Long-day Photoperiod Research Articles

Dopamine and serotonin in the larval CNS of a drosophilid fly, Chymomyza costata: are they involved in the regulation of diapause?

Developmental profiles of dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) in the larval CNS of Chymomyza costata were measured by HPLC using electrochemical detection. Larvae of two strains, wild-type (W) and nondiapause mutant (M), were maintained either under long-day (LD, inducing pupariation) or short-day (SD, inducing diapause in W-strain) photoperiods. The levels of DA ranged from 10 fmol/CNS (early 3rd instar larvae) to 60 fmol/CNS (150-day-old diapausing larvae); the range for 5-HT was from 10 fmol/CNS to 75 fmol/CNS in the same larvae. During the 3rd larval instar, which is the decisive stage for photoperiodic induction of diapause, no differences were found in DA developmental profiles between different strains or conditions. Some differences were found in 5-HT developmental profiles, but only after the end of sensitive stage, and were therefore regarded as insignificant for regulation of developmental mode. Similarly, no clear correlations between the developmental profiles of DA and 5-HT and the course of developmental changes during the maintenance and termination of a few-month-long larval diapause were observed. Furthermore, the DA and 5-HT levels in the CNS were pharmacologically manipulated by feeding the larvae with either precursors or enzyme inhibitors of DA and 5-HT biosynthesis. Although retardations of growth and development were observed, the treated larvae retained full capacity for the photoperiodic response, irrespective of the level of DA or 5-HT in their CNS. Larvae with their 5-HT depleted to trace levels survived and were capable of diapause induction, maintenance, and termination. Depletion of DA to trace levels resulted in 100% mortality. Collectively, the present study indicates that 5-HT in the CNS is dispensable for the photoperiodic response in C. costata. More information is needed to elucidate the potential role of DA.

Changes in Patterns of Corticosterone Secretion Concurrent with Migratory Fattening in a Neotropical Migratory Bird

Several studies on free-living birds have shown a change in corticosterone secretion (elevated baseline levels and a reduced corticosterone response to stress) during migration. It was not known, however, if this change was concurrent with the development of migratory condition or if it was an independent response to unknown environmental stressors experienced by the birds prior to capture. In this study, a Neotropical annual migrant, the yellow-rumped warbler (Dendroica coronata), held under controlled laboratory conditions, was used to test the Migration Modulation Hypothesis (MMH): during the migratory period migrants exhibit (1) elevated baseline corticosterone to facilitate migratory fattening and (2) a reduced corticosterone stress response, a means by which skeletal muscle needed for migration can be protected against catabolism by high levels of corticosterone. Fifteen hatching-year warblers were maintained on insect larvae and water ad libitum for 43 weeks, experiencing two transitions from a short- to long-day photoperiod to bring them into spring migratory condition. Corticosterone profiles comprising three blood samples from each individual (baseline at the time of initial disturbance and 30 and 60 min later), body mass, fat reserves, molt, and state of cloacal protuberance (males only) were measured at key intervals throughout the study. Over the entire study, mean baseline corticosterone levels were positively correlated with mean body mass, which increased predictably in response to long days. Individual baseline corticosterone was not correlated with individual body mass at any time. During periods when the birds were lean and held on short days, the corticosterone stress profiles were characterized by low initial hormone concentration followed by a significant increase in corticosterone with handling time. In response to long days, the warblers showed a significant increase in body mass and fat reserves concurrent with corticosterone stress profiles characterized by significantly elevated baseline levels and no further increase in corticosterone with handling time. These results support both components of the MMH illustrating changes in corticosterone secretion concurrent with migratory fattening but the exact nature of this change is unknown.

The Arabidopsis blue light receptor cryptochrome 2 is a nuclear protein regulated by a blue light-dependent post-transcriptional mechanism.

Cryptochrome 2 is a flavin-type blue light receptor mediating floral induction in response to photoperiod and a blue light-induced hypocotyl growth inhibition. cry2 is required for the elevated expression of the flowering-time gene CO in response to long-day photoperiods, but the molecular mechanism underlying the function of cry2 is not clear. The carboxyl domain of cry2 bears a basic bipartite nuclear localization signal, and the cry2 protein was co-fractionated with the nucleus. Analysis of transgenic plants expressing a fusion protein of CRY2 and the reporter enzyme GUS (GUS-CRY2) indicated that the GUS-CRY2 fusion protein accumulated in the nucleus of transgenic plants grown in dark or light. The C-terminal domain of cry2 that contains the basic bipartite nuclear localization signal was sufficient to confer nuclear localization of the fusion protein. Phenotypic analysis of transgenic plants expressing the fusion protein GUS-CRY2 demonstrated that GUS-CRY2 acts as a functional photoreceptor in vivo, mediating the blue light-induced inhibition of hypocotyl elongation. These results strongly suggest that cry2 is a nuclear protein. Although no obvious light regulation was found for the nuclear compartmentation of GUS-CRY2 fusion protein, the abundance of GUS-CRY2 was regulated by blue light in a way similar to that of cry2.

