Photoperiod Is the Main Cue That Triggers Supercooling Ability in the Land Snail, Helix aspersa (Gastropoda: Helicidae)

Helix aspersa hibernates in Brittany (western France), where it may experience subzero temperatures. Studies on cold hardiness, although scarce in land snails, have shown a seasonal variation in supercooling ability, associated with high temperatures of crystallization (Tc). In the present work, two key environmental factors, temperature and photoperiod, were studied to elucidate, how they may affect the enhancement of supercooling ability in the snails from the end of summer to winter. Nine groups of adult snails were acclimated to different combinations of photoperiod (LD-16:8, LD-12:12, and LD-8:16 h) and temperature (15, 10, and 5°C). Temperature of crystallization, hemolymph osmolality, and water content were measured. The results demonstrate a significant effect of the photoperiod on Tc, i.e., shorter photoperiods induce lower Tc (LD-16:8 h, mean Tc = −3.0°C, SD = 2.0; LD-12:12 h, mean Tc = −4.3°C, SD = 1.9; LD-8:16 h, mean Tc = −5.2°C, SD = 1.9; n = 90), whereas the acclimation temperature had no effect. Measurements of hemolymph osmolality and water content showed that osmolality is negatively correlated with water content. Mechanisms such as dehydration are involved in the decrease of Tc. A declining photoperiod triggers a lower Tc, long before the onset of winter conditions. This response may have an adaptive component, allowing individuals to cope with the mild winters typically observed in oceanic regions.     

Bimodal life cycle of the burying beetle Nicrophorus quadripunctatus in relation to its summer reproductive diapause

Abstract 1. Under natural conditions in Kyoto, Japan, the reproductive activities of Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae) decreased in summer and the species showed a bimodal life cycle.
2. In the laboratory, most adult pairs raised at 20 °C under a LD 12:12 h regime reproduced when provided with a piece of chicken. In adults raised at 20 °C under a LD 16:8 h regime, however, both reproductive behaviour and ovarian development were reduced. It is concluded that these adults entered a reproductive summer diapause.
3. High temperature (25 °C) also suppressed the reproductive behaviour even under a favourable LD 12:12 h regime. In the field, therefore, adults reduce their reproductive activity in summer because of diapause induced by long-day photoperiods and direct inhibition of reproduction by high temperatures.
4. When the temperature was changed from 20 °C to 25 °C immediately after hatching of larvae, they reached the wandering stage in 95% of adult pairs. When the temperature was changed from 20 °C to 25 °C immediately after oviposition, however, no larvae hatched in 85% of pairs. Egg mortality was significantly higher at 25 °C than at 20 and 22.5 °C; no eggs hatched at 27.5 °C. The physiological mechanisms for reducing reproduction probably prevent the beetles from inefficient oviposition in summer.     

光周期对西葫芦185品系顶芽和叶片衰老的调控

在短日照下 ,西葫芦 (CucurbitapepoLinn .) 185品系的植株发生衰老。结构学、基因表达与系列生化分析证实 :短日照启动了顶端分生组织由营养生长锥向花芽的转化 ,进而其组成细胞发生编程性死亡 (PCD) ,导致顶端生长势的丧失 ;与长日照处理相比 ,短日照处理在发育晚期也引起大量叶肉细胞发生PCD ,进而叶片出现衰老。核酸酶活性的高度表达是PCD过程中一个非常重要的分子事件。实验证实 ,西葫芦 185品系植株衰老进程的发生与顶端分生组织和叶肉细胞中发生PCD密切相关。     

Circannual Growth Rhythm in a Brown Alga,Pterygophora californica

A circannual rhythm was found in the kelp Pterygophora californica which forms a new blade with a free running period of 7 ? 8 months under constant conditions. Individual plants exposed to cycles of daylength with T = 12, 6, or 3 months performed 1, 2, or 4 growth cycles, respectively, in one calendar year showing the entrainment of the endogenous circannual rhythm. The annual growth cycle also followed a phase shift of the annual cycle of daylength (T = 12 months) by 3 or 6 months.     

A mutant strain of Chymomyza costata (Diptera: Drosophilidae) insensitive to diapause-inducing action of photoperiod

ABSTRACT. From a Japanese population of Chymomyza costata which has been known to have a photoperiodic larval diapause, we selected a mutant strain which did not respond to photoperiod. However, about 70% of the individuals of this strain entered diapause at 11^oC irrespective of photoperiod, and about the same percentage of those of the photoperiod-sensitive strain also did so in continuous illumination at 11^oC. This indicates that low temperature induces diapause independently of photoperiod. On the other hand, a temperature drop from 18 or 25^oC to 15^oC and chilling at 4^oC did not induce diapause.     

The critical field photoperiod inducing ovarian diapause in the cabbage whitefly, Aleyrodes proletella (Homoptera: Aleyrodidae)

ABSTRACT. The ovarian and fat body development of cabbage whitefly, Aleyrodes proletella L., has been determined from field samples taken during the transition from a summer to an overwintering population. Between mid and late September 1983, the state of ovarian development decreases as the proportion of diapausing females increases. This is accompanied by maximum fat body development. Diapausing females emerge from late August onwards, and the critical photoperiod, based upon known larval sensitivity and including civil twilight as part of the photophase, is LD 15.5:8.5h. This is in agreement with laboratory studies. The majority of overwintering females are mated. Very few males survive the autumn.     

The endocrine control of reproduction in Nereidae: a new multi-hormonal model with implications for their functional role in a changing environment

Nereidae are vital to the functioning of estuarine ecosystems and are major components in the diets of over-wintering birds and commercial fish. They use environmental cues to synchronize reproduction. Photoperiod is the proximate cue, initiating vitellogenesis in a temperature-compensated process. The prevailing paradigm in Nereidae is of a single ‘juvenile’ hormone controlling growth and reproduction. However, a new multi-hormone model is presented here that integrates the environmental and endocrine control of reproduction. This is supported by evidence from in vitro bioassays. The juvenile hormone is shown to be heat stable and cross reactive between species. In addition, a second neuro-hormone, identified here as a gonadotrophic hormone, is shown to be present in mature females and is found to promote oocyte growth. Furthermore, dopamine and melatonin appear to switch off the juvenile hormone while serotonin and oxytocin promote oocyte growth. Global warming is likely to uncouple the phase relationship between temperature and photoperiod, with significant consequences for Nereidae that use photoperiod to cue reproduction during the winter in northern latitudes. Genotypic adaptation of the photoperiodic response may be possible, but significant impacts on fecundity, spawning success and recruitment are likely in response to short-term extreme events. Endocrine-disrupting chemicals may also impact on putative steroid hormone pathways in Nereidae with similar consequences. These impacts may have significant implications for the functional role of Nereidae and highlight the importance of comparative endocrinology studies in these and other invertebrates.     

Effect of photoperiod and allatectomy on reproduction and (second) diapause induction in post-diapause adult females of the Colorado potato beetle,Leptinotarsa decemlineata Say

Summary

The effect of photoperiod and allatectomy on the rates of oviposition and juvenile hormone (JH) synthesis was studied in female beetles after the break of adult diapause. The results indicate that after diapause, photoperiod has no effect on oviposition rates. However, the photoperiodic effect on diapause induction is restored within a few days after the break of the first diapause. Allatectomy performed within one day after diapause did not induce a second diapause, whereas about 40% of the beetles allatectomized after 3 or more days responded by entering a second diapause. Oogenesis in the operated animals was never completely prevented under long and short day conditions. These preliminary results suggest a change in the sensitivity of post-diapause beetles to photoperiodic and endocrine manipulation as compared with pre-diapause insects.