Genetic association between progesterone-induced and maternal nesting in mice

Increases in nesting during pregnancy may be mediated by progesterone in mice. If the behaviors, maternal nesting (MN) and nesting induced by exogenous progesterone (PN), are controlled by the same physiological mechanism, it would be expected that they share a common genetic basis. The present experiment was designed to quantify the extent of genetic association between PN and MN. At Wesleyan University, baseline nesting was measured on females of 4 inbred strains. Subsequently, half of the mice in each strain received progesterone implants. There were significant increases in nesting due to progesterone treatment. After 21 days, implants were removed and nesting levels returned to baseline. The mice were mated and nesting measured throughout pregnancy. The strain rank order was the same for levels of PN and MN. The genetic correlation between PN and MN estimated from analysis of covariance within and between strains was not significantly different from 1.0. These results were replicated at the University of Iowa. The high genetic correlation implies a common physiological mechanism underlying PN and MN.