Light has no role in spermatogenesis in the frog Rana cyanophlyctis (Schneider)

The effect of 3 months exposure to short day length (L:D, 9:15) on spermatogenesis in R. cyanophlyctis was studied. There was no difference in the qualitative and quantitative aspect of spermatogenesis between control frogs exposed to ambient photoperiod (L:D, 12.16:11.44) and frogs exposed to short day light. The present findings indicate that light has no role in spermatogenesis in the frog.     

Effect of various photoperiods on testicular weight, weekly sperm output and plasma levels of LH and testosterone over the reproductive season in male turkeys

The effects of duration and variation in photoperiod on testis weight, testicular sperm production, semen output, and hormone status over the reproductive season in male turkeys were investigated. In Experiment 1, four groups of males raised from 17 to 23 wk of age under a constant short photoperiod were subjected to a constant short (Group 1: 7L:17D; Group 2: 10.5L:13.5D), constant long (Group 3: 14L:10D) or progressively increasing photoperiod (Group 4: 7L:17D to 14L:10D) up to 60 wk of age. In Experiment 2, four groups of males first raised as in Experiment 1 up to 23 wk of age were placed under a constant short (Group 5: 10.5L:13.5D), constant long (Group 6: 14L:10D), or night-interrupted photoperiod (Group 7: 6L:2.5D:1L:14.5D, referred to as subjective 9.5L:14.5D; Group 8: 6L:3.5D:1L:13.5D), referred to as subjective 10.5L:13.5D) up to 60 wk of age. Males in Groups 2-4 had similar reproductive characteristics, whereas sexual maturity was delayed from 29 to 49 wk in males from Group 1. In Experiment 2, males in Groups 5 and 8 had similar reproductive characteristics, whereas sexual maturity was delayed in males in Group 7 in a manner similar to that observed in Group 1. In both experiments, plasma LH and testosterone concentrations were poor indicators of testis development and semen production, irrespective of age and photoperiod. We conclude that a moderately short photoperiod such as 10.5L:13.5D or subjective 10.5L:13.5D may stimulate reproductive characteristics of male turkeys in a manner comparable to constant long or increasing photoperiods. We inferred the existence of a threshold of photosensitivity in male turkeys for photoperiods longer than 9.5L:14.5D, but shorter than or equal to 10.5L:13.5D.     

The relationship between nectar supply and the rate of capture of a nectar-dependent small marsupial Tarsipes rostratus

The influence of mild temperature (20 C) combined with different photoperiods (natural day length; 16L: 8D; 8L: 16D) on the testis of Gambusia affinis holbrooki during the early (Experiment I) and late (Experiment II) phases of the testicular quiescence period was studied by histologic quantitative methods. In Experiment I (October-January), spermatogenic development was not found in either the initial and final control fishes or the experimental groups. In Experiment II (January-March), neither initial nor final controls showed spermatogenic development. The group subjected to the short photoperiod showed development of secondary spermatogonia but no spermatocytes. Complete spermatogenesis was observed in both the group exposed to the natural day length photoperiod and the group exposed to the long photoperiod. These results indicate that a mild temperature combined with a long photoperiod induces spermatogenesis in G. affinis in the late phase of quiescence.     

