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Participation of the Eyes in the Photostimulation of Chickens
Participation of the Eyes in the Photostimulation of Chickens T. D. SIOPES1 and W. O. WILSON Department of Avian Science, University of California, Davis, California 95616 (Received for publication March 23, 1979)
1980 Poultry Science 59:1122-1125 INTRODUCTION It has been established t h a t light can profoundly affect the reproductive activity of b o t h mammals and birds and t h a t the effect of light involves a n e u r o e n d o c r i n e reflex. T h e eyes have been reported to serve as an essential c o m p o n e n t of this reflex in m a m m a l s (Wurtman, 1967, 1974) whereas in birds it has been generally reported t h a t t h e eyes are n o t essential (Benoit, 1 9 6 4 b ; Menaker and Keatts, 1 9 6 8 ; Menaker et. al, 1970). In a review of his pioneering and extensive work on the p h o t o s e x u a l response of the domestic duck (Anas platyrhynchos), Benoit (1964a,b) concluded t h a t t w o t y p e s of p h o t o receptors existed, a superficial retinal r e c e p t o r and a deep h y p o t h a l a m i c or extraretinal receptor. We ( H o m m a et al, 1 9 7 2 ; Siopes and Wilson, 1974) reported t h a t t h e eyes were involved in t h e p h o t o s e x u a l response of Japanese quail (Coturnix coturnix japonica). In addition, Y o k o y a m a and Farner ( 1 9 7 6 ) have reported t h a t t h e eyes participated in t h e p h o t o p e r i o d i cally induced secretion of LH in t h e White Crowned sparrow, Zonotrichia leucophyrs gambelii. Chickens possess extraretinal p h o t o receptors a n d d o n o t require t h e eyes for egg p r o d u c t i o n (Harrison and Becker, 1 9 6 9 ; Harrison, 1972). However, Harrison ( 1 9 7 4 ) has suggested t h a t t h e eyes m a y be involved in the p h o t o p e r i o d i c control of oviposition time. T h e purpose of the present study was to d e t e r m i n e
' Present address: Department of Poultry Science, North Carolina State University, Raleigh, NC 27650.
if t h e eyes can participate in the p h o t o s e x u a l response of t h e domestic chicken (Gallus domesticus). MATERIALS AND METHODS White Leghorn pullets from the University of California strains 150 and 170 were used in this e x p e r i m e n t . One-day-old chicks of each strain were equally distributed in wire-floor b r o o d e r s within t w o bioclimatic chambers. T h e birds remained in these chambers t h r o u g h o u t t h e 27 week testing period. The t e m p e r a t u r e for all birds was maintained at 35 C after hatching. This was decreased 2.8 C weekly. After 4 weeks the t e m p e r a t u r e was maintained at 23 ± 1 C t h r o u g h o u t the e x p e r i m e n t . In o n e of t h e bioclimatic chambers light was provided from eight 40-watt warm w h i t e fluorescent tubes hung from the ceiling. In the o t h e r c h a m b e r t h e light source was four 150-watt incandescent lamps which were located on the ceiling. T h e physical characteristics of these light sources were measured with an ISCO m o d e l SP spectroradiometer and are detailed in Table 1. For t h e first 2 4 hr following hatching all chicks received 2 4 hr of light ( 2 4 L L ) . Thereafter, all birds were e x p o s e d t o 8 h r of light per day ( 8 L : 1 6 D ) for the d u r a t i o n of the e x p e r i m e n t . At 12 weeks of age all pullets were moved from colony growing cages into individual laying cages. There were 4 0 individual cages (birds) per chamber. At 14 weeks of age, eight birds in each chamber were anesthetized with sodium p e n t o b a r b i t a l and u n d e r w e n t bilateral ocular enucleation. Within each c h a m b e r half of the enucleated birds were from strain 150 and
1122
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
ABSTRACT This study examined the participation of the eyes in the photosexual response of chickens to incandescent and fluorescent light. Intact and blinded female chickens were exposed to short photoperiods (8L:16D) of incandescent and fluorescent light and the age at first egg and rate of egg production were determined. Incandescent light was inhibitory to the age at first egg and the early rate of egg production. Blinding prevented this response. It was concluded that the eye is not essential to the photosexual reponse of chickens but that it may modify the response to light in certain conditions.
