Plastic changes in cold and drought tolerance of Drosophila nepalensis correlate with sex-specific differences in body melanization, cuticular lipid mass, proline accumulation, and seasonal abundance

The Sex Ratio Indicates the Conclusion and Onset of Population Cycles in the Beet Webworm Loxostege sticticalis L. (Lepidoptera: Pyralidae)

Beet webworms, Loxostege sticticalis L. (Lepidoptera: Pyralidae), are one of the most destructive pest insects in northern China, and their populations outbreak periodically. Developing an indicator that defines the ending and beginning of the occurrence period cycle is urgent for the population forecast and theoretical study. The sex ratio can be a primary pathway through which species regulate population size. We measured the maximum mating potential of both females and males and the population net reproductive rate under different sex ratios (e.g., 3:1, 2:1, 1:1, 1:2, 1:3). The maximum mating frequency of males was 2.91 times that of females. The progeny contribution per mating decreased with increased mating times in males. The variation in population net reproductive rate affected by the sex ratio fits the parabolic curve analysis and peaked at 1.82 for females vs. males. Our results illustrate the quantitative connection phenomenon shown by the historical data: population outbreaks occur at a sex ratio of two or more and collapse at a sex rate lower than one. Simultaneously, the sex ratio may be utilized as a definite indicator for the beginning and end of the future occurrence cycle in the beet webworm.

Early-life exposure to tobacco smoke alters airway signaling pathways and later mortality in D. melanogaster

Early life environmental influences such as exposure to cigarette smoke (CS) can disturb molecular processes of lung development and thereby increase the risk for later development of chronic respiratory diseases. Among the latter, asthma and chronic obstructive pulmonary disease (COPD) are the most common. The airway epithelium plays a key role in their disease pathophysiology but how CS exposure in early life influences airway developmental pathways and epithelial stress responses or survival is poorly understood. Using Drosophila melanogaster larvae as a model for early life, we demonstrate that CS enters the entire larval airway system, where it activates cyp18a1 which is homologues to human CYP1A1 to metabolize CS-derived polycyclic aromatic hydrocarbons and further induces heat shock protein 70. RNASeq studies of isolated airways showed that CS dysregulates pathways involved in oxidative stress response, innate immune response, xenobiotic and glutathione metabolic processes as well as developmental processes (BMP, FGF signaling) in both sexes, while other pathways were exclusive to females or males. Glutathione S-transferase genes were further validated by qPCR showing upregulation of gstD4, gstD5 and gstD8 in respiratory tracts of females, while gstD8 was downregulated and gstD5 unchanged in males. ROS levels were increased in airways after CS. Exposure to CS further resulted in higher larval mortality, lower larval-pupal transition, and hatching rates in males only as compared to air-exposed controls. Taken together, early life CS induces airway epithelial stress responses and dysregulates pathways involved in the fly's branching morphogenesis as well as in mammalian lung development. CS further affected fitness and development in a highly sex-specific manner.

Adaptive changes in energy reserves and effects of body melanization on thermal tolerance in Drosophila simulans

Seasonally polyphenic types have been documented in many Drosophilids, which differ significantly during thermal stress. Although Drosophila simulans is a sibling species to Drosophila melanogaster, both thrive in the temperate and tropical climates, but various climatic factors are expected to impact their distribution and abundance. As a result, D. simulans may use phenotypic plasticity to adapt to colder and drier circumstances in temperate zones, although such studies are less known. In the present study, our main aim was to find a link between adaptive plasticity and thermal tolerance in D. simulans. We characterized two morphs in D. simulans flies based on the abdominal melanization collected from the same locality and season, as this trait is highly associated with the larval developmental conditions. Our results suggested that flies reared from dark and light morph showed significant differences in the basal level of proline, carbohydrates (trehalose, glycogen), and lipids (cuticular lipids and total body lipids) within simulated seasons and morph lineages in D. simulans flies. We further showed that D. simulans reared from dark morph are better adapted to cold conditions, whereas light flies are more adapted to warm conditions. The flies, both from light and dark morph lineages, when reared at 15 °C, showed an increase in the level of total body lipids after acclimation at 0 °C but a decrease in the level of proline and carbohydrates (trehalose, glycogen). Heat acclimation increases glycogen levels in the flies from light morph lineage while decreases trehalose and proline.