Critical Daylength Research Articles

Seasonal Changes in the Incidence of Embryonic Diapause in the Band-Legged Ground Cricket, Dianemobius nigrofasciatus

Abstract The incidence of embryonic diapause in the band-legged ground cricket, Dianemobius nigrofasciatus was examined in regard to egg production by individual females both in the laboratory and in the field in Osaka, Japan. (1) Females were classified into three types: diapause egg-producers (laid only diapause eggs), nondiapause egg-producers (laid only nondiapause eggs) and mixed egg-producers (laid both diapause and nondiapause eggs). (2) The longer the photophase, the smaller was the incidence of diapause egg-producers, and the larger was that of the nondiapause egg- and mixed egg-producers. The critical day-length was between 13 and 14 hr. (3) The longer the photophase, the smaller was the incidence of diapause eggs laid by mixed egg-producers. (4) In the field, both nondiapause egg-producers and mixed egg-producers were observed from June to August. In September and October, most of the females were diapause egg-producers. The present findings revealed that adults of the overwintered generation o...

Ectopic expression of oat phytochrome A in hybrid aspen changes critical daylength for growth and prevents cold acclimatization

Survival of temperate‐zone tree species under the normal summer‐winter cycle is dependent on proper timing of apical growth cessation and cold acclimatization. This timing is primarily based on the perception of daylength, and through evolution many tree species have developed photoperiodic ecotypes which are closely adapted to the local light conditions. The longest photoperiod inducing growth cessation, the critical photoperiod, is inherited as a quantitative character. The phytochrome pigment family is the probable receptor of daylength, but the exact role of phytochrome and the physiological basis for the different responses between photoperiodic ecotypes are not known. This report shows for the first time that over‐expression of the oat phytochrome A gene (PHYA) in a tree significantly changes the critical daylength and effectively prevents cold acclimatization. While the critical daylength for elongation growth in the wild‐type of hybrid aspen (Populus tremula × tremuloides) was approximately 15 h, transgenic lines with a strong expression of the oat PHYA gene did not stop growing even under a photoperiod of 6 h. Quantitative analysis of gibberellins (GA) as well as indole‐3‐acetic acid (IAA) revealed that levels of these were not down‐regulated under short days in the transgenic plants expressing high levels of oat PHYA, as in the wild‐type. These results indicate that photoperiodic responses in trees might be regulated by the amount of PHYA gene expressed in the plants, and that the amount of phytochrome A (phyA) affects the metabolism of GAs and IAA.

Seasonal Life Cycle of Aelia fieberi (Hemiptera: Pentatomidae) in Relation to the Phenology of Its Host Plants

Adults and nymphs of Aelia fieberi Scott were observed on grasses in the field in Osaka, Japan, from April to August. This species produced 2 generations a year and adults of the 2nd generation entered diapause in August. At 25°C in tbe laboratory, adults raised under long-day conditions reproduced promptly after ecdysis, whereas those raised under short-day conditions entered diapause. The critical daylength was 14.5 h, which corresponds in Osaka to the length of early-August days, including twilight. However, seeds of grasses were available consistently in the field from April to October, and temperatures were high enough for nymphal development even after August. When eggs were kept under outdoor conditions, nymphs developed to adults on a favorable food after August, and the bugs survived until the next spring. Nymphs reared at 25°C in the laboratory reached adulthood on seeds of grasses available in the field from spring to summer, although all nymphs died on seeds produced in summer. The relatively long critical daylength inducing diapause in August prevents reproduction of the 2nd generation which would face the lack of favorable food in autumn.

