Genetic analysis of tonic immobility in young Japanese quail (Coturnix coturnix japonica).

Abstract

Data were obtained on tonic immobility from 10th-generation matings of replicated lines of Japanese quail. These lines had been selected for high and low mating ability and included the random-bred control population from which the selected lines originated. At 6, and again at 12 days of age, each bird was subjected to uniform procedures of immobilization and was given two scores, one indicating the number of trials required to induce immobility, another the duration of induced immobility. Although there were no differences between sexes, lines were significantly different for duration and percentage incidence to the immobility response at both ages. Individuals that responded faster also exhibited longer durations of immobility, suggesting a high degree of susceptibility. Heritability estimates indicate that the additive genetic variation effecting tonic immobility is low to moderate in magnitude. These results, when taken in an evolutionary context, suggest prior natural selection for tonic immobility and indicate that this trait is associated with fitness.