Temporal pattern in foraging behaviour of the Indian pond heron,Ardeola grayii at Ratanpur,Chhattisgarh, India

In avian population, the biological clock is synchronized with the photoperiod as a significant time cue. However, information on feeding behaviour of the Indian Pond Heron, Ardeola grayii at Ratanpur, Chhattisgarh, India is not available. In present study we examined the effect of ‘time of the day’ and ‘photoperiod’ on daytime feeding behaviour of A. grayii at Ratanpur (85º17’E longitude and 22º3’N latitude), Chhattisgarh, India. The different feeding techniques of A. grayii, were recorded for two consecutive days each during long days (May and June 2014) and during short days (December 2014 and January 2015). One-way ANOVA (using SPSS 16.0) was applied to find out the effects of ‘photoperiod’ and ‘time of the day’ on daytime feeding activity with respect to frequency of feeding techniques. The rhythms in daytime feeding activity were evaluated using the Cosinor rhythmometry at 24 h and 12 h. The present study revealed that the A. grayii adopted three major techniques viz., slowly walking, probing and striking on which the slowly walking and striking was popularly used feeding technique as compared to the probing technique during the feeding. Moreover, the A. grayii is found to be bimodal viz., morning and evening type during both of long and short days. Furthermore, bird was more active during short day as compared to the long day.     

Differences in swimming and diving abilities between two sympatric species of water shrews: <Emphasis Type="Italic">Neomys anomalus</Emphasis> and <Emphasis Type="Italic">Neomys</Emphasis><Emphasis Type="Italic">fodiens</Emphasis> (Soricidae)

Swimming and diving abilities of two syntopic species of water shrews, Neomys anomalus and Neomys fodiens, were tested in aquaria using video recordings taken from three views (lateral distant, lateral close and dorsal). The frequency and total duration of diving, as well as the mean duration of diving and floating bouts, were significantly higher in N. fodiens than in N. anomalus. Frequency of paddling during surface swimming was lower in N. fodiens than in N. anomalus. N. fodiens dived mainly for long distances at the bottom of the aquarium and performed a wider range of dive profiles than N. anomalus, which preferred rather short and shallow dives. The two species differed also significantly in their fineness ratios (describing how streamlined their bodies are) when diving. When swimming, N. fodiens had a relatively wider body and performed narrower movements with its tail than N. anomalus. These results show quantitatively and qualitatively for the first time that N. fodiens is more proficient at swimming and diving than N. anomalus. The results also help to explain the inter-specific differences in efficiency of underwater foraging, and support the idea of segregation of ecological niches of these species based on their different foraging modes (diving vs. wading).     

Personality-dependent inter- and intraspecific foraging competition in the invasive round goby,Neogobius melanostomus

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as “bold,” fish that took more time to resume movement were categorized as “shy” and those that fell in between these two categories were determined to have “intermediate” boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.     

Blooming rhythms of cactus Cereus peruvianus with nocturnal peak at full moon during seasons of prolonged daytime photoperiod

Cereus peruvianus (Peruvian apple cactus) is a large erect and thorny succulent cactus characterized by column-like (cereus [L]: column), that is, candle-shaped, appendages. For three successive years (1100 days), between early April and late November, we studied the flowering patterns of eight cacti growing in public gardens and rural areas of north and central Tunisia, far from nighttime artificial illumination, in relation to natural environmental light, temperature, relative humidity and precipitation parameters. Flower blooming was assessed nightly between 23:00 h and until at least 02:00 h, and additionally around-the-clock at ~1 h intervals for 30 consecutive days during the late summer of each year of study to quantify both nyctohemeral (day–night) and lunar patterns. During the summer months of prolonged daytime photoperiod, flower blooming of C. peruvianus exhibited predictable-in-time variation as “waves” with average period of 29.5 days synchronized by the light of the full moon. The large-sized flower (~16 cm diameter) opens almost exclusively at night, between sunset and sunrise, as a 24 h rhythm during a specific 3–4-day span of the lunar cycle (full moon), with a strong correlation between moon phase and number and proportion of flowers in bloom (ranging from r = +0.59 to +0.91). Black, blue and red cotton sheets were used to filter specific spectral bands of nighttime moonlight from illuminating randomly selected plant appendages as a means to test the hypothesis of a “gating” 24 h rhythm phenomenon of photoreceptors at the bud level. Relative to control conditions (no light filtering), black sheet covering inhibited flower bud induction by 87.5%, red sheet covering by 46.6% and blue sheet covering by 34%, and the respective inhibiting effects on number of flowers in bloom were essentially 100%, ~81% and ~44%. C. peruvianus is a unique example of a terrestrial plant that exhibits a circadian flowering rhythm (peak ~00:00 h) “gated” by 24 h, lunar 29.5-day (bright light of full moon) and annual 365.25-day (prolonged summertime day length) environmental photoperiod cycles.     

