Maternally Instigated Diapause in Aedes albopictus: Coordinating Experience and Internal State for Survival in Variable Environments

The role of insulin receptor InR in photoperiod-regulated reproductive diapause of Chrysoperla nipponensis

Insects usually diapause, a process regulated by hormonal signals as an adaptive mechanism developed through long-term evolution to survive unfavorable environmental conditions. Chrysoperla nipponensis is classified as a photoperiod-sensitive insect. Treatments with short-day (SD) and long-day (LD) conditions have distinct effects on ovarian development and lipid accumulation in adults, with SD condition inducing diapause. Injecting bovine insulin promoted ovarian development and egg formation in diapause females, while injecting insulin receptor induced diapause-like traits in reproductive females. This study investigate the biological function of insulin signaling in the reproductive diapause of females of C. nipponensis. Under SD treatment the mRNA expression level of InR1 and InR2, as well as the protein expression level of InR1 were significantly reduced. This reduction led to stagnant ovarian development, increased adipose tissue mass, and a significant rise in triglyceride (TG) content. Silencing InR1 under LD conditions resulted in halted ovarian development and enhanced lipid accumulation, with the expression levels of Akt, Kr-h1, and Vg significantly decreased mirroring those observed under SD conditions. Interestingly, silencing InR2 under LD condition did not affect ovarian development. Furthermore, transcriptome analysis identified six genes (Akt, PkN, Skp2, CycB3, BTrC, and AurkA) associated with reproductive regulation and eight genes (FadΔ11, EchA, EcI, Ugts (2A3, 1-9), AR, Gpdh and Cbr) linked to lipid metabolism, all of which are involved in InR1 mediated regulation of C. nipponensis reproduction.

Elevated developmental temperatures below the lethal limit reduce Aedes aegypti fertility

Aedes aegypti mosquitoes are the principal vectors of dengue and continue to pose a threat to human health, with ongoing urbanization, climate change and trade all impacting the distribution and abundance of this species. Hot periods are becoming increasingly common and their impacts on insect mortality have been well established, but they may have even greater impacts on insect fertility. In this study, we investigated the impacts of high temperatures on Ae. aegypti fertility both within and across generations. Mosquitoes developing under elevated temperatures exhibited higher critical thermal maxima (CTmax), reflecting developmental acclimation, but their fertility declined with increasing developmental temperature. In females, elevated developmental temperatures decreased fecundity while in males it tended to decrease the proportion of eggs that hatched and the proportion of individuals producing viable offspring. Rearing both sexes at 35°C increased fecundity in the subsequent generation but effects of elevated temperatures persisted across gonotrophic cycles within the same generation. Moreover, exposure of adults to 35°C further decreased fertility beyond the effects of developmental temperature alone. These findings highlight sub-lethal impacts of elevated temperatures on Ae. aegypti fertility and plastic responses to thermal stress within and across generations. This has significant implications for predicting the distribution and abundance of mosquito populations thriving in increasingly warmer environments.

Differentially expressed microRNAs in brains of adult females may regulate the maternal block of diapause in Sarcophaga bullata

The maternal regulation of diapause is one type of phenotypic plasticity where the experience of the mother leads to changes in the phenotype of her offspring that impact how well-suited they will be to their future environment. Sarcophaga bullata females with a diapause history produce offspring that cannot enter diapause even if they are reared in a diapause inducing environment. Accumulating evidence suggests that microRNAs regulate diapause and, possibly, maternal regulation of diapause. We found significant differences in the abundances of several microRNAs (miR-125-5p, miR-124-3p, miR-31-5p, and miR-277-3p) in brains dissected from adult female S. bullata that had experienced diapause compared to females with no diapause history. We also found moderate differences in the mRNA expression of the circadian-clock related genes, clock, clockwork orange, and period. MiR-124-3p and miR-31-5p are part of a gene network that includes these circadian clock-related genes. Taken together our results suggest the maternal block of diapause in S. bullata is regulated, at least in part, by a network that includes microRNAs and the circadian clock.

The effect of artificial light at night (ALAN) on the characteristics of diapause of Aedes albopictus

BACKGROUND

Recently, the effect of artificial light at night (ALAN) on the physiology and behavior of insects has gradually attracted the attention of researchers and has become a new research topic. Aedes albopictus is an important vector that poses a great public health risk. Further studies on the diapause of Ae. albopictus can provide a basis for new vector control, and it is also worth exploring whether the effect of ALAN on the diapause of Ae. albopictus will provide a reference for the prevention and control of infectious diseases mediated by Ae. albopictus.

