Adaptations to environment in the mountain hare (Lepus timidus): thermal physiology and histochemical properties of locomotory muscles

Abstract

PYORNILA, A., PUTAALA, A., HISSA, R., and SULKAVA, S. 1992. Adaptations to environment in the mountain hare (Lepus timidus): thermal physiology and histochemical properties of locomotory muscles. Can. J. Zool. 70: 1325-1330. Oxygen consumption of mountain hares (Lepus timidus) subjected to different ambient temperatures was measured. The basal metabolic rate was 3.91 + 0.05 W . kg-' in winter and 4.75 + 0.06 W kg-' in summer. These values are 162 and 186% of the weight specific values, respectively. Minimum thermal conductances (winter, 0.076 f 0.017 W . kg-. "C-'; summer, 0.141 k 0.018 W kg-' . "C-I) were 74 and 134% of the values predicted from body weight, respectively. It appears that adaptation of the mountain hare to winter is largely based on insulation. The fibre type composition of a flexor and an extensor muscle in the hindlimb was studied from sections stained for succinate dehydrogenase and myosin adenosine triphosphatase. More than 60% of the cells were fast-twitch oxidative glycolytic fibres, and 30-40% were fast-twitch glycolytic fibres. The greatest difference between the muscles was in the relative number of the slow-twitch oxidative fibres, with the flexor containing 13.7 and the extensor 2.9% of this fibre type. The histochemical properties of the muscles studied are consistent with the locomotory pattern of the mountain hare, which is characterized by darting or sprinting movements, and endurance in flight run. PYORNILA, A., PUTAALA, A., HISSA, R., et SULKAVA, S. 1992. Adaptations to environment in the mountain hare (Lepus timidus): thermal physiology and histochemical properties of locomotory muscles. Can. J. Zool. 70 : 1325 -1330. La consommation d'oxygkne a CtC mesurCe chez des Likvres variables (Lepus timidus) soumis A diffkrentes tempkratures ambiantes. Le taux de mktabolisme de base a CtC CvaluC A 3,91 f 0,05 W . kg-' en hiver, et A 4,75 f 0,06 W kg-' en CtC. Ces valeurs reprksentent respectivement 162 et 186% des valeurs spkcifiques A la masse. Les conductances thermiques minimales (hiver, 0,076 f 0,017 W -kg-' -"C-'; CtC, 0,141 f 0,018 W kg-' . "C-') reprksentent respectivement 74 et134% des valeurs thCoriques dCterminCes en fonction de la masse du corps. I1 semble que l'adaptation de ce likvre au cours de l'hiver soit en grande partie attribuable B ses propriCtCs isolantes. La composition typique d'une fibre du muscle flexeur et d'une fibre du muscle extenseur de la patte arrikre a CtC CtudiCe par examen de coupes prCparCes pour mettre en Cvidence la succinate dCshydrogCnase et la myosine adCnosine triphosphatase. Plus de 60% des cellules sont des fibres glycolitiques oxydantes A contraction rapide et 30-40%, des fibres glycolytiques A contraction rapide. La principale diffkrence entre les deux muscles est le nombre relatif des fibres oxydantes A contraction lente; le flexeur contient 13,7% de fibres de ce type et l'extenseur n'en contient que 2,9%. Les propriCtCs histochimiques des muscles rCvClCes par cette Ctude conviennent bien au systkme de locomotion qu'utilise le Likvre variabl...

Metabolism and Thermal Response in Winter-Acclimatized Pygmy Rabbits (Brachylagus idahoensis)

“…Using a regression developed from three studies that empirically determined the upper and lower limits of thermoneutrality (Hinds, 1973;MacArthur and Wang, 1973;Wang et al, 1973), the predicted thermoneutral range for an averagesized (432 g) pygmy rabbit would be 8.4'C. This is only slightly less than is predicted (9.2'C) by a regression for six cold-adapted North American lagomorphs that includes cases for which we estimated upper critical temperature from the published data (Hart et al, 1965;Pyornila et al, 1992;Rogowitz, 1990).…”

“…However, species that do not rigidly distinguish between physical and chemical thermoregulation may vary both conductance and oxygen consumption simultaneously (McNab, 1980;Pyornila at al., 1992). Pygmy rabbits increased oxygen consumption at temperatures less than their presumed lower critical temperature (15-200C, Fig.…”

Differential sex-related winter energetics in free-ranging snowshoe hares (Lepus americanus)

“…This indicates that during our overwinter study, natural food levels likely were energetically adequate for hares (Ellsworth et al 2013). Alternatively, hares may be simply well adapted to their ambient natural conditions (e.g., via the use of coprophagy: Hirakawa 2001; via metabolic rate changes: Pyörnilä et al 1992;Rehnus et al 2010). Hare densities were generally low throughout the study and increased from 1999 to 2003 (D.L.…”

Seasonal temperature acclimatization in a semi-fossorial mammal and the role of burrows as thermal refuges

“…Small endotherms often are limited in their capacity to add insulation via fat deposits or thicker winter pelage, and T lc fluctuates very little, if at all, as a result ( McNab, 2002 ; Marchand, 2013 ). Although a seasonal shift in T lc has been documented for several larger-bodied, non-burrowing leporids ( Sylvilagus audobonii— Hinds, 1973 ; Lepus alleni and L. californicus— Hinds, 1977 ; L. townsendii— Rogowitz, 1990 ; L. timidus— Pyornila et al, 1992 ; L. americanus— Sheriff et al, 2009 ), constancy of T lc between seasons has been documented in several small endotherms including red squirrels ( Irving, Krog & Monson, 1955 ), black-capped chickadees ( Cooper & Swanson, 1994 ), greenfinches ( Carduelis chloris ; Saarela, Klapper & Heldmaier, 1995 ), and dark-eyed juncos ( Junco hyemalis ; Swanson, 1991 ). Use of thermal refuges has an important influence on thermal physiology ( Jackson et al, 2002 ).…”