Summer and winter diapause in pupae of the cabbage butterfly, Pieris melete Ménétriés

The cabbage butterfly, Pieris melete is multivoltine with a pupal summer and winter diapause. Summer and winter diapause are induced principally by relatively long and short daylengths, respectively. The intermediate to relatively short daylengths of autumn permitted some pupae to develop without diapause in the field. A short daylength had a stronger diapause inducing effect than a relatively long one under higher temperatures. The principal sensitive phase for photoperiodic response occurred before the late 3rd larval instar. The critical daylength for wild autumnal populations was between 12 h 30 min and 12 h 40 min at an average temperature of 20.5°C. A night interruption by 2 h of light averted diapause most effectively when it was placed 10 to 12 h after lights-off. High temperatures and long days during summer inhibited the incidence of diapause, suggesting that the occurrence of summer diapause is due to the specific climatic conditions occurring in April and early May, rather than to the high temperatures in summer. This indicates that the butterfly has a cryptic ability to reproduce in summer. High temperatures delayed diapause development, whereas low temperatures enhanced it, indicating that the optimum temperature of diapause development is lower. The diapause regulating mechanisms thus ensure that the species synchronises its development and reproduction with the growth seasons of the host plants and provide the species with a high degree of flexibility in its life cycle.

Effects of photoperiod and low temperature on diapause termination in the yellow‐spotted longicorn beetle (Psacothea hilaris)

Abstract. .The effects of photoperiod and low temperature on diapause termination in the yellow‐spotted longicorn beetle, Psacothea hilaris (Pascoe) (Coleoptera: Cerambycidae), were examined using a population from Ino, Japan. Diapausing insects obtained by rearing larvae under short daylength (12 or 13 h) at 25oC were subjected to various treatments. When the photoperiod was changed at the same temperature, diapausing larvae showed a long‐day response with a critical daylength between 13.5 and 14h. The diapause was terminated and consequently pupation occurred if the daylength was longer than 13.5 h. Chilling the diapausing larvae at 10oC for 30 or more days also terminated diapause in most larvae irrespective of the photoperiods during and after chilling treatment. In contrast, the post‐chilling photoperiod had a critical effect on development of diapausing larvae chilled for only 15 days.

REGULATION OF TUBER INDUCTION IN POTATO BY DAYLENGTH AND PHYTOCHROME

Many potato species require short days for the induction of tuberization and will not tuberize if maintained in photoperiods longer than their critical daylength, or if the dark period of a short day regime is interrupted by a light treatment (what is termed a night-break). Phytochrome is known to be involved in photoperiodic responses such as tuberization and flowering because the effects of a red light night-break can be reversed by a far-red light treatment given immediately afterwards-a well- documented characteristic of phytochrome responses. Which of the several phytochromes that are known to exist is/are responsible for the photoperiodic response, however, has not been shown. Transgenic short-day requiring Solanum tuberosum ssp. andigena plants have been produced which have much lower levels of phytochrome B as a result of antisense technology. These plants are now able to tuberize in long days as well as short days. The reduction in phytochrome B levels has thus led to the loss of the photoperiodic control of tuberization in these plants and implicates phytochrome B in this response. Preliminary grafting experiments have indicated that a graft-transmissible tuberinducing signal is produced in the transgenic plants in long days as well as short days, whereas in wild-type plants this signal is only produced in short days. The existence of a possible inhibitor of tuberisation is also discussed.

遠隔地からの緑化植物の移植が昆虫の地域個体群へ及ぼす影響

These days, plant materials for the revegetation have been transported over the long distance in Japan. Because the plant materials have been carried with large quantities of soil and other plants, they must have been accompanied by many living things, including a wide range of insects. In this paper, we demonstrated that the evidence of the genetic divergence among five local populations of the small insect, Thrips nigropilosus, living on the one of the plant materials for the revegetation, Artemisia princeps; critical daylengths at 18°C for induction of the reproductive diapause and the brachypterous form in females of four populations, Wakkanai, Abashiri, Kyoto and Nagasaki populations, were between 11hrs and 14hrs and different from each other, whereas Naha population dose not show critical daylengths between 8hrs and 15hrs. Inter-population crosses between the local populations probably disturbe their genetic constructions. This possibly results in a decrease in the number of individuals in the population, because the diapause and the wing form are life history traits directly affecting the reproductive success. Thus, the transportation of the plant materials may disturbe genetic construction of local populations of living things. A general rule for the use of plant materials for the revegetation should be proposed.

