20 meters Anaerobic dives increase time by 30-45 min 2 hr max depth – ave > 50 m; 90 m max

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Sea Snake Diving One elongate cylindrical lung that extends for almost the entire length of their body which is very efficient for gas exchange

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Sea Snake Diving They are also able to carry out cutaneous respiration Oxygen diffuses from sea water across the snake’s skin into tiny blood vessels and carbon dioxide diffuses out

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Venom! Sea snake venom is extremely toxic – neurotoxin + nasty enzymes lecithinase – lysis of eurythrocytes anticoagulase – delays or prevents blood cooagulation hyaluronidase – leads to diffusion of venom into cells Paralyzes prey; for defense Not usually aggressive – many victims on shore

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Salt Removal Sea snakes are able to avoid excess salt accumulation from sea water using a salt excreting gland, the posterior sublingual gland that sits under the tongue Skin of sea snakes is very resistant to water, and does not let water in the snake easily One feature is that it does not resist water passage equally in both directions - allows the water to move inward faster than outward, thus giving it an advantage in the marine environment

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Like all snakes and lizards, male sea snakes have two penises – hemipenes Each is an autonomous independently functioning penis and only one is used during mating Mating takes place for long periods and sea snakes must surface for air during that time Repro-man Diving 4 Images                                                                                                                

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All sea snakes except the latidcaudids give birth to live young after gestation periods that range from four to eleven months Most species reproduce every year Timing of the reproductive cycle highly variable Born Free