628 Influence of Cooling, Long-day Lighting Regime, and Propagule Type on Flowering of Phlox paniculataL. Cultivars

Rooted terminal cuttings and dormant 1-year-old transplants of Phlox paniculata L. `Ice Cap' and `Red Eyes' were cooled for 0, 4, 8, 12 or 16 weeks and forced under long-day photoperiod provided by incandescent lights as either a night-interruption (2200–0200 hr) or extended-day (1700–2200 hr). The influence of cooling duration, long-day lighting regime, and propagule type on forcing days to flower, flowering stem counts, and flowering stem length was evaluated in a 3 × 2 × 5 factorial experiment. Cooling accelerated flowering and increased stem yield and length. Days to flower for both cultivars decreased and flowering stems and length increased linearly as cooling increased from 0 to 16 weeks, regardless of lighting or propagule type, but cooling for 8 weeks or more was necessary to produce marketable cut flower stems. Extended-day lighting produced longer stems than night interruption, and stem counts were higher among plants grown from transplants, regardless of cooling duration, lighting regime, or cultivar. Flowering stems from rooted cuttings were generally longer than those from transplants. Cut flower stems of `Ice Cap' were longer than those of `Red Eyes', but days to flower and yields for the two cultivars were similar.

Juvenile hormone biosynthesis in diapausing and nondiapausing Culex pipiens (Diptera: Culicidae).

The synthesis of juvenile hormone in vitro by diapausing and nondiapausing Culex pipiens L. was measured by radiochemical assay. Paired corpora allata from diapausing females synthesized < 18 fmols of juvenile hormone per hour during the first 3 wk after emergence. In contrast, juvenile hormone synthesis in nondiapausing females increased rapidly reaching a peak of 87.3 +/- 21 (mean +/- SE) fmol/h 3 d after emergence. By 3 wk, juvenile hormone synthesis had decreased in both groups of females, but corpora allata from nondiapausing mosquitoes still were 3 times more active than those from diapausing mosquitoes. By 16 wk after diapause induction, females maintained at 8:16 (L:D) h and 15 degrees C produced levels of juvenile hormone similar to 3-wk-old nondiapausing females. When females were held in diapause conditions for up to 22 wk, follicles gradually grew longer and by 15 wk were significantly longer than in the previous 14 wk. Blood feeding also increased in older females, indicating that over time, juvenile hormone synthesis gradually stimulated blood-feeding behavior. When 21-d-old diapausing mosquitoes were moved to a long-day photoperiod of 16:8 (L:D) h and 26 degrees C, juvenile hormone synthesis increased rapidly and peaked 5 d later while the ovarian follicles grew to the resting stage. Allatectomy of young diapausing females prevented follicle growth and blood feeding when diapause was terminated prematurely, demonstrating that the physiological events associated with diapause termination were associated with juvenile hormone biosynthesis.

Larval development, emergence and seasonal regulation in Asiagomphus pryeri (Selys) (Odonata : Gomphidae)

Larval development and seasonal regulation in a spring-emerging gomphid dragonfly, Asiagomphus pryeri (Selys), was investigated mainly by repeated sampling in the field and also by laboratory experiments. Eggs exhibited direct development. Larval duration was usually 3 or 4 years. Larvae in the penultimate instar (i.e. F-1) that entered the final instar (F-0) synchronously in their third autumn emerged in the following spring but F-1 of the same age-cohort that failed to enter F-0 in the autumn did not emerge in the following spring (i.e. cohort splitting); they had a smaller head width, underwent a supernumerary ecdysis and entered F-0 in the following autumn together with a cohort one year younger. Reduction of temporal variation in emergence, which lasted about 3 weeks, from late May to mid June, was achieved by synchronized entry to F-0 in the previous autumn. No additional synchronisation was detected in the overwintering F-0 population. Long-day photoperiod (LD 15:9; corresponding to the summer solstice) induced in F-1 intense diapause which was terminated by intermediate photoperiod (LD 13:11; the equinox). In nature, such photoperiodic responses apparently mediate the synchronous entry to F-0 in autumn. Discussion on the mechanisms of seasonal regulation is made.

