Photoperiodic regulation of avian physiology: From external coincidence to seasonal reproduction

Abstract

Seasonal cycles of environmental cues generate variation in the timing of life‐history transition events across taxa. It is through the entrainment of internal, endogenous rhythms of organisms to these external, exogenous rhythms in environment, such as cycling temperature and daylight, by which organisms can regulate and time life history transitions. Here, we review the current understanding of how photoperiod both stimulates and terminates seasonal reproduction in birds. The review describes the role of external coincidence timing, the process by which photoperiod is proposed to stimulate reproductive development. Then, the molecular basis of light detection and the photoperiodic regulation of neuroendocrine timing of seasonal reproduction in birds is presented. Current data indicates that vertebrate ancient opsin is the predominant photoreceptor for light detection by the hypothalamus, compared to neuropsin and rhodopsin. The review then connects light detection to well‐characterized hypothalamic and pituitary gland molecules involved in the photoperiodic regulation of reproduction. In birds, Gonadotropin‐releasing hormone synthesis and release are controlled by photoperiodic cues via thyrotropin‐stimulating hormone‐β (TSHβ) independent and dependent pathways, respectively. The review then highlights the role of D‐box and E‐box binding motifs in the promoter regions of photoperiodic genes, in particular Eyes‐absent 3, as the key link between circadian clock function and photoperiodic time measurement. Based on the available evidence, the review proposes that at least two molecular programs form the basis for external coincidence timing in birds: photoperiodic responsiveness by TSHβ pathways and endogenous internal timing by gonadotropin synthesis.

FSHβ links photoperiodic signaling to seasonal reproduction in Japanese quail

“…The photoperiodic induction of gonadal growth in quail is dependent on circadian timing mechanisms ( Follett and Sharp, 1969 ). However, only a few proximal promoters of photoperiodic genes contain D-box elements required for circadian timing input and include eyes absent-3 ( EYA3 ) and TSHβ , but not FSHβ ( Liddle et al, 2022 ). Similarly, E-box elements are only identified in the proximal promoter of EYA3 .…”

FSHβ links photoperiodic signalling to seasonal reproduction in Japanese quail

“…The photoperiodic induction of gonadal growth in quail is dependent on circadian timing mechanisms (Follett and Sharp, 1969). However, only a few proximal promoters of photoperiodic genes contain D-box elements required for circadian timing input and include eyes absent-3 ( EYA3 ) and TSH β, but not FSH β (Liddle et al, 2022). Similarly, E-box elements are only identified in the proximal promoter of EYA3 .…”

The influence of light on elasmobranch behavior and physiology: a review

“…Vertebrates use external light cues to modulate diel and seasonal rhythms (Figure 2, Tosini et al, 2001;Cowan et al, 2017;Mishra and Kumar, 2017;Liddle et al, 2022). The mechanisms of detection of external light varies across taxa, but the result (rhythmic hormone production) is highly conserved.…”