Temperature and Photoperiodic Response of Diapause Induction in Anastatus japonicus, an Egg Parasitoid of Stink Bugs

Anastatus japonicus Ashmead is a widely used biological control agent against stink bugs that can be successfully reared using the large eggs of the Chinese silkworm. In this study, environmental factors responsible for the induction of diapause in A. japonicus were investigated on host eggs of the Chinese silkworm. A. japonicus exhibited a facultative, mature larval diapause within its host eggs. Second–third instar larva are the most sensitive stages to diapause stimuli. The accumulation of diapause stimuli during all the larval stages maximized the diapause response. A short photoperiod of 10L:14D and temperature of 17 °C led to the occurrence of the highest diapause response, while a long photoperiod (14L:10D) and low temperatures (11 and 14 °C) prevented the diapause. A specific exposure period was required to reach high diapause incidence. Diapausing mature larvae had a significantly higher survival rate after 180 days storage at 10 °C than that of nondiapausing mature larvae. Taken together, results suggest methods that could be exploited in the developmental regulation, field-release pretreatment technology, and long-term storage of A. japonicus.

Comparative Study of the Phenotypic Structure and Photoperiodic Responses of Female Asian Ladybirds Harmonia axyridis (Pallas) (Coleoptera, Coccinellidae) from Moscow, Belgorod, and Sochi

Insect invasions are often accompanied by changes in the phenotypic structure of the populations and in the photoperiodic responses that regulate seasonal cycles. The Asian ladybird Harmonia axyridis has been recently discovered in Krasnodar Territory, from whence it is now gradually colonizing Central Russia. Our comparative study of individuals collected in 2020 in Sochi, Belgorod Province, and Moscow Province shows that interpopulation differences in their phenotypic structure are nonsignificant. The proportion of the light morph succinea is 77–83%; the proportion of the most common dark morph, spectabilis, is 13–20%. Laboratory experiments show that females from all the studied populations exhibit only a weak photoperiodic response. Comparative analysis reveals that females from the more northerly Moscow and Belgorod populations have a somewhat greater tendency to diapause and slightly delay reproductive maturation.

Gene duplication and loss of AANAT in mammals driven by rhythmic adaptations

Arylalkylamine N-acetyltransferase (AANAT) plays a crucial role in synchronizing internal biological functions to circadian and circannual changes. Generally speaking, only one copy of AANAT gene has been found in mammals, however, three independent duplications of this gene were detected in several cetartiodactyl lineages (i.e., Suidae, Hippopotamidae, and Pecora) that originated in the middle Eocene, a geological period characterized with the increased climate seasonality. Lineage-specific expansions of AANAT and the associated functional enhancement in these lineages strongly suggest an improvement in regulating photoperiodic response to adapt to seasonal climate changes. In contrast, independent inactivating mutations or deletions of the AANAT locus were identified in the four pineal-deficient clades (cetaceans, sirenians, xenarthrans, and pangolins). Loss of AANAT function in cetaceans and sirenians could disrupt the sleep-promoting effects of pineal melatonin, which might contribute to increasing wakefulness, adapting these clades to underwater sleep. The absence of AANAT and pineal glands in xenarthrans and pangolins may be associated with their body temperature maintenance. The present work demonstrates a far more complex and intriguing evolutionary pattern and functional diversity of mammalian AANAT genes than previously thought, and provides further evidence for understanding AANAT evolution as driven by rhythmic adaptations in mammals.

Oviposition-promoting pars intercerebralis neurons show period-dependent photoperiodic changes in their firing activity in the bean bug

Animals show photoperiodic responses in physiology and behavior to adapt to seasonal changes. Recent genetic analyses have demonstrated the significance of circadian clock genes in these responses. However, the importance of clock genes in photoperiodic responses at the cellular level and the physiological roles of the cellular responses are poorly understood. The bean bug Riptortus pedestris shows a clear photoperiodic response in its reproduction. In the bug, the pars intercerebralis (PI) is an important brain region for promoting oviposition. Here, we analyzed the role of the photoperiodic neuronal response and its relationship with clock genes, focusing on PI neurons. Large PI neurons exhibited photoperiodic firing changes, and high firing activities were primarily found under photoperiodic conditions suitable for oviposition. RNA interference-mediated knockdown of the clock gene period abolished the photoperiodic response in PI neurons, as well as the response in ovarian development. To clarify whether the photoperiodic response in the PI was dependent on ovarian development, we performed an ovariectomy experiment. Ovariectomy did not have significant effects on the firing activity of PI neurons. Finally, we identified the output molecules of the PI neurons and analyzed the relevance of the output signals in oviposition. PI neurons express multiple neuropeptides—insulin-like peptides and diuretic hormone 44—and RNA interference of these neuropeptides reduced oviposition. Our results suggest that oviposition-promoting peptidergic neurons in the PI exhibit a circadian clock-dependent photoperiodic firing response, which contributes to the photoperiodic promotion of oviposition.

