Revealing a circadian clock in captive arctic-breeding songbirds, lapland longspurs (calcarius lapponicus), under constant illumination

Noah T. Ashley, Takayoshi Ubuka, Ingrid Schwabl, Wolfgang Goymann, Brady M. Salli, George E. Bentley, C. Loren Buck

    Research output: Contribution to journalArticle

    9 Citations (Scopus)

    Abstract

    Most organisms in temperate or tropic regions employ the light-dark (LD) cycle as the primary Zeitgeber to synchronize circadian rhythms. At higher latitudes (>66°33), continuous illumination during the summer presents a significant time-keeping dilemma for polar-adapted species. Lapland longspurs (Calcarius lapponicus), arctic-breeding migratory songbirds, are one of the few recorded species maintaining an intact diel rhythm in activity and plasma melatonin titers during polar summer. However, it is unknown whether rhythms are endogenous and entrain to low-amplitude polar Zeitgeber signals, such as daily variations in light intensity and the spectral composition of the sun (as measured by color temperature). Wild-caught male and female longspurs were brought into captivity, and locomotor activity was assessed using infrared detection. To examine if rhythms were endogenous, birds were exposed to constant bright light (LL; 1300 lux) or constant darkness (DD; 0.1 lux). All birds exhibited free-running activity rhythms in LL and DD, suggesting the presence of a functional circadian clock. Mean periods in LL (22.86 h) were significantly shorter than those in DD (23.5 h), in accordance with Aschoff's rule. No birds entrained to diel changes in light intensity, color temperature, or both. To examine endogenous molecular clock function, the Per2 gene was partially cloned in longspurs (llPer2) and transcripts were measured in hypothalamic tissue punches, eye, and liver using competitive polymerase chain reaction. Ocular llPer2 gene expression was periodic in LL and elevated at ZT24 (CT24) for LD or constant conditions (LL and DD), but llPer2 rhythmicity was not detected in hypothalamus or liver. Plasma melatonin was significantly lower in LL compared with LD or DD. In conclusion, rhythmic ocular Per2 expression and melatonin secretion may maintain the circadian activity rhythm across the polar day.

    Original languageEnglish
    Pages (from-to)456-469
    Number of pages14
    JournalJournal of Biological Rhythms
    Volume29
    Issue number6
    DOIs
    Publication statusPublished - 2014 Dec 16

    Fingerprint

    Circadian Clocks
    Songbirds
    Lighting
    Breeding
    Light
    Melatonin
    Birds
    Circadian Rhythm
    Color
    Temperature
    Liver
    Darkness
    Photoperiod
    Solar System
    Periodicity
    Locomotion
    Running
    Hypothalamus
    Gene Expression
    Polymerase Chain Reaction

    Keywords

    • circadian rhythm
    • clock genes
    • Lapland longspur
    • melatonin
    • Per2

    ASJC Scopus subject areas

    • Physiology
    • Physiology (medical)

    Cite this

    Revealing a circadian clock in captive arctic-breeding songbirds, lapland longspurs (calcarius lapponicus), under constant illumination. / Ashley, Noah T.; Ubuka, Takayoshi; Schwabl, Ingrid; Goymann, Wolfgang; Salli, Brady M.; Bentley, George E.; Buck, C. Loren.

    In: Journal of Biological Rhythms, Vol. 29, No. 6, 16.12.2014, p. 456-469.

    Research output: Contribution to journalArticle

    Ashley, Noah T. ; Ubuka, Takayoshi ; Schwabl, Ingrid ; Goymann, Wolfgang ; Salli, Brady M. ; Bentley, George E. ; Buck, C. Loren. / Revealing a circadian clock in captive arctic-breeding songbirds, lapland longspurs (calcarius lapponicus), under constant illumination. In: Journal of Biological Rhythms. 2014 ; Vol. 29, No. 6. pp. 456-469.
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