Evidence of two subaggregations of humpback whales on the Kodiak,Alaska, feeding ground revealed from stable isotope analysis

Knowledge of humpback whale (Megaptera novaeangliae) foraging on feeding grounds is becoming increasingly important as the growing North Pacific population recovers from commercial whaling and consumes more prey, including economically important fishes. We explored spatial and temporal (interannual, within‐season) variability in summer foraging by humpback whales along the eastern side of the Kodiak Archipelago as described by stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of humpback whale skin (n = 118; 2004–2013). The trophic level (TL) of individual whales was calculated using basal food web δ¹⁵N values collected within the study area. We found evidence for the existence of two subaggregations of humpback whales (“North,” “South”) on the feeding ground that fed at different TLs throughout the study period. Linear mixed models suggest that within an average year, Kodiak humpback whales forage at a consistent TL during the feeding season. TL estimates support mixed consumption of fish and zooplankton species in the “North” (mean ± SE; 3.3 ± 0.1) and predominant foraging on zooplankton in the “South” (3.0 ± 0.1). This trend appears to reflect spatial differences in prey availability, and thus, our results suggest North Pacific humpback whales may segregate on feeding aggregations and target discrete prey species.     

Effects of softness of bedding materials upon overnight excretion of urinary catecholamines and sleep quality in warm environmental conditions

The purpose of this study was to investigate whether, when subjects were living in a moderately warm environment: (1) the softness of clothing worn during the daytime could influence the subjects’ preference in the evening for the softness of clothing and a face towel; and (2) the softness of bedding materials could modulate their nocturnal body temperature, overnight urinary catecholamine excretion, and sleep quality. Six females were tested during the luteal phase of their menstrual cycles. The experiment was conducted over three consecutive days and nights in a climatic chamber controlled at 28 ± 0.2 °C and 50% RH during the evening (from 19:30 to 21:30 h) and at 29 ± 0.2 °C and 50% RH during the sleep period (from 22:30 to 07:00 h). The first night was for adaptation to the experimental chamber. Five different sets of clothing and bedding were used; these were identical except for the softness/hardness of the materials used (due to treatment with fabric softener or starch), and material softness decreased in the order: Type A (softest)?>?Type B > Type C > Type D > Type E (hardest). There were two phases to the experiment, conducted in random order. In one phase, subjects wore “soft type” (Type B) T-shirt and shorts in the daytime and, in the other phase, “hard type” (Type D/E) T-shirt and shorts. In both phases, subjects were asked at 21:30 h to select a T-shirt and a face towel which they felt would be most comfortable to use. At night, they slept on bedding (a mattress cover, a pillowcase and a covering blanket) which was of the same degree of softness as the T-shirt and shorts that had been worn in the daytime in that phase. Rectal temperature, skin temperatures at seven sites, and body movement were measured during sleep, an overnight urine sample was taken for measurement of urinary excretion of adrenaline and noradrenaline, and subjective sleep quality was assessed on being woken the following morning. The main results were as follows: (1) T-shirt preference in the evening showed large inter-individual variation but did not differ significantly between the two phases (when “hard type” or “soft type” clothing had been worn during the daytime). The preferred texture of the face towel was softer than that of the T-shirt, the difference in softness between the chosen face towel and T-shirt being significant (p < 0.05 and p < 0.10, respectively, when having worn “soft type” and “hard type” clothing in the daytime). (2) Rectal temperature and mean skin temperature were not significantly different when sleeping with “soft type” (Type B) and “hard type” (Type D/E) bedding materials. (3) Overnight secretions of urinary adrenaline and noradrenaline were significantly less with “soft type” than “hard type” (p < 0.01 and p < 0.05 for adrenaline and noradrenaline, respectively) bedding. (4) When sleeping with “soft type” bedding materials, five out of the six subjects showed less body movements during the sleep period and reported that they had slept better. These results suggest that, in a moderately warm environment, bedding materials with a softer texture might be more comfortable to the subject (due to less tactile stimulation of the skin, which results in neurophysiological relaxation) and provide them with better sleep quality.     

