Australian Reptiles Research Paper

Australian Reptiles take advantage of their environment. Their success is dependent on external heat source. Reptiles are ectothermic creatures, they require light and warmth for their daily survival. The external heat both enhances a reptile’s digestion and rejuvenates their energy enabling them to feed more often. (Life History Evolution In Reptiles). Reptiles in arid ecosystems have a greater temperature regulation whereas in cooler climates reptiles face a more difficult battle of survival. Adaptions to the dry land of Australia and their ability to tolerate such a habitat will be investigated.

Reptiles have a low metabolic rate and many physiological attributes that enable them to adapt to an arid environment. Reptiles have to contend with varied climates, sustaining consistent temperatures in extreme heat throughout the day but also surviving the cold nights. To survive the cold nights, they bask at sunrise the next morning. Many Australian reptiles utilise

colour change to increase body temperate easily, and to reduce vulnerability while basking. Australian Reptile Park (2010) describes the change of colouration in an Inland Taipan (Oxyuranus microlepidotus). The snake can vary from a light straw-like colouration to dark browns. Darker pigments absorb more heat suitable for the winter time, and the reverse in the summer time. They do this in seasonal patterns, darker in the winter and lighter in summer time. Inland Taipans use this adaptation is a survival mechanism to endure the harsh Australian weather.

Ectotherms need warmer weather to reproduce.

Majority of reptiles are oviparous, which is when the eggs are fertilized internally, then deposited external of the mother. For this process to occur the male reptile’s penis injects sperm in the female. The reptile’s penis becomes rigid and penetrates far into the female’s reproductive system. These eggs are enclosed by a leathery shell which is placed as the egg goes through the oviduct. Temperature is fundamental of sex determination. A small number of reptiles are ovoviviparous or viviparous, which is when the forming eggs develop into embryos internal of the mother (Peter. H. Raven | George. B. Johnson). Blue Tongued Lizards (Tiliqua scincoides scincoides) are examples of viviparous, they give birth live rather than eggs. Mating time can be difficult and can be rough, with females resulting in scrape marks from the teeth of the male. The offspring are born three-five months after mating, and become immediately independent from birth (Australia

Zoo).

To escape the harsh heat some reptiles demonstrate bipedal locomotion to sprint across the scorching sands. The bipedal locomotion prevents the abdomen being in contact with hot grounds, which removes warm hair emission from the ground surface. Climbing trees, swimming, jumping and slithering without limbs are the more commonly seen behaviours reptiles embark on in avoidance of predation and excess heat (P. Aerts, R. Van Damme, B. Vanhooydonck, A. Zaaf And A. Herrel).

Finding water is scarce in a dry environment; majority of water intake is from the reptile’s diet. Reptiles have scales or plates which resist osmotic movement from the reptile to the surrounding, this reduces dryness. The Thorny Dragon (Moloch horridus), also commonly called the Thorny Devil doesn’t sweat or lose water through its skin. They don’t require a lot of water, but of course it needs to drink it at some point. The Thorny Devil has an amazing adaptation to survive in a harsh dry environment. The lizard’s body is covered in tiny channels that lead to the mouth corners, the channels absorb water with use of the capillary action. Thorny Devils can also capture rain by absorbing droplets off vegetation. When the water is in the grooves, the lizard can draw the water to its mouth by gulping (Withers, P (Withers, P) (Sep 1993)).

Majority of reptiles are insectivorous or carnivorous and they have reasonably short digestive tracts. A Reptile’s digestion is slow, which suggests they have a slow resting metabolism and incapable to divide and masticate their food. Reptile’s poikilothermic metabolisms have minimal energy requirements, which allow large reptiles to survive off a large meal for a longer period of time by the slow digestion. Turtles and Tortoises are the only remaining herbivorous reptiles left that can live entirely on plants. Herbivorous reptiles lack complex teething, and in replacement many species swallow rocks and pebbles to assist them in digestion, this is seen in carnivorous reptiles too. The swallowed rocks are washed throughout the stomach, grinding up plant material (Laurie J. Vitt, Janalee P. Caldwell (2014)). (Henderson, Donald M (1 August 2003)) describes how Salt water Crocodiles have a large set of teeth designed to rip into their prey, as it is swallowed whole. Salt water crocodiles inject rocks to help with breaking down food for a better digestion and for buoyancy.
Being cold-blooded, reptiles have limitations of keeping a consistent body temperature and so rely on external sources of heat. To be able to metabolise over a range of different temperatures they require enzymes that are capable to work efficiently with inconsistent temperatures. Optimal temperatures are encountered when the reptile is active, a low metabolic rate causes body temperature to drop when the reptile is inactive. Low resting metabolisms are beneficial because it requires less fuel to support body function. With the use of temperatures varying in the surroundings, or remaining cold when they don’t require movement, reptiles conserve higher amounts of energy compared to endothermic creatures of same sizing (Huey, R.B. & Bennett, A.F. (1987)).

Reptiles excrete using two small kidneys. Dispsids which have two holes on each side of the skull secrete uric acid as a waste product, turtles expel urea. Dehydration leads to an accumulation of nitrogen waste, which can be deadly if it isn’t removed or diluted down. Reptiles lack a structure called a loop of Hendle, which makes it unable to produce urine that’s more concentrated that the body fluid. Due to the lacking of the loop of Hendle, reptiles use their colon as a substitute to assist in reabsorbing water. Some reptiles can take up water that’s stored in the bladder (Cragg, M, Balinsky, J, & Baldwin, E 1961). The excess salt is excreted via nasal or salt glands in a few reptiles. (Cramp, RL De Vries, I Anderson, WG Franklin, CE. (2010)) discusses how Salt water Crocodiles (Crocodylus porosus) use their blood system to remove unwanted salt. They have salt glands fixed into the tissue of their tongue which excrete excess salt when they live in a saline environment.

DEFENCE MECHANISMS

Retiles all breathe using lungs, although aquatic turtles have more permeable skin to increase area for gas exchange. Even with this adaptation it’s never fully successful without lungs present. Lung ventilation is seen differently in each main reptile group. Scaled reptiles (squamates) lungs are ventilated by the axial musculature. Due to the limitations scaled reptiles are required to hold their breath during a run. Monitors (varanids) and a few other species of lizards use buccal pump alongside their axial breathing. This allows the reptile to fill the lungs entirely during locomotion, hence remaining aerobically active for a longer duration. Snakes use a trachea extensions that sticks out like a straw when they’re swallowing a large prey, it prevents them from asphyxiating. Crocodiles have a muscular diaphragm which brings the liver down to allow for more space for lung expansion. What makes crocodiles unique is that they have a secondary plate that allows them to breath underwater. Turtles and tortoises shells don’t allow for expansion and contractions like others reptiles use to ventilate their lungs. Turtle lungs are attached to the top inside of the shell (carapace), with connective tissue attaching the bottom of the lung to the remaining viscera. With use of specific muscles, turtles can push their viscera up and down (Taylor, E.W. (2010)).