Reproductive effects of olfactory bulbectomy in the Syrian hamster

The effects of olfactory bulbectomy on circulating gonadotropin, prolactin and testosterone levels and on the testicular and pituitary responses to shortening of day length were studied in Syrian hamsters. Adult animals maintained on a 14L:10D cycle were sham-operated or sustained bilateral radical olfactory bulbectomies by aspiration to remove the main and accessory olfactory bulbs and the adjacent regions of the anterior olfactory nucleus. They were then maintained either on the long photoperiod or housed on a 10L:14D cycle. Testicular length was measured at weekly intervals over a 5-mo period. Sham-operated controls exhibited the normal pattern of testicular regression and eventual recrudescence on the short photoperiod. Testicular regression was significantly reduced in bulbectomized animals. Many of these animals showed no regression; others exhibited a reduced degree and/or shortened duration of regression. Serum levels of follicle-stimulating hormone (FSH) were substantially elevated in bulbectomized males maintained in long days. Their serum levels of luteinizing hormone (LH), prolactin and testosterone remained within the range for shams on long photoperiod. In short days, the bulbectomized animals showed the normal, pronounced decline in circulating prolactin levels. Serum FSH and LH levels also showed substantial declines, but the FSH levels were not reduced below the range for controls in long days, and the decline in LH levels was not as great as that for controls in short days.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of photoperiod on life history and blood‐feeding activity in Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Several studies have examined how climatic variables such as temperature and precipitation may affect life history traits in mosquitoes that are important to disease transmission. Despite its importance as a seasonal cue in nature, studies investigating the influence of photoperiod on such traits are relatively few. This study aims to investigate how photoperiod alters life history traits, survival, and blood‐feeding activity in Aedes albopictus (Skuse) and Aedes aegypti (Linnaeus). We performed three experiments that tested the effects of day length on female survival, development time, adult size, fecundity, adult life span, and propensity to blood feed in Ae. albopictus and Ae. aegypti. Each experiment had three photoperiod treatments: 1) short‐day (10L:14D), 2) control (12L:12D), and 3) long‐day (14L:10D). Aedes albopictus adult females were consistently larger in size when reared in short‐day conditions. Aedes aegypti adult females from short‐day treatments lived longer and were more likely to take a blood meal compared to other treatments. We discuss how species‐specific responses may reflect alternative strategies evolved to increase survival during unfavorable conditions. We review the potential impacts of these responses on seasonal transmission patterns, such as potentially increasing vectorial capacity of Ae. aegypti during periods of shorter day lengths.     

Long day photoperiods and temperature of 20 degrees C induce spermatogenesis in blinded and non-blinded marbled newts during the period of testicular quiescence

Adult male marbled newts (Triturus marmoratus) were collected at the end of the spermatogenesis period and exposed to different photoperiods (natural-daylength-simulated photoperiod, total darkness, 8L:16D, 12L:12D, 16L:8D, and continuous light) for 3 mo. Temperature was maintained at 20 degrees C. Two additional groups of newts were blinded and exposed to either the natural-simulated photoperiod and to 16 h of light per day respectively. Quantitative histologic studies on testicular development and germ cell volume per testis were performed. The newts captured in the field at the beginning (initial controls) or at the end of the experiments (final controls) were in the period of testicular quiescence. Newts kept in total darkness or exposed to a short photoperiod (8L:16D) showed germ cell development up to primary spermatocytes, whereas germ cell development in the newts exposed to long photoperiods (12L:12D or 16L:8D) progressed to elongated spermatids. The newts exposed either to intermediate photoperiods (natural-simulated photoperiod) or to constant light showed an intermediate degree of germ cell development (up to round spermatids). No significant differences between non-blinded and blinded animals were found. These results suggest that (1) mild temperature initiates testicular development in the period of testicular quiescence, (2) long photoperiods associated with mild temperatures produce spermatogenesis in this period, (3) complete darkness or constant light are less effective than some intermediate photoperiod, and (4) the effect of photoperiod on testicular function in newts is not related to ocular photoreception.     

The influence of light wavelength on reproductive photorefractoriness in migratory blackheaded bunting (Emberiza melanocephala).

There are two effects of long day length on reproductive responses in birds, one is the photoinduction of gonadal growth and maturation and the other is the induction of gonadal regression and photorefractoriness. Although it is likely that the same photoreceptors are involved in the photoinduction of gonadal growth and the onset and maintenance of photorefractoriness. and so the influence of wavelength should be similar, this has not been investigated. Therefore, we investigated the influence of light wavelength on reproductive photorefractoriness in the migratory male blackheaded bunting held under long photoperiods. In mid May, when photoperiod was approximately 14L:10D (14 hours light:10 hours darkness), eight groups of sexually mature birds were moved indoors on an artificial photoperiod of 14L:10D (L - 450 lux. D - 0 lux). Then after 3 weeks, for six groups, a 4-h light period in the morning (zt 0-4; zt 0 [zeitgeber time 0] refers to the beginning of lights-on period) or in the evening (zt 10-14) was substituted with green (428 nm), red (654 nm) or white light at 16 +/- 2 lux intensity. Of the remaining two groups, one was maintained on 14L: 10D and the other transferred to 10L:14D: these served as controls. At the end of 4 weeks, all birds were found to have undergone testicular regression, irrespective of LD cycle they were exposed to. When these gonadally regressed birds were subjected to 16L:8D for another 4 weeks, to test their responsiveness to the stimulatory effects of long day lengths, only those exposed to 10L:14D and 14L:10D with a 4-h green light period showed testicular regrowth. On the other hand, birds exposed to 14L:10D with a 4-h white or red light period remained fully regressed, similar to 14L:10D controls. Except for some individual difference, there was no difference in response between the groups that received a 4-h light period in the morning and that received it in the evening. These results suggest that the wavelengths of light influence induction of buntings from the photosensitive state into the photorefractory state. Whereas the short light wavelengths facilitated recovery from the photorefractoriness, the long light wavelengths were more effective in maintaining the photorefractoriness.     

