Reproductive Cycles

Most multicellular organisms live through a period of development during which they are not capable of sexually reproducing followed by a transition to reproductive maturity, when mating and producing offspring is possible. Some organisms experience repetitive transitions during which they cycle from reproductive to non-reproductive competence that is regulated by extrinsic factors, such as seasonal changes or mate availability, or by regular intrinsic cycles that determine when an individual can reproduce. Some organisms reproduce for their entire lifetimes while others lose their ability to reproduce again well before they die (reproductive senescence). How are these different stages of reproductive timing and capacity regulated?