title: Both thyroid hormone levels and resting metabolic rate decrease in African striped mice when food availability decreases.
abstract: In response to variation in food availability and ambient temperature (Ta), many animals show seasonal adaptations in their physiology. Laboratory studies showed that thyroid hormones are involved in the regulation of metabolism, and their regulatory function is especially important when the energy balance of an individual is compromised. However, little is known about the relationship between thyroid hormones and metabolism in free-living animals and animals inhabiting seasonal environments. Here, we studied seasonal changes in triiodothyronine (T3) levels, resting metabolic rate (RMR) and two physiological markers of energy balance (blood glucose and ketone bodies) in 61 free-living African striped mice (Rhabdomys pumilio) that live in an semi-arid environment with food shortage during the dry season. We predicted a positive relationship between T3levels and RMR. Further, we predicted higher T3levels, blood glucose levels and RMR, but lower ketone body concentrations, during the moist season when food availability is high compared with summer when food availability is low. RMR and T3levels were negatively related in the moist season but not in the dry season. Both RMR and T3levels were higher in the moist than in the dry season, and T3levels increased with increasing food availability. In the dry season, blood glucose levels were lower but ketone body concentrations were higher, indicating a change in substrate use. Seasonal adjustments in RMR and T3levels permit a reduction of energy expenditure when food is scarce, and reflect an adaptive response to reduced food availability in the dry season.
authors.affiliation: University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS 2050, Johannesburg, South Africa Rebecca.Rimbach@wits.ac.za.
authors.forename: Rebecca
authors.identifier: 0000-0003-3059-0382
authors.initials: R
authors.lastname: Rimbach
authors.affiliation: University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS 2050, Johannesburg, South Africa.
authors.forename: Neville
authors.initials: N
authors.lastname: Pillay
authors.affiliation: University of the Witwatersrand, School of Animal, Plant & Environmental Sciences, Private Bag 3, WITS 2050, Johannesburg, South Africa.|IPHC, UNISTRA, CNRS, 23 rue du Loess, Strasbourg 67200, France.
authors.forename: Carsten
authors.initials: C
authors.lastname: Schradin
mesh_terms: D000818:Animals; D001481:Basal Metabolism; D049628:Body Size; D005215:Fasting; D005260:Female; D005508:Food Deprivation; D008297:Male; D051189:Murinae / Q000097:blood* / Q000502:physiology*; D012621:Seasons; D013696:Temperature; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014284:Triiodothyronine
keywords: Drought; Energetics; Fasting; Metabolism; Starvation; Triiodothyronine