THE THERMAL PHYSIOLOGY OF THE MOUNTAIN PYGMY-POSSUM BURRAMYS PARVUS (MARSUPIALIA: BURRAMYIDAE)

MICHAEL R. FLEMING

Fleming, M. R. 1985. The thermal physiology of the Mountain Pygmy-possum Burramys parvus (Marsupialia: Burramyidae). A ust. Mammal. 8: 79-90. The Mountain Pygmy-possum Burramys parvus is restricted to the Australian alpine region. Laboratory studies of the thermo-physiology of this species found that body temperature (T") was tightly regulated at 36.1 oc, but animals quickly become hyperthermic at ambient temperatures Cta) above 30 °C, causing the thermal neutral zone to be truncated. Basal metabolic rate was 2.15 W kg -"· ' 5 (mean body mass 44.3 g) and weight-specific thermal conductance was 0.112 rnl 1 O, g-' h-' oC- . These values are 9% and 44% lower, respectively, than the mass predicted value for a marsupial, showing that the overall rate of energy expenditure is considerably reduced in this species. Huddling also reduces individual rates of energy expenditure. Burramys parvus enters prolonged bouts of deep torpor lasting up to one week, during which T" is very low and close to T. and the rate of oxygen consumption greatly reduced. Spontaneous arousal occurred from a T" as low as 6oc and the overall rate of rewarming was 0.17 oc;rnin. Attainment of a critical body mass appeared to be necessary before an animal would enter torpor. Burramys parvus shows physiological adjustments similar to that described in many placental mammals from cold climates and this species represents a true marsupial hibernator. M. R. Fleming, Department of Zoology, Monash University, Clayton, Victoria, Australia 3168. Present address: Wildlife Research Section, Conservation Corn­ mission of the Northern Territory, P.O. Box 1046, Alice Springs, Northern Territory, Australia 5750.

THE comparative thermophysiology of Localised, low-density populations have many northern hemisphere placental mam­ been recorded from Mt Hotham and the mals has been studied in detail with parti­ Bogong High Plains in Victoria and in the cular attention being given to arotic mam­ Kosciusko National Park in New South mals (reviews: Hart 1964, 1971 and Miller Wales (Mansergh 1984). Fossi-l remains 1978). The physiological adjustments found close to the modern form of B. parvus in placentals f·rom cold environments have have been found in owl deposits at much been used to infer general corrdations be­ lower altitudes (Broom 1896 and Wakefield tween climate and single physiological para­ 1972). These deposits are Pleistocene and meters (Scholander et al. 1950, Irving et Recent in age indicating that this species al. 1955, Hart 1964, McNab 1966 and had a much wider distribution in the recent Withers et al. 1979). These generalized past. placental 'adaptat•ions to cold' include in­ Extant populations are strongly associat­ creased insul•ation of the surface layers, ed wit1h peri-glacial boulder streams which peripheral cooling, increased body size, a are usually shrub covered (Gullen and basal metabolic rate higher than predicted Norris 1981) . This habitat would provide by mass, increased summit metabolism and an extensive sub-nivean environment during the ability to become torpid. the five months of t•he year that the ground Burramys parvus Broom is the only is usually snow-covered. The ecology of marsupial restricted to the alpine and sub­ B. parvus is reviewed by Kerle ( 1984) and alpine habitats of southeastern Australia. Mansergh ( 1984). This study describes 80 AUSTRALIAN MAMMALOGY thermoregulation and torpor in B. parvus The chamber was placed in a lighted as an example of a small marsupial adapt­ constant-temperature cabinet regulated ed to a cold environment. within ± 0.5°C of the desired setting. Temperature within the chamber was METHODS recorded on a Leeds and Northrup Speedo­ max W multipoint recorder. Dried room METABOLIC MEASUREMENTS OF air passed through a copper heat exchanger NORMOTHERMIC ANIMALS before entering the metabolic chamber. The animals used in this study were Oxygen consumption rates were deter­ obtained from two sources. Five captive­ mined on resting post-absorptive animals bred adults were obtained from a colony in held in the metabolic chamber for more Canberra. J1he original stock for this colony than I hour at a selected Ta. The minimum came from a number of sub-alpine local­ metabolic rate for a Ta was calculated ities within the Kosciusko National Park, from the lowest value of the fractional N.S.W. A further three adult female B. difference lasting for at least 5 min. All parvus were live-trapped at Mt Hotham, measurements were made between 0800 Victoria. One female had four pouch young and 1900 h. vo2 was calculated from the when captured and these were successfully equations of Withers (1977) with all gas reared. The animals were housed as pairs volumes corrected to STP. or individuals in steel mesh cages (I m) in a constant temperature room. The female METABOLIC MEASUREMENTS OF with pouch young was housed in a large TORPID ANIMALS cage (1.5 x 2 x 1 m) in the same constant temperature room. All cages contained The initial study on torpor was made in nestbox-metabolic chambers fitted with the Department of Zoology, Australian thermocouples for the continuous measure­ National University, Canberra in 1976. ment of fur surface temperature (Godfrey Three captive-bred adults which had been 1968) . The B. parvus were maintained on maintained in a large outdoor cage were a diet of raw peanuts, sunflower seed, and individually housed in a 2 x I x I m cabinet commercial baby food with added vitamin made from 50 mm thick polystyrene foam. powder. A calcium supplement was added The cabinet was placed in an isoiated room to the drinking water which was available and a constant temperature of 5-8 °C was ad libitum. maintained within the cabinet by the daily renewal of tubs of crushed ice placed above

