Meeting Abstract

63.1  Jan. 7  Anemia associated with egg production is estrogen-dependent: a basis for the cost of reproduction? WAGNER, E.C.*; PREVOLSEK, J.S.; WYNNE-EDWARDS, K.E.; WILLIAMS, T.D.; Simon Fraser University; Simon Fraser University; Queen’s University; Simon Fraser University ewagner@sfu.ca

The �cost of reproduction� (i.e. trade-offs between current reproduction and future fecundity and/or survival) is a central concept in life history theory, yet we still know very little about the physiological mechanisms underlying such costs. Recently it has been recognised that reproduction itself or the regulatory (physiological) mechanisms underlying reproduction might result in �costs� (cf. the more traditional resource-allocation based mechanisms). The antagonistic pleiotropic effects of hormones represent such a mechanism, where the endocrine networks regulating reproduction have multiple effects in other body systems, with negative non-reproductive effects considered resource-independent costs. Previously we have proposed a specific mechanism, the development of anemia (decreased hematocrit) during egg production in birds, which may play a role in associated costs of egg production via reductions in oxygen carrying capacity, aerobic capacity, and thus negatively impacting parental care. Here we demonstrate that anemia during egg-laying is dependent on endogenous estrogens: blocking estrogen receptors using the anti-estrogen tamoxifen completely inhibits development of anemia in female zebra finches (Taeniopygia guttata) such that hematocrit of tamoxifen-treated laying females is not significantly different from pre-breeding or non-breeding values, and is significantly higher than control laying values. Thus, this mechanism is a good candidate for a regulatory-network based trade-off involving antagonistic pleiotropic effects of estrogens, which otherwise have essential reproductive functions during egg production.