Photoperiod of Poinsettia Stock Plants Influences Rooting of Cuttings

Rooting of cuttings from three cultivars of Euphorbia pulcherrima Willd. was evaluated after regulating the photoperiod during the stock plant stage. One group of stock plants was exposed to a night break (4 hours) and another group was exposed to natural daylength during September. Cuttings harvested in late September from `Freedom Red' and `Monet' stock plants grown under the 4-hour night break rooted more rapidly and had greater root mass than `Freedom Red' and `Monet' grown under natural daylength, whereas rooting of cuttings from `V-17 Angelika Marble' was not influenced by the photoperiods tested. Using a night break to prevent flower initiation of stock plants produced a higher-quality cutting when propagation took place after the critical daylength for flowering had passed.

The influence of each parent and geographic origin on larval diapause in the blow fly, Calliphora vicina

The blow fly, Calliphora vicina R.-D. (Diptera: Calliphoridae), displays a larval diapause in response to short daylengths experienced by the adult female. The range of daylengths inducing diapause varies among geographic populations of fly and differences are genetic in origin, being maintained under laboratory conditions. The critical daylength for a southern, English strain is 14.5 hours of light and for a northern, Finnish strain is 16 hours. Crosses between these strains revealed that diapause incidence was produced entirely by maternal induction and was not influenced by the male. Diapause duration, in contrast, was affected by both parents; larvae with mothers of the northern strain and southern fathers entered diapause at the same rate as the pure bred northern larvae but emerged from it much more quickly. Thus diapause duration is a characteristic of the larvae themselves, influenced by the genetic background of both parents.

Strategies in avian breeding cycles

Abstract Birds show pronounced seasonal breeding at all latitudes, and many are able to predict and prepare for a forthcoming breeding opportunity, thereby maximizing reproductive potential. The preparatory phase of the breeding cycle is characterized by a complex of sexually motivated behaviours including courtship, selection of nest sites and territoriality. This phase of the breeding cycle is often initiated in response to initial predictive information derived from the decreasing daylengths of autumn or winter. Exposure to short daylengths dissipates long day-induced photorefractoriness allowing the reproductive neuroendocrine system to ‘switch on’. The resulting modest increase in the secretion of reproductive hormones stimulates pre-nuptial sexual behaviour, and in some birds, may be great enough to support short day breeding. For many birds, the increase in daylength in spring above the critical daylength for photoperiodically-induced gonadotrophin secretion is an essential supplementary source of predictive information for breeding resulting in the final maturation of the gonads. The increase in daylength above the critical daylength is also important for determining the date at which breeding terminates, by inducing the development of photorefractoriness. Although photorefractoriness is usually dissipated by exposure to short days, in some species it is dissipated after prolonged exposure to long days. This phenomenon may explain the generation of autonomous rhythms of reproductive activity. These may be used by migratory species, some sub-tropical birds breeding in the autumn, and birds breeding on the equator to generate initial predictive information for seasonal breeding.

Entrainment of circadian system under variable photocycles (T‐photocycles) alters the critical daylength for photoperiodic induction in blackheaded buntings

AbstractThe present study was designed to investigate the photoperiodic responses of blackheaded buntings to various T‐photocycles [T =the period length of light:dark (LD) cycle]. Two series of experiments were performed. In series I, groups of buntings (n =8‐12) were exposed to LD cycles of 22 to 26 hr with photoperiods of 6, 10, or 11 hr (T22 =6L:16D, 10L:12D, 11L:11D; T24 =6L:18D, 11L:13D; T26 =6L:20D, 11L:15D). Among these groups, birds subjected to 11L:11D showed heavy deposition of fat, weight gain, and testicular recrudescence, a response that is characteristic of long day (≥ 12 hr photoperiod per day) photostimulation, indicating that a T‐photocycle of less than 24 hr (T =22 hr) was photoinductive in buntings when presented with a photophase long enough to interact with the photoinducible phase (ϕi), located in the middle of the photocycle. Experiments in series II included an interrupted‐night lighting protocol with a main photophase of 6 hr and 1‐hr light break in photocycles of T =22 hr, T =24 hr, and T =26 hr. The results revealed that a 1‐hr light pulse was inductive when it was introduced in the middle of the photocycles, and, thus, was coincident with the ϕi. It is suggested that the critical daylength for photoperiodic induction in buntings is altered as a result of entrainment to various T‐photocycles. © 1995 Wiley‐Liss, Inc.