「イチョウイモ」の花穂と新芋の発育に及ぼす日長と温度の影響

The effects of photoperiod, air temperature, and root zone temperature (RZT) on the development of spikes and new tubers in Chinese yam (Dioscorea opposita Thunb. cv. Ichoimo) were investigated. The development of the main shoot and spikes was promoted by both 16-hr and 24-hr photoperiods, 24/19°C and 30/25°C (day/night), and an RZT of 25°C. Shoot and spikes development was severely inhibited by an 8-hr photoperiod, 17/12°C, and an RZT of 10°C. These data indicate that the development of main shoot and spikes is promoted by the long-day photoperiods, 24/19°C and 30/25°C, and the 25°C RZT. Under these environmental conditions, spikes emerged relatively early. Development of new tubers was significantly promoted by an 8-hr photoperiod, 24/19°C, and the 25°C RZT. Moderate development occured at 30/25°C, and the 17°C RZT. In contrast, new tubers were severely inhibited by both 16-hr and 24-hr photoperiods, and 10°C RZT.

Seasonal variation in long-day stimulation of prolactin secretion in ewes.

Whereas ewes initiate reproductive activity in response to a photoperiod signal initiated after the winter solstice of 35 long days (35 LD) followed by short days, the reproductive axis fails to respond to this signal between the autumn equinox and the winter solstice. The aim of experiment 1 was to determine whether the prolactin axis, like the reproductive axis, is unresponsive to a 35 LD photoperiod signal followed by continuous exposure to short days between the autumn equinox and the winter solstice. Whereas the 35 LD signal from September 21 (</= 6 h increase in day length) failed to influence prolactin secretion, all other long-day treatments (> 6 h increase in day length) initiated a rise in prolactin in at least 75% of ewes in each group (p < 0.05). The aim of experiment 2 was to determine whether ewes failed to secrete prolactin during a 35 LD photoperiod from September 21 because they did not recognize a 6-h increase in day length at any time of year as a stimulatory photoperiod signal or because hypothalamic/pituitary regulation of prolactin synthesis or secretion is compromised in September. The results demonstrated that while hypothalamic regulation of prolactin secretion and pituitary stores of prolactin were normal at all times of year examined, the ability of ewes to secrete prolactin in response to a long-day photoperiod signal appears to be dependent on photoperiodic history rather than the time of year of the photoperiodic challenge.

OVARIAN DEVELOPMENT IN OVERWINTERING PEAR PSYLLA, CACOPSYLLA PYRICOLA (HOMOPTERA: PSYLLIDAE): SEASONALITY AND EFFECTS OF PHOTOPERIOD

AbstractEffects of photoperiod, time of year, temperature, and an insect growth regulator (fenoxycarb) on ovarian development rate in overwintering pear psylla, Cacopsylla pyricola (Foerster), were determined. Winterform pear psylla were collected from the field at intervals between October and February, and reared at 20 °C and one of three treatments: short-day photoperiod, long-day photoperiod, or short-day photoperiod + fenoxycarb. Insects were then dissected at intervals to score ovarian development. Baseline scores (i.e., ovarian development in the field on date of collection) increased very slowly between October and February. By mid-February, only about 20% of insects in the field were categorized as having postdiapause status based upon ovarian development. In the laboratory, time required for insects to reach postdiapause status decreased between the October and February collection dates. Number of days necessary for 50% of the long-day insects to reach postdiapause status was approximately 2 weeks in October, 6 days in December, and &lt; 2 days in February. Short-day insects also required fewer than 2 days in February, but required &gt; 2 weeks in the October and December samples. Our results suggested that insects collected in January and February had completed diapause but that ovarian development was subsequently prevented in the field by low temperatures. Fenoxycarb caused rapid ovarian development even in October-collected insects; rate of development was only slightly more rapid in the February-treated psylla.

Effects of photoperiod and age on secretory patterns of luteinizing hormone and testosterone and semen production in male domestic turkeys.

