Seasonal changes in the transcriptome of bat eyes reveal adaptive changes to exploit summer twilight

Sensory systems of many organisms display periodic adjustments to accommodate cyclical changes in the local environmental conditions. Seasonal fluctuations in visual perception are documented in many species, including humans, but the mechanisms and ecological significance of these adaptations often remain obscure. Despite limited knowledge of bat visual ecology relative to hearing, the diversity of bat species makes them useful models for studying sensory adaptation mechanisms. Here, we analyze daily and seasonal changes in gene expression in the eyes of a temperate echolocating bat, the Mexican free-tailed bat (Tadarida brasiliensis). A total of 44 wild-caught bats were sampled from the same location across all four seasons, with whole eyes sequenced for total mRNA expression. Expression patterns were analyzed using differential expression analysis and clustering techniques for identifying correlation networks and evidence of cyclical enrichment. In addition, a target gene list representing key physiological processes was applied to assess which biological pathways displayed the most robust seasonal or daily changes. About 17.8% of genes showed significant differential expression based on season, compared with 11.5% of genes for daily expression. Several gene networks related to the circadian clock, phototransduction, and metabolic function displayed significant rhythmic seasonal effects. Quantum catch modeling indicates higher photon capture potential in summer based on weighted opsin expression, consistent with an adaptive response to lower twilight irradiance. Seasonal remodeling of the ocular transcriptome is consistent with enhanced phototransduction in summer, suggesting vision may play a greater role during this period.NEW & NOTEWORTHY The visual ecology of insectivorous bats remains obscure due to challenges studying their natural behaviors in the wild. Using functional genomics, we can identify physiological changes that may highlight when vision matters most for bats. Our results reveal a dynamic sensory response to environmental light, with visual sensitivity optimized for summer twilight. This study provides the first evidence of seasonal plasticity in bat vision and underscores the importance of studying nonmodel species in natural contexts.