Oxygen consumption rate ('V02 , irrcli­ the animal cages. A little light penetrated cated hereafter by symbol V02) was from an external light source set at 14 measured continuously using an open-circuit hours dark, 10 light. system connected to a paramagnetic oxygen analyser (see Fleming 1980 for details). Animals were supplied with a nestbox­ T,he oxygen consumption of indivi­ metabolic chamber made from a hemis­ duals and groups was determined by the pherical lidded plastic bowl (diameter = following procedure. Animals were weighed 100 mm) with a perspex entrance tube to the nearest 0. I g and placed in an air­ attached (30 x 50 mm). Torpor was detect­ tight perspex metabolic chamber equipped ed by continuously monitoring temperature with inlet and outlet ports and a wire mesh within the nest (Godfrey 1968). Oxygen platform. Single animals were measured in use during torpor was measured by draw­ a 0.5 I metabolic chamber with a flowrate ing air through a small hole in the Ed, over of about 300 ml air min-1 and groups of H1e animal and out through a rubber bung, four animals were measured in a 1.2 1 which was used to seal the entrance tube. chamber with a flowrate of about 900 ml Jlhe air was dried and sampled for oxygen air min·1 . content every two minutes with a Beckman FLEMING: THERMAL PHYSIOLOGY OF BURRAMYS PARVUS 81

(.) 0

41... • :I • ~ 41 c. • • E • ~ .... • • • ...... t•• ,> .. •.. .. • .. • .... •t 0 .... • 0:1 .. .. • .. •

• 'I J: ~ 'j' • Ol rS E d.j ·> .. 1 ...... ~·......