The objective of this study was to determine effects of photoperiod and age on the circulating concentrations of LH, testosterone (T), thyroxine (T4), and semen production in male turkeys. Male turkeys from 10 or 12 wk of age were maintained under either a long-day (LD) photoperiod of 16L:8D up to 35 wk (LL), or a short-day (SD) photoperiod of 6L:18D to 29 wk and then an LD photoperiod of 16L:8D up to 35 wk of age (SL). Plasma concentrations of both LH and T increased by 17 or 18 wk of age under both photoperiods, but higher levels were attained in the LL group prior to 29 wk of age. Both LH and T levels increased significantly within days in the SL group after the group was switched to LD at 29 wk of age. Higher levels of T4 were present in the LL group prior to sexual maturation. No differences were observed in T4 concentration between lighting treatments after sexual maturation. The LL group first produced semen at 20-22 wk of age, which was about 1 wk earlier than first semen production in the SL group. A significantly larger volume of semen was produced in the LL group at most ages. No further increase in semen production was observed in the first 6 wk after the SL group was switched to the LD photoperiod at 29 wk of age. Pulsatile patterns of LH and T were characterized by serial blood sampling at 13, 23, and 35 wk of age under both the LL and SL photoperiods. The baseline levels of both LH and T in male turkeys were influenced by age and photoperiod. However, pulse characteristics (numbers, duration, and amplitude) of LH did not change with age or lighting treatment, while pulse characteristics of T did change with age. We conclude that exposing male turkeys to an LD photoperiod from 10 or 12 wk of age advanced the age of sexual maturation and induced earlier increased concentrations of LH and T.

Urinary 6-sulfatoxymelatonin profiles in male Djungarian hamsters (Phodopus sungorus) responding and not responding to short-day photoperiods: possible role of elevated daytime levels.

The lack of endocrine and physiological responses of some Djungarian hamsters (Phodopus sungorus) to the transition from long to short photoperiods (L:D 16:8 --> L:D 8:16) has been known for a long time but is not yet understood. We investigated the role of melatonin synthesis in this context because melatonin, as part of the circadian system, may play a role in non-responsiveness. In ten responding and ten non-responding male hamsters, the urinary 24 hr 6-sulfatoxymelatonin (aMT6s) profiles under L:D 8:16 and L:D 16:8 were measured. Both short day responding and non-responding hamsters showed diurnal aMT6s excretion rhythms. Whereas responders reacted to the transition L:D 16:8 --> L:D 8:16 with a marked elevation of aMT6s excretion, in non-responders no adjustment of the melatonin rhythm to the change of the photoperiod was seen. Furthermore, under L:D 16:8 the daytime levels of aMT6s were significantly (P<0.001) lower in responders compared to non-responders whereas under L:D 8:16 these levels were higher (P<0.01). It is speculated that high daytime levels of aMT6s under long-day photoperiods in non-responders result in down-regulation of melatonin receptors of the nucleus suprachiasmaticus, the pacemaker for the pineal gland, leading to a lack of response to the transition to short-day photoperiods.

Does Exercise Affect Female Hamster Gonadotropins by Reducing Estradiol Negative Feedback?

Exercise stimulates reproductive function in hamsters exposed to short-day photoperiod (SDP) in contrast to its inhibitory effects in women and rats. SDP inhibits hamster reproduction in part by increasing the sensitivity of the hypothalamo–pituitary–gonadal axis (HPGA) to the negative feedback of gonadal steroids. To determine whether EX facilitates reproduction in female hamsters by affecting this mechanism, we examined the influence of estradiol (E 2) on basal LH and FSH concentrations in exercising and sedentary hamsters maintained on long-day photoperiod (LD 14:10, LDP) or SDP (LD 8:16). In the LDP, serum LH and FSH were unaffected or reduced by exercise in ovariectomized (OVX) nonhormone-replaced hamsters, and LH was increased after tonic E 2 replacement compared to sedentary controls. In the SDP, serum LH and FSH were significantly higher in OVX exercising than in sedentary hamsters, whether the exercisers were injected with a high dose of E 2 or not. Thus, the effects of exercise on basal gonadotropin secretion in female hamsters appear to depend on the level of estradiol negative feedback (ENF). When this feedback is low (LDP OVX condition), exercise is either ineffective or inhibitory. When the ENF is increased by exposure to SDP and/or by treatment with E 2, exercise has a stimulatory effect on basal gonadotropin secretion. Exercise may stimulate hamster gonadotropin secretion by reducing the ENF either by lowering the sensitivity of the HPGA to steroid negative feedback or by other means.

Effects of gonadotropin-releasing hormone pulse frequency modulation on the reproductive axis of photoinhibited male Siberian hamsters.

