Mammals : reproduction

 The reproduction :

    In mammals, the mode of reproduction makes it possible to distinguish three main types :

 • Monotremes : they lay eggs, and there are only three species.

 • Marsupials : they carry their babies in a pocket.

 • Placental mammals (most common type) : they carry their babies inside the body, where they feed on an organ called the placenta.

 Some mammals only produce one young at a time and take care of them to give them a good chance of survival. Others have many young and do not provide them much more than milk. The majority of them perish, but a few do reach adulthood.

Baby food :

    Although male mammals have nipples, only females produce milk {with one bizarre exception : the Dyak fruit bat or dyacoptera}. Milk is a mixture of water and nutrients : proteins, fats, carbohydrates and vitamins. It also contains antibodies, which protect the little ones from disease. Indeed, its content varies enormously from one species to another. Sea lion's milk contains about 50% fat, which allows babies to double their weight in a few days, but human milk contains only 4%. While lioness milk is very sweet, providing cubs with the immediate energy they need to play.

Game of seduction !

    Reproduction begins with the court. It's about attracting a partner. In most species, it's the females that choose, so the males have to go to great lengths to impress them. Often, males attempt to prove their worth by fighting rivals or conquering territory. Mating can take place at a specific time of the year - the mating season - so that the young are born when food is plentiful.

Rapid multiplication !

    The common tenrec (a sort of Madagascan hedgehog) has more udders "29" and a more numerous litter "up to 32" than all the other mammals. In theory, a single individual could produce several million in a year.

Placental mammals :

    Placental mammals give their young a head start in life by letting them develop to an advanced stage in the mother's body. Baby elephants spend 20 months, and are born so well developed that they can run within minutes of being born. Before birth, the placentals are nourished by a placenta, a complex organ in which baby's blood and mother's blood cross without mixing.

Monotremes :

    They are the only mammals to lay eggs. The echidna carries them in a pocket, the platypus places them in a nest.

 The monotremes have no udders, the mother's milk then diffuses into her fur like sweat.

Marsupials :

    Marsupials give birth to worm-shaped babies, much smaller than babies of placental mammals. A newborn kangaroo is the size of a bean and does not even have hind legs. After birth, the young squeeze through the mother's coat into a pouch, where they stay for up to a year.