Effect of temperature on circadian rhythm controlling the crepuscular activity of the burying beetle Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae)

Locomotor activity rhythm was examined at various temperatures under a 16 h light : 8 h dark photoperiod (LD 16:8) or LD 12:12 using adults of the burying beetle Nicrophorus quadripunctatus. At 20°C, the locomotor activity of the beetles showed a bimodal daily pattern with two peaks around lights on and lights off under both photoperiods. This bimodal activity rhythm persisted under constant darkness; therefore, the activity of adult N. quadripunctatus is controlled by a circadian clock. Adults showed a bimodal activity pattern for temperatures ranging from 15 to 25°C. The evening peak of the daily activity was earlier at lower temperatures. These findings suggest that in the field, N. quadripunctatus shows crepuscular activity, and is active earlier in the afternoon in cooler seasons. In this species, therefore, temperature appears to play an important role in the determination of daily activity patterns.     

Interaction of photoperiod and nutritive state in female reproduction of Lymnaea stagnalis

Summary

A study was made of the interaction of the photoperiod and the availability of food in influencing egg laying of the freshwater snail Lymnaea stagnalis. At a long day photoperiod (LD = 16 h light/8 h dark) egg laying of fed snails had increased compared with that of fed animals kept at a medium day photoperiod (MD = 12 h light/12 h dark). In MD snails oviposition ceased within a week of the beginning of a starvation period. This is most probably due to a reduction in the activities of the neuroendocrine caudodorsal cells which secrete an ovulation hormone. In contrast, in starved LD snails a low rate of ovipository activity continued, indicating that a lowered frequency of caudodorsal cell release cycles occurred under these conditions. The decreased mean size (number of eggs) of the egg masses in starved LD snails indicates that the activities of the endocrine dorsal bodies, which control vitellogenesis and synthetic activities in the female accessory sex organs, had decreased.

All MD snails survived, but nearly all LD snails died during the course of the experiment. Determinations of the mantle glycogen stores of LD snails suggest that the high mortality of LD snails is due to exhaustion of the animal's energy reserves.     

Photoperiodic regulation of seasonal responses in Indian weaver bird (Ploceus philippinus)

Photoperiod (=day length) is the vital factor for the regulation of behavioral and physiological activities in many avian species. This study investigated the seasonal cycles of testicular growth and secondary sexual characteristics of Indian weaver bird under natural day length (NDL) and the effects of duration and intensity of light on photoperiodic induction. In the first experiment, groups of birds (n = 7 each) were exposed to under NDL in April 2008 and May 2009 for 8 and 12 months, respectively. In second and third experiment, birds (n = 6 each group) were exposed to different photoperiods (11.5L:12.5D, 12L:12D, 13L:11D, and 15L:9D) at the same (500 lux) light intensity, and to 13L:11D at different light intensities (10-, 50-, 500-, and 800-lux). Observations on testis size, molt, and plumage score were recorded 2-week (molt and plumage) or at 4-week intervals (testes). Both the NDL groups showed similar seasonal cycles of testicular growth-regression and secondary sexual characteristics. Second and third experiments suggest that the photoperiodic induction was depending upon duration and intensity of the light. Birds showed testicular growth-regression cycle followed by molt and plumage color change only under 13L:11D and 15L:9D and only 500- and 800-lux under 13L:11D photoperiod but not under 11.5L:12.5D and 12L:12D and 10- and 50-lux light intensities. Pre- and post-nuptial molting on body feathers were progressed with gonadal stimulation–maturation and regression cycle under 13L:11D and 15L:9D. Results under different light–dark cycles suggest that day length of about 12 h or more and above the threshold level of light intensity are essential for the induction of photoperiodic responses.     