0 15 20 25 30 35 Ambient Temperature ( °C)

Fig. 1. The relationship of body temperature and oxygen consumption rate to ambient temperature for individual Burramys parvus. The solid line in the lower part is the regression equation VO, = 4.24-0.123 T •. 82 AUSTRALIAN MAMMALOGY

E2 paramagnetic oxygen analyser. To chamber. Respiration rate was measu reel measure the very low rates of oxygen use by a pressure transducer connected to the during torpor, the nestbox-metabolic cham­ metabolic chamber and the output was dis­ ber was sealed for up to l hour, then un­ played on a Grass polygraph. sealed and oxygen use recorded until the value prior to sealing was reached. The STATISTICAL AN A LYSIS area under the curve was integrated over All averaged data is presented as Mean time to measure total oxygen use. ± Standard Deviation (n = number of The induction of torpor in B. parvus was measu rements, N = number of indivi­ attempted at the Department of Zoology, duals). Areas under oxygen consumption Monash University, under three different curves were determined by finding the area conditions. For the first winter ( 1978), five of an irregular polygon. Linear regressions animals were housed in a constant tempera­ were fitted by the least squares method and ture room set at 7 ± 2 oc with the light inflexion points were determined by a pro­ regime identical to natural photo-period. gramme called TURNPOINT (Fleming Torpor was monitored from outside the 1985) . constant temperature room by continuous­ ly recording nestbox temperature. The constant temperature room also housed RESULTS other species being used for other experi­ mental work. For the second winter, four N::>RMOTHERM IC: INDIVIDUALS animals were kept in the same constant Burramys parvus strictly regulate their temperature room in 0.30 x 0.45 x 0.15 m body temperatures at ambient temperatures tubs with wire mesh tops and nestbox­ (T,,) between 2°C and 28 °C (Fig. l). With­ metabolic chambers. The tubs were placed in this range T" is 36.1 ± 0.53 oc (n = within a cabinet (2 x l x I m) made from 28, N = 6). A pronounced inflexion in 5 em thick polystyrene foam to reduce the body temperature curve occurs at Ta disturbance by noise. For the third winter, = 28.0 oc with T" increasing at a rate of the polystyrene cabinet was placed in an 0.68 oc per degree Ta. B . parvus were isolated room and cooled by a silent refri­ noticeably stressed by Ta> 29 °C. The geration unit with a remote cooling coil. animals lay on their flanks, their ears were The cooling coil was immersed in a super­ fully-expanded, the naked tail was engorged saturated salt solution within the poly­ with blood and saliva was spread on the styrene cabinet and connected to the refri­ forepaws. The only indication of active geration unit by flexible hoses. Two animals cooling was dampness and matting of fur were placed in wire topped tubs with nest­ around the scrotum. Exposure to a Ta of box-metabolic chambers. 33 °C for less than one hour was found to be lethal.

BODY TEMPERATURE The metabolic response of individual B. Body temperature (T0 ) was measured parvus is shown in Fig. I. The lower critical with a silastic - shea~hed thermocouple temperature (T~c. ), as determined by inserted into the rectum to a depth of TURNPOINT, is 27.7 oc. Only two V02

2-3 em. Rectal thermocouples were con­ measurements were made at T 11 higher than nected to either a Leeds and Northrup 30 °C as the animals quickly became hyper­ Speeclomax multipoint recorder (accuracy, thermic. These measurements indicate that

± 0.25°C) or a Comark Electronic thermo­ the upper critical temperature (T11 ,.) is meter Type 1624 (accuracy, ± 0.1 °C) . T" about 30 oc within the narrow thermal of single animals was measured within 30 neutral zone (TNZ), the rate of oxygen 1 seconds of removal from the metabolic usc is 0 83 ± 0. 14 ml 02 g· lr' (n = 6, FLEMING: THERMAL PHYSIOLOGY OF BURRAMYS PARVUS 83

c:: • • E ..... • • -.Q • • • • • ...Cl) • • • • cti • • • a: • • • • • • • ~ 30 • • • • • • ...0 •• cti.... ·c. 20 ' (/J Q) a: 10

0 5 10 15 20 25 30 35 Ambient Temperature ( °C)

Fig. 2. The relationship of respiratory rate wi th ambient temperature for Burramys parvus.

N = 4; body mass 44.29 ± 13.81 g, n =6) at Ta > 27 °C. High breathing rates and which is a standard metabolic rate of 2.15 panting were not observed. W kg ·0 -75 (assuming R.Q. = 0.86).