Latitude of origin influences photoperiodic control of reproduction of deer mice (Peromyscus maniculatus)

Three subspecies of Peromyscus maniculatus originating from different latitudes were maintained from birth in light dark cycles that provided between 10 and 18 h of light per day. At 50 days of age, Chihuahua, Mexico mice (latitude of origin 27 degrees N) and South Dakota, U.S.A. mice (44 degrees N) kept in the 10L:14D photoperiod had reduced gonadal and seminal vesicle weights and a lower spermatogenic index than corresponding mice kept in a 14L:10D photoperiod. Some Chihuahua and South Dakota mice, apparently constituting nonphotoperiodic subpopulations, developed their gonads while kept in the short-day photoperiod. The critical day length for stimulation of sexual maturation was greater for mice from Manitoba, Canada (55 degrees N) than for mice from the lower latitudes. At 70 days of age, testes and seminal vesicle weights, and the spermatogenic index of Manitoba mice in the 14L:10D photoperiod, were lower than those of animals maintained in 16L:8D and 18L:6D photoperiods. Responsiveness to short day lengths was greater among adult South Dakota than adult Chihuahau mice and melatonin treatment significantly reduced testes weights of South Dakota but not of Chihuahua adult mice. Photoperiodic regulation of the reproductive system varies with latitude of origin. Differences in the critical day length necessary for stimulating development of functional reproductive activity and variations in the percent of photoperiodic animals within each subspecies, appear to contribute to latitudinal gradients in reproduction.     

Spermatogenesis in the turkey (Meleagris gallopavo): quantitative approach in immature and adult males subjected to various photoperiods

The objectives of this study were to identify and quantitate the germ cell populations of the testes in sexually mature male turkeys (Trial 1), determine the duration of meiosis based on BrdU labeling and stereological analyses (Trial 2), and examine the impact of various photoperiods on germinal and somatic cell populations in immature and adult males (Trial 3). In Trial 1, both testes within a male had similar stereological components (P>0.05) for all parameters analyzed. In Trial 2, the duration of Type-1 spermatocytes and round spermatids in turkeys lasted 4.5+/-0.5 and 2.0+/-0.5 days, respectively. In Trial 3, the short photoperiod (7L:17D) delayed testicular growth (in the stereological parameters analyzed). In contrast, the effect of a moderately short photoperiod (10.5L:13.5D) was comparable to the effect of a long (14L:10D) or increasing photoperiod (7L:17D to 14L:10D) on the stereological parameters examined. With the exception of the short photoperiod, all other photoperiods used in this study induced comparable early testicular maturation, with maximum testis weight at 29-35 weeks of age. As the males got older, there was a progressive, linear decline in testis weight through 60 weeks, at which time there were no significant differences among photoperiods. In conclusion, the duration of meiosis in the turkey was similar to that observed in the fowl and guinea-fowl. The existence of a threshold of photosensitivity to gonad stimulation in male turkeys is suggested to be between 7.0 and 10.5 h of light.     

Maternal transfer of photoperiodic information in Siberian hamsters. III. Melatonin injections program postnatal reproductive development expressed in constant light

In Siberian hamsters, transference of photoperiodic information from dam to fetus influences pubertal testicular development of the young when reared either in constant light (LL) or postnatal photoperiods of intermediate length (i.e. 14L:10D). The effects of short photoperiods during gestation can be mimicked by administering melatonin to pregnant females. This experiment examined whether there exists a daily pattern of sensitivity to melatonin when it is administered to pineal-intact pregnant females housed on a long photoperiod. Groups of pregnant and lactating females received melatonin at each hour of the day. The young were not treated with exogenous melatonin. At the approximate time of maturation of their endogenous pineal melatonin rhythm (Day 15), the young were placed in LL to suppress pineal melatonin secretion. Young males were killed at 28 days of age. Afternoon (1200 h-2000 h) and late night (0400 h) injections of melatonin into females caused their male young to develop as though gestation occurred on a short photoperiod. Melatonin injections at other times were ineffective. The daily pattern of effectiveness of exogenous melatonin administration to pregnant females resembles that observed in adult males of this and other hamster species and is consistent with the hypothesis that a daily rhythm in sensitivity to melatonin is involved in the transduction of photoperiodic signals.     

