Gordon K R, Levy C, Perl M, Weeks O I
Department of Biological Sciences, Florida International University, Miami 33199.
Growth Dev Aging. 1994 Summer;58(2):95-104.
BALB/c mice were raised for 30 days under nine treatment regimens to determine their effects on sexual dimorphism for size of the femur and of the body. Treatment groups were divided into three experiments: 1) burrowing in a high litter cage; eight times normal gravity for a total of one hour per day; a voluntary exercise control. 2) Unilateral femoral and sciatic nerve ablation; the opposite unoperated leg. 3) Swimming exercise; anabolic steroid; swimming and anabolic steroid; normal exercise control. Traits measured were body weight gain and thirteen femoral characters: moment at failure, length, cross-sectional area, anteroposterior and lateromedial diameters of the cross section, wall thickness for all four quadrants of the shaft, moments of inertia of the cross section in the anteroposterior and lateromedial directions, deflection of the shaft before failure, and total mineral content. Sexual dimorphism of the traits studied varied significantly with treatment. The greatest dimorphism was seen in the controls and the burrowing group. The least dimorphism was seen in the eight times gravity, the steroid, and the exercise and anabolic steroid groups. Reduction in the extent of sexual dimorphism was not correlated with a reduction in the loading regimen but rather seemed mediated by systemic changes in physiology brought on by several factors. Change in the amount of sexual dimorphism for size from the control reflects change in growth rates for males and females in response to different treatments. Change in growth rates of juvenile males and females will likely result in changes in the size of femoral characters and body weight in the adult. Change in the size of femoral characters affects the strength of the femur. In natural populations, a change in the body size of adult males and females could adversely affect reproductive success in groups that normally exhibit strong dimorphism, and hence, select against any conditions that reduce sexual dimorphism. Ordinarily, a significant change in sexual dimorphism--of the magnitude seen here--through natural selection, would take several generations.
将BALB/c小鼠在九种处理方案下饲养30天，以确定它们对股骨和身体大小的性二态性的影响。处理组分为三个实验：1）在高垫料笼中打洞；八倍正常重力，每天共一小时；自愿运动对照。2）单侧股骨和坐骨神经切除；对侧未手术的腿。3）游泳运动；合成代谢类固醇；游泳和合成代谢类固醇；正常运动对照。测量的性状包括体重增加和13个股骨特征：破坏时的力矩、长度、横截面积、横截面的前后径和内外侧径、骨干所有四个象限的壁厚、横截面在前后和内外侧方向的惯性矩、破坏前骨干的挠度以及总矿物质含量。所研究性状的性二态性随处理而有显著差异。在对照组和打洞组中观察到最大的二态性。在八倍重力、类固醇、运动和合成代谢类固醇组中观察到最小的二态性。性二态性程度的降低与负荷方案的降低无关，而是似乎由多种因素引起的生理系统变化介导。与对照组相比，大小性状性二态性的变化反映了雄性和雌性对不同处理的生长速率变化。幼年雄性和雌性生长速率的变化可能会导致成年后股骨特征大小和体重的变化。股骨特征大小的变化会影响股骨的强度。在自然种群中，成年雄性和雌性身体大小的变化可能会对通常表现出强烈二态性的群体的繁殖成功产生不利影响，因此，会选择反对任何减少性二态性的条件。通常，通过自然选择，性二态性发生如此大的显著变化需要几代人的时间。
