Koalas Life Cycle - Essay Example

Koalas Life Cycle Organism Phylum – Vertibrata – Mammalia Genus –Phascolarctos Species- P. Cinereus Common name - Koala 2.Distinguishing external characteristic: Koalas are basically classified as Marsupials due to the pouch attached to their bodies to bear their babies, the joeys. On an average, Koalas weigh about 9 kg. They are often confused with bears, however this is a misperception. It has a thick fur, long limbs and big ears. It has sharp claws with five fingers to support climbing activities. They have sharp incisors which help them in grinding and chewing the food. A male Koala has a forked penis meant for reproduction, while a female Koala has two uterine forms (Martin, Roger and Handasyde 1999). 3.Distinguishing or unusual internal characteristics: Internally, Koalas have a small brain, a circulatory system, respiratory system, a heart, a reproductive system and all other characteristics apparent for other mammals. However, they have a vestiginial bone and distinct digestive glands to digest the leaves. 4.Normal habitat, including world geographical location: A Koala is basically the native of Australia as it is the only place where it is found. These Koalas are usually found in Southern Australia and Eastern Australia over the coasts of these regions. They are found most commonly in the East where they enhabit the strip near the Pacific Ocean where the eucalyptus plant is found in abundance. However, they are not found in the Western region of Australia at all. (Martin, Roger and Handasyde 1999). As for the natural habitat, they have thick furs to sustain cold climates, and as mentioned above they are found in the areas where they can find eucalyptus leaves in large quantities. 5.Means of solving the following problems of life: a. Nutrient procurement The Koalas rely on Eucalyptus leaves for nutrition, and prior to the intake of these leaves the Koala smells them to find any indication of poisonous material in the leaves. Thus, Koalas are selective about the species of eucalyptus leaves they acquire. In general, this is a low nutrient diet on which Koalas survive (Martin, Roger and Handasyde 1999). b. Digestion: Koalas have a special chamber used for fermentation called “hindgut chamber” since it is present at the rear part of the digestive tract. The Koalas digestive system consists of enlarged proximal and caecum colon to help digest the Eucalyptus leaves. Fermentation takes a long time to digest the food, thus like other carnivores the food stays longer in the stomach of Koalas. Though the digestive system of a Koala is small, the digestive glands are comparatively larger (Martin, Roger and Handasyde 1999). c.Gas exchange The breathing medium in Koalas is the nose and the mouth as these belong to the kingdom of Mammalia. When the air passes through the tract, it is moisturized in the way for effective breathing. The lungs of the Koala contain alveoli for exchanging CO2 and Oxygen. When air reaches here, CO2 passes into alveoli and oxygen diffuses inside the blood. This oxygen then gets attached with the hemoglobin, so that effective respiration takes place (Martin, Roger and Handasyde 1999). d. Internal transport, that is, circulatory system: The heart of the Koala is similar to that found in any of the mammals. There is a right artio-ventricular valve and the articular extensions in the heart to enable flow of blood. According to Sontagg (1922), normal heart rate is about 90 beats per minute. Aortic arch along with the sub-clavian enables the easy respiration in the Koalas. In the cells, bodies like the jolly body, erythrocytes, aniscocytosis and the poikilocytosis are apparent though the blood smears to allow respiration as indicated by Sontagg (1922). e. Excretion of metabolic wastes: There are two kidneys found in the body of the Koala, along with the ureters and the urinary bladder. The kidney of a Koala is unilobar in nature and it consists of a papilla as well. (Burger and Cross 1981).Like a typical kidney found amongst the mammals, the renal features of a Koala also consist of cortex, medulla; however, in Marsupials the interlobular vessels run perpendicular to the arcuates. The urine discarded by the Koala is far more concentrated as compared to the urine of other mammals, as indicated by Burger and Cross (1981). f. Support: The support system of the Koala consists of bones, skull and the ribs. A distinctive feature of the skeletal system of the Koala is the detachment between the phascolartids and the bullae. It basically consists of various Zygomata arranged in a parallel manner, however being marsupials there is a set arrangement of presacral vertebrae. This