EYES AND PHOTOSTIMULATION
RESULTS AND DISCUSSION The effect of blinding on the age at first egg (sexual maturation) of chickens raised under incandescent and fluorescent light is given in Table 2. Incandescent light was inhibitory to the maturational processes as intact chickens raised on short photoperiods of incandescent light had significantly delayed onset of egg laying from those reared under fluorescent light. Blinding had no effect on the onset of egg laying of the birds raised under fluorescent light. However, blinded birds maintained under incandescent light laid at a significantly earlier age than the intacts given incandescent light and were comparable to either of the fluorescent light treated groups. This demonstrated that the inhibitory effect of incandescent light is mediated via the eye. Although the eye is not essential to the photosexual development of chickens, it can function as a modifier of the photosexual response. It has been clearly demonstrated that the eyes are not required for photostimulated sexual development in many species of birds, including the chicken (Benoit, 1964b; Menaker
and Keatts, 1968; Sayler and Wolfson, 1968; Siopes and Wilson, 1974; Underwood and Menaker, 1970; Harrison, 1974). However, as seen in the current study, this does not preclude participation of the eye in photosexual responses. Benoit (1964b) has also reported ocular participation in photoreception, however, he observed a stimulatory rather than inhibitory response involving the eye. In Figure 1 the rate of egg production between intact and blinded birds exposed to incandescent or flourescent light is compared. With flourescent lighting egg production was not different between the intact and blinded birds at any time during the test period. However, when the birds were exposed to incandescent light the intact group had a significantly lower rate of lay during the early production period (20 to 23 weeks of age) than the blinded group. Thereafter, there was no significant difference in the rate of egg production between the two groups. Under the conditions of this test, incandescent lighting was inhibitory to egg production during the early part of the egg laying cycle and this response was mediated by the eyes. Why incandescent light was inhibitory to the rate of sexual maturation and early egg production is not known. Certainly, an obvious difference between the incandescent and fluorescent light used was the spectral distribution (Table 1). This, as well as the total energy and quanta of the two light sources are potential sources of the differences in the observed responses. However, Oishi and Lauber (1973) reported that neither the energy level nor the number of photons was the key variable for the response of quail to light. They suggested that wavelength per se is the most important aspect of light for control of the photosexual response.
TABLE 1. Radiometric and photometric characteristics of the two light regimens used Light at bird height1 P n . ^ , ( M watts) (cm 2 )
Wavelength (nm) Light type
Peak
Range
Total
Visual
Lux
Incandescent Fluorescent
925 558
400-1050 4 0 0 - 750
146 81
59 81
103 263
1
Light energy measured with an ISCO Model SR spectroradiometer (Instrumentation Specialties Co., Lincoln, NE).
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
half from strain 170. No mortality resulted from the surgical procedures. The birds were given University of California chick starter (20%) protein) during the rearing period. From 12 weeks of age all birds were given UC breeder peilets (16% protein) and fresh water ad libitum. Individual egg production was recorded daily and the mean age at first egg (onset of sexual maturation) was determined. The data were analyzed by the analysis of variance and mean separations were done by either the method of Tukey or Scheffe (Becker, 1959).
1123
1124
SIOPES AND WILSON TABLE 2. The effect of blinding on the age at first egg of chickens exposed to fluorescent and incandescent lighting (8L.16D). Mean ± standard error Fluorescent
Age at first egg (days) No. birds
Incandescent
Intact
Blind
Intact
Blind
139.7 ± 1 . 2 a 32
140.6 ± 2.7 a 8
150.0 ± 1 . 6 b 32
136.6 ± 3.2 a 8
Different letters indicate statistically significantly difference (P<.05).