The change in V02 as T a increases from NORMOTHERMIC: GROUPS OF FOUR ANIMALS 3 oc to 27 oc is described by the linear The measurements of Y02 of a group regression equation: of four B. parvus were made at Tn less

than T 10 • The huddling behaviour of B. V0 (ml 0 g ·1 h ·1 ) = 4.24-0.123 Tn 2 2 parvus differs markedly from that observed r2 = 0.93, n = 37, N = 5, p < 0.001 in two other species of small possums. At = 0.24, = o.oo6) . s)'.)' s" Tn close to the TNZ, the animals lay on A mass specific measure of the insulative their flanks, but not in contact. As Tn properties of fur and surface tissues can be decreased, the animals assumed a curled calculated from V02 and T" (McNab 1980) . posture with the head held under the body; For B. parvus the mean mass specific ther­ usually individuals were not in contact. At low Ta (i.e., 5°C), the curled posture was mal conductance at Tn less than T 1c is 0.112 ± 0.013 ml 02 g· 1 h· 1 oc ·1 (n = 22) . maintained and Vhe animals formed a tight group with their flanks and backs in con­ The respiratory frequency of B. parvus tact. A!t no time did individuals lie across as a function of Tn is shown in Fig. 2. The each other as observed in Sugar Gliders minimum breathing rate of about 33 (Petaurus breviceps) and Feathertail breaths/min·1 was reached at Tn = l8°C Gliders (Actobates pygmaeus) (Fleming and the breathing rate started to increase 1980, 1985). 84 AUSTRAL IAN MAMMA LOGY

The metabolic response of a group of eel on only one occasion during the three four B . par vus is shown in Fig. 3. There is winters in which observations were made. little difference between the vo2 of indivi­ The continuous monitoring of nest tem­ duals alone and that of groups at higher perature showed that an adult female B. Ta, but as T" decreases a difference becomes parvus had entered torpor during the first apparent. The regression equation for V02 winter for a period of 12.5 h with Ta = of a group of four as a function of Ta is: 9.0°C. Food had been available ad libitum 1 1 V02 (ml 0~ g- h- ) = 3.4 - 0.091 Ta and body mass was 45 .1 g. Subsequent (r = 0.82, n = 23, p < 0.001; s)'.X attempts to induce torpor centred on the = o.29, s" = o.oo9). reduction of environmental noise and dis­ The T" of groups was not measured, but turbance. No attempt was made to induce the mass specific thermal conductance was torpor by starvation. calculated from V02 and T" measurements by assuming Th = 36.2 oc. The mean During the Canberra study, the three B. thermal conductance for a group of four parvus were housed in the polystyrene 1 1 B. parvus was 0.096 ± 0.013 ml 02 g- h- cabinet for 135 days during the winter. °C 1 (n = 20). Thirteen episodes of torpor were recorded, six of which were not disturbed and are TORPOR detailed in Table I. The remaining seven At Monash University torpor was record- episodes were interrupted ~0 measure vo2

4

.a. 3 'i ...... I: ...... 'i' C) ' ...... N ...... a. 0 t ...... a. 2 ...... ,, ""'-.£ E ...... N .a. .a. )...... _""' 0 ·> ... ~ 1

0 5 10 15 20 25 30 Ambient Temperature ( °C)