Reproductive photoresponsiveness in Aethomys ineptus and A. namaquensis (Rodentia: Muridae) from southern Africa

Male Tete veld rats Aethomys ineptus and Namaqua rock mice A. namaquensis were independently subjected to a long photoperiod of 16L:8D and a short photoperiod of 8L:16D for 3 months in order to assess the effect of photoperiod on testicular function. Testicular parameters examined included testicular mass relative to body mass, testicular volume, seminiferous tubule diameters and changes in circulating plasma testosterone concentration. On a long day (LD) length, both species exhibited significantly higher testicular mass relative to body mass and testicular volume, and larger seminiferous tubule diameters. Circulating plasma testosterone concentrations in A. ineptus were not significantly different between the two photoperiodic treatments, but A. namaquensis showed significantly higher testosterone concentration in males on a LD length than on a short day (SD) length. This suggests that both A. ineptus and A. namaquensis are photoperiodically responsive to LDs.     

Hormonal regulation of the annual pelage color cycle in the Djungarian hamster, Phodopus sungorus. I. Role of the gonads and pituitary

The Djungarian hamster exhibits an agouti pelage in the summer and a predominantly white pelage in the winter. This pelage color cycle is known to be regulated by the length of the daily photoperiod probably acting through the pineal gland, as is the seasonal cycle of reproductive function with which it is closely correlated ( Figala et al., '73; Hoffmann, ' 78b ). The possibility of a causal relationship between the decline in gonadal hormone secretion and the coat color change occurring in short photoperiod was examined. Gonadectomized and intact male and female hamsters were exposed to either long (16L:8D) or short ( 10L : 14D ) photoperiod for several months. Gonadectomy neither induced the change to the winter pelage color in long photoperiod-housed animals, nor prevented either the change to the winter pelage or the spontaneous return to summer pelage color in short photoperiod-housed animals. Chronic implants of testosterone in castrated males delayed and attenuated the short photoperiod-induced coat color change. Administration of ovine prolactin (100 micrograms/day) stimulated pigmentation in hamsters with the winter pelage, whereas administration of a alpha MSH (30 micrograms/day) was without effect. These results suggest that changes in pelage color may be regulated largely by changes in pituitary prolactin secretion and modified to some extent by changes in gonadal steroid hormone secretion.     

Photoperiod and temperature affect reproductive and nonreproductive functions in male prairie voles (Microtus ochrogaster)

Adult male prairie voles (Microtus ochrogaster) were housed for 10 wk and exposed to long (16L:8D) or short (8L:16D) photoperiods at 21 degrees or 5 degrees C. Maintenance in short day lengths reduced testicular, epididymal, and seminal vesicle mass and also significantly depressed spermatogenic activity. Cold ambient temperature further suppressed gonadal size in voles exposed to short days. Several pelage characteristics were affected by photoperiod, but not by temperature. Increased fur density, fur depth, and length of guard hair and underhair were observed in voles exposed to short days. Intrascapular brown fat and gonadal fat pad mass as well as body mass were significantly less in voles housed in cold temperatures than in voles exposed to warm ambient temperatures; photoperiod did not affect these parameters. Approximately 30% of the male voles exposed to short days maintained their reproductive systems, yet they clearly processed photoperiodic information; all short-day males, regardless of reproductive condition, had comparable winter pelage development. Our results suggest that in prairie voles, photoperiod may be a predictive cue for reproductive function in nature; however, it appears that pelage development is a more obligatory response to photoperiod than is reproduction.     

