Which ages first--the chicken or the egg? A comparative test of the ovarian depletion hypothesis of female reproductive aging
Donna J. Holmes, Mary Ann Ottinger, Sharon L. Thomson, Julie M. Wu
Department of Biological Sciences,University of Idaho, Moscow, ID 83844-3051, USA.
Conventional wisdom holds that depletion of finite oocyte stores is the
prime mover in reproductive aging in female birds and mammals. This
idea remains pervasive, despite 1. published evidence that some
laboratory rat strains reach infertility with a considerable pool of
eggs still in reserve; and 2. little rigorous comparative testing.
Ovarian declines may be secondary in some species to decaying function
of the hypothalamic-pituitary-ovarian (HPO) axis or other factors. We
are comparing key aspects of female reproductive aging in
distantly-related, similar-sized laboratory birds: the short-lived (6
yrs maximum) Japanese quail, which becomes infertile in its second year
of life, and the long-lived (20 yrs maximum) budgerigar parakeet, in
which breeding declines after several years. Aged quail hens, like
domestic chickens, indeed appear to have depleted numbers of primary
ovarian follicles, as predicted by the oocyte depletion model. However,
non-laying, aged female budgies retain apparently ample stores of eggs.
Our data suggest that absolute oocyte numbers are not a reliable
indicator of the ability of to mount a viable hierarchy of ovarian
follicles and ovulate successfully. We suggest a modified paradigm for
reproductive aging in female homeotherms, both birds and mammals,
incorporating a stronger emphasis on early aging cues apart from oocyte
stores.
Key words:
ovarian aging, infertility, birds, oocytes, hypothalamic-pituitary-ovarian axix
Problems or questions regarding this site should be directed to
the organiser