Fine-scale spatial age segregation in the limited foraging area of an inshore seabird species,the little penguin

Competition for food resources can result in spatial and dietary segregation among individuals from the same species. Few studies have looked at such segregations with the combined effect of sex and age in species with short foraging ranges. In this study we examined the 3D spatial use of the environment in a species with a limited foraging area. We equipped 26 little penguins (Eudyptula minor) of known age, sex, and breeding output with GPS (location) and accelerometer (body acceleration and dive depth) loggers. We obtained dietary niche information from the isotopic analysis of blood tissue. We controlled for confounding factors of foraging trip length and food availability by sampling adults at guard stage when parents usually make one-day trips. We observed a spatial segregation between old (>11 years old) and middle-aged penguins (between 5 and 11 years old) in the foraging area. Old penguins foraged closer to the shore, in shallower water. Despite observing age-specific spatial segregation, we found no differences in the diving effort and foraging efficiency between age classes and sexes. Birds appeared to target similar prey types, but showed age-specific variation in their isotopic niche width. We hypothesize that this age-specific segregation was primarily determined by a “cohort effect” that would lead individuals sharing a common life history (i.e. having fledged and dispersed around the same age) to forage preferentially together or to share similar foraging limitations.     

The choice of foraging methods of the Brown Dipper,Cinclus pallasii (Aves: Cinclidae)

The Brown Dipper,Cinclus pallasii, forages for large prey by diving deeply among submerged rocks, and for small prey in shallow water by wading and pecking on the bottom. Foraging by diving entailed a higher energy cost but resulted in taking larger prey than foraging by wading-and-pecking. Foraging by diving was seldom observed from May to October, but increased from December to April, when the dippers came into breeding condition and the proportion of large prey in the benthic fauna increased. During the breeding season, adult dippers fed themselves mainly by foraging by wading-and-pecking, whereas those feeding nestlings and fledglings foraged by diving. The foraging methods employed was determined by the individuals being fed and the abundance of the large prey. Foraging by diving may be advantageous for individuals provisioning their young because of the high gross intake rate, but may be less advantageous for the foragers themselves because of the high energy cost.     

Spatiotemporal variability in activity patterns of urban street cattle as function of environmental factors

ABSTRACT

In the current study, we studied behavioral patterns, such as foraging, activity, standing, and laying in a population of cattle wandering on streets of Raipur city. We also determined the effects of four environmental factors (temperature, humidity, light, and noise intensities) on these behaviors. We recorded all four behavioral variables at four time points each day over a period of three consecutive days at 10 randomly selected locations using on-site human observation method, digital video, and still camera. We used Cosinor rhythmometry to analyze the time series data on all four behavioral variables. One-way ANOVA was performed to determine the impact of the factor “time of the day” on all observed behavioral variables. Pearson correlation was also employed to evaluate the relationship between the environmental and behavioral variables. Cosinor analyses revealed statistically significant 24-h rhythms in all observed behavioral variables, at the group level, with peaks of foraging, activity, standing, and laying located at 11.54 h, 14.54 h, 18.66 h, and 23.88 h, respectively. Factor “time of the day” had statistically significant effect on all observed behavioral variables. Foraging and activity were found to be positively correlated with temperature, light, and noise intensities; and negatively correlated with humidity. The laying behavior was found to be negatively associated with temperature, light, and noise intensities; and positively correlated with humidity. The findings of this study might be helpful in the management of cattle menace that has become an annoying phenomenon on the streets and highways of almost all Indian cities.     