INTACT
(32)
AGE (WEEKS)
FIG. 1. Sexual development and rate of egg production of intact and blinded chickens maintained under 8 hr of fluorescent (A) or incandescent (B) light per day. "Indicatesstatistical significance between groups (P<.05).
spectrum. However, t h a t blinded birds on incandescent light m a t u r e d at t h e same rate as either intact (sighted) or blinded birds on fluorescent light suggested t h a t this is n o t the case. Rather, incandescent light was app a r e n t l y inhibitory via the eye in s o m e u n k n o w n m a n n e r , presumably wavelength d e p e n d e n t . Note in Table 1 t h a t light m e a s u r e m e n t s expressed in /i w a t t s / c m 2 most accurately expressed t h e a m o u n t of light present in different light t y p e s w i t h o u t t h e bias of spectral sensitivities inherent in footcandle meter photo-cells. It is well established t h a t t h e p h o t o s e x u a l responses are wavelength d e p e n d e n t and that t h e far end of the visible spectrum (orange-red) is m o s t stimulatory to b o t h sighted and blinded birds (Benoit, 1 9 6 4 b ; Harrison et al., 1 9 7 0 ; Foss et al, 1972). Incandescent light consists primarily of wavelengths at the far end of t h e visible spectrum yet it caused an inhibition of reproductive development. Harrison et al. ( 1 9 7 0 ) have reported t h a t short day-lengths were m o s t inhibitory t o reproductive function of chickens when t h e light consisted of t h e far end of t h e visible s p e c t r u m . T h e inhibitory response to incandescent light in t h e present s t u d y seemed to be related to t h e d u r a t i o n of light and, thus, the rate of response. T h e rate of sexual d e v e l o p m e n t in chickens is p r o p o r t i o n a l t o t h e d u r a t i o n of light t o which t h e birds are exposed. T h e inhibitory effect of incandescent light o n sexual m a t u r a t i o n and egg p r o d u c t i o n evident in the present s t u d y t h u s could be t h e result of t h e slowed rate of development due to e x p o s u r e t o short p h o t o p e r i o d s ( 8 L : 1 6 D ) from hatching. Accelerated gonadal d e v e l o p m e n t induced by long p h o t o p e r i o d s masks this response (Siopes and Wilson, unpublished results). A similar response can be observed in t h e hen-day egg p r o d u c t i o n figure presented by Harrison ( 1 9 7 2 ) .
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
In the present s t u d y t h e energy of the flourescent light was distributed within the visible light spectrum whereas t h e incandescent light had most of its energy (59%) o u t of t h e visible spectrum (Table 1). F u r t h e r m o r e , within the visible s p e c t u r m , fluorescent light had m o r e t h a n 2.5 times as m u c h intensity t h a n incandescent light (263 vs. 103 lux) whereas the energy c o n t e n t of flourescent light was 1.4 times greater than incandescent (81 vs. 59 /J w a t t s / cm ). It would therefore be t e m p t i n g to speculate t h a t fluorescent light was most stimulatory to sexual development d u e to increased a m o u n t s of energy within t h e visible
EYES AND PHOTOSTIMULATION
It is of interest that, with t h e exception of one s t u d y with White C r o w n e d sparrows ( Y o k o y a m a and Farner, 1 9 7 6 ) , participation of the eyes in the p h o t o s e x u a l response of birds has best been shown in domestic species (Benoit, 1 9 6 4 b ; H o m m a et al., 1 9 7 2 ) ; Oishi and Lauber, 1 9 7 3 ; Siopes and Wilson, 1 9 7 4 ) . T h e physiological i m p o r t a n c e of this difference remains to be established. REFERENCES Becker, W. A., 1959. Recent statistical procedures for experimental investigators. Inst. Agr. Sci., State College of Washington, Pullman, WA. Benoit, J., 1964a. The structural components of the hypothalmo-hypophysical pathway, with particular reference to photostimulation of the gonads in birds. Ann. New York Acad. Sci. 117:23-24. Benoit, J., 1964b. The role of the eye and of the hypothalamus in the photostimulation of gonads in the duck. Ann. New York Acad. Sci. 117: 204-214. Foss, D. C , L. B. Carew, Jr., and E. L. Arnold, 1972.
