Defending body mass during food restriction inAcomys russatus: a desert rodent that does not store food

Abstract

Golden spiny mice, which inhabit rocky deserts and do not store food, must therefore employ physiological means to cope with periods of food shortage. Here we studied the physiological means used by golden spiny mice for conserving energy during food restriction and refeeding and the mechanism by which food consumption may influence thermoregulatory mechanisms and metabolic rate. As comparison, we studied the response to food restriction of another rocky desert rodent, Wagner's gerbil, which accumulates large seed caches. Ten out of 12 food-restricted spiny mice (resistant) were able to defend their body mass after an initial decrease, as opposed to Wagner's gerbils (n = 6). Two of the spiny mice (nonresistant) kept losing weight, and their food restriction was halted. In four resistant and two nonresistant spiny mice, we measured heart rate, body temperature, and oxygen consumption during food restriction. The resistant spiny mice significantly (P < 0.05) reduced energy expenditure and entered daily torpor. The nonresistant spiny mice did not reduce their energy expenditure. The gerbils' response to food restriction was similar to that of the nonresistant spiny mice. Resistant spiny mice leptin levels dropped significantly (n = 6, P < 0.05) after 24 h of food restriction, and continued to decrease throughout food restriction, as did body fat. During refeeding, although the golden spiny mice gained fat, leptin levels were not correlated with body mass (r(2) = 0.014). It is possible that this low correlation allows them to continue eating and accumulate fat when food is plentiful.

Physiological and behavioural effects of fruit toxins on seed-predating versus seed-dispersing congeneric rodents

“…In addition, A. russatus appeared more tolerant to O. baccatus diets in terms of defending body mass when feeding on the mash diet, which contained the toxic components of the mustard oil bomb. This result is consistent with other studies showing the ability of A. russatus to maintain body mass under various conditions (Shkolnik and Borut, 1969;Kam and Degen, 1993;Gutman et al, 2006). Physiologically, the unique adaptive mechanisms of the diurnal A. russatus for desert survival (Haim and Borut, 1981;Haim et al, 1994;Haim et al, 2005;Ehrhardt et al, 2005;Levy et al, 2011) may also explain their low variability under the different treatments across various examined parameters.…”

Specialist-generalist model of body temperature regulation can be applied on the intraspecific level

“…Nevertheless, the use of heterothermy correlated positively with the duration of food deprivation. Such a correlation agrees with thermoregulatory adjustments observed in response to prolonged fasting or food restriction in rats (Wang et al, 2006;Yoda et al, 2000;McCue et al, 2017a), laboratory mice (McCue et al, 2017b), spiny mice (Acomys russatus; Gutman et al, 2006) and Chilean mouse-opossums (Thylamys elegans; Bozinovic et al, 2007). The lack of prolonged torpor in fasted male mice might be related to sex.…”

“…Torpor, in turn, is a state of regulated decrease of T b and metabolic rate (MR) (Heldmaier and Ruf, 1992;Ruf and Geiser, 2015;Snyder and Nestler, 1990), which brings about benefits when food is unavailable or when costs of foraging are too high (Hudson and Scott, 1979;Ruf and Heldmaier, 2000;Schubert et al, 2010; but see Humphries et al, 2003 andWojciechowski et al, 2011 for a discussion of increased predation risk associated with torpor). In recent decades, several studies have focused on torpor use as a response to energy deficit (Bae et al, 2003;Gutman et al, 2006;Nespolo et al, 2010;Schubert et al, 2010Schubert et al, , 2008. Wild house mice (Mus musculus), as well as different laboratory strains, enter daily torpor in the face of low food availability or low ambient temperature (T a ), or both (Morton, 1978;Tomlinson et al, 2007;Webb et al, 1982;Williams et al, 2002), indicating that facultative heterothermy is a response to increased energy demands (Dikic et al, 2008;Gordon, 2012;Hudson and Scott, 1979;Schubert et al, 2010).…”

Biology's response to dieting: the impetus for weight regain

“…4B), by the length of time in weight maintenance after weight loss (149), and by physical activity levels (151). The relative contribution of the adaptations in appetite and expenditure can vary between and even within animal models (92,93). Regardless of which side of the energy balance equation is most affected, the energy gap imparts a substantial pressure to eat in excess of the energy requirements.…”