Comparative Haematology International 52000) 10:68±73 COMPARATIVE ß 2000 Springer-Verlag London Limited HAEMATOLOGY INTERNATIONAL

Original Article

Seasonal Effects on the Haematology and Blood Chemistry of Wild Brushtail Possums, Trichosurus vulpecula Marsupialia: Phalangeridae) in NewZealand

R. M. G. Wells1, A. Jones1, M. N. Clout1, S. D. Sarre1 and R. K. Anderson2 1School of Biological Sciences, The University of Auckland, Auckland; 2Diagnostic Medical Laboratory, Auckland, New Zealand

Abstract. Seasonal adjustments to red cell haematology ately higher metabolic rates resulting from the inverse that support altered metabolic requirements in Australian relationship between body size and energy expenditure marsupials are either not expressed, or are minimal in 5Sealander 1964). brushtail possums introduced into New Zealand. Raised Hibernators have well-developed strategies for energy leucocyte differentials in winter imply seasonal chal- conservation in extreme environments and show corres- lenges to the immune system. A small increase in plasma ponding seasonal adjustments in erythrocyte functions. In glucose, fall in plasma protein, and generally high winter, these include increased red cell mass and smaller condition index are consistent with the relatively high erythrocytes 5Hellgren et al. 1993), a reduction in blood quality of habitat enjoyed by the marsupial immigrant. viscosity 5Snyder 1971) and a decrease in erythrocyte 2,3- diphosphoglycerate in order to improve haemoglobin± Keywords: 2,3-Diphosphoglycerate; Erythrocyte; Glu- oxygen binding 5Harkness et al. 1974; Maginniss and cose; New Zealand; Possum; Season; Stress; Total Milsom 1994). Further, signi®cant differences in the protein seasonal acclimatisation response may occur between the sexes 5JakuboÂw et al. 1984; Cross et al. 1994). Animals kept in captivity however, may not exhibit seasonal adjustments 5Wenberg et al. 1973). Seasonal adjustments in red cell haematology also Introduction occur in monotremes 5Andersen et al. 2000) and marsupials and thus appear to be an early evolutionary strategy for energy conservation in the Mammalia. Here, It is not uncommon for endothermic animals living in however, the responses appear qualitatively different temperate climates to show seasonal adjustments in from those in eutherian mammals. In the wild, both haematological parameters. Observations from birds haemoglobin and haematocrit show a winter decline in 5Breuer et al. 1995), bats 5Wolk and Bogdanowicz dasyurids 5Schmitt et al. 1989; Bradley 1990; Agar and 1987), bears 5Hellgren et al. 1993), deer 5Cross et al. McAllan 1995), macropods 5Shield 1971), and phalan- 1994) and rodents 5Maclean and Lee 1973; JakuboÂw et gerids 5Barnett et al. 1979a). al. 1984; Suarez et al. 1991) suggest that red cell Haemoglobin and haematocrit are generally sexually characterisics are adjusted to support altered energetic dimorphic in marsupials 5Giacometti et al. 1972; Barnett demands resulting from seasonal changes in temperature et al. 1979a; Presidente and Correa 1981) but do not and food availability. These adjustments may be appear to change during breeding and lacatation pronounced in small mammals due to their proportion- 5Viggers and Lindenmayer 1996). Marsupials held in captivity do not seem to show these responses. Captive Correspondence and offprint requests to: R. M. G. Wells, School of Biological Sciences, The University of Auckland, Private Bag 92019 koala incrase haematocrit in winter 5Cleva et al. 1994) Auckland, New Zealand. Email: [email protected] whereas quokkas show no alteration 5Shield 1971). Seasonal Variation in Possum Haematology 69 Haematological red cell indices are therefore a Haematology and Plasma Chemistry potentially useful tool for examining seasonal rhythms that re¯ect nutritional condition and habitat quality, reproductive or breeding status, and factors of the A pilot study was carried out in early summer 5late physical environment including temperature and rainfall. November) in order to ascertain possible capture and Seasonal changes may also be detected in the white handling effects on haematological parameters. Six blood cell differential 5JakuboÂw et al. 1984; Cross et al. possums were sampled in the ®eld. Approximately 0.5 1994) and appear related to altered states of stress and ml blood was taken into EDTA tubes from the tail vein. immunity 5Grif®n 1989). During the 30±180 s required to complete sampling, it The brushtail