Physiological development of cockerels as influenced by selected wavelengths of environmental light. Poultry Sci. 51:1922-1927. Harrison, P. C , 1972. Extraretinal photocontrol of productive responses of leghorn hens to photoperiods of different length and spectrum. Poultry Sci. 51:2060-2064. Harrison, P. C , 1974. Spectum influence on extraretinal control of daily oviposition cycles. Poultry Sci. 53:560-564. Harrison, P. C , and W. C. Becker, 1969. Extraretinal photocontrol of oviposition of pinealectomized domestic fowl. Proc. Soc. Exp. Biol. Med. 132: 161-164. Harrison, P. C , J. D. Latshaw, J. M. Casey, and J. McGinnis, 1970. Influence of decreased length of different spectral photoperiods on testis development of domestic fowl. J. Reprod. Fert. 22; 269-275. Homma, K., W. O. Wilson, and T. D. Siopes, 1972. Eyes have a role in photoperiodic control of sexual activity of cotumix. Science 178:421 — 423. Menaker, M., and H. Keatts, 1968. Extraretinal light perception in the sparrow. II. Photoperiodic stimulation of testis growth. Proc. Nat. Acad. Sci. 60:146-151. Menaker, M., R. Roberts, J. Elliott, and H. Underwood, 1970. Extraretinal light perception in the sparrow. III. The eyes do not participate in photoperodic photoreception. Proc. Nat. Acad. Sci. 67:320-325. Oishi, T., and J. K. Lauber, 1973. Photoreception in the photosexual response of quail. II. Effects of intensity and wavelength. Amer, j . Physiol. 225:880-886. Sayler, A., and A. Wolfson, 1968. Role of eyes and superior cervical ganglia on the effects of light on the pineal and gonads of the Japanese quail. Arch. Anat. Histol. Embryol. 51:615—626. Siopes, T. D., and W. O. Wilson, 1974. Extraocular modification of photoreception in intact and pinealectomized coturnix. Poultry Sci. 53: 2035-2041. Underwood, A., and M. Menaker, 1970. Photoperiodically significant photoreception in sparrows. Is the retina involved? Science 167:298-301. Wurtman, R. J., 1967. Effects of light and visual stimuli on endocrine function. Pages 19—59 in Neuroendocrinology. Vol. 2 L. Martini, W. F. Ganong, ed. Academic Press, New York, NY. Wurtman, R. J., 1974. The effects of light on man and other mammals. Ann. Rev. Physiol. 37:467-482. Yokoyama, K., and D. S. Farner, 1976. Photoperiodic responses in bilaterally encleated White-Crowned sparrows, Zonotrichia leucopbyrs gambelii. Gen. Comp. Endocrinol 30:528-533.
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
Whatever the specific cause of inhibition by incandescent light m a y be, it appears t h a t the eyes are serving as a m e d i a t o r of the response. H o m m a et al. ( 1 9 7 2 ) and Siopes and Wilson ( 1 9 7 4 ) have clearly d e m o n s t r a t e d a role for the eyes in t h e regressive phases of t h e p h o t o s e x u a l response of Cotumix. Y o k o y a m a and Farner ( 1 9 7 6 ) have r e p o r t e d t h a t t h e eyes suppress the levels of LH in White Crowned sparrows. Harrison (1974) suggested t h a t the eye may be involved in t h e p h o t o p e r i o d i c c o n t r o l of oviposition time in chickens. However, it was uncertain whether this was a passive or active involvement by the eye. Certainly, extraretinal p h o t o r e c e p t i o n is well established in birds b u t from the foregoing, t h e eye should n o t be c o m p l e t e l y discounted as a p h o t o r e c e p t o r in the p h o t o s e x u a l process. Benoit, in a classical series of experiments starting as early as 1 9 3 5 , has proposed that t h e eyes c o n t r i b u t e to b u t are not essential for the reproductive developm e n t of the duck by light (Benoit, 1964a,b). T h e results of t h e present s t u d y s u p p o r t a similar conclusion for the domestic chickens with the exception that t h e eye participated in an inhibitory manner.
