wild-type Drosophila and the mutant. There- fore, it cannot be attributed to the effect of the mutation. 15. For quantitative verification of this statement, autocovariance functions of the bump noise were calculated for both the wild type and the mutant, norpAH52. The autocovariance function C(T) gives a picture of how the signal correlates to its future (or past) at an interval r. If the occurrence of bumps is totally uncotrelated, the autocovariance function would describe the time course of individual bumps. In the above calculation, the autocovariance functions of bump noise for the wild type and the mutant were found to have very similar dependence on T, suggesting that the time course of individual bumps is similar. 16. D. A. Baylor and M. G. F. Fuortes, J. Physiol. (London) 207, 77 (1970); S. Yoshikami and W. A. Hagins, Biophys. J. 11, 47a (1971). 17. N. H. Horowitz and M. Fling, Genetics 38, 360 Brief (I) periods of sensory experience can profoundly affect a developing orga- nism. The evidence for this in verte- brates has been limited to studies of the visual system after birth (2). We now re- port that brief stimulation of the auditory system can also affect vertebrate devel- opment. Moreover, this sensitivity exists during the prenatal period of devel- opment. Our results indicate that brief prenatal exposure of an avian embryo to atuditory stimulation can accelerate the time of hatching, reducing the normal in- cubation time by as much as 10 percent. Many species of precocial ground- nesting birds brood egg clutches whose eggs hatch within a short time of one an- other (3). This synchronization of hatch- ing is of putative adaptive advantage in thait it reduces the period during which the parents must choose between care for unhatched eggs and newly hatched yoLing. That is, during incubation the eggs must be maintained within a narrow range of environmental conditions (4). The behaivior required of the parents to provide these incubation conditions is in conflict with the behavior required later for the care of the highly mobile, pre- cocial brood. After the eggs hatch the parents must utilize new tactics to pro- tect the young from predators and must introduce the young to available food re- sources before their embryonic reserves are exhausted. The strategy of synchro- nization of hatching allows the most effi- cient division of the demands on the par- ents for care of the young before and af- ter hatching. 26 NOVEMBER 1976 (1953); A. Campbell, Virology 14, 22 (1961); R. S. Edgar and R. H. Epstein, in Proceedings of the XI International Congress of Genetics (Per- gamon Press, London, 1964), p. 1. 18. D. T. Suzuki, L. K. Piternick, S. Hayashi, M. Tarasoff, D. Baillie, V. Erasmus, Proc. Natl. Acad. Sci. U.S.A. 57, 907 (1967). 19. See, for example, W. A. Hagins in Annu. Rev. Biophys. Bioeng. 1, 131 (1972). 20. We thank S. Conrad and M. Wilson for their technical assistance. This work was supported by grants from the National Science Foundation (GB 35316X) and the National Institutes of Health (EY 00033). * Present address: Department of Genetics, Mo- nash University, Clayton, Victoria, Australia 3168. t Present address: Division of Biology, California Institute of Technology, Pasadena 91109. 7 June 1976; revised 27 July 1976 Synchronization of hatching is mediat- ed by acoustic communication between the individual members within a clutch. Audible clicks, which are correlated with the embryo's respiratory cycle (5), pro- vide the basis for the inter-egg communi- cation (6). Acoustic presentation of syn- thetic clicks (such as brief, broad-band bursts of noise) has shown that the hatch- ing of embryos following acoustic stimu- lation is accelerated or retarded depend- ing on the click repetition rate (7). the du- ration of the stimulating period, and gestational age of the embryo. Under normal incubation conditions. Japanese quail (Coturnix coturnixjaponi- 18.0 17 5 F 170 F 16 5 'G 'o2 m10 C:Q 0 a .q,v C7, 0 01 C .c Q a -r 160 IL t55 L 14 14 5 15 15 5 16 Control Incubation age at stimulotion (days) Fig. 1. Hatching age for the five experimental groups and the unstimulated control group. Experimental groups were exposed to audi- tory stimulation for 2 hours at the incubation age indicated (9). Means and standard errors are shown. Sample sizes for experimental groups days 14 through 16 and controls are 35, 46, 41. 39, 39, and 96. respectively. ca) hatch on day 17 of incubation. Con- tinuous exposure during the final 2 days of incubation to synthetic clicks at stimu- lation rates of approximately three per second optimally advances the hatching of Japanese quail, while rates above or be- low the optimum produce less significant hatching advancement or even hatching retardation, as compared to unstimu- lated controls (7). We first studied the developmental stages at which exposure of the embryo to synthetic clicks at the optimal repeti- tion rate would accelerate the hatching of Japanese quail, and found that the hatching time could be advanced only if the embryos were stimulated during the final 3 days of incubation. We then sys- tematically examined the effects of stimu- lation during this interval and report here that very brief exposures to synthetic clicks at any point within this 3-day sensi- tive period significantly advance the hatching time. Japanese quail eggs (Cornell Universi- ty. Department of Poultry Science) were incubated in Jamesway forced-draft in- cubators (37.50C. 60 percent relative hu- midity), in which the eggs were turned automatically every 3 hours (8). Before day 14 the eggs were checked for via- bility (candled), and the viable embryos were randomly grouped into clutches of six eggs. The eggs within a clutch were formed into a 2 by 3 array. with each egg in contact with its nearest neighbors. Experimental clutches were stimulat- ed for 2 hours at 14. 14.5. 15. 15.5. or 16 days of incubation (9). In the procedure for sound presentation. the tray con- taining the clutch was rapidly transferred from the control incubator to a second in- cubator that was equipped with a KLH model 11 loudspeaker. The temperature and relative humidity of both incubators were identical. The speaker was centered 12.5 cm above the clutch and the stimuli were presented at 80-db sound pressure level peak (General Radio model 33 sound level meter) at the optimal rate of three per second (7). The stimuli were 37-msec, broad-band (0.1 to 8 khz) bursts of noise generated by a uni- junction relaxation oscillator, whose re- sistance-capacitance values were chosen to maximize the spectral flatness of the speaker output. Control clutches were treated identically but not exposed to the 2-hour stimulation period. After 16 days of incubation the eggs were placed on an automated device that recorded the individual hatching times. Each egg was placed on a separate bal- anced spoon that held down a micro- switch. When the animal hatched, the mi- 959 Prenatal Experience and Avian Development: Brief Auditory Stimulation Accelerates the Hatching of Japanese Quail Abstract. A single 2-lhoutr exposture to auiditory stimitlation at ainy point diuring tile finil 3 datys oj incuibation accelerates the hatching (o. Japanese quail. The 3-daiy sen- sitive period includes hot/i prenaital and perinatal staiges of incubation. So ftir as is knowin these r-esiults provide the first unequivocal evidence thlait short-term pr-enatal sensory stimiultition can affect the development ojfan avian embryo. on August 5, 2015 www.sciencemag.org Downloaded from on August 5, 2015 www.sciencemag.org Downloaded from