Influence of photoperiod, nutrition and water availability on reproduction of male California voles (Microtus californicus)

Male California voles were maintained in long (14L:10D) or short photoperiods (10L:14D) for 10 weeks and fed a standard diet of rabbit chow and water ad libitum. One additional group in each photoperiod received the standard diet plus supplements of spinach 3 times weekly. A fifth group was housed in 14L:10D and fed the standard diet, but for 10 weeks water availability was restricted to several hours each morning. Testes and seminal vesicles were heaviest in long-day voles fed spinach supplements and lightest in short-day voles fed only the standard diet; the latter animals manifested reduced testicular spermatogenesis. Testicular weights were also depressed in voles with restricted access to water. It is suggested that photoperiods that simulate those of winter induce regression of the reproductive organs of male California voles but the availability of green vegetation counteracts the inhibitory effects of short daylengths.     

光周期对布氏田鼠幼仔生长发育的影响

通过比较法对实验室内布氏田鼠 (Microtusbrandti)幼仔生长发育与光周期关系的研究表明 ,尽管出生和断乳时的窝仔数及断乳时窝仔存活率不受光周期的影响 (t test,P >0 0 5 ) ,每种光周期条件下出生和断乳时雌雄比例差异不显著 (Chi square检验 ,P >0 0 5 ) ,不同光周期间雄性比例无明显差异 (百分数的检验 ,P >0 0 5 ) ,但是 ,随着幼仔的生长 ,出生并饲养在长光照周期 (LD ,14L∶10D)下的个体体重、体长和肥满度显著大于短光照周期 (SD ,10L∶14D)下的幼体 ,尤在出生 9或 14天以后的各阶段 (t test,P <0 0 5 )。在 6 0日龄时 ,LD雄鼠的睾丸、附睾及储精囊成熟指数显著高于SD鼠 (t test,睾丸 ,t =3 30 9,df =14,P <0 0 1;附睾 ,t=3 6 2 2 ,df =14,P <0 0 1;储精囊 ,t=3 379,df =14,P <0 0 1)。但LD组的皮毛厚度和绒毛长度显著低于SD组 (t test,皮毛厚度t=- 5 185 ,df =14,P <0 0 1;绒毛长度t=- 2 415 ,df =14,P <0 0 5 )。作者认为体重、肥满度和性腺成熟指数 (GSI)高的LD鼠较SD鼠更适应于繁殖期的繁殖生存 ;而生长发育缓慢 ,皮毛厚度、绒毛长度高的SD鼠更能适应越冬生存。在自然环境中 ,光周期可能被布氏田鼠作为季节环境变化的信号 ,使其在形态和生殖方面提前作好准备 ,采取不同的策略以适     

Pupal diapause of Helicoverpa armigera (Lepidoptera: Noctuidae): sensitive stage for thermal induction in the Okayama (western Japan) population

Helicoverpa armigera (Hübner) exhibits a facultative pupal diapause, which depends on temperature and photoperiod. Pupal diapause is induced at 20 degrees C by short photoperiods and inhibited by long photoperiods during the larval stage. However, in some pupae (35% of males and 57% of females) of a non-selected field population from Okayama Prefecture (34.6 degrees N), diapause is not induced by short photoperiods. In the present experiment, the importance of temperature for diapause induction was studied in the non-diapausing strain, which was selected from such individuals reared at 20 degrees C under a short photoperiod of 10L:14D. Furthermore, the sensitive stage for thermal determination of pupal diapause was determined by transferring larvae of various instars and pupae between 20 degrees C and 15 degrees C. Diapause was induced by 15 degrees C without respect to photoperiod. When larvae or pupae reared from eggs at 20 degrees C under a short or a long photoperiod were transferred to 15 degrees C in the periods of the middle fifth instar to the first three days after pupation, the diapause induction rate was significantly reduced in both males and females, especially in females. In contrast, when larvae or pupae reared at 15 degrees C were transferred to 20 degrees C in the same periods, diapause was induced in males, but not in females. However, the diapause induction rate of pupae transferred to 20 degrees C on the fourth day after pupation was significantly increased in females. The results show that temperature is the major diapause cue in the photoperiod-insensitive strain and the periods of middle fifth larval instar to early pupal stage are the thermal sensitive stages for pupal diapause induction with some different responses to temperatures between males and females in H. armigera.     