1125
1980 Poultry Science 59:1122-1125 INTRODUCTION It has been established t h a t light can profoundly affect the reproductive activity of b o t h mammals and birds and t h a t the effect of light involves a n e u r o e n d o c r i n e reflex. T h e eyes have been reported to serve as an essential c o m p o n e n t of this reflex in m a m m a l s (Wurtman, 1967, 1974) whereas in birds it has been generally reported t h a t t h e eyes are n o t essential (Benoit, 1 9 6 4 b ; Menaker and Keatts, 1 9 6 8 ; Menaker et. al, 1970). In a review of his pioneering and extensive work on the p h o t o s e x u a l response of the domestic duck (Anas platyrhynchos), Benoit (1964a,b) concluded t h a t t w o t y p e s of p h o t o receptors existed, a superficial retinal r e c e p t o r and a deep h y p o t h a l a m i c or extraretinal receptor. We ( H o m m a et al, 1 9 7 2 ; Siopes and Wilson, 1974) reported t h a t t h e eyes were involved in t h e p h o t o s e x u a l response of Japanese quail (Coturnix coturnix japonica). In addition, Y o k o y a m a and Farner ( 1 9 7 6 ) have reported t h a t t h e eyes participated in t h e p h o t o p e r i o d i cally induced secretion of LH in t h e White Crowned sparrow, Zonotrichia leucophyrs gambelii. Chickens possess extraretinal p h o t o receptors a n d d o n o t require t h e eyes for egg p r o d u c t i o n (Harrison and Becker, 1 9 6 9 ; Harrison, 1972). However, Harrison ( 1 9 7 4 ) has suggested t h a t t h e eyes m a y be involved in the p h o t o p e r i o d i c control of oviposition time. T h e purpose of the present study was to d e t e r m i n e
' Present address: Department of Poultry Science, North Carolina State University, Raleigh, NC 27650.
if t h e eyes can participate in the p h o t o s e x u a l response of t h e domestic chicken (Gallus domesticus). MATERIALS AND METHODS White Leghorn pullets from the University of California strains 150 and 170 were used in this e x p e r i m e n t . One-day-old chicks of each strain were equally distributed in wire-floor b r o o d e r s within t w o bioclimatic chambers. T h e birds remained in these chambers t h r o u g h o u t t h e 27 week testing period. The t e m p e r a t u r e for all birds was maintained at 35 C after hatching. This was decreased 2.8 C weekly. After 4 weeks the t e m p e r a t u r e was maintained at 23 ± 1 C t h r o u g h o u t the e x p e r i m e n t . In o n e of t h e bioclimatic chambers light was provided from eight 40-watt warm w h i t e fluorescent tubes hung from the ceiling. In the o t h e r c h a m b e r t h e light source was four 150-watt incandescent lamps which were located on the ceiling. T h e physical characteristics of these light sources were measured with an ISCO m o d e l SP spectroradiometer and are detailed in Table 1. For t h e first 2 4 hr following hatching all chicks received 2 4 hr of light ( 2 4 L L ) . Thereafter, all birds were e x p o s e d t o 8 h r of light per day ( 8 L : 1 6 D ) for the d u r a t i o n of the e x p e r i m e n t . At 12 weeks of age all pullets were moved from colony growing cages into individual laying cages. There were 4 0 individual cages (birds) per chamber. At 14 weeks of age, eight birds in each chamber were anesthetized with sodium p e n t o b a r b i t a l and u n d e r w e n t bilateral ocular enucleation. Within each c h a m b e r half of the enucleated birds were from strain 150 and
1122
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
ABSTRACT This study examined the participation of the eyes in the photosexual response of chickens to incandescent and fluorescent light. Intact and blinded female chickens were exposed to short photoperiods (8L:16D) of incandescent and fluorescent light and the age at first egg and rate of egg production were determined. Incandescent light was inhibitory to the age at first egg and the early rate of egg production. Blinding prevented this response. It was concluded that the eye is not essential to the photosexual reponse of chickens but that it may modify the response to light in certain conditions.