A genetic analysis of photoperiodic reproductive diapause in Drosophila triauraria

Abstract. Recombinant inbred lines were produced from hybrids between diapausing and non‐diapausing strains of Drosophila triauraria Bock & Wheeler by twenty generations of full‐sib mating. The analysis of these inbred lines suggests that the difference in the photoperiodic response between the original diapausing and non‐diapausing strains is due to genes at three or four loci and at least one of these loci is located on the X chromosome. The original diapausing strain and two inbred lines exhibited circadian peaks when subjected to the Nanda‐Hamner protocol, although they had different critical daylengths. This suggests that critical daylength is modified independently of the circadian oscillation system in this species. On the other hand, diapause duration was correlated with critical daylength among the inbred lines and the original diapausing strain, suggesting that these two traits are under the control of the same genetic system.

The Interaction of Photoperiod and Temperature in Diapause Timing: A Copepod Example.

In many organisms, photoperiod and temperature are thought to be the most significant token cues for seasonally timed life history events, including diapause in arthropods. A common pattern in many species of terrestrial insects and several copepod species is the existence of a critical daylength on one side of which the animals do not enter diapause and on the other side of which they do. Temperature plays a secondary role as modifier of the critical daylength. In some species, however, including the freshwater copepod Diaptomus sanguineus, the fraction of females making subitaneous eggs (eggs that hatch immediately) undergoes a very gradual transition as daylength changes over the natural range of photoperiods experienced in nature. Here we show that temperature is as important as photoperiod in cuing diapause timing in a population of D. sanguineus living in Bullhead Pond, Rhode Island. When ecologically relevant photoperiod and temperature cues are provided in the laboratory, the copepods rapidly switch from producing subitaneous eggs to producing diapausing eggs in a way that is typical of the seasonal switch seen in the pond. We provide a graphical model that illustrates how copepod sensitivities to photoperiod and temperature interact to produce an abrupt transition, and we discuss how natural selection should act on D. sanguineus diapause response to produce the variation in diapause timing seen within and between natural populations.

Reproductive Adaptations to Breeding in the North

The paper discusses how birds by changing their responses to the critical daylength can adjust the time for the initiation of the gonadal growth to more northern latitudes. Some remarks are also given on how changes in an individual's sensitivity towards non-photoperiodic factors, such as, for example the temperature, play an important role in adapting the gonadal growth rate to the flexibility of the local environment. Special attention has been given studies on swans and great tits.

Control of growth habit in determinate lablab bean ( Lablab purpureus) by temperature and photoperiod

Long days and high temperatures changed the growth habit of the normally determinate lablab bean ( Lablab purpureus) plant to indeterminate. The critical daylength for the change was 13 h at 25 °C and between 10 and 11 h at 30 °C. No change in habit occurred at 20 °C in any daylength, indicating the existence of a minimum temperature for the change. Plants of indeterminate growth habit showed an increased number of nodes and a greater length of internodes. It is suggested that daylength affects internode length rather than number of nodes, while the main factor determining number of nodes seems to be temperature.

