Ontogeny of the Daily Profile of Plasma Melatonin in European Starlings Raised under Long or Short Photoperiods

Abstract

Photoperiodic manipulation of young European starlings suggests that their reproductive physiology is incapable of responding to a short photoperiod until they are fully grown. This study aimed to determine whether the lack of response to a short photoperiod is reflected in the daily profile of plasma melatonin concentrations. Five-day-old starlings taken from nest boxes showed a significant (p < 0.0001) rhythm in plasma melatonin concentrations, with high values during night. In nestlings hand-reared from 5 days of age on a long photoperiod (LD 16:8), equivalent to natural photoperiod at the time, the amplitude of the daily rhythm in melatonin increased significantly (p < 0.01) with age until birds were fully grown (20 days old). In nestlings reared on a short photoperiod (LD 8:16), the daily melatonin profile remained almost identical to that of long photoperiod birds until they were fully grown. However, after 20 days old, the duration of elevated nighttime melatonin began to extend to encompass the entire period of darkness. In contrast, fully grown starlings transferred from a long to a short photoperiod had partially adapted to the short photoperiod after 5 days; by 10 days, the daily melatonin profile was identical to that of birds held chronically on a short photoperiod. Thus, consistent with responses of reproductive physiology, the pineal of young birds appears to be incapable of perceiving, or adapting to, a short photoperiod.

Light increases the rate of embryonic development: implications for latitudinal trends in incubation period

“…After the formation of the pineal gland (H-H stage 17, d3 in chickens), entrainment of the avian embryo to photoperiod is mediated by production of melatonin (Hill et al 2004). Light reduces melatonin production (Akasaka et al 1995) while increased melatonin production occurs at night (Dawson & Van't Hof 2002). As little as 1 h of light decreases melatonin production in embryonic chickens (Zeman et al 1999); and even very low light intensity (e.g.…”

“…Light reduces melatonin production (Akasaka et al. 1995) while increased melatonin production occurs at night (Dawson & Van’t Hof 2002). As little as 1 h of light decreases melatonin production in embryonic chickens (Zeman et al.…”

Daily Cycles in Body Temperature in a Songbird Change with Photoperiod and Are Weakly Circadian

“…The daily cycle in melatonin has been implicated in the control of cycles in Tb (Binkley et al, 1971; Oshima et al, 1989; Underwood, 1994). Daily melatonin cycles in young starlings do not develop fully until after they become homeothermic (Dawson and Van’t Hof, 2002). However, melatonin rhythms in adult starlings are highly circadian and maintain the profile of the previous day when birds are transferred to DD (Dawson and King, 1994), unlike cycles in Tb.…”

“…Daily melatonin cycles in young starlings do 13 not develop fully until after they become homeothermic (Dawson and Van't Hof, 2002).…”