possum, Trichosurus vulpecula, was was evident that the animals differed in their behavioural introduced from Australia to New Zealand in the 19th responses, and subsequent haematological analysis century to establish a fur trade 5Cowan 1990a). In the resulted in exceptionally high white blood cell counts absence of indigenous land mammals or predators, with 5WBC), haematocrits and unacceptably large standard reduced parasite load, and with a ¯ora that evolved in the deviations 5Table 1). Subsequently, possums were absence of browsing animals 5Clout and Ericksen 2000), sedated with ZolatilTM 5tiletamine/zolazepam) following the possum has ¯ourished to the point where numbers the recommendations of Viggers and Lindenmayer may exceed 60 million and are spread over more than 51995). Blood samples 51 ml) were obtained from the 90% of the country 5Cowan 1996). The damage in¯icted cephalic vein of healthy animals into tubes containing on native forests 5Cowan 1990a), on rare and endangered EDTA as the anticoagulant. Immediately after collec- birdlife 5Innes et al. 1999), and as a vector of disease tion, aliquots of whole blood were mixed with 0.6m ice- among domestic mammals 5Paterson et al. 1995; Kean et cold perchloric acid, centrifuged for 3 min, and the clear al. 1999) has stimulated strong interest in scienti®c supernatant assayed for red cell ATP and 2,3-dipho- studies that might underpin successful control schemes sphoglyceric acid 52,3-DPG) using Sigma enzymatic test 5Clout and Sarre 1997). reagents. Haematocrit and haemoglobin concentration In the present study, we have compared summer and were measured using standard procedures and the winter values of haematological indices from non- derived parameters mean cell haemoglobin concentra- breeding female possums living in typical forest habitat. tion 5MCHC), mean cell volume 5MCV), and mean cell We have asked the question whether the introduced haemoglobin 5MCH) were computed 5Dacie and Lewis brushtail possum shows seasonal haematological varia- 1984). Red blood cells were counted 5RBC) and the red tions in a benign climate and epicurean habitat. Attention cell distribution width 5RDW) was computed from the has also been given to the possible in¯uence of handling statistical output of ¯ow cytometry data from a 4- and sampling stress on haematological measurements. Channel Bayer Technicon H1 Haematology Analyzer. Total and differential white blood cell parameters were obtained from the Technicon analyser. Calibration of the analyser for use with possum blood was carried out as Materials and Methods described by Cross et al. 51994) where leucogram sectors from ¯ow cytometry data were de®ned following Study Area and Experimental Design inspection of manual data counts. In order to avoid errors of interpretation from the leucogram, results are reported in absolute cell counts 5Ettinger and Feldman Two separate 5 ha blocks of typical possum habitat were 1995). chosen for their similarity. Both sites are contained within fragments of mixed native broadleaved forest Total plasma protein and glucose were measured adjacent to rural properties and lie within 50 km to the using biuret reagent and Sigma hexokinase test reagents northwest 5Coatesville) and west 5Huapai) of Auckland respectively. at approximately 36850'S. All animals within the study sites carried ear tags and were regularly trapped for measurement and inspection as part of a population study over a three-year period prior to our investigation Table 1. Haematological results from a pilot study conducted to 5Sarre et al. 2000). Approximatley 30 traps were ascertain possible effects of handing stress in Trichosurus vulpecula 5n =6) arranged in a grid at 50 m intervals, set with apple bait in the evenings, and inspected before sunrise the Parameter Mean + SD 5range) following day. Blood sampling was carried out in the summer 5late January, early February) and in winter 5late Haematocrit % .40.0+4.8 536±47) June, early July) of 1997 and corresponded with pre- and RBC 1012/l .5.2+0.9 53.7±6.4) postbreeding periods. Condition indices were acquired WBC 109/l .9.89+3.60 56.56±16.02) from measurements of 5body mass 5kg)/snout±anus body Lymphocyte:neutrophil ratio 1:2.12+0.47 51:2.73±1:1.41) length 5cm)) 6 100 5Bamford 1970). Data are presented Body mass 5kg) .1.77+0.30 51.5±2.3) for 24 tagged mature females that had been captured Condition index .3.85+0.56 53.3±4.8) both in summer and in winter. 70 R. M. G. Wells et al.