EYES AND PHOTOSTIMULATION
RESULTS AND DISCUSSION The effect of blinding on the age at first egg (sexual maturation) of chickens raised under incandescent and fluorescent light is given in Table 2. Incandescent light was inhibitory to the maturational processes as intact chickens raised on short photoperiods of incandescent light had significantly delayed onset of egg laying from those reared under fluorescent light. Blinding had no effect on the onset of egg laying of the birds raised under fluorescent light. However, blinded birds maintained under incandescent light laid at a significantly earlier age than the intacts given incandescent light and were comparable to either of the fluorescent light treated groups. This demonstrated that the inhibitory effect of incandescent light is mediated via the eye. Although the eye is not essential to the photosexual development of chickens, it can function as a modifier of the photosexual response. It has been clearly demonstrated that the eyes are not required for photostimulated sexual development in many species of birds, including the chicken (Benoit, 1964b; Menaker
and Keatts, 1968; Sayler and Wolfson, 1968; Siopes and Wilson, 1974; Underwood and Menaker, 1970; Harrison, 1974). However, as seen in the current study, this does not preclude participation of the eye in photosexual responses. Benoit (1964b) has also reported ocular participation in photoreception, however, he observed a stimulatory rather than inhibitory response involving the eye. In Figure 1 the rate of egg production between intact and blinded birds exposed to incandescent or flourescent light is compared. With flourescent lighting egg production was not different between the intact and blinded birds at any time during the test period. However, when the birds were exposed to incandescent light the intact group had a significantly lower rate of lay during the early production period (20 to 23 weeks of age) than the blinded group. Thereafter, there was no significant difference in the rate of egg production between the two groups. Under the conditions of this test, incandescent lighting was inhibitory to egg production during the early part of the egg laying cycle and this response was mediated by the eyes. Why incandescent light was inhibitory to the rate of sexual maturation and early egg production is not known. Certainly, an obvious difference between the incandescent and fluorescent light used was the spectral distribution (Table 1). This, as well as the total energy and quanta of the two light sources are potential sources of the differences in the observed responses. However, Oishi and Lauber (1973) reported that neither the energy level nor the number of photons was the key variable for the response of quail to light. They suggested that wavelength per se is the most important aspect of light for control of the photosexual response.
TABLE 1. Radiometric and photometric characteristics of the two light regimens used Light at bird height1 P n . ^ , ( M watts) (cm 2 )
Wavelength (nm) Light type
Peak
Range
Total
Visual
Lux
Incandescent Fluorescent
925 558
400-1050 4 0 0 - 750
146 81
59 81
103 263
1
Light energy measured with an ISCO Model SR spectroradiometer (Instrumentation Specialties Co., Lincoln, NE).
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
half from strain 170. No mortality resulted from the surgical procedures. The birds were given University of California chick starter (20%) protein) during the rearing period. From 12 weeks of age all birds were given UC breeder peilets (16% protein) and fresh water ad libitum. Individual egg production was recorded daily and the mean age at first egg (onset of sexual maturation) was determined. The data were analyzed by the analysis of variance and mean separations were done by either the method of Tukey or Scheffe (Becker, 1959).
1123
1124
SIOPES AND WILSON TABLE 2. The effect of blinding on the age at first egg of chickens exposed to fluorescent and incandescent lighting (8L.16D). Mean ± standard error Fluorescent
Age at first egg (days) No. birds
Incandescent
Intact
Blind
Intact
Blind
139.7 ± 1 . 2 a 32
140.6 ± 2.7 a 8
150.0 ± 1 . 6 b 32
136.6 ± 3.2 a 8
Different letters indicate statistically significantly difference (P<.05).
