The Physiological Cost of Being Hot: High Thermal Stress and Disturbance Decrease Energy Reserves in Dragonflies in the Wild

Anthropogenic disturbance alters macro and microclimatic conditions, often increasing ambient temperatures. These changes can strongly affect insects, particularly those experiencing high thermal stress (i.e, large differences between body and environmental temperature), as prolonged exposure to elevated temperatures can reduce their energetic reserves due to increased metabolic demands and physiological stress. We evaluated thermal stress in 16 insect dragonfly species during two sampling periods (2019 and 2022) in preserved and disturbed sites within a tropical dry forest in western Mexico. Also, we compared energetic condition (lipid and protein content) and thoracic mass for the seven most abundant species between both habitat types. In preserved sites, insects showed higher thermal stress at lower maximum temperatures, which decreased as temperatures increased. Dragonflies in disturbed sites maintained consistent levels of thermal stress across the temperature gradient. Thermal stress and body size were positively associated, and both were linked to lower lipid and protein content. Despite this, individuals from disturbed sites were larger but had lower energy reserves than those from preserved sites. Our findings suggest that although species can persist in disturbed environments, their energetic condition may be compromised, especially in individuals experiencing high thermal stress — potentially affecting their performance and fitness. Preserving suitable habitats is essential not only for maintaining species diversity but also ensuring ecological functions, particularly those performed by flying insects with high thermal stress such as dragonflies.