METHODS

In this study, we experimentally studied the diapause characteristics of different geographical strains of Ae. albopictus under the interference of ALAN, explored the effect of ALAN on the diapause of Ae. albopictus and explored the molecular mechanism of ALAN on the diapause process through RNA-seq.

RESULTS

As seen from the diapause incidence, Ae. albopictus of the same geographic strain showed a lower diapause incidence when exposed to ALAN. The differentially expressed genes (DEGs) were mainly enriched in signaling and metabolism-related pathways in the parental females and diapause eggs of the ALAN group.

CONCLUSIONS

ALAN inhibits Ae. albopictus diapause. In the short photoperiod induced diapause of Ae. albopictus in temperate strain Beijing and subtropical strain Guangzhou, the disturbance of ALAN reduced the egg diapause rate and increased the egg hatching rate of Ae. albopictus, and the disturbance of ALAN also shortened the life cycle of Ae. albopictus eggs after hatching.

The population genetics of partial diapause, with applications to the aestivating malaria mosquito Anopheles coluzzii

Diapause, a form of dormancy to delay or halt the reproductive development during unfavourable seasons, has evolved in many insect species. One example is aestivation, an adult-stage diapause enhancing malaria vectors' survival during the dry season (DS) and their re-establishment in the next rainy season (RS). This work develops a novel genetic approach to estimate the number or proportion of individuals undergoing diapause, as well as the breeding sizes of the two seasons, using signals from temporal allele frequency dynamics. Our modelling shows the magnitude of drift is dampened at early RS when previously aestivating individuals reappear. Aestivation severely biases the temporal effective population size (N e $$ {N}_e $$ ), leading to overestimation of the DS breeding size by1 / 1 - α 2 $$ 1/{\left(1-\alpha \right)}^2 $$ across 1 year, whereα $$ \alpha $$ is the aestivating proportion. We find sampling breeding individuals in three consecutive seasons starting from an RS is sufficient for parameter estimation, and perform extensive simulations to verify our derivations. This method does not require sampling individuals in the dormant state, the biggest challenge in most studies. We illustrate the method by applying it to a published data set for Anopheles coluzzii mosquitoes from Thierola, Mali. Our method and the expected evolutionary implications are applicable to any species in which a fraction of the population diapauses for more than one generation, and are difficult or impossible to sample during that stage.

Context and the functional use of information in insect sensory ecology

Context-specific behaviors emerge from the interaction between an animal's internal state and its external environment. Although the importance of context is acknowledged in the field of insect sensory ecology, there is a lack of synthesis on this topic stemming from challenges in conceptualizing 'context'. We address this challenge by gleaning over the recent findings on the sensory ecology of mosquitoes and other insect pollinators. We discuss internal states and their temporal dynamics, from those lasting minutes to hours (host-seeking) to those lasting days to weeks (diapause, migration). Of the many patterns reviewed, at least three were common to all taxa studied. First, different sensory cues gain prominence depending on the insect's internal state. Second, similar sensory circuits between related species can result in different behavioral outcomes. And third, ambient conditions can dramatically alter internal states and behaviors.

Maternal body condition and season influence RNA deposition in the oocytes of alfalfa leafcutting bees (Megachile rotundata)

Maternal effects are an important source of phenotypic variance, whereby females influence offspring developmental trajectory beyond direct genetic contributions, often in response to changing environmental conditions. However, relatively little is known about the mechanisms by which maternal experience is translated into molecular signals that shape offspring development. One such signal may be maternal RNA transcripts (mRNAs and miRNAs) deposited into maturing oocytes. These regulate the earliest stages of development of all animals, but are understudied in most insects. Here we investigated the effects of female internal (body condition) and external (time of season) environmental conditions on maternal RNA in the maturing oocytes and 24-h-old eggs (24-h eggs) of alfalfa leafcutting bees. Using gene expression and WGCNA analysis, we found that females adjust the quantity of mRNAs related to protein phosphorylation, transcriptional regulation, and nuclease activity deposited into maturing oocytes in response to both poor body condition and shorter day lengths that accompany the late season. However, the magnitude of these changes was higher for time of season. Females also adjusted miRNA deposition in response to seasonal changes, but not body condition. We did not observe significant changes in maternal RNAs in response to either body condition or time of season in 24-h eggs, which were past the maternal-to-zygotic transition. Our results suggest that females adjust the RNA transcripts they provide for offspring to regulate development in response to both internal and external environmental cues. Variation in maternal RNAs may, therefore, be important for regulating offspring phenotype in response to environmental change.