Aerobic power, huddling and the efficiency of torpor in the South American marsupial, Dromiciops gliroides

Abstract

SummaryDuring periods of cold, small endotherms depend on a continuous supply of food and energy to maintain euthermic body temperature (Tb), which can be challenging if food is limited. In these conditions, energy-saving strategies are critical to reduce the energetic requirements for survival. Mammals from temperate regions show a wide arrange of such strategies, including torpor and huddling. Here we provide a quantitative description of thermoregulatory capacities and energy-saving strategies in Dromiciops gliroides, a Microbiotherid marsupial inhabiting temperate rain forests. Unlike many mammals from temperate regions, preliminary studies have suggested that this species has low capacity for control and regulation of body temperature, but there is still an incomplete picture of its bioenergetics. In order to more fully understand the physiological capacities of this “living fossil”, we measured its scope of aerobic power and the interaction between huddling and torpor. Specifically, we evaluated: (1) the relation between basal (BMR) and maximum metabolic rate (MMR), and (2) the role of huddling on the characteristics of torpor at different temperatures. We found that BMR and MMR were above the expected values for marsupials and the factorial aerobic scope (from CO2) was 6.0±0.45 (using CO2) and 6.2±0.23 (using O2), an unusually low value for mammals. Also, repeatability of physiological variables was non-significant, as in previous studies, suggesting poor time-consistency of energy metabolism. Comparisons of energy expenditure and body temperature (using attached data-loggers) between grouped and isolated individuals showed that at 20°C both average resting metabolic rate and body temperature were higher in groups, essentially because animals remained non-torpid. At 10°C, however, all individuals became torpid and no differences were observed between grouped and isolated individuals. In summary, our study suggests that the main response of Dromiciops gliroides to low ambient temperature is reduced body temperature and torpor, irrespective of huddling. Low aerobic power and low time-consistency of most thermoregulatory traits of Dromiciops gliroides support the idea of poor thermoregulatory abilities in this species.

Effects of reproductive condition, roost microclimate, and weather patterns on summer torpor use by a vespertilionid bat

“…The influence of social behavior on thermoregulation was also demonstrated by Franco et al. ( 2012 ), who observed higher T b s in Dromiciops gliroides huddling in groups compared with single individuals at 20°C because solitary individuals quickly entered torpor. In our study, irregular evening emergence counts showed that caves were typically inhabited by colonies of 50–100 bats, likely providing Rafinesque's big-eared bats with opportunities for clustering and decreased costs of remaining normothermic.…”

“…The presence of a bat colony on roost temperatures is significant, decreasing the amount of energy required to remain normothermic in roosts with temperatures below the thermal neutral zone (Willis and Brigham 2007). The influence of social behavior on thermoregulation was also demonstrated by Franco et al (2012), who observed higher T b s in Dromiciops gliroides huddling in groups compared with single individuals at 20°C because solitary individuals quickly entered torpor. In our study, irregular evening emergence counts showed that caves were typically inhabited by colonies of 50-100 bats, likely providing Rafinesque's big-eared bats with opportunities for clustering and decreased costs of remaining normo- For each variable, roosting structures not sharing common superscript letters for a variable were significantly different at P < 0.05. thermic.…”

The ecology and evolution of the Monito del monte, a relict species from the southern South America temperate forests

“…Occasionally, nests are used more than once, although they prefer to build new ones. Based on these observations, Franco et al (2012; and Celis-Diez et al (2012) showed that communal nesting is common in D. gliroides using nest-boxes in two localities of southern Chile (near Valdivia and in Chiloe), with a mean of 2.3 animals per nesting box. Monitoring of nest boxes suggested that D. gliroides is resident throughout the year and uses torpor during cold seasons.…”

Friends with benefits: the role of huddling in mixed groups of torpid and normothermic animals

“…Not surprisingly, a few heterothermic species, such as small marsupials, bats, rodents and primates, that enter torpor during the cold and/or during periods of food shortages are known to combine both strategies and nest in groups during the torpor season (Fleming, 1980;Vogt and Lynch, 1982;Arnold, 1988;Arnold et al, 1991;Perret, 1998;Blumstein et al, 2004;Séguy and Perret, 2005;McKechnie et al, 2006;Pretzlaff et al, 2010;Franco et al, 2012;Dausmann and Glos, 2014). Well-known examples of social hibernators are marmots (Marmota spp.…”