Fig. 3. The relationship of oxygen consumption rate with ambient temperature for groups of four Burramys parvus. Solid line is the regression line for individuals. Dashed line is the reg ression line for groups of four, namely: YO, = 3.4-0.091 T,. FLEMING: THERMAL PHYSIOLOGY OF BURRAMYS PARVUS 85 and TIJ during arousal. YO" and TIJ during variation in T 1, (Bartholomew and Hudson torpor are given in Table 2. Overall arousal 1962 and Fleming 1985). The diurnal labi­ rates atTn = 8°C varied from 0.17 to 0.22 lity of TIJ was not measured directly, but °C/min with a mean rate of 0.17 ± 0.03 the continuous measurements of T,J,in of °C/ min (n = 5) . The fastest rate measured of B. parvus did not show the cyclical varia­ over a 20 min period was 0.44 °C/min. tion that has been observed in other pygmy Burramys parvus appears to enter torpor possums and smcrH clasyurids (Bartholomew only when body mass has attained a critical and Hudson 1962, Godfrey 1968, Wallis level (Fig. 4) . Torpor did not occur while I 976, Morton and Lee 1978 and Fleming body mass was below 50 g. Partial starva­ 1985). In contrast to their strictness of tion of one animal over 18 days, causing a regulation at low T,., B. parvus become weight loss of 43%, did not induce torpor rapidly hyperthermic at Tn > 28 °C. This and complete starvation of a second animal intolerance of high temperature is not for 48 hr al so did not induce torpor (Fig. shared by C. nanus or A. pygmaeus or other 5). smal"l marsupials, which are able to survive Tn of 38 ° C and higher (Robinson and Morrison 1957, Bartholomew and Hudson DISCUSSION 1962 and Fleming 1985).

NORMOTHERMIC INDIVIDUALS The body temperature of B. parvus is The mass specific thermal conductance 1 tightly regulated at T" < 28 oc unlike that of B. parvus (0.112 ml 02 g· h-1 oc -1) of the possums Cercartetus nanus and is 44 % lower than the weight predicted Acrobates pygmaeus, which show large value (Fleming 1982) . The fine dense fur ·"

\ \ Cl - S1 Ill Ill Cl) ~ 30 > "C 0 9l 20

10

0 2 3 4 Time in C. T. Cabinet (months)

Fig. 4. The changes in body mass associated with episodes of torpor for three Burramys parvus maintained at an air temperature of 5-8 oc_ T, marks the initiation of an episode of torpor. Sl , food rationed for 18 days (dashed line); S2, food withdrawn for 2 days (solid line). 86 AU STRALIAN MAMMALOGY +

I C) I t3 ;-,·+ I I 1 1 IJj IJj I t ~ I T11 :::! ~ t I 5 1 T I I I + 8 -r- I --r I I I I 3 2 201- ;- 6

10t 0 2 4 6 8 10 12 Month

F ig. 5. The seasonal changes in body mass of wild caught adult (solid bars) and juvenile (slashed bars) Burramys parvus. The bar is the mean body mass, the vertical line connects the range and sample size is given below this range. (Data from Dixon 1971, Gullan and Norris 1981, Green pers. comm. and Fleming pers. obs.) . of this species probably accounts for most whereas C. nanus has tripled its breathing of the insulation because there is very little rate. This reflects differences in conduct­ subdermal fat (Dimpel, personal communi­ ance. At high T 8 , the difference in patterns cation) . The SMR (2.15 W kg ·0 .i5) is also is more striking. The respiratory rate of reduced, being 91 o/o of the mass predicted C. nanus did not increase from minimum value (Fleming 1982). This gives an over­ leve-ls until Ta exceeded 36°C, and then all metabolic response (Fig. 1) which con­ breathing rate tripled by Ta = 38 °C. siderably reduces the energy expenditure of Burramys parvus showed an increased B. parvus at all Tn. 'fhis is reflected by breathing rate at Tn = 28 °C, but this