In Siberian hamsters, photostimulation evokes differential release of the gonadotropins, with FSH rising rapidly and LH levels rising much later. We have tested the hypothesis that differential release of gonadotropins in this species can be mediated by changes in the frequency of pulsatile GnRH stimulation. Photoinhibited Siberian hamsters received GnRH pulses at frequencies of 1 pulse every 45 (fast), 90 (medium), or 180 min (slow). Animals were killed at 0, 3, 5, 10, 20, and 30 days after treatment. There was a clear GnRH pulse frequency effect on LH release, with fast pulses > medium pulses > slow pulses > short-day (SD) controls. In addition, 10 days of fast-frequency GnRH pulses produced LH levels significantly greater than LH levels in animals exposed to 10 days of medium or slow GnRH pulse frequencies. Pulsatile GnRH produced the following serum FSH relationships: medium pulses > fast pulses > SD. The FSH response to slow GnRH frequency fell between the two faster frequencies. The effect of GnRH pulse frequency on paired testes weight was as follows: fast pulses = medium pulses > slow pulses > SD controls. The differing GnRH pulse frequencies produced the following testosterone relationships; fast pulses > medium pulses = slow pulses = SD controls. These results agree with studies showing that slower GnRH pulse frequencies facilitate FSH release, while faster GnRH pulse frequencies favor LH release. Our observations are also consistent with the idea that the singular release of FSH after transfer of hamsters to a long-day photoperiod is mediated by alterations in the frequency of endogenous pulsatile GnRH release.

Influence of cooling and photoperiod on growth and flowering of Aquilegia L. cultivars

Four cultivars of Aquilegia flabalata and four cultivars of Aquilegia× hybrida were cooled 0, 4, 8, or 12 weeks and forced in either long-day (LD) or short-day (SD) photoperiods. Cultivars of both species cooled eight or 12 weeks flowered in fewer forcing days than non-cooled plants, however, days to flower were similar for LD and SD photoperiods regardless of cooling level. Flower stem length increased with increasing cooling duration, and flowering stems were longer in LD photoperiod than in SD. Plants cooled eight or 12 weeks were either larger than or similar in size at flowering to non-cooled plants or those cooled four weeks. In this study, eight weeks cooling and LD photoperiod enhanced forcing phase growth and flowering of the columbine cultivars most efficiently.

Photoreception in entrainment of rhythms and photoperiodic regulation of diapause in a hemipteran, Graphosoma lineatum.

The role of compound eyes in photoperiodic regulation of diapause and entrainment of circadian rhythms was studied in a hemipteran, Graphosoma lineatum. Bilateral removal of compound eyes resulted in the loss of locomotor rhythmicity under both 24-h light cycle and constant darkness. The arrhythmicity was associated with the loss of photoperiodic regulation of diapause. Females with removed compound eyes had similar incidence of oviposition under diapause preventing long-day photoperiod (light:dark [LD] 18:6) and diapause inducing short-day photoperiod (LD 12:12). By contrast, both locomotor rhythmicity and photoperiodic regulation of diapause were maintained after unilateral removal of compound eyes. The results suggest that the compound eye-optic lobe axis is involved in the transmission of light signals for both entrainment of rhythms in locomotor activity and photoperiodism. The compound eyes probably act as photoreceptors in both transmission chains. Sites of the clocks for the two phenomena are discussed.

Diapause Termination in Sesamia nonagrioides (Lepidoptera: Noctuidae) Under Laboratory and Field Conditions

The influence of photoperiod and temperature on the termination of diapause of Sesamia nonagrioides (Levebvre) was evaluated under laboratory and field conditions. Long-day photoperiod enhanced termination of diapause. Larvae held under a short-day photoperiod (10:14 [L:D] h) for various times and then transferred to a long-day photoperiod (16:8 [L:D] h) proceeded to pupate in a14 d, indicating that regardless of the state of diapause intensity, diapause completion and postdiapause development lasted similar lengths of time. Larval diapause termination was not hastened when diapausing larvae kept at a photoperiod of 10:14 (L:D) h and 25°C were exposed for short periods at 30, 35, and 40°C, whereas it was shortened when diapausing larvae were transferred from 25 to 30°C and kept continuously at this temperature. At higher temperatures (35 and 40°C), all transferred larvae died. It was also shown that exposure of diapausing larvae to low temperature (5°C) simply accelerated diapause development but termination of diapause did not require a period of chilling. Moreover, after low temperature treatment, diapausing larvae showed a faster diapause development when transferred to a long-day photoperiod than those kept in a short-day photoperiod. In the latter case, the longer the exposure the faster the termination occurred. Diapause termination of field-collected larvae was practically spontaneous. After transfer to laboratory conditions, 25°C and a photoperiod of 16:8 (L:D) h, they quickly proceeded to pupate. Field-diapausing larvae terminated diapause in January but exhibited a postdiapause development; the 1st record of pupation was observed in the field at the end of March.

