Growth of the parma wallaby, Macropus parma Waterhouse

Abstract

Data are presented for growth in length of head, ear, arm, leg, foot, head and body, and tail, and growth in weight of M. parma from birth to maturity. Foot and ear have ceased growing by 2 years of age in both males and females. Growth measured by other parameters has ceased in females by about 3 years of age, but males continue growing in arm length and leg length until about 4.5 years. Adult size is taken as the size of animals 3 years of age and older. The changing relative sizes of the body parts during pouch life are considered. These are discussed in terms of their functional and adaptive significance during development in the pouch. Growth in weight during pouch life can be divided into two phases based upon changes in the instantaneous relative growth rate (k). During the first phase of growth (to about 84 days) k declines rapidly from a mean value of 12.51% per day during the first week to a mean of 2.93% per day for the interval 63-84 days. It is suggested that this phase may represent a continuation of embryonic organogenesis and differentiation. The second phase of growth is a period during which k is constant and extends from about 84 days until almost the end of pouch life. Values of k for individual animals are normally between 2.15% per day and 2.60% per day. This period of growth is considered to be essentially a period of maturation and growth in size of the organ systems developed during the gestation period and first phase of growth. Young first leave the pouch for short periods when they weigh between 7.5 and 10% of the mean adult female weight. They permanently leave the pouch at a mean weight of 21.3% of the adult female value. Comparison with other macropodids indicates an apparent high degree of uniformity in relative sizes of macropodid young at permanent exit from the pouch. Parma young are finally weaned at about 50% of the mean adult female weight. Females raised in captivity reached sexual maturity at about 70% of the adult female weight. Males are larger than females, but sexual dimorphism becomes statistically significant only after males become sexually mature. The forearms of males are shown to be remarkably elongated compared with those of females and it is suggested that this is an adaptation for holding the female during copulation.