Environmental control of ovarian dormancy in natural populations of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Drosophila melanogaster from Australia, Europe and North America enter an adult ovarian dormancy in response to short days and low temperatures. The independent effects of temperature and day length in the determination of dormancy have been examined only in one long-established laboratory line (Canton-S). In all other studies of natural or laboratory populations, dormancy has been assessed at either a single short day or a single moderately low temperature. Herein, we determine the relative roles of temperature, photoperiod, and their interaction in the control of ovarian dormancy in D. melanogaster from two natural populations representing latitudinal extremes in eastern North America (Florida at 27°N and Maine at 44°N). In both natural populations, temperature is the main determinant of dormancy, alone explaining 67% of the total variation among replicate isofemale lines, whereas photoperiod has no significant effect. We conclude that ovarian dormancy in D. melanogaster is a temperature-initiated syndrome of winter-tolerant traits that represents an adaptive phenotypic plasticity in temperate seasonal environments.     

Photoperiodic regulation of the diapause of the progeny in <Emphasis Type="Italic">Trichogramma embryophagum</Emphasis> Htg. (Hymenoptera,Trichogrammatidae): Dynamics of sensitivity to photoperiod at the immature stages of maternal females

Photoperiodic regulation of T. embryophagum progeny prepupal diapause was investigated under laboratory conditions. Maternal females developed at 20°C, the position of the photosensitive period was detected by transferring immature stages between the diapause-inducing “short” day (L:D = 12:12) and the diapause-averting “long” day (L:D = 20:4). Progeny generation developed at L:D = 12:12 under the near-threshold temperature of 13°, 14°, or 15°C. Experiments showed that, at least under the used photo-thermal regimens, only the pupal stage was sensitive to the photoperiod influence. The highest photosensitivity was recorded during the last two days before the adult emergence. In this critical period, even a single short day cycle induced diapause in most of individuals. However, the reaction to the long day was weaker: at least two long light days immediately preceding the maternal adult emergence were necessary to avert the diapause. If a short day was preceded by a long day by more than 2–3 days before the adult emergence, the stepwise photoperiodic response caused an increase in the tendency to diapause. The results of this study could be used in pest biocontrol practice for elaboration of optimal methods for Trichogramma mass rearing and storage and also for prediction of its seasonal cycles under natural conditions.     

Foraging behavior of redheads (Aythya americana) wintering in Texas and Louisiana

Redheads, Aythya americana, concentrate in large numbers annually in traditional wintering areas along the western and northern rim of the Gulf of Mexico. Two of these areas are the Laguna Madre of Texas and Chandeleur Sound of Louisiana. We collected data on 54,340 activities from 103 redhead flocks in Texas and 51,650 activities from 57 redhead flocks in Louisiana. Males and females fed similarly, differing neither in levels of feeding (percent of all birds in flock that were feeding) (p>0.90) nor in percentages of birds feeding by diving, tipping, dipping, or gleaning from the surface (p>0.10). The foraging level of redheads in the upper Laguna Madre region was relatively constant throughout two winters. Foraging of redheads in early winter in Louisiana was significantly greater than redhead foraging in the upper Laguna Madre, but by late winter, foraging by redheads in Louisiana had declined to the same level as that shown by redheads foraging in the upper Laguna Madre. The overall foraging level of redheads from Chandeleur Sound was greater (41%) than that of redheads in the upper Laguna Madre (26%), yet it was quite similar to the 46% foraging level reported for redheads from the lower Laguna Madre. Redheads in the upper Laguna Madre region of Texas fed more by diving than did those in the Chandeleur Sound and the lower Laguna Madre. Diving increased in frequency in late winter. Greater reliance by redheads on diving in January and February indicates that the birds altered their foraging to feed in deeper water, suggesting that the large concentrations of redheads staging at this time for spring migration may have displaced some birds to alternative foraging sites. Our results imply that the most likely period for food resources to become limiting for wintering redheads is when they are staging in late winter.     

Effects of photoperiod and temperature on reproductive diapause in Ophraella communa (Coleoptera: Chrysomelidae), a potential biocontrol agent against Ambrosia artemisiifolia

