Daily sperm release rhythms in wild geometer moths: comparative characteristics across ecologically diverse species.

Temperate-zone Geometridae moths, active across seasons, offer an excellent model for investigating how related species respond to varying environmental conditions, particularly photoperiod-a major Zeitgeber regulating biological oscillators. In this study, we examined the daily cycle of sperm release from the testes in 9 geometer moth species, including univoltine and bivoltine taxa, as well as diurnal and nocturnal species. We found that sperm release into the upper vasa deferentia differs consistently between day-flying and night-flying species. Moreover, we observed marked differences in the diel regulation of sperm release between spring and summer generations of the same species. Experimental evidence suggests that these intergenerational differences are photoperiod-dependent. Further manipulation confirmed that a long photoperiod not only abolishes rhythmic sperm release but also significantly reduces the number of eupyrene sperm bundles transferred into the vasa deferentia. This is the first demonstration, under near-natural conditions, of photoperiodic regulation of a physiological rhythm in a peripheral organ via its suppression. These findings underscore the importance of environmental timing cues in reproductive physiology and provide new insights into the temporal plasticity of insect reproductive systems. Importantly, they also highlight the potential for integrating agro-chronobiological knowledge with mechanistic studies of temporal regulation in insect pests. Finally, this work adds to our understanding of how peripheral oscillators may be shaped by selective pressures in closely related species occupying distinct ecological niches, where differences in the timing of life-history processes serve as key axes of divergence.