T 1c for B. parvus which is three degrees increase was accompanied by rapid hyper­ lower than the mass predicted value of thermia, suggesting that these possum are 30.6°C (Fleming 1980). As a consequence, unable to lower Tb by evaporative cooling. absolute food requirements would be Bun ·amys parvus is the only mammal reduced at time of food shortage and sur­ restricted to the Australian Alps, where vival time on body fat reserves would be snow cover may last for five months and increased. the mean monthl y maximum air tempera­ The pattern of respiratory rate observed ture for summer does not exceed 16°C. in B. parvus (Fig. 2) differs from that The thermophysiology of B. parvus shows found in the similar sized C. nanus (Bartho­ modifications similar to those described for lomew and Hudson 1962) in two respects. some placenta-l mammals from cold environ­ At T" = 5°C, the breathing rate of B. ments (Scholander et a!. 1950 and Casey parvus is only double the minimum value et a!. 1979). The reduction in thermal con- FLEMING: THERMAL PHYSIOLOGY OF BURRAMYS PARVUS 87

Length of Days active Date Animal Mass (g) T, (°C) episode of prior to torpor (h) next episode

12 June 4 54.7 7.5 78.8 7 9 July 4 61.2 5.5 12.5 3 21 July 4 57.5 5.5 9.0 3 24 July 4 57.5 5.5 112.6 5 19 Aug. 2 53.9 7.0 80.1 5 12 Sept. 2 50.7 6.5 154.8

Table 1. Episodes of undisturbed torpor for Burramys parvus. ductance from the expected value falls of the thermal neutral zone. It is not known within the range of values (33-49%) if B. parvus undergoes a summer moult recorded for winter acclimated arctic in the wild but a reduct·ion in the insulation mammals (Casey et al. 1979) . A higher of the pelt would reduce the risk of hyper­ than expected BMR is usually considered thermy. 'fhe diminution of the distribution adaptive to cold environments, so that a of B . parvus that has occurred from Pleisto­ high ( = 39°C) and stable Th can be main­ cene times (Wakefield 1972) to the present tained (Scholander et al. 1950, Bartho­ may have resulted directly from the physio­ lomew 1977 and Withers et al. 1979) . How­ logical inability of this species to cope with ever, B. parvus maintains a constant T" of the genera1 warming of the Australian 36.2°C with a BMR that is only 63% of climate (Galloway and Kemp 1981), leaving that predicted for an equivalent sized it isolated in the few remaining areas close placental. The reduced BMR of B. parvus to or above the snowline. may be associated with the need to reduce energy expenditure during times of critical NORMOTHERMIC GROUPS winter food shortage (Wang et al. 1973) The mode of huddling in B . parvus differs or to facilitate entry into torpor (Morrison from that observed in A. pygmaeus and 1960, Hudson and Bartholomew 1964 and P. breviceps (Fleming 1980, 1985) , but the Hudson and Deavers 1973) . Torpor is an metabolic benefits of huddling are still important component of the thermal apparent (see Fig. 3) with the regression strategy of B. parvus (see below) so the equation for groups of four having a signi­ latter interpretation is more likely. ficantly smaller slope than the equation for single animals (t-test, p < 0.0 I). This differ­ Possibly as a consequence of these adap­ ence in slope can lead to considerable sav­ tations to cold, B. parvus is unable to tole­ ings at low T" ; for example, the V02 of a rate heat, as is reflected in the truncation group of four at a T" = 0°C is 20% lower

Method of calculation of VO, Mass (g) T, (°C) Tb (°C) Area under curve Mean 11

59.3 7.5 8.0 - 0.051 8 57.5 5.5 - 0.031 0.042 10 57.5 5.5 - - 0.022 17 57.5 5.5 6.0 0.131 0.136 13 58.0 7.0 8.0 0.085 0.084 12

