Breeding season

The platypus breeding season varies widely depending on location. Mating is thought to occur:

  • from July to October in mainland Australia
  • as late as February in Tasmania (Grant, 2007)

Reproductive system:

  • Both sexes have a structure called a cloaca - a single external opening into which the reproductive, excretory and digestive systems open.
  • In the female platypus only the left ovary is functional.
  • The male testicles are inside the abdomen, rather than in an external scrotum (Grant, 2007).

Sex determination:

  • Platypuses have multiple sex chromosomes with some homology to the bird Z chromosome. 
  • Males have 5 X and 5 Y chromosomes, which form a chain at meiosis and segregate into 5 X and 5 Y sperm. 
  • Sex determination and sex chromosome dosage compensation remain unclear (Warren et al., 2008).

Egg production

It took 93 years from when platypuses were discovered to get scientific proof that they were oviparous (meaning that they lay eggs) (Griffiths, 1978). 

Females produce 1-3 eggs annually, usually 2 (Carrick et al., 2008).

After fertilisation the first shell layer is laid down and the egg passes down the oviduct into the uterus where second and third layers of the shell, secreted by glands in the walls of the uterus, are added.

The uterus also supplies nutrients to the egg, facilitating a size increase to about 14mm in diameter and 17mm in length by the time it is laid.

Incubation time is unknown but is possibly 10 days (Grant, 2007).