Developmental and photobiological factors affecting photoperiodic induction inArabidopsis thalianaHeynh. Landsbergerecta

We have tested whether the promotion of flowering by long days (LD) in Arabidopsis thaoliana is a consequence of photoperiodic induction. To achieve this, the flowering responses of Arabidopsis thalina (L.) Heynh. Landsberg erecta (Ler) and the long-hypocotyl mutants hy2, hy3 and hy4 were determined with respect to age, daylength and light quality. Ler was capable of distinguishing between short days (SD) and long days (LD) from about 4 d after sowing at 20 o C, the time at which cotyledons were expanding and greening. At this stage, the critical daylength was between 8 h and 10 h. At 7 d, seedlings required five LD for induction and, as the seedlings aged, they became more sensitive so that by day 20, one LD was fully inductive. The response to SD in newly germinated seedlings was to delay flowering without altering leaf number, but after about 10 d, delay of flowering by SD was accompanied by extra leaves. In light quality experiments, blue light (B) was inductive for 5-d-old plants and in all subsequent treatments, far-red (FR) caused induction in treatments at 12 d and 18 d and low pressure sodium, equivalent to red, was not inductive at 5 d and 12 d, but partially inductive at day 18. Hence, both a specific blue-light photoreceptor and phytochrome A in High Irradiance Response mode promote floral induction. In daylength transfer experiments all three hy mutants responded to LD by earlier flowering. Both hy2 and hy3 produced substantially fewer leaves than Ler in SD and hy3 flowered slightly earlier than Ler. The hy4 mutants flowered later than Ler in SD and had a higher leaf number. A scheme is proposed in which photoperiodic induction depends on the ability of the plant to sense photoperiod, the stage of development and the photobiological input. We also propose that phytochrome A and the blue photoreceptor promote flowering whereas phytochrome B promotes vegetative development

Critical Day Lengths for Egg Production and Photorefractoriness in the Domestic Turkey

Critical day lengths (CDL) for ovarian growth, egg production, and photorefractoriness were estimated in turkey hens during winter and summer seasons. In two experiments, one in each season, fixed day length treatments ranging from 10.5 to 16 h/d were applied to photosensitive hens at 30 wk of age. Daily egg production was used to estimate CDL for the induction of egg production as well as optimal egg production. After 24 wk on light treatments, hens used during the winter season were exposed to 20 h light:4 h dark and subsequent changes in egg production were used to evaluate photorefractoriness. In two additional experiments, a night-interruption design was used to evaluate CDL and ovarian photoresponsiveness during winter and summer.The CDL for inducing egg production varied by season and was estimated to be 10.5 h or less during winter and about 11 h during summer. Likewise, the CDL for optimal egg production varied by season, being 11 to 11.5 h during winter and >14 h during summer. The CDL for photorefractoriness in winter photostimulated hens was between 12 and 12.5 h.It was concluded that CDL vary by season and are not fixed, but are dynamic characteristics of photoperiodic processes. Thus, photoresponsiveness of turkey hens changes by season. In addition, CDL for initiating egg production, stimulating egg production, and inducing photorefractoriness are all different, with the CDL for photorefractoriness being longest.

Photoperiod Influences Vegetative Growth of Heuchera Cultivars (Saxifragaceae)

