The Effect of Auditory Stimulation on the Spermatogenetic Cycle of the Male English Sparrow

Abstract

IN recent years, many investigators have clearly demonstrated the importance of environmental factors in initiating and controlling the sexual cycle in a large number of fish, reptiles, birds, and mammals. According to the most widely accepted hypothesis (Bissonnette, 1936; Marshall, 1936) these environmental factors stimulate the anterior pituitary periodically to produce an increased amount of gonadotropic hormone which, in turn, causes seasonal changes in the sexual mechanism. These changes include hypertrophy of the gonads, active spermatogenesis and various secondary sexual changes in coloration and plumage. The question at issue is concerned with the factors which arouse the cyclic activity of the pituitary gland of the bird. According to one theory (Bissonnette, 1931, 1932), an increase in the daily light ration is essential to the appearance of the seasonal sexual changes in birds. According to a second theory, the activityt theory of Rowan (1938a, b), light rays are not directly responsible for, nor even essential to, the occurrence of these changes. Rowan's theory assumes that an increase in bodily activity produces metabolic and hormonal changes which, in their turn, stimulate the sexual mechanism. Accordingly, various environmental agencies, as long as they cause heightened activity in the animal, can be effective in producing the seasonal sexual changes. As one line of evidence in support of this view, Rowan (1938b) reports some observations which indicate that London Starlings become sexually active several weeks in advance of country birds. He attributes this difference primarily to the sounds of city traffic which keep the birds in a state of prolonged wakefulness and agitation. However, Bissonnette (1932), Riley (1940), and Kendeigh (1941) have proved without doubt that exercise has no effect on the avian sexual cycle. Rowan's explanation of the premature sexual activity of the city Starlings would consequently appear inadequate. Kendeigh (1941) has suggested that the enforced wakefulness of the city birds has allowed them to respond to the feeble illumination of the street lights. Nevertheless, the possible effectiveness of the auditory pathway as a mechanism which may control sexual periodicity has not been sys-