Abstract To investigate the seasonal adaptation strategies of Ophraella communa to new habitats, the effects and regulation mechanisms of photoperiod and temperature on the reproductive diapause in a population collected from Changsha, Hunan were examined. Adults showed obvious reproductive diapause, which was regulated by photoperiod and temperature. At 30°C, there was no adult diapause occurring under either long‐day or short‐day conditions; at 25°C the pre‐oviposition period was short and fecundity was high in adult females under L : D 16 : 8 h, whereas under L : D 12 : 12 h, a few females entered reproductive diapause; at 20°C under short‐day conditions, all female adults entered diapause. The pre‐oviposition period was significantly prolonged when the pupae and adults were transferred from long‐days to short‐days, but the day length influence was not obvious when they were transferred only in the adult stage. However, the fecundity dropped greatly no matter whether the photoperiod shifted to short‐days only in the adult stage or whether the shift occurred in both the pupal and adult stage. The fecundity was extremely low when photoperiod shifted from long‐days to short‐days in both pupal and adult stages. This was an indication that the pupal and adult stages were the photoperiod‐sensitive stage for adult reproductive diapause. This was especially true for the photoperiod in the pupal stage, which has a distinctly significant regulative effect on reproductive diapause. Additionally, this article also addresses the reason for different photoperiodic response patterns in reproductive diapause induction between the Changsha strain and the Tsukuba strain (Japan) of O. communa.     

Photoperiodic Regulation of the Daily Rhythm of <Emphasis Type="Italic">Trichogramma</Emphasis> Adult Emergence (Hymenoptera,Trichogrammatidae)

Laboratory experiments demonstrate that the adult emergence rhythms of two Trichogramma species (T. telengai Sor. and T. principium Sug. et Sor.) significantly depend on photoperiod. The synchronicity of adult emergence is maximal at day lengths of 12–16 h. Under longer days (18–20 h) adult emergence is extended, whereas under very short days (4–8 h) a substantial proportion of adults emerge before light-on. The pattern of T. telengai emergence under day length of 4 h suggests the possibility of the existence of two fractions (the first that emerges in the dark and the second that waits for light-on) which results in two peaks of emergence. As a whole, these data agree well with the hypothesis of the periods of “potential readiness” and “obligate activity” forwarded by V.B. Chernyshev. The results of the study can be used for optimization of the methods for laboratory and mass rearing of Trichogramma species.     

Germination responses to GA3 and short‐time chilling of three endemic species: Tripleurospermum pichleri,Cirsium leucopsis and Senecio olympicus (Asteraceae)

In the present study, the germination characteristics of three endemic species from Turkey, Tripleurospermum pichleri (Boiss.) Bornm., Cirsium leucopsis D.C and Senecio olympicus Boiss. (Asteraceae), were investigated. Germination was studied for fresh seeds, for seeds subjected to short‐time chilling (15 days, moist +4°C), to GA₃ (100, 150 and 250 ppm) and a combination of chilling and GA₃; in all cases seeds were incubated either at 20/10°C day/night with light daytime or at 20°C in darkness with daily short‐time dim light (DSDL). In C. leucopsis seeds, all GA₃ treatments enhanced the final germination percentages. The mean germination time (MGT) of C. leucopsis was lower under DSDL than with photoperiod. The chilling treatment with GA₃ in DSDL significantly increased germination in S. olympicus seeds (from 45 to 87%). Germination increased to 55% in T. pichleri by chilling under photoperiod compared with 32% by chilling followed by DSDL. In conclusion, these three co‐existing endemic Asteraceae species have different germination behaviours; something that should be taken into account for ex situ propagation. However, an efficient way to germinate all species is to use 250 ppm GA₃ and 20/10°C with photoperiod.     

Diel and lunar variation in diving behavior of rough-toothed dolphins (Steno bredanensis) off Kauaʻi,Hawaiʻi

Observational studies describe rough-toothed dolphins (Steno bredanensis) actively foraging during the day on epipelagic species. Using data from depth-transmitting satellite tags deployed on nine individuals off Kauaʻi, we investigated diving behavior and the effects of lunar phase and solar light levels on vertical movements. Overall, tagged rough-toothed dolphins primarily used near-surface waters, spending between 83.6% and 93.7% of their time in the top 30 m of the water column. When diving, grand mean, median, and maximum dive depths were 76.9 m, 67.5 m, and 399.5 m, although individuals were in water with depths from approximately 700–1,450 m. Dive rates varied by time of day, being lowest during the day and at dawn and highest at dusk and night. Dives were deepest (M = 133.7 m, SD = 52.6 m, median = 106.5 m) and longest (M = 4.0 min, SD = 0.4 min, median = 4.0 min) at dusk, suggesting dolphins were taking advantage of prey rising to the surface in response to reduced light levels. Lunar phase indirectly affected diving, with deeper and longer dives occurring with increasing illumination. The variations in dive behavior across solar and lunar cycles indicate diving patterns shift based on the distribution of prey.     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA. III. A RELATIONSHIP BETWEEN MEDIUM COMPOSITION AND THE OPPOSITE PHOTOPERIODIC RESPONSES OF L. PERPUSILLA 6746 AND L. GIBBA G3

