Abstract
Seasonal endocrinal changes, such as modulation of insulin-like growth factor 1 (IGF-1) levels, may allow animals to cope with temperature variations. To test this hypothesis, we evaluated the effects of season on thermoregulatory capacities in a photoperiod-responsive species, the gray mouse lemur (Microcebus murinus). Adult male mouse lemurs were exposed to ambient temperatures (Tas) of 12, 25, and 34 °C, and we monitored changes in daily rhythms of body temperature (Tb) and IGF-1 blood levels. Additionally, we observed the exploration and choice of Ta in a thermal gradient over 24 h after animals had been acclimated to 25 °C. Under winter-like short photoperiod (SP) exposure, mouse lemurs in the thermal gradient showed marked behavioral adjustments and Tb fluctuations, in response to Ta fluctuations similar to those occurring in the Malagasy winter. In contrast, under summer-like long photoperiod (LP), behavioral responses and Tb changes were only moderate, corresponding to the lower Ta fluctuations observed in summer. Overall, IGF-1 levels remained higher under LP than under SP, whatever the Ta. Thermal challenges evoked different modulations of IGF-1 according to season, e.g., a slight increase under SP and a transient decrease under LP after heat challenge. Altogether, our results indicate that photoperiod exerts a major influence on thermoregulatory capacities, with IGF-1 playing an important role in mechanisms of thermogenesis/thermolysis.
Résumé
Les changements endocriniens saisonniers, telles que les modulations des niveaux d’IGF-1 (Insulin-like Growth Factor 1), pourraient permettre aux animaux de faire face aux variations de température. Pour tester cette hypothèse, nous avons évalué les effets de la saison sur les capacités thermorégulatrices chez une espèce sensible à la photopériode, le Microcèbe gris (Microcebus murinus). Des microcèbes mâles adultes ont été exposés à des températures ambiantes (Tas) de 12, 25 et 34°C. Nous avons suivi les changements de rythmes journaliers de la température corporelle (Tb) et des niveaux sanguins d’IGF-1. De plus, nous avons observé l’exploration et le choix de Ta dans un gradient thermique sur 24 h, après avoir acclimaté les animaux à 25°C. En photopériode courte (SP), les microcèbes placés dans un gradient thermique ont montré des ajustements comportementaux et des fluctuations de Tb marqués, suivant des fluctuations de Ta semblables à celles observées pendant l’hiver malgache. En photopériode longue, en revanche, les variations de Tb et la réponse comportementale sont plus modérées, correspondant à de plus petites fluctuations de Ta observées en été. Globalement, les niveaux d’IGF-1 sont plus élevés en LP qu’en SP, quelle que soit la Ta. Les challenges thermiques ont montré des modulations de l’IGF-1 différentes selon la saison, comme par exemple une légère augmentation en SP et une diminution progressive en LP lors de l’exposition à 34°C. Ensemble, ces résultats indiquent que la photopériode exerce un effet majeur sur les capacités thermorégulatrices, l’IGF-1 jouant un rôle important dans les mécanismes de thermogenèse et thermolyse.
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Terrien, J., Aujard, F. (2012). Photoperiod-Related Changes in Thermoregulatory Capacity in Gray Mouse Lemurs (Microcebus murinus) . In: Masters, J., Gamba, M., Génin, F. (eds) Leaping Ahead. Developments in Primatology: Progress and Prospects. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-4511-1_22
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DOI: https://doi.org/10.1007/978-1-4614-4511-1_22
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