Monotremes and Electroreception :: Monotremes and Electroreception

Abstract Through their evolution, monotremes have developed several characteristics that make them unique from most other mammals. The focus of this paper lies on the electroreceptive capabilities of monotremes. Electroreception of monotremes is partially comparable to that in fish. The bill of the platypus, Ornithorhynchus anatinus, and the beaks of the echidnas, Tachyglossus aculeatus and Zaglossus bruijni, all contain three types of receptors: push-rod mechanoreceptors, serous gland electroreceptors, and mucous gland electroreceptors. The information collected by these receptors is sent to the somatosensory cortex. The platypus, whose electroreceptive system is more complex than that of the echidna, uses electroreception to capture prey and is the only mammal know to so. (It is not yet known if the echidna uses electroreception to capture prey.) Introduction Monotremes have fascinated scientists since their discovery in 1799 (Moyal 4). The isolation of monotremes in Australia has allowed monotremes to evolve several unique characteristics. One newly discovered mystery of these animals is their electroreceptive capability. This discovery brings up many questions. How did monotremes evolve this elaborate sensory system? What do these electroreceptors look like, and how do they function? How do monotremes perceive this "sixth sense?" This paper will attempt to address these questions. Monotreme Diversity Order Monotremata is split into two families and three species. Ornithorhynchus anatinus, commonly called the platypus, can be found in eastern Australian rivers and creeks from Queensland all the way down the coast and across the Bass Strait into Tasmania (Moyal 18). The platypus is not a large animal. Males, which can weigh 2.35 kg and reach .56 m in length, are larger than the females (Dawson 9-10). The platypus swims with its mouth, ears, and eyes shut (Dawson 10). O. anatinus sifts the bottom for food, which is mainly non-insect invertebrates, crustaceans, worms, some vertebrates, and benthic larvae of various insects (Dawson 10). The two other surviving species of monotremes are Tachyglossus aculeatus, the short-beaked echidna, and Zaglossus bruijni, the long-beaked echidna. Echidnas range throughout Australia and New Guinea as well as islands adjacent to both land masses (Collins 17). Both species have characteristic modified hairs that function as spines (Dawson 10-12). T. aculeatus is a stocky animal (3-5kg) with a small head and pointed snout (Dawson 10-11). Z. bruijni is larger than T. aculeatus (~10kg) and has a downward curving snout (Dawson 11-12). The snouts and tongues of T. aculeatus and Z. bruijni are ideal for diets of termites, ants, and earthworms (Dawson 10-12).