INTACT
(32)
AGE (WEEKS)
FIG. 1. Sexual development and rate of egg production of intact and blinded chickens maintained under 8 hr of fluorescent (A) or incandescent (B) light per day. "Indicatesstatistical significance between groups (P<.05).
spectrum. However, t h a t blinded birds on incandescent light m a t u r e d at t h e same rate as either intact (sighted) or blinded birds on fluorescent light suggested t h a t this is n o t the case. Rather, incandescent light was app a r e n t l y inhibitory via the eye in s o m e u n k n o w n m a n n e r , presumably wavelength d e p e n d e n t . Note in Table 1 t h a t light m e a s u r e m e n t s expressed in /i w a t t s / c m 2 most accurately expressed t h e a m o u n t of light present in different light t y p e s w i t h o u t t h e bias of spectral sensitivities inherent in footcandle meter photo-cells. It is well established t h a t t h e p h o t o s e x u a l responses are wavelength d e p e n d e n t and that t h e far end of the visible spectrum (orange-red) is m o s t stimulatory to b o t h sighted and blinded birds (Benoit, 1 9 6 4 b ; Harrison et al., 1 9 7 0 ; Foss et al, 1972). Incandescent light consists primarily of wavelengths at the far end of t h e visible spectrum yet it caused an inhibition of reproductive development. Harrison et al. ( 1 9 7 0 ) have reported t h a t short day-lengths were m o s t inhibitory t o reproductive function of chickens when t h e light consisted of t h e far end of t h e visible s p e c t r u m . T h e inhibitory response to incandescent light in t h e present s t u d y seemed to be related to t h e d u r a t i o n of light and, thus, the rate of response. T h e rate of sexual d e v e l o p m e n t in chickens is p r o p o r t i o n a l t o t h e d u r a t i o n of light t o which t h e birds are exposed. T h e inhibitory effect of incandescent light o n sexual m a t u r a t i o n and egg p r o d u c t i o n evident in the present s t u d y t h u s could be t h e result of t h e slowed rate of development due to e x p o s u r e t o short p h o t o p e r i o d s ( 8 L : 1 6 D ) from hatching. Accelerated gonadal d e v e l o p m e n t induced by long p h o t o p e r i o d s masks this response (Siopes and Wilson, unpublished results). A similar response can be observed in t h e hen-day egg p r o d u c t i o n figure presented by Harrison ( 1 9 7 2 ) .
Downloaded from http://ps.oxfordjournals.org/ at Mount Allison University on June 21, 2015
In the present s t u d y t h e energy of the flourescent light was distributed within the visible light spectrum whereas t h e incandescent light had most of its energy (59%) o u t of t h e visible spectrum (Table 1). F u r t h e r m o r e , within the visible s p e c t u r m , fluorescent light had m o r e t h a n 2.5 times as m u c h intensity t h a n incandescent light (263 vs. 103 lux) whereas the energy c o n t e n t of flourescent light was 1.4 times greater than incandescent (81 vs. 59 /J w a t t s / cm ). It would therefore be t e m p t i n g to speculate t h a t fluorescent light was most stimulatory to sexual development d u e to increased a m o u n t s of energy within t h e visible
EYES AND PHOTOSTIMULATION
It is of interest that, with t h e exception of one s t u d y with White C r o w n e d sparrows ( Y o k o y a m a and Farner, 1 9 7 6 ) , participation of the eyes in the p h o t o s e x u a l response of birds has best been shown in domestic species (Benoit, 1 9 6 4 b ; H o m m a et al., 1 9 7 2 ) ; Oishi and Lauber, 1 9 7 3 ; Siopes and Wilson, 1 9 7 4 ) . T h e physiological i m p o r t a n c e of this difference remains to be established. REFERENCES Becker, W. A., 1959. Recent statistical procedures for experimental investigators. Inst. Agr. Sci., State College of Washington, Pullman, WA. Benoit, J., 1964a. The structural components of the hypothalmo-hypophysical pathway, with particular reference to photostimulation of the gonads in birds. Ann. New York Acad. Sci. 117:23-24. Benoit, J., 1964b. The role of the eye and of the hypothalamus in the photostimulation of gonads in the duck. Ann. New York Acad. Sci. 117: 204-214. Foss, D. C , L. B. Carew, Jr., and E. L. Arnold, 1972.
