Short-Beaked Echidna (Tachyglossus aculeatus): A Reproductive Rarity
What is an echidna?
Echidnas are a unique and strange typeof mammal called a monotreme, a category thatalso includes platypuses and is often thought of as intermediary between mammals and reptiles. Like mammals, monotremes are warm-blooded, hairy, and feed their young by producing milk. Like reptiles, monotremes have a single duct for waste elimination and reproduction called a cloaca, and they lay eggs. The Short-beaked echidna (Tachyglossus culeatus) is the most widespread native mammal in Australia.
While solitary throughout the remainder of the year, echidnas form trains of up to 11 males follow a single female during their mating season from May to September. These trains forage, walk, and rest together. During this time, males produce a distinctive musk by turning out their cloacas. This can last for four weeks before the female chooses her mate. It is not known exactly how females choose their mates, though it may have something to do with the musk.
Before mating, male echidnas smell females for up to a few hours, during which time a female may reject a male. If the female does not reject the male, the male digs a small crater in which the male and female lie abdomen to abdomen on their sides. Both male and female echidnas have cloacas, but whereas the female’s is used for waste elimination as well as reproduction, the male’s cloaca is used strictly for waste elimination. Males have a four-headed, branched penis to aid injection of sperm into the female’s paired uteri, which open separately into the urinogenital sinus. Echidna females mate once during the season, and every mating is successful.
Fertilization occurs and eggshell formation begins in the oviduct. Final shell layers are added in the uterus, and the resulting egg is cream-colored and leathery. Females spend the 23-day gestation period and subsequent 10-day incubation period in a ‘nursery burrow,’ where they’ll carry the egg in a pouch that develops on their abdomens. Echidna females only produce and lay one egg at a time.
Early in development, embryos form an egg tooth on the upper jaw, and a bump of hardened epithelium on the snout called the caruncle. The embryo uses these structures to break the shell, and uses strong fore and hind feet to pull itself out. The egg tooth and caruncle disappear soon after hatching. Hatchlings are known as ‘puggles’ and can climb with well-developed limbs and digits, though they are born blind and hairless.
Illustration by Andhi Spath
Echidnas have no nipples; instead mammary glands open up into ‘milk patches’ in the pouch. Pouch young grow quickly, up to 20% within two hours of suckling. Babies stay in their mother’s pouch for 45 days, after which time they spend four more months in the covered nursery burrow. During the period, the mother will often leave for stretches of 5-10 days to find food. About a month after birth, echidna babies have begun to grow spikes and are left on their own with no further contact between baby and mother.