vertebrae consists of seven joints for the neck, 13 for the chest region and 13 for the ribs. Caudal vertebrae is however rare, along with a vestigial tail attached. (Thomas 1888). A unique feature of the support system of Koala is the pattern of perforations apparent in the seventh vertebrae and the presence of cartilage at the Vental arch instead of bones. (Sontag 1992). g. Locomotion: As identified by Sontagg (1992), the Koala is structured in a way that it becomes easier to climb the trees. The limbs are longer to create a fast movement of ground as well as on the trees. The fists of the Koala are especially designed to cling to the branches of the trees, and forelimbs are utilized for running. However, a unique feature is the absence of the Patella, an undivided deltoid muscle and a single scapula insertion. (Sontagg 1992). The pads present on the hands and feet allow effective and convenient locomotion, with a forcipate manus, as pointed out by Strahan (1978). h. Sensory perception Though the Koalas can sense the smell of the leaves, there is no specific olfactory sense organ in these creatures. The eyes of these Marsupials are distinct as the slits are vertical in horizon and not circular. The brain of these Koalas is also very small in size, with small cerebral hemispheres. However, there is a large endocranium present, which is about 20-30% bigger in size than the brain. (Haight and Nelson 1987). i. Nervous and chemical (hormonal) control Adrenal gland stimulated by the liver of the Koala is present to control stress levels and increase endurance in their bodies. Endocrine gland relates to the digestive activities apparent in their bodies. However, Sternal gland acts as the sebaceous gland and undergoes seasonal changes as it is affected by the androgenic controls. (Sontagg 1921). j. Means of reproduction There is a set of 16 diploid chromosomes present in the Koala`s cell. (Greenwood 1923).The ovaries of the female Koala are flat while the Fallopian tube is convoluted. The wall of the vagina consists of cervical tissues which can be dilated easily. The female Koala is a polyestrous with a cycle period of 35 days, while the gestation period is about 34-36 days. The breeding season is believed to be around August or May, and the reproductive hormones are present in small quantities. (Martin and Lee 1984). The mail reproductive system consists of the Couper`s gland and a penis, with ductless glands in the male tract. The testis consists of Setolli cells with androgen secreting hormones present to assist reproduction. (Hardick, Carrey and Shorey 1981). At the age of 2 years, both sexes are ready to mate, which they do without any courtship. The male holds the female from the back, snaps her with the teeth and plug the semen with the urinogenital tract of the female (Smith 1979). k. Protection from environment and/or predators Koalas generally don`t have problems with predators, however young Koalas do need to protect themselves from the predators like dogs, foxes, cats etc. Pythons or Goannas are also predators for Koalas occasionally. Birds like hawks and eagles can also be potential threats. Man is also an apparent predator contributing towards the extinction of the species. They need to be carefully watched to be protected against these hazards and for the most part they are helpless. In extreme case they climb trees or hide in bushes to protect themselves. l.Unique Behaviour: The most unique characteristic of Koalas is their seasonal ability to mate with the opposite sexes. It is fascinating how their glands are active during certain points of the year i.e. May or August to be more particular. Works cited: Kalman, Bobbie, and Heather Levigne. The Life Cycle of a Koala. New York: Crabtree Pub. Co, 2002. Print. Martin, Roger, K A. Handasyde, and Sue Simpson. The Koala: Natural History, Conservation and Management. Sydney, Australia: UNSW Press, 1999. Print Sonntag, C.F. (1921b). The comparative anatomy of the Koala (Phascolarctos cinereus) and Vulpine Phalanger (Trichosurus vulpecula). Proceedings of the Zoological Society of London, 1921: 547–577. Print Haight, J.R. & Nelson, J.E. A brain that doesn’t fit its skull; a comparative study of the brain and endocranium of the Koala, Phascolarctos cinereus. pp. 331-352 in Archer, M. (ed.) Possums and Opossums: Studies in Evolution. Surrey Beatty & Sons : Sydne,1987. Print Burger, C.H. & Cross, R.B. The renal vascular organisation of the marsupial (Phascolarctos cinereus). p. 8. in Proceedings of the Lone Pine Koala Symposium 21-22 August 1981. Department of Veterinary Anatomy, University of Queensland & Lone Pine Koala Sanctuary : Brisbane,1981. Print Read More