Adaptation to Hot and Humid Climates in the Silkworm: Energy Reallocation and Cuticle Transpiration

Area of Science:

• Insect physiology and genetics
• Climate change adaptation
• Evolutionary biology

Background:

• Silkworms (Bombyx mori) possess valuable germplasm, including strains adapted to tropical/subtropical humid climates.
• Understanding thermotolerance mechanisms is crucial for insect adaptation to climate change.

Purpose of the Study:

• To investigate the physiological and transcriptomic responses of silkworm strains with varying heat tolerance under combined temperature and humidity stress.
• To identify genes and molecular pathways involved in heat resistance and adaptation to hot, humid environments.

Main Methods:

• Comparative analysis of two thermotolerant and one sensitive silkworm strain under controlled temperature and humidity conditions.
• Physiological measurements and transcriptomic profiling (RNA sequencing) of fifth instar larvae.
• Co-expression network analysis to identify evolved thermoplastic genes (Evo_TPGs) and evolved non-plastic genes (Evo_non-PGs).

Main Results:

• High humidity exacerbates heat stress effects only under high temperatures.
• Identified 88 Evo_TPGs and 1338 Evo_non-PGs specific to thermotolerant strains.
• Downregulation of cuticular protein genes in thermotolerant strains may enhance heat dissipation via transpiration.
• Thermotolerant silkworms exhibit suppressed metabolic rates and enhanced oxidative stress response.
• Heat resistance genes show higher SNP frequency, indicating natural selection.

Conclusions:

• Thermotolerant silkworms adapt by dynamically regulating cuticle respiration and metabolic processes to manage internal temperature and oxidative stress.
• These findings highlight the role of evolved genetic mechanisms in insect adaptation to climate change.
• Insights into silkworm heat resistance provide a model for understanding insect adaptation to global warming.