Williams T D
Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
Horm Behav. 1999 Apr;35(2):135-43. doi: 10.1006/hbeh.1998.1506.
Steroids hormones have numerous "activational" effects in adult birds, regulating sexual behavior, and more recently maternal androgens have been shown to have potentially important "organizational" effects in ovo, influencing offspring growth, development, and behavior. In this study I investigated parental and first-generation effects of exogenous estrogens on female reproduction in zebra finches (Taeniopygia guttata). 17beta-Estradiol (E2; 1.2 microg/g, 4 daily injections i.m.) elevated plasma levels of the yolk precursors, vitellogenin (VTG) and very low-density lipoprotein (VLDL), in nonbreeding females to levels similar to those of breeding females. However, E2-treatment of breeding females caused no significant change in plasma VTG or VLDL levels compared to control birds (measured at the 1-egg stage), and there was no difference in reproductive performance between groups (egg size, clutch size, timing of laying). E2-treated females produced significantly more daughters than sons (21F:8M) at fledging, compared to control females (18F:19M). Nestling mortality was significantly higher in broods of E2-treated females, suggesting that the skewed sex ratio may have resulted from differential mortality of male chicks. The pattern of chick mortality in E2-broods was not consistent with this being caused by estrogen-mediated changes in parental behavior (e.g., provisoning). Mean egg mass of daughters of E2-treated females was typical of experienced, adult breeders, and larger than normal, first-time breeders or control offspring (0.947 vs 0.850 g). There was no treatment effect on offspring clutch size or laying interval. These results suggest that early exposure to maternal estrogens in ovo might be involved in establishing intraindividual variation in female-specific phenotypic traits, as has previously been demonstrated for androgens and male behavioral traits (e.g., aggression).
类固醇激素在成年鸟类中具有多种“激活”作用，可调节性行为，最近还发现母体雄激素在胚胎发育过程中具有潜在的重要“组织”作用，会影响后代的生长、发育和行为。在本研究中，我调查了外源性雌激素对斑胸草雀（Taeniopygia guttata）雌性繁殖的亲代及第一代效应。17β-雌二醇（E2；1.2微克/克，每日肌肉注射4次）使未繁殖雌性的血浆中卵黄前体、卵黄蛋白原（VTG）和极低密度脂蛋白（VLDL）水平升高至与繁殖雌性相似的水平。然而，与对照鸟类相比（在产1枚卵阶段测量），对繁殖雌性进行E2处理并未导致血浆VTG或VLDL水平发生显著变化，且两组之间的繁殖性能（卵大小、窝卵数、产卵时间）没有差异。与对照雌性（18只雌性：19只雄性）相比，经E2处理的雌性在雏鸟出飞时产生的雌性后代明显多于雄性后代（21只雌性：8只雄性）。经E2处理的雌性所育雏鸟的死亡率显著更高，这表明性别比例失衡可能是由于雄性雏鸟的不同死亡率所致。E2处理组雏鸟的死亡模式与雌激素介导的亲代行为变化（如育雏）导致的情况不一致。经E2处理的雌性所生雌性后代的平均卵质量为经验丰富的成年繁殖者的典型水平，且大于正常的首次繁殖者或对照后代（0.947克对0.850克）。对后代的窝卵数或产卵间隔没有处理效应。这些结果表明，胚胎期早期暴露于母体雌激素可能参与了雌性特异性表型特征个体内变异的建立，正如之前雄激素和雄性行为特征（如攻击性）所证明的那样。
