Trade-offs between Winter Survival and Reproduction in Female Insects

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.

Endocrine and enzymatic shifts during insect diapause: a review of regulatory mechanisms

Insect diapause is a vital survival strategy that enables insects to enter a state of suspended development, allowing them to withstand unfavorable environmental conditions. During diapause, insects significantly lower their metabolic rate and build up energy reserves, which they gradually utilize throughout this period. The regulation of diapause involves a complex interaction of hormones and enzymes. Juvenile hormones (JHs) affect adults and larvae differently; in adults, the absence of JH typically triggers diapause, while in larvae, the presence of JH encourages this state. Ecdysteroids, which regulate molting and metamorphosis, are carefully controlled to prevent premature development. Reduced signaling of insulin-like peptides enhances stress resistance and promotes energy storage. Several enzymes play crucial roles in the metabolic adjustments necessary for diapause. These adjustments include the degradation of JH, the ecdysteroidogenic pathway, and the metabolism of fatty acids, glycogen, cryoprotectants, and stress responses. Understanding diapause's molecular and biochemical mechanisms is essential for fundamental entomological research and practical applications. Despite recent advances, many aspects of diapause regulation, especially the interactions among hormonal pathways and the role of enzymes, remain poorly understood. This review analyzes approximately 250 papers to consolidate current knowledge on the enzymatic and hormonal regulation of diapause. It offers a comprehensive overview of key processes based on recent studies and suggests future research directions to fill gaps in our understanding of this significant biological phenomenon. The review also lays the groundwork for enhancing pest control strategies and ecological conservation by deepening our understanding of diapause mechanisms.

Introduction to the Symposium: An Integrative Look at Whole-organism Trade-offs from the Female-centered Perspective of Biology

Trade-offs during reproduction have long been a central focus within biology and much of the foundational work within life history evolution has focused on females, as the fitness of females is more easily quantified for use in theoretical models. However, in many regards, the field of organismal biology has deviated from this early focus on females, particularly as it relates to the nuances and dynamic nature of female reproduction. Regardless, at the organismal level, reproduction is thought to trade-off with other simultaneously occurring processes. Recent papers have sought to outline the issues with our current understanding of whole-organism trade-offs, though the field as a whole has not come to a consensus on what trade-offs mean to a reproducing female. To rectify this important gap in how trade-offs are discussed in organismal biology as well as confusion about what constitutes a trade-off, our overarching goal of this symposium was to discuss trade-offs from an integrative perspective that places female reproduction at the center. By answering what trade-offs are and what they mean to reproducing females, what has been neglected in the context of whole-organism physiology, and how maternal effects fit within this framework, our group of speakers and their associated papers will crystalize nuances of measuring and determining presence (if any) of trade-offs in reproducing females in a range of taxa and subfields.

Light pollution disrupts seasonal reproductive phenotypes and reduces lifespan in the West Nile vector, Culex pipiens

Females of the Northern House mosquito, Culex pipiens, are important disease vectors as they transmit pathogens including West Nile virus. These females survive the winter by entering diapause, a state of dormancy, characterized by the accumulation of lipids, cessation of blood-feeding, and reproductive arrest. Diapause is cued by photoperiod, so as days become short in late summer and early fall, female Cx. pipiens prepare to overwinter and disease transmission decreases. We previously demonstrated that Artificial light at night (ALAN) causes female Cx. pipiens to avert diapause and continue to blood-feed when reared under short-day conditions. Additionally, light pollution alters seasonal differences in mosquito activity and nutrient reserves. However, it is unclear how exposure to ALAN affects blood-feeding and fecundity in long-day reared females, as well as the survival of Cx. pipiens exposed under both short and long-day conditions. In this study, we hypothesized that females exposed to ALAN in long-day conditions would have a lower proclivity to blood-feed, reduced fecundity, and reduced survival. Results from our lab-based experiments demonstrate that females exposed to ALAN in long-day conditions were less likely to blood-feed but were more fecund than long-day reared females that were not exposed to ALAN, and that ALAN exposure did not affect lifespan of long-day reared females. Additionally, we hypothesized ALAN exposure under short-day conditions would reduce survival, and our data supports this hypothesis. Overall, our results demonstrate that ALAN is an important urban stressor that has the potential to affect reproduction and lifespan in mosquitoes, and therefore has the potential to create evolutionary tradeoffs.