Meeting Abstract
113.3 Tuesday, Jan. 7 11:00 Huddling reduces evaporative water loss but not metabolic rate in torpid bats BORATYNSKI, J.S.; WILLIS, C.K.R.; JEFIMOW, M.; WOJCIECHOWSKI, M.S.*; Nicolaus Copernicus Univ., Torun, Poland; Univ. of Winnipeg; Nicolaus Copernicus Univ., Torun, Poland; Nicolaus Copernicus Univ., Torun, Poland mwojc@umk.pl
Huddling is thought to reduce thermoregulatory energy expenditure in normothermic mammals and birds. Theoretical predictions suggest that during hibernation huddling also may reduce evaporative water loss (EWL) by reducing the surface area of huddled animals, which is exposed to air. However, to our knowledge it has not been tested empirically. We hypothesized that huddling affects not only energy expenditure but also water balance in torpid animals. We predicted that huddled individuals would have lower EWL than solitary ones and that this difference would be greater in dry than in humid air. We also predicted that huddling would reduce individual energy expenditure during torpor. We tested these predictions by measuring EWL and torpid metabolic rate (tMR) of insectivorous bats, Myotis nattereri, housed as solitary individuals or huddling in groups of five or six. Bats were measured for 24h at an ambient temperature (Ta) of ~6.5 °C, consistent with their natural hibernation. As predicted, after adjusting for tMR and body mass (mb), bats in huddles had ~27% lower EWL per individual than solitary animals (p < 0.05). However, surprisingly, after adjusting for Ta and mb, tMR per individual was ~45% higher for huddled bats compared to individuals (p < 0.01). These results provide the first experimental evidence that a primary benefit of huddling by hibernating bats is reduced EWL. Our calculations indicate that huddling bats would have to hibernate at Ta of ~3.5 °C to be able to reduce tMR to the level we recorded for solitary bats. That could bring about even greater reduction of EWL during hibernation.