光周期对两种色型豌豆蚜种群参数的影响

为探讨光周期对红绿两种色型豌豆蚜种群增长的影响,于室内模拟光周期22L∶2D、16L∶8D、10L∶14D和4L∶20D四个水平,研究了红绿两种色型豌豆蚜的发育、繁殖和生命表。结果表明:相对于其它光周期,在光周期22L∶2D时,红绿两种色型豌豆蚜若蚜存活率最高,繁殖力最强;其红色型豌豆蚜种群增长内禀增长率(r_m=0.3263)高于绿色型豌豆(r_m=0.2863)。光周期16L∶8D时,红色型豌豆蚜的若蚜存活率(72.22%)高于绿色型豌豆蚜(69.45%),而成蚜寿命(6.58d)较短;但绿色型豌豆蚜内禀增长率(r_m=0.2648)高于红色型豌豆蚜(r_m=0.2249),其种群繁殖力强。光周期10L∶14D时,红色型豌豆蚜与绿色型豌豆蚜相比,若蚜存活率(80.55%)高,内禀增长率(r_m=0.2490)高,种群增长力强,而绿色型豌豆蚜成蚜寿命(12.71d)较长。光周期4L∶20D时,两种色型豌豆蚜若蚜存活率最低,繁殖力最弱,成蚜寿命显著延长;红色型豌豆蚜若蚜存活率(64.67%)高于绿色型(35.50%),成蚜没有产生后代;绿色型豌豆蚜内禀增长率(r_m=-0.0366),其种群为负增长。综上,短光照条件(4L∶20D)延长了两种色型豌豆蚜的若蚜发育历期及成蚜寿命,降低了若蚜存活率、繁殖力及生命表各项参数;长光照条件(22L∶2D)缩短了两种色型豌豆蚜的若蚜发育历期及成蚜寿命,若蚜存活率高、繁殖力强;红色型豌豆蚜更适宜光周期10L∶14D,而绿色型豌豆蚜更适宜光周期16L∶8D。     

Geographic variation in critical photoperiod for diapause induction and its temperature dependence in Hyphantria cunea Drury (Lepidoptera: Arctiidae)

The fall webworm, Hyphantria cunea Drury (Lepidoptera: Arctiidae), was introduced from North America to Japan half a century ago. The critical photoperiod for diapause induction and its temperature dependence, as defined by the difference in the critical photoperiod between 20 and 25°C, were investigated in order to understand the mechanisms behind a shift from bi- to trivoltine life cycles. The critical photoperiod for diapause induction was shorter in the southern trivoltine populations than in the northern bivoltine populations, and this was more marked at 25°C than at 20°C. Although the critical photoperiod showed a positive correlation with the original latitude, the correlation was relatively low at both temperatures. Conversely, temperature dependence of the critical photoperiod for diapause induction correlated negatively with the original latitude. The trivoltine populations showed greater temperature sensitivity than the bivoltine populations. These results suggest that an increase in temperature sensitivity of the diapause response to photoperiods was involved in the shift to a trivoltine life cycle. The crossing experiments suggested that the photoperiodic control of diapause induction and its temperature dependence are under polygenic control without sex-linkage. Received: 29 October 1996 / Accepted: 26 February 1997     

CONSTANS delays Arabidopsis flowering under short days

Long days (LD) promote flowering of Arabidopsis thaliana compared with short days (SD) by activating the photoperiodic pathway. Here we show that growth under very‐SD (3 h) or darkness (on sucrose) also accelerates flowering on a biological scale, indicating that SD actively repress flowering compared with very‐SD. CONSTANS (CO) repressed flowering under SD, and the early flowering of co under SD required FLOWERING LOCUS T (FT). FT was expressed at a basal level in the leaves under SD, but these levels were not enhanced in co. This indicates that the action of CO in A. thaliana is not the mirror image of the action of its homologue in rice. In the apex, CO enhanced the expression of TERMINAL FLOWER 1 (TFL1) around the time when FT expression is important to promote flowering. Under SD, the tfl1 mutation was epistatic to co and in turn ft was epistatic to tfl1. These observations are consistent with the long‐standing but not demonstrated model where CO can inhibit FT induction of flowering by affecting TFL1 expression.     