1 1 Table 2. VO, (ml O, g- h· ) and T" during torpor in Burramys parvus. 88 AUSTRALIAN MAMMALOGY than the V02 of a single animal. The lower 1960, Bartholomew and Hudson 1962, thermal conductance for groups of four Wakefield 1970 and Fleming 1985) can all has not led to a reduction in T1c as found be torpid at low Th ( < 6°) for extended in other possums (Fleming 1980, 1985). periods ( > 24 hrs). However, B. parvus This may be due to the lack of group differs from this general pattern in the cohesiveness at Tn close to the TNZ. important areas of induction of torpor and the seasonal occurrence of torpor. TORPOR Starvation induces torpor in all species Torpor in captive B. parvus has been of small marsupial (mass < 200 g) so far described in two studies. Dimpel and studied, except in B. parvus, where the Cal a by ( 1972) recorded three episodes of induction of torpor appears to be a func­ torpor during winter in an adult female tion of mass, for torpor occurred only when kept in an unheated basement in Canberra, body mass exceeded 50 g (Fig. 4). A where Tn varied from 9 to 13 °C. This similar pattern of induction has been study recorded thirteen episodes of torpor described in the small placental hibernators, in two adult male B. parvus, which were the Golden Hamster (Mesocricetus aura­ housed within a polystyrene cabinet cooled tus) and the Eastern Chipmunk (Lyman by ice. Both of these studies provided the 1954 Wang and Hudson 1971), where in­ captive animals with an environment that creases in food storage and body weight was cold, dark, humid and with little dis­ were required for the onset of torpor. An turbance, conditions simil1ar to those found annual cycle of change in body mass, with in the subnivean environment (Pruitt an increase prior to the season of torpor, 1978) . The failure to induce more than is characteristic of placental mammals using one episode of torpor in B. parvus during prolonged torpor (Mrosovsky and Barnes the first two winters of the Monash study 1974) and limited evidence from field work may have been due to excessive disturb­ suggests that B. parvus fattens during late ance, noise from the refrigeration unit and summer and autumn (Fig. 5). If there is a a lack of seasonal acclimatization. body mass threshold that must be exceeded Acclimatization to seasonal changes in before torpor can be induced, the torpor air temperature has been shown to be an season in B. parvus would be confined to important factor in the induction of torpor the part of the year when body mass is in a number of small mammals using winter greatest; i.e., winter. Torpor has not been torpor (Lyman 1954 and Gaertner et al. observed in captive B. parvus during spring 1973). The two studies that were successful and summer (Dimpel, pers. comm.), unlike in inducing torpor in B. parvus both used C. nanus and A . pygmaeus which readily animals that had been housed outdoors, enter torpor throughout the year (Hickman whereas the pygmy possums used during and Hickman 1960, Bartholomew and Hud­ the first two winters of the Monash study son 1962 and Frey and Fleming 1984). had been maintained indoors at a Tn of The decrease in V0 during torpor at 22°C. For the third winter, two naturally 2 T. = 6°C (Table 2) represents a reduc­ acclimatized animals were wild-caught in tion in metabolic rate to a level between early autumn and transferred immediately 0.6% and 3.9% of the normothermic rate to the polystyrene cabinet. Their failure to at that temperature. When this reduction enter torpor is difficult to interpret. is integrated over episodes of torpor last­ The pattern of torpor found in B. parvus ing up to seven days (Table 1, Dim pel and shows many features common to all Cal a by 1972), an animal would make con­ burramyids and other tiny possums so far siderable energy savings. These savings may studied. Cercartetus nanus, C. concinnus not represent the maximum that could be and A. pygmaeus (Hickman and Hickman attained by B. parvus because it was not FLEMING : THERMAL PHYSIOLOGY OF BURRAMYS PARVUS 89 possible to expose the animals to tempera­ manicured