Melatonin rhythms and pineal structure in a tropical bat, Anoura geoffroyi, that does not use photoperiod to regulate seasonal reproduction

Abstract

It has been hypothesized that pineal structure and function might differ between temperate zone and tropical species of mammals because of lower amplitudes of seasonal change in photoperiod and, in some areas, less seasonal climatic variation. Anoura geoffroyi produce a single offspring in November or December of each year on the Caribbean island of Trinidad, at 10 degrees N latitude in the deep tropics. Previous work has shown that this population lacks reproductive responses to photoperiod, and must be enforcing seasonal breeding using a non-photoperiodic cue. Anoura geoffroyi have a minute, thin, and rod-like pineal gland. Throughout much of its length, the pineal courses irregularly within the ventrolateral wall of the great cerebral vein. This intimate relationship may have functional implications. Despite having a very small pineal gland, this species produced a nocturnal rise in serum melatonin. Serum melatonin levels in most individuals were below or near undetectable levels during the light period and rose to a peak averaging 100 pg/ml in the last third of the dark period. Our results indicate that, although the pineal gland of A. geoffroyi is extremely small, serum melatonin levels are comparable to those of other mammals.

Melatonin affects steroidogenesis and delayed ovulation during winter in vespertilionid bat, Scotophilus heathi

“…Thus, the variation in circulating melatonin concentrations and/or ovarian responsiveness to melatonin may be responsible for the unique pattern of steroid synthesis, which in turn may be responsible for the suppression, and resumption of ovulation in S. heathi. Melatonin as a key factor in adjusting seasonal reproduction has been shown earlier in several mammalian species including bats [56,30]. Likewise, in adult humans, higher than normal nocturnal melatonin level may be associated with irregular menstruation and ovulation [57].…”

Can melatonin reduce the severity of COVID-19 pandemic?

“…Thus, they are less exposed to daylight which would reduce their melatonin level. Indeed, a number of studies indicate that the concentration of melatonin in bats at night varies from 60 to 500 pg/ml and that the daytime concentration also remains at a high level of 20-90 pg/ml depending on the species [20,21]. As described above, melatonin levels are lower in humans, especially in elderly populations.…”

Light Microscopic and Ultrastructural Observations on the Vomeronasal Organ of Anoura (Chiroptera: Phyllostomidae)

“…Adult male Anoura geoffroyi (Geoffroy's hairy‐legged, long‐tongued bat: family Phyllostomidae) were captured from Tamana cave (10° 28′ N, 61° 12′ E, 240 m elevation) in central Trinidad in 1990 and 1992 and brought to the University of Texas (Heideman et al, 1992, 1996). This species subsists on a diet of pollen, nectar, soft fruits, and soft‐bodied insects.…”

“…The interest in the vomeronasal complex of Anoura geoffroyi developed as a somewhat serendipitous exploration emanating from a study on the pineal gland in this species (Heideman et al, 1996). It was then that the VNO was observed in A. geoffroyi , appearing to be relatively large compared with the vomeronasal cartilage, and lacking cilia in the receptor‐free epithelium (Bhatnagar, 1998).…”