Physiological development of cockerels as influenced by selected wavelengths of environmental light. Poultry Sci. 51:1922-1927. Harrison, P. C , 1972. Extraretinal photocontrol of productive responses of leghorn hens to photoperiods of different length and spectrum. Poultry Sci. 51:2060-2064. Harrison, P. C , 1974. Spectum influence on extraretinal control of daily oviposition cycles. Poultry Sci. 53:560-564. Harrison, P. C , and W. C. Becker, 1969. Extraretinal photocontrol of oviposition of pinealectomized domestic fowl. Proc. Soc. Exp. Biol. Med. 132: 161-164. Harrison, P. C , J. D. Latshaw, J. M. Casey, and J. McGinnis, 1970. Influence of decreased length of different spectral photoperiods on testis development of domestic fowl. J. Reprod. Fert. 22; 269-275. Homma, K., W. O. Wilson, and T. D. Siopes, 1972. Eyes have a role in photoperiodic control of sexual activity of cotumix. Science 178:421 — 423. Menaker, M., and H. Keatts, 1968. Extraretinal light perception in the sparrow. II. Photoperiodic stimulation of testis growth. Proc. Nat. Acad. Sci. 60:146-151. Menaker, M., R. Roberts, J. Elliott, and H. Underwood, 1970. Extraretinal light perception in the sparrow. III. The eyes do not participate in photoperodic photoreception. Proc. Nat. Acad. Sci. 67:320-325. Oishi, T., and J. K. Lauber, 1973. Photoreception in the photosexual response of quail. II. Effects of intensity and wavelength. Amer, j . Physiol. 225:880-886. Sayler, A., and A. Wolfson, 1968. Role of eyes and superior cervical ganglia on the effects of light on the pineal and gonads of the Japanese quail. Arch. Anat. Histol. Embryol. 51:615—626. Siopes, T. D., and W. O. Wilson, 1974. Extraocular modification of photoreception in intact and pinealectomized coturnix. Poultry Sci. 53: 2035-2041. Underwood, A., and M. Menaker, 1970. Photoperiodically significant photoreception in sparrows. Is the retina involved? Science 167:298-301. Wurtman, R. J., 1967. Effects of light and visual stimuli on endocrine function. Pages 19—59 in Neuroendocrinology. Vol. 2 L. Martini, W. F. Ganong, ed. Academic Press, New York, NY. Wurtman, R. J., 1974. The effects of light on man and other mammals. Ann. Rev. Physiol. 37:467-482. Yokoyama, K., and D. S. Farner, 1976. Photoperiodic responses in bilaterally encleated White-Crowned sparrows, Zonotrichia leucopbyrs gambelii. Gen. Comp. Endocrinol 30:528-533.
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Whatever the specific cause of inhibition by incandescent light m a y be, it appears t h a t the eyes are serving as a m e d i a t o r of the response. H o m m a et al. ( 1 9 7 2 ) and Siopes and Wilson ( 1 9 7 4 ) have clearly d e m o n s t r a t e d a role for the eyes in t h e regressive phases of t h e p h o t o s e x u a l response of Cotumix. Y o k o y a m a and Farner ( 1 9 7 6 ) have r e p o r t e d t h a t t h e eyes suppress the levels of LH in White Crowned sparrows. Harrison (1974) suggested t h a t the eye may be involved in t h e p h o t o p e r i o d i c c o n t r o l of oviposition time in chickens. However, it was uncertain whether this was a passive or active involvement by the eye. Certainly, extraretinal p h o t o r e c e p t i o n is well established in birds b u t from the foregoing, t h e eye should n o t be c o m p l e t e l y discounted as a p h o t o r e c e p t o r in the p h o t o s e x u a l process. Benoit, in a classical series of experiments starting as early as 1 9 3 5 , has proposed that t h e eyes c o n t r i b u t e to b u t are not essential for the reproductive developm e n t of the duck by light (Benoit, 1964a,b). T h e results of t h e present s t u d y s u p p o r t a similar conclusion for the domestic chickens with the exception that t h e eye participated in an inhibitory manner.
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