Testicular prolactin receptors and serum growth hormone in golden hamsters: effects of photoperiod and time of day

Investigations were conducted to determine effects of exposure to short photoperiod--with its accompanying reductions in serum prolactin (Prl) concentrations--for various durations on testicular Prl receptors. An additional study investigated the possibility of nyctohemeral fluctuations in testicular Prl receptors and serum growth hormone (GH) concentrations and their alteration by photoperiod. After 10 and 28 days of exposure to a short photoperiod consisting of 5 h of light and 19 h darkness (5L:19D) (and prior to changes in testicular weight), there were progressive and significant reductions in the concentration of testicular Prl receptors (fmol/mg protein) when compared with long-photoperiod controls (14L:10D). After 12 weeks of 5L:19D, when testicular weights were dramatically decreased, Prl receptor concentration was reduced to 39% of long-photoperiod controls in one study, without alteration of affinity of Prl receptors for their labeled ligand. When measured at 6-h intervals in hamsters on 14L:10D, and on 5L:19D for 12 weeks, there were no significant changes in concentration or total content (fmol/testes) of testicular Prl receptors throughout the day. Although serum GH concentrations fluctuated markedly in hamsters on both photoperiods, no definitive nyctohemeral patterns were detected. These data provide indirect evidence for the ability of Prl to regulate its own testicular receptors, and demonstrate that diurnal fluctuations in testicular sensitivity to injected Prl are not a consequence of changes in Prl receptors. The data also suggest the absence of effects of photoperiod on serum GH concentrations in male golden hamsters.     

Effects of photoperiod and social variables on reproduction and growth in the male musk shrew (Suncus murinus)

In Exp. 1, the time course for the photoperiodic response in juvenile male musk shrews was examined by exposing animals to short (10L:14D) or long (14L:10D or 18L:6D) daylengths for 10, 20, 40 or 56 days. When compared with the response of animals maintained in long days, those exposed to short days showed an inhibition of reproductive maturation by 40 days of treatment. In Exp. 2, the combined effects of photoperiod and social cues were investigated in juvenile males that were either housed in short days (with or without a female) or in long days (with or without a female) for 40 days. The short photoperiod was generally inhibitory to sexual maturation, while the presence of an adult female was generally stimulatory, i.e. animals living with a female in long days had the greatest level of sexual maturity, while those living alone in short days had the lowest level of maturity. Animals that received opposing signals, i.e. short days in the presence of a female, had an intermediate response which was equivalent to the response seen in males living alone in long days. These results suggest that the presence of a female can partly reverse inhibitory effects of short days. In Exp. 3, the effects of photoperiod and social cues on the reproductive physiology of the adult male (same design as in Exp. 2) were investigated. The results show that the adult male musk shrew is responsive to both photoperiodic and social cues, in a manner similar to that of juvenile animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

光周期和温度对草地螟滞育诱导的影响

草地螟Loxostege sticticalis以老熟幼虫滞育越冬。在室内通过人工诱导的方法对其滞育的光周期和温度诱导条件进行了研究。结果表明:草地螟是一种典型的长日照发育型种类。光周期、温度及其交互作用均对草地螟滞育诱导具有重要影响, 其中光周期起主导作用, 温度伴随着光周期起作用。对幼虫滞育诱导最有效的光周期是L12∶D12; 随着温度的升高, 临界光周期呈缩短趋势（18℃除外）。18, 22, 26和30℃条件下幼虫滞育的临界日长依次为13.97, 14.48, 13.92 和12.88 h。光敏感实验揭示:21℃时草地螟对光照反应最敏感时期为幼虫孵化后的11～17 d（约5龄幼虫）, 但孵化后7～11 d（约4龄幼虫）的短光照积累对提高滞育率也有重要作用, 可以将滞育率从40.0%提高到90.0%。     

The effects of photoperiod on androgen-induced reproductive behavior in male ring doves, Streptopelia risoria

The effect of photoperiod on reproductive behavior in male ring doves (Streptopelia risoria) was studied in androgen-injected castrates maintained under long (16L:8D) or short (86:16D) photoperiods. Behavioral recordings were made over a 2-week period during which each male was paired with a female for 6.5 hr/day. There was some indication that males held on long days display higher levels of courtship activity during the initial period following pairing, but the evidence was not conclusive. Day length had no effect upon copulatory behavior. Long-day males exhibited consistently higher levels of nest building than short-day males, indicating that photoperiod affects building through some mechanism other than changes in endogenous androgen levels.