Biology of the platypus (Ornithorhynchus anatinus)

Platypuses were brought to the attention of the Western World in 1799 when George Shaw of London described them in "The Naturalist Miscellany". The animals occupy much the same general areas as they did prior to the European settlement in Australia, except that they are not currently populated in the State of South Australia. Also, Kangaroo Island is now inhabited by those animals due to their successful introduction in 1940. The platypuses are found in rivers and streams of eastern Australia, from around Cooktown in northern Queensland to Tasmania. When they forage in winter, they must contend with the cold water, the temperature of which may drop to zero degree Celsius. Yet, they can maintain the normal body temperature of 32 deg C by adjusting their metabolic rate. In the upper Shoalhaben River, New South Wales, the population estimated by the mark-recapture method was a minimum of 14-18 individuals in approximately 1.5km. In Badger Creek. Victoria, the estimate by the radio tracking and by the mark-recapture methods was 1.3-2.1 adults or subadults per kilometer of streams. Radio-telemetry was used to estimate the home range size of the adult males in Gouldburn River. Victoria. The size varied greatly between individuals from 2-45 ha, but the differences in the body weight of individuals did not account for this variability. There were no correlations between the number of burrows used by males and their body size. Because platypuses are nocturnal, and close their eyes, ears and nostrils while underwater, they use electrosensitivity to locate food sources at the bottom of the freshwater river systems where they live. The electroreceptors on the bill are sensitive to electrical waveforms that imitate the electromyogenic potentials of fleeing preys. Platypuses are seasonal in breeding activities and mate in autumn through late winter. Young animals first appear in streams in January or February after gestation and incubation periods of unknown length, but probably 27 and 10 days, respectively, and lactation period between 3 and 4 months. Although home-ranges of adult males overlap extensively during the non-breeding period, there are evidence of spatial separation during the breeding season. Adult male platypuses produce protein venom in the crural system, which is unusual in the mammals. The crural gland and testis increase in size before the mating season,and decrease after the season. The toxic activity was purified by gel permeation HPLC and subsequent analyses by SDS-PAGE revealed that the activity was associated with the 4,200 dalton peptide. Three other major proteins isolated prom the venom had molecular weights of 14,000, 55,000 and 16,000. Before the arrival of European settlers in Australlia, the platypuses probably suffered little from diseases. Among other thing, the European settlement has caused substantial environmental perturbation by introduction of large preadators, introduction of motor vehicles, and translocation of potential pathogens. As a result, platypuses are now often killed by motor vehicles, dogs, foxes, cats and discarded plastic litter. In spite of all that are known about the platypus, one mystery that remains unsolved is its antiquity. The animal's peculiar mixture of reptilian and mammalian traits suggests a long evolutionary history, perhaps as long as 150 million years. It is now clear, in spite of its antiquity and its mosaic of reptilian and mammalian characteristics, that the platypus is a highly specialized animal, well adapted to its amphibious existence in the waterways of eastern Australia.