Changes in embryonic development associated with long-term selection for high growth rate in Japanese quail.

Selection for rapid growth in the quail resulted in a changed growth pattern of the embryo and the extra-embryonic membranes (the yolk sac and allantois). The early part of the incubation period was characterized by a reduced embryo weight and a more rapid early development of the extra-embryonic membranes. These changes were followed by an increased growth rate of the embryo. The increased growth rate was apparently linked to the more rapid early development of the extra-embryonic membranes. Thus, the growth rate was most likely restricted by the capacity to absorb and utilize yolk. It also appears that at least part of the increase in growth rate was made possible by the change in the early embryonic growth pattern.