Developmental Stability Across Seasons but Not Months: Wing Asymmetry Responses of an Orchid Bee to Short-Term Climate Variability

Fluctuating asymmetry (FA) and wing shape variation have been widely proposed as sensitive indicators of developmental instability and environmental stress in insects, yet their temporal dynamics remain poorly explored in tropical systems. In this study, we examined fine-scale temporal and environmental variation in wing FA and shape of the orchid bee Euglossa imperialis Cockerell, 1922 within a tropical dry forest of central Panama. Using geometric morphometrics, we quantified bilateral wing asymmetry and shape variation across monthly sampling periods spanning dry and rainy seasons, integrating high-resolution climatic data. Overall FA values were low and showed no significant differences between seasons, indicating high developmental stability across broad seasonal regimes. Similarly, wing shape exhibited extensive overlap between dry and rainy seasons, with no discrete seasonal differentiation. In contrast, both FA and wing shape varied significantly among months, revealing a gradual and continuous temporal signal. Minimum temperature and relative humidity emerged as the main environmental variables associated with FA, whereas precipitation showed no detectable effect. These results indicate that developmental instability and wing morphology in E. imperialis are primarily shaped by short-term climatic variability rather than by categorical seasonal contrasts. Our findings highlight the importance of fine temporal resolution when evaluating morphological responses to environmental conditions and suggest that FA and wing shape function as scale-dependent indicators of environmental variation. Integrating geometric morphometrics with high-resolution climate data provides a powerful framework for refining the use of orchid bees as bioindicators in tropical ecosystems.