Photoperiodic Response of In Vitro Cannabis sativa Plants

The majority of commercial Cannabis sativa L. (cannabis) cultivators use a 12.0-hour uninterrupted dark period to induce flowering; however, scientific information to prove this is the optimal dark period for all genotypes is lacking. Knowing genotype-specific photoperiods may help to promote growth by providing the optimal photoperiod for photosynthesis. To determine whether the floral initiation of cannabis explants respond to varied photoperiods in vitro, explants were grown under one of six photoperiod treatments: 12.0, 13.2, 13.8, 14.4, 15.0, and 16.0 hours per day for 4 weeks. The percentage of flowering explants was highest under 12.0- and 13.2-hour treatments. There were no treatment effects on the fresh weight, final height, and growth index. Based on the results, it is recommended that an uninterrupted dark period of at least 10.8 hours (i.e., 13.2-hour photoperiod) be used to induce flowering for the ‘802’ genotype. In vitro flowering could provide a unique and high-throughput approach to study floral/seed development and secondary metabolism in cannabis under highly controlled conditions. Further research should determine if this response is the same on the whole-plant level.

In Planta Monitoring of Cold-Responsive Promoter Activity Reveals a Distinctive Photoperiodic Response in Cold Acclimation

Plant cold acclimation involves complicated pathways that integrate signals from temperature changes and light conditions. To understand plant responses to environmental signals in detail, molecular events that are regulated by temperature and light must be investigated at the whole-plant level in a nondestructive way. Using the promoter of COR15A connected to the luciferase reporter gene as a cold-responsive indicator, we developed an in planta monitoring system for gene expression under controlled temperature and photoperiod conditions. COR15A promoter activity was intensified by day–night cycles at 2°C, while its induction was abruptly suppressed in the dark at 8°C or higher, indicating a difference in responsiveness to photocycle between these two acclimation conditions. Freeze–thawing tests of whole plants proved that lower acclimation temperature resulted in higher tolerance to freezing, consistent with the temperature-dependent induction of COR15A. Inhibition of photosynthetic electron transport by 3-(3,4-dichlorophenyl)-1,1-dimethylurea eliminated the responsiveness to the day–night cycles at 2°C, indicating a possibility that the photosynthetic redox and/or the accumulation of photosynthates modulate COR15A responsiveness to photoperiod during cold acclimation, in addition to the well-known regulation by CBF (C-repeat binding factor) genes. These findings indicate that the cold-responsive promoter is regulated by distinctive mechanisms dependent on temperature and simultaneously affected by photocycle and photosynthesis.

Photoperiodic Response of in vitro Cannabis sativa Plants

Most commercial Cannabis sativa L. (cannabis) genotypes are short-day plants and cultivators typically use a 12.0 h uninterrupted dark period to induce flowering; however, scientific information is lacking to prove this is the optimal dark period for all genotypes, and cultivar specific photoperiods may increase productivity. Tissue culture can be used for research requiring multiple treatments, proper replication, and in a controlled environment on a smaller scale compared to greenhouse and indoor facilities. To determine whether cannabis explants can flower under varied photoperiods in vitro, explants were grown under one of six photoperiod treatments: 12.0, 13.2, 13.8, 14.4, 15.0, and 16.0 h for four weeks. The percentage of flowering explants was highest under 12.0 and 13.2 h treatments. There were no treatment effects on the fresh weight, final height, or growth index of the explants. The results suggest an uninterrupted dark period of at least 10.8 h (i.e. 13.2 h photoperiod) is needed to induce the flowering of this genotype. In vitro flowering could provide a unique and high throughput approach to study floral/seed development and secondary metabolism in cannabis under highly controlled conditions. Further research should determine if this response is the same on a whole plant level.

Adaptive value of circadian rhythms in High Arctic Svalbard ptarmigan

SUMMARYThe arctic archipelago of Svalbard (74 to 81° North) experiences extended periods of uninterrupted daylight in summer and uninterrupted darkness in winter. Species native to Svalbard display no daily rhythms in behaviour or physiology during these seasons, leading to the view that circadian rhythms may be redundant in arctic environments [1, 2]. Nevertheless, seasonal changes in the physiology and behaviour of arctic species rely on photoperiodic synchronisation to the solar year. Since this phenomenon is generally circadian-based in temperate species, we investigated if this might be a preserved aspect of arctic temporal organisation.Here, we demonstrate the involvement of the circadian clock in the seasonal photoperiodic response of the Svalbard ptarmigan (Lagopus muta hyperborea), the world’s northernmost resident bird species. First, we show the persistence of rhythmic clock gene expression under constant conditions within the mediobasal hypothalamus and pars tuberalis, the key tissues in the seasonal neuroendocrine cascade. We then employ a “sliding skeleton photoperiod” protocol, revealing that the driving force behind seasonal biology of the Svalbard ptarmigan is rhythmic sensitivity to light, a feature that depends on a functioning circadian rhythm. Our results suggest that the unusual selective pressure of the Arctic relaxes the adaptive value of the circadian clock for organisation of daily activity patterns, whilst preserving its importance for seasonal synchronisation. Thus, our data simultaneously reconnects circadian rhythms to life in the Arctic and establishes a universal principle of evolutionary value for circadian rhythms in seasonal biology.