by Chris Kittle and Sue Cawood. tubes lower than 6°C with the equipment My research at Monash University was available. facilitated by a Commonwealth Post­ graduate Research Award. The two brief episodes of torpor which lasted only 9.0 and 12.5 h (Table 1) may represent test drops as they occurred three REFERENCES days before a longer bout of torpor. The BARTHOLOMEW , G . A., 1977. E nergy m etabolism. longer episodes of torpor were separated Pp. 57-110 in "Body temperature and energy metabolism" pp. 364-449 in "Anima l physio­ by periods of normothermia lasting five to logy: principles and adaptations" eel M. S. seven days (Table I) . If this represents the Gordon. MacMillan Publ. Co.: N ew York. natural pattern of torpor in the wild, B. BARTH OLOMEW, G. A. AN D HUDSON , J. W., pan1us may use these periods of activity 1962. Hibernation, estivation, temperature to feed on seeds cached inside the nest or regulation, evaporative water loss, heart rate of the pygmy possum Cercaertus nanus. nearby (Kerle 1984) . Food hoarding and Physio/. Zoo/. 35: 94-107. extended periods of nomothermia between BROOM , R ., 1896. On a small fossi l m arsupial with episodes of torpor appear to be a pattern large, grooved premolars. Proc. Linn. Soc. of behaviour common to hibernators of N.S. W. 10: 563-67. small body size ( <200 g) because they are CASEY , T. M. , WITHERS, P . C. AND CASEY, K. K., unable to store sufficient body fat 1979. Metabolic and respiratory responses of a rctic ma mma ls to ambient temperature (Lyman 1954, Wang and Hudson 1971 and during the summer. Camp. Biochem. Physiol. Maclean 1981) . 64A: 331-41. Hibernation is a term that has been used DIMPEL, H . AND CALABY, J. H ., 1972. Further observations on the Mountain P ygmy Possum to describe many different forms of winter (Burramys parvus) . Vic. Nat. 89: 101-06. thermal strategy. Concise physiologically­ DIXON, J. M ., 1971. Burramys parvus Broom based definitions define hibernation as very (Marsupialia) from Falls Creek area of the deep torpor with body temperature below Bogong High Plains, Victoria. Vic. Nat. 88: 10 °C, a small Tn to T" difference, meta­ 133-38. bolism reduced to less than 1/20th of the FLEM ING , M. R., 1980. Thermoregulation and torpor in the Sugar Glider Petaurus breviceps normothermic level and episodes of torpor (Marsupialia : Petauriclae). A ust. J. Zoo!. which last a week or more (Lyman and 28: 521-34. Chatfield 1955, Hudson 1973 and Bartho­ FLEMING, M. R. , 1982. "Thermal strategies lomew 1977) . This study has shown that of three small possums from south-eastern the thermal physiology of B . parvus meets Australia". PhD thesis, Dept. of Zoology, Monash University: Clayton. these criteria and that this species, there­ FLEM ING, M. R ., 1985. The thermal physiology fore, qualifies as a true marsupial hiber­ of the Feathertail Glider Acrobates pygmaeus nator. (M arsupia lia: Burramyiclae). Aust. J. Zool. (in press) . ACKNOWLEDGEMENTS FR EY, H. AND FLEMING, M . R., 1984. Torpor a nd thermoregulatory behaviour in free-ranging Part of this study was carried out while Feathertail Gliders Acrobates pygmaeus I studied in the Department of Zoology, (Marsupialia: Burramyiclae) in Victoria. Pp. Australian National Univers·ity in Canberra. 393-401 in "Possums and gliders" eel by A. P . Smith and I. D. Hume. Aust. M a mmal Soc.: I thank Dick Barwick and Wayne Hocking Sydney. for all the assistance they gave me during G AE RTNER, R . A., HART, J. A . AND RoY, 0. Z., those early days. Hans Dimpel's love of 1973. Seasonal spontaneous torpor in the Burramys parvus inspired my research on \Vhite Footed Mouse, Peromyscus leucopu s. this unique creature. My studies at Monash Camp. Biochem. Ph ysiol. 45A: 169-81. were supervised by Tony Lee and I thank GALLOWAY, R . W . AN D K EM P, E. M., 1981. Late Cainozoic environments in Australia. him for his support at all stages of this Pp. 55-80 in "Ecological biogeography of research. This paper was capably typed and Australia" eel by A. K east. Junk: The Hague. 90 AUSTRALIAN MAMMALOGY

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