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1 August 2002 ABSENCE OF DAILY RHYTHMS OF PROLACTIN AND CORTICOSTERONE IN ADÉLIE PENGUINS UNDER CONTINUOUS DAYLIGHT
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Abstract

Plasma prolactin and corticosterone levels were measured in free-living Adélie Penguins (Pygoscelis adeliae) at Torgersen Island, Antarctica (64°S latitude), at 4-hr intervals throughout the day during early January 1997 and examined for evidence of a 24-hr rhythm. At this season and latitude, natural daylight is continuous. No significant change in the plasma level of either corticosterone or prolactin was found across the day in this population. In contrast, hormone levels in birds at lower latitudes typically fluctuate between night and day. Our data would not have revealed circadian rhythms within individuals even if they exist, because each bird was only sampled once. The lack of hormone rhythms in the population, however, suggests that changes in light intensity at this latitude in the Antarctic summer are not sufficient to entrain, or perhaps even to maintain, circadian rhythms of individuals.

Ausencia de Ciclos Diarios de Prolactina y Corticosterona en Pygoscelis adeliae bajo Luz Solar Continua

Resumen. A principios de enero de 1997 en la Isla Torgersen, Antártica (latitud 64°S), se midieron cada 4 horas los niveles de prolactina y corticosterona en el plasma de Pygoscelis adeliae en busca de evidencia de un ciclo hormonal de 24 horas. Durante esta estación del año y a esta latitud, la luz solar es continua. No se encontraron cambios significativos en los niveles de prolactina ni de corticosterona en el plasma a través del día en esta población. En contraste, los niveles hormonales en aves en menores latitudes fluctúan típicamente entre el día y la noche. Aún si existiesen, nuestros datos no habrían revelado la existencia de ritmos circadianos para cada individuo, dado que cada animal fue muestreado una sola vez. Sin embargo, la ausencia de ciclos hormonales a nivel poblacional, sin embargo, indica que los cambios de luz a esta latitud en el verano antártico no son suficientes para sincronizar, o quizás ni siquiera para mantener, ritmos circadianos en los individuos.

Carol M. Vleck and Jessamyn A. Van Hook "ABSENCE OF DAILY RHYTHMS OF PROLACTIN AND CORTICOSTERONE IN ADÉLIE PENGUINS UNDER CONTINUOUS DAYLIGHT," The Condor 104(3), (1 August 2002). https://doi.org/10.1650/0010-5422(2002)104[0667:AODROP]2.0.CO;2
Received: 4 October 2001; Accepted: 1 April 2002; Published: 1 August 2002
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