Meeting Abstract
Triiodothyronine (T3) is considered a regulatory hormone of thermoregulation in mammals and birds; however, its influence on maximal heat production (Summit metabolic rate, Msum) remains unknown. Thyroid hormones are also thought to be linked to food consumption. In cold environments both metabolic rate and food intake naturally increase to support thermoregulatory demands. It is therefore difficult to tease apart the role of T3 in heat production or energy turnover, separately. We studied indoor captive red knots (Calidris canutus islandica) maintained under two thermal treatments (cold and thermoneutrality) and at a natural photoperiod over a complete annual cycle. In the spring, the birds underwent a hyperphagic phase, which allowed us to tease apart the role of T3 in heat production and energy turnover. We predicted that if T3 is mainly involved in energy turnover, we would observe a peak in T3 during the hyperphagic phase for both thermal treatments and there would be no relationship between T3 and Msum. In contrast, if T3 is mainly involved in thermogenic capacity, then cold-acclimated birds would maintain higher T3 levels and T3 would correlate positively with Msum but we would not observe a peak for either treatment during hyperphagia. Our results did not show a peak in T3 during the hyperphagic phase for red knots held at cold or thermoneutral conditions. Further, Msum was positively correlated with T3 levels. These results are consistent with T3 playing a significant role in metabolic heat production. The correlation between energy turnover and thyroid hormones is likely resulting from cold environments requiring increases in both energy intake and heat production.