Hillman , William S. (Yale U., New Haven, Conn.) Experimental control of flowering in Lemna. III. A relationship between medium composition and the opposite photoperiodic responses of L. perpusilla 6746 and L. gibba G3. Amer. Jour. Bot. 48(5): 413–419. Illus. 1961.—In a simple Hoagland-type medium, L. perpusilla 6746 flowers, irrespective of daylength; L. gibba G3 does not flower under any daylength, as long as the medium is changed frequently. Ethylenediaminetetraacetic acid (EDTA) prevents the flowering of L. perpusilla in long days but not in short, and brings about the flowering of L. gibba in long days but not in short. The same results are obtained with medium “aged” by the growth in it of L. gibba for several weeks (in any photoperiod) as well as with tartaric acid. The effectiveness of both EDTA and “aged” medium is greater at pH levels near 5 than at 4 or below, probably reflecting action through metal-chelation. These results are most easily interpreted as effects on photoperiodic sensitivity, and suggest a central role of metals in photoperiodism.     

Responses to stepwise photoperiodic changes for the larval diapause of the Indian meal moth Plodia interpunctella

Abstract The Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae) diapauses as a last‐instar (fifth) larva. At 30 °C, no larvae enter diapause under any photoperiodic conditions; at 25 °C, the photoperiodic response curve is a long‐day type with a critical length of approximately 13 h light; at 20 °C, diapause is induced moderately even under long days (> 13 h). Cumulative effects of short days or long days on diapause induction are determined by alternate, stepwise and gradually changing regimes of photoperiod at 25 °C. When the larvae are repeatedly exposed to LD 16 : 8 h and LD 12 : 12 h photoperiods every other day, the incidence of diapause is 37%. When the larvae are placed under an LD 16 : 8 h photoperiod for 2 days and then under an LD 12 : 12 h photoperiod for 1 day, it is 38 %. Exposure to an LD 16 : 8 h photoperiod for 1 day and then to an LD 12 : 12 h photoperiod for 2 days induces only 15% diapause. This may indicate that the photoperiodic information is not accumulated in a simple fashion despite the generally accepted hypothesis (i.e. photoperiodic counter). Larvae exposed to an LD 16 : 8 h photoperiod for 5 days after oviposition express a very high incidence of diapause even under short days between an LD 2 : 22 h and LD 12 : 12 h photoperiod. After 10 days exposure to an LD 16 : 8 h photoperiod, however, the short day does not induce diapause strongly. On the other hand, an LD 12 : 12 h photoperiod in the early larval life is highly effective in the induction of diapause. A gradual increase or decrease of photoperiod (2 min day^?1) shows that the direction of photoperiodic change does not affect the diapause determination.     

Flower bud differentiation in Salix pentandra as affected by photoperiod, temperature and growth regulators

Flower bud initiation in seedlings and vegetatively propagated plants of Salix pentandra from different locations has been studied under controlled conditions. In mature plants flower bud formation was induced by 2-chloroethyltrimethylammoniumchloride (CCC) and by short day treatment. The effect of CCC was antagonized by GA₃. The critical photoperiod for flower bud formation was about 18 h for a southern clone (from 49°48'N), but cuttings of a northern ecotype (from 69°39'N) formed flower buds even at 24 h photoperiod. Generally, flower bud formation occurred simultaneously with apical growth cessation. However, apical growth cessation was not a prerequisite for floral initiation and flower buds were also found in elongating plants. Seedlings up to 60 days old did not form flower buds in growth chamber studies. The length of the juvenile phase has not been studied in detail, but cuttings taken from seedlings approximately 20 cm high and 60 days old were able to develop flower buds when treated with CCC. A gradual transition from the juvenile to the mature phase was obtained by repeated pruning of seedlings grown at 18°C and 24 h photoperiod.