Endogenous regulation of behavior and reproductive physiology in a resident passerine songbird†

Seasonal timing of reproductive events requires the interaction of the circannual clock and environmental cues. Many avian species exhibit robust circannual rhythms in controlled environments. However, the molecular changes preceding changes in physiology and behavior are poorly understood. The spotted munia (Lonchura punctulata) is an ideal experimental animal to investigate this question as it shows a strong annual cyclicity under prolonged captive conditions. In the current experiment, birds (18 males + 18 females) were maintained under equinox photoperiod (12L:12D, L = light, ~1.86 W/m2; D = dark, <0.00014 W/m2) with constant temperature (22 ± 2°C) and humidity (58 ± 2%) for ~10 months. Based on gonadal status, we identified pre-breeding, breeding, and onset of regression phases and measured body weight, histological changes, active and sleep behavior, and hypothalamic gene expressions. Body fattening, gonadal recrudescence, and organ-specific lipid accumulation were observed during the breeding phase. Increased allopreening behavior coupled with reduced sleep suggested increased social interaction and nighttime vigilance during the reproductive period. The elevated hypothalamic Gonadotropin-Releasing Hormone expression, plasma testosterone, and corticosterone levels during the pre-breeding phase prepared the birds for upcoming reproductive processes. Overall, our data provide evidence of endogenous molecular changes under constant environmental conditions that might inform conserved mechanisms across species.