Frost hardening and photosynthetic performance of Scots pine ( Pinus sylvestris L.) needles. I. Seasonal changes in the photosynthetic apparatus and its function

Photosynthetic CO2 uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO2 with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state.

Seasonal plasticity of the song control system in wild Nuttall's white-crowned sparrows.

Seasonal plasticity in the morphology of telencephalic nuclei that control song behavior has been reported for diverse species of songbirds. The only published report of a lack of seasonal changes in the song nuclei of a seasonally breeding bird is that of Baker et al. in the Nuttall's subspecies of white-crowned sparrow (Zonotrichia leucophrys nuttalli). In this study, they brought wild birds into the laboratory and exposed them to either "summer" or "winter" photoperiods. Previous studies have shown that exposing wild-caught white-crowned sparrows to long-day photoperiods in the laboratory may not induce circulating concentrations of testosterone (T) as high as those seen in wild breeding birds. Changes in circulating T are primarily responsible for the seasonal morphological changes in the song nuclei. To determine whether there is seasonal plasticity of the song system in this subspecies, we measured circulating T, morphological attributes of the song nuclei, and song behavior in wild Nuttall's white-crowned sparrows during the spring and fall. Testis size and circulating T concentrations were greater in spring than fall birds. The absolute volumes of the song nuclei HVc, RA, and Area X, and their volumes relative to those of either the total telencephalon or three thalamic nonsong nuclei, were significantly greater in the spring than fall sparrows. Song behavior also changed seasonally; fall birds sang shorter songs than did spring birds. These results show that there is seasonal plasticity of the song system in wild Nuttall's white-crowned sparrows. Seasonal plasticity can now be regarded as a common feature of the seasonally breeding songbirds studied thus far.

Effects of Environmental Factors on Diapause Development and Postdiapause Oviposition in a Phytophagous Insect, Dybowskyia reticulata

Abstract Environmental factors that regulate the induction, maintenance and termination of adult diapause and postdiapause oviposition were examined in a phytophagous insect, Dybowskyia reticulata (Heteroptera: Pentatomidae). When insects were reared from eggs at 25°C in the laboratory, all adults under a short-day photoperiod of 12:12 (L:D) hr and most adults under a long-day photoperiod of 16:8 (L:D) hr entered diapause. Overwintering adults started oviposition after being transferred to the long-day or short-day photoperiod at 25°C in March. Under the short-day photoperiod, however, they entered diapause again after a short oviposition period. Transferral to a long-day photoperiod after a long exposure to a short-day photoperiod synchronously terminated diapause. After exposure to a low temperature during diapause, the adults began to lay eggs under both long-day and short-day photoperiods. Low temperature in winter probably plays a dominant role in the termination of diapause in nature. In addition, t...

The effect of temperature and photoperiod on primary floral induction in three lines of alpine bluegrass

The effects of temperature and photoperiod on primary floral induction in three lines of alpine bluegrass (Poa alpina L.) were studied in controlled environments. These lines were developed at the Alberta Environmental Centre from single plant accessions collected from the Alberta Rocky Mountains. Plants representing all three lines were subjected to temperatures of 3, 9, and 12 °C under dark (0 h), short-day (8 h), and long-day (18 h) photoperiods for durations of 6, 10, and 14 wk. Plants were subsequently transferred to conditions of 22 °C/15 °C, 18 h photoperiod and heading response was recorded. Primary floral induction was found to be favoured by low temperatures and/or short days with marked inhibition at 12 °C. Complete dark conditions were not inductive. Six weeks of primary induction was suboptimal with only 15% of plants flowering. However, 100% of plants flowered after 10 wk of primary induction at 3 °C under both long-day and short-day conditions. Differences among lines were significant for number of heading plants, number of heads per plant, time to heading, and critical induction duration. Primary induction in line 907 occurred at longer photoperiods, warmer temperatures, and in shorter durations than the other lines indicating a lesser induction requirement. Possible implications are discussed in the use of alpine bluegrass populations for revegetating disturbed mountain sites. Key words: Floral induction, temperature, photoperiod, Poa alpina, alpine bluegrass