The brain's calendar: neural mechanisms of seasonal timing

The suprachiasmatic nucleus (SCN) of the hypothalamus is the principal component of the mammalian biological clock, the neural timing system that generates and coordinates a broad spectrum of physiological, endocrine and behavioural circadian rhythms. The pacemaker of the SCN oscillates with a near 24 h period and is entrained to the diurnal light-dark cycle. Consistent with its role in circadian timing, investigations in rodents and non-human primates furthermore suggest that the SCN is the locus of the brain's endogenous calendar, enabling organisms to anticipate seasonal environmental changes. The present review focuses on the neuronal organization and dynamic properties of the biological clock and the means by which it is synchronized with the environmental lighting conditions. It is shown that the functional activity of the biological clock is entrained to the seasonal photic cycle and that photoperiod (day length) may act as an effective zeitgeber. Furthermore, new insights are presented, based on electrophysiological and molecular studies, that the mammalian circadian timing system consists of coupled oscillators and that the clock genes of these oscillators may also function as calendar genes. In summary, there are now strong indications that the neuronal changes and adaptations in mammals that occur in response to a seasonally changing environment are driven by an endogenous circadian clock located in the SCN, and that this neural calendar is reset by the seasonal fluctuations in photoperiod.     

温度和光周期对两种瓢虫捕食习性和发育的影响

[目的]在农业上,气候变化影响作物产量、蚜虫动态以及捕食性瓢虫对蚜虫的调节作用.一些瓢虫为广布种,而另一些瓢虫种类却只在特定地理范围内分布,而有关气候因子如何影响瓢虫分布了解甚少.[方法]评价不同温度(15℃,20℃,25℃,30℃和35℃)和光周期(8L:16D,12L:12D和16L: 8D)对两种瓢虫[七星瓢虫Coccinella septempunctata (Linnaeus)(一种广布种)和狭臀瓢虫Coccinella transversalis Fabricius(一种东方/南亚瓢虫)]幼虫取食和利用豌豆蚜Acyrthosiphon pisum(Harris)的影响.[结果]尽管两种瓢虫的捕食作用和发育速率均在25℃时最高,但是随着日长的增加(即光周期从8L:16D增加到16L:8D)捕食作用进一步增强.与狭臀瓢虫相比,在所有温度和光周期下,七星瓢虫幼虫的取食量更高,生长和发育速率更快,其新羽化的成虫体重更重.非线性回归模型显示,七星瓢虫和狭臀瓢虫的最低发育温度分别为11℃和10.5℃左右,最高发育温度分别为41℃和43℃左右.狭臀瓢虫的幼虫捕食和发育速率对气候因子的依赖性强于七星瓢虫.[结论]本研究表明,广布种瓢虫对气候因子的敏感性比土著种瓢虫弱,因而可以广泛分布于不同的地理区域.因此,与土著种瓢虫相比,广布种瓢虫更适于作为生防因子.     

Effect of laminaran accumulation on maturation in sporophyte fragments from Ecklonia cava (Phaeophyceae,Laminariales) under various laboratory light and temperature conditions

Fragments of Ecklonia cava Kjellman were cultured under controlled laboratory conditions of light irradiance, water temperature, and photoperiod. To clarify the relationship between the maturation of E. cava and the photosynthetic products, laminaran, the content in the fragments was measured with the progress of maturation. The culture conditions ranged from 12.5 to 100 µmol m^?2 s^?1, 10–25°C, and 14 : 10 h LD (light : dark) to 10 : 14 h LD. In the case of low light conditions, despite an optimum temperature for maturation, the fragments did not form sori and laminaran was not accumulated during the culture period. In the case of sufficient light and non‐optimum temperature conditions, the fragments did not form sori, but laminaran was accumulated. When the fragments were cultured under optimum light and temperature conditions for maturation, laminaran was accumulated in the early stage of maturation, just before or after cortex of the bladelets thickened, and decreased with the progress of maturation, and all fragments matured regardless of the length of the photoperiod. So, these results support the idea that laminaran is used as the main respiratory substrate in the maturation of E. cava.