Evolution of testis size and its relation to breeding system

Bill Breed | Chris Leigh | Eleanor Peirce | Brian Setchell | David Taggart
Harsha Wechalekar

In our earlier studies we have shown marked differences in absolute and relative testis mass in the old endemic Australian rodents (Breed & Taylor, 2000). Recently we have found that adult male hopping mouse, Notomys alexis, invariably have remarkably small testes size regardless of the reproductive activity of the population or age of the male. However males will nevertheless mate with, and can fertilise, the eggs of several females within a short period of time. This surprising high fertility is probably due in large part to the very rapid sperm transport that takes place along the reproductive tract in these animals. This highly derived reproductive anatomy appears to be an unique adaptation of this species to the unpredictable arid environment in which the animals occur (Bauer & Breed, 2008).