Light receptors in the avian brain and seasonal reproduction

Abstract

Detection and transduction of photic cues by nonvisual photoreceptors, located in the deep brain, is a critical component of timing seasonal reproduction in birds.However, the precise identity of the photoreceptors responsible for detection of salient photic cues remains uncertain and debated. Here I review of the existing evidence for each of the three candidate photoreceptive opsins: Vertebrate Ancient Opsin, Melanopsin, and Neuropsin, including localization, action spectrum, and data from experimental manipulation of opsin expression. These findings are compared to an updated list of key criteria established in the literature as a litmus for classifying an opsin as the "breeding photoreceptor." Integrating evidence for each of the candidate photoreceptors with respect to these criteria reveals support for all three opsins in regulation of seasonal reproduction. Taken together these findings strongly suggest that transduction of seasonal photoperiodic information involves the activity of multiple photoreceptor types and populations functioning in concert. This review also highlights the need to shift attention from simply identifying "the breeding photoreceptor" to a more integrative approach aiming to parse the contribution of specific photoreceptor populations within the brain.

An Expanding Role for Nonvisual Opsins in Extraocular Light Sensing Physiology

“…The pineal organ, which expresses pinopsin and parapinopsin, was the first extraocular photoreceptive structure associated with seasonal behavior. Later studies suggested the presence of extraretinal, extrapineal photoreceptive pathways deep within the brain, given that ablation of the hypothalamus was shown to disrupt responses to light (for a review, see Pérez 2022). These studies supported the idea of deep brain photoreception.…”

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

“…The highest testosterone and sperm motility has been reported in captive sand tiger sharks (Carcharias taurus) when environmental conditions mimic natural seasonal photoperiods and temperatures (Wyffels et al, 2020). Finally, Sumpter and Dodd (1979) report that pituitary gonadotropin (involved in photic control of reproduction in nonmammalian vertebrates (Peŕez, 2022)) concentrations in mature female lesser spotted dogfish (Scyliorhinus canicula) are up to 100 times higher between February and April than other months, coinciding with peak egg-laying and highest levels of GSI.…”