Heuchera sanguinea Engelm. 'Torch', 'Firefly', and H. micrantha Dougl. ex Lindl. 'Palace Purple' were studied to examine the influence of photoperiod and cold temperature storage on vegetative and reproductive growth. Petioles were longer and total leaf area was greater when plants were grown under a 15-h photoperiod than under a 9-h photoperiod. There was no photoperiod x plant maturity interaction with regards to reproductive growth. Plants held in a 70C night greenhouse flowered sooner than those stored in a constant 40C cooler. Mature plants produced more inflorescences and flowered earlier than young plants. Storage in the cooler had a detrimental effect on the number of florets per inflorescence of 'Palace Purple' plants. 'Torch' plants produced significantly more inflorescences per plant when held in the cold greenhouse before forcing. More vegetative growth occurred under long photoperiods greater than 12 hours. Long days of 15 h accelerated flowering after exposure to cold storage. Photoperiod affects the growth of many plant species. Salvia leucantha, a herbaceous perennial, has a critical daylength requirement of 12 hours for bud development and a requirement of 10 hours for subsequent flower development (Armitage and Lauschman, 1989). Vegetative development of Zinnia elegans, an annual species, is increased under long days (LD's) of 12 to 14 hours (Boyle and Stimart, 1983). Cosmos sulphureus and Callistephus chinensis, both annual species, exhibit thermophotoperiodism (Biebel, 1936). Cosmos responds to LD's and 200C temperatures with increased height and short days (SD's) and 200C temperatures with increased leaf area. The reverse occurs when plants are grown at 120C; plants under LD's have the greater leaf area. Callistephus responds with increased height and greater leaf area at 200C under LD's. Leucanthemum x superbum [formerly Chrysanthemum x superbum (see Soreng and Cope, 1991)] seedlings need LD's, others need low temperatures, and yet others need both or neither to induce flowering (Shedron and Weiler, 1982b).

Environmental Regulation and Geographical Adaptation of Diapause in Cotesia plutellae (Hymenoptera: Braconidae), a Parasitoid of the Diamondback Moth Larvae

Photoperiodic response in two different geographic populations of Cotesia plutellae (Hymenoptera: Braconidae) was investigated. Short photoperiods induced prepupal diapause in the Kuroishi population but did not produce any developmental arrest in the Kobe population. The difference in the photoperiodic response in these populations reflects life-cycle adaptations to local environmental conditions. In the Kuroishi strain the critical daylength fell between 12.5 h and 13 h hours of light per day. Under 11L-13D conditions, high temperatures tended to decrease the occurrence of the diapause: as the temperature increased from 17°C to 20°C the diapause incidence diminished, ceasing altogether at 25°C. Parasite larvae of second and third instar stages were sensitive to diapause-inducing stimuli, whereas egg and first instar stages were not. The diapause termination depended not on the photoperiod but on the temperature: high temperature hastened termination of the diapause.

Sensitivity of Syrian hamsters (Mesocricetus auratus) to amplitudes and rates of photoperiodic change typical of the tropics.

Empirical data suggest that reproductive photoresponsiveness occurs in some populations of mammals above 13 degrees of latitude, but may be absent in populations from 0 degrees to 10 degrees of latitude. The present experiments examined the degree to which the low amplitude of change in photoperiod in the tropics constrains mammals from using daylength as a seasonal cue. The Syrian hamster, a temperate-zone species, was studied because of its well-documented ability to respond to small changes in photoperiod, and because of the absence of an alternative robustly responding species from the tropics. We subjected adult male hamsters to photoperiods that mimicked the amplitude and rate of photoperiod change of 30 degrees, 20 degrees, 10 degrees, and 5 degrees of latitude, but centered around an estimate of their critical daylength. For comparison, a fifth group was subjected to an abrupt change in daylength of a magnitude equal to the total annual variation occurring at 30 degrees. The two groups experiencing the gradually changing daylengths of 30 degrees and 20 degrees showed less within-group synchrony during testicular regression; in other dimensions of the annual testis cycle, including the degree of synchrony exhibited during recrudescence, they reacted similarly to the hamsters given the abrupt change in daylength. Some of the hamsters exposed to the gradually changing daylengths of 10 degrees responded to this challenge, as did a few in the 5 degrees treatment--in both cases, with poor within-group synchrony and a submaximal decrease in testis size. In an abbreviated second experiment, hamsters given abrupt decreases in daylength of magnitudes equal to those of the 10 degrees and 5 degrees groups responded slightly more frequently, and with maximal decreases in testis size. This suggests that mammals may not be constrained absolutely by an inability to respond to changes in photoperiod at 5 degrees to 10 degrees latitude. Seasonally breeding populations of mammals in the deep tropics that do not use photoperiod to regulate reproduction may use nonphotoperiodic cues because they offer a higher signal-to-noise ratio than do tropical changes in photoperiod.