Statistics Table 3. Seasonal white cell total numbers and differentials expressed as absolute counts 5109/l) in brushtail possums, Trichosurus vulpecula Site differences were tested using a two-tailed t-test. 524 animals) Two-tailed paired t-tests were performed on each parameter to evaluate possible differences attributable Summer Winter 5mean+SEM) 5mean+SEM) to season. Data are expressed as means + SEM and tested by analysis of variance for unequal sample sizes WBC 5.37+0.49 6.77+0.49 after Bartlett's test for homogeneity of variance. Lymphocytes 1.62+0.35 1.34+0.18 Signi®cance was established at p<0.05. Data entry was Neutrophils 3.50+0.38 5.01+0.46* carried out using MS Excel 98 spreadsheets. Statistical Monocytes 0.23+0.03 0.38+0.07* analyses were undertaken using the SAS 6.10 statistical Basophils 0.05+0.01 0.19+0.02* package. Eosinophils 0.01+0.00 0.04+0.01*

*.p<0.05 paired t-test. Results

From 16 mature female possums trapped during the therefore, unlikely. The principal red cell metabolites summer at Huapai and 15 at Coatesville, 13 and 11 2,3-DPG and ATP, arising from glycolysis and oxidative individuals were recaptured at the same respective sites phosphorylation, are seasonally constant and thus in winter. There were no signi®cant differences between represent a constant oxygen transport potential. Plasma sites for any of the measured parameters 5p>0.05). glucose rose signi®cantly in winter, and total plasma Accordingly, data from 24 mature female possums were protein declined. Several components of the white cell available for paired analysis. differential showed seasonal differences 5Table 3). The Mean body mass was 2.16 + 0.28 kg SD 5range 1.6± lymphocyte:neutrophil ratios changed from approxi- 2.7 kg) in summer and 2.06 + 0.27 kg 5range 1.3±2.5 mately 1:2 in summer to nearly 1:4 in winter. kg) in winter. Corresponding seasonal condition indices were 4.57 + 0.52 and 4.75 + 0.51, respectively and are, therefore, not signi®cantly different 5p>0.5). Local mean summer maximum and minimum temperatures for January were 24.98C and 14.08C Discussion 5range 8.1±27.18C), respectively. Corresponding winter temperatures for June were 13.08C and 3.28C 5range Observations on Capture and Handling Stress 72.8±16.88C). Average summer and winter rainfall was 12.5 and 173.2 mm, respectively 5Auckland Metro Obtaining reliable haematological measurements from Weatherwise Ltd). wild animals in the ®eld is a notoriously dif®cult No signi®cant differences in haemoglobin or haema- problem for which there is no simple solution. We tocrit were observed, but small changes in mean cell observed elevated haematocrits and white cell counts volume and red cell distribution width occurred 5Table with large standard deviations in acutely sampled, 2). The use of paired observations means that accepting unsedated possums. Many animals possess highly the null hypothesis when it is false 5type II error) is, contractile spleens acting under adrenergic control to rapidly elevate blood oxygen-carrying capacity in Table 2. Seasonal red blood cell and plasma chemistry values for response to anticipated exercise challenge 5Wells brushtail possums, Trichosurus vulpecula 524 paired animals) 1993). The endocrine stress response in T. vulpecula is reported to be low in comprison with eutherian mammals Summer Winter 5mean+SEM) 5mean+SEM) 5Than and McDonald 1973), although the possum spleen is clearly a reservoir for erythrocytes 5Dawson and Haemoglobin g/l 114.0+2.4 113.3+3.2 Denny 1968). Highly stressed T. vulpecula showed Haematocrit % 34.0+0.7 33.3+1.0 haematocrit values of up to 57% 5Presidente and Correa MCHC g/l 344.7+5.2 343.1+8.1 1981). Values of >50% 5Parsons et al. 1971; Barnett et RBC 1012/l 4.9+0.1 5.0+0.1 al. 1979a) are therefore likely to be characteristic of MCH pg 23.4+0.3 23.2+0.3 capture-stressed animals 5cf Tables 1, 2). MCV ¯ 68.8+1.0 67.7+0.7* A high neutrophil:lymphocyte ratio in Australian RDW % 13.6+0.2 14.6+0.2* possum and koala populations is also a characteristic ATP mmol/g Hb 2.3+0.2 2.1+0.1 of capture-stressed animals or those in poor health and 2,3-DPG mmol/g Hb 25.4+1.0 24.2+0.8 condition 5Parsons et al. 1971; Presidente and Correa Glucose mmol/l 8.1+0.2 9.0+0.2* 1981; Presidente 1982; Hajduk et al. 1992; Baker et al. Protein g/100 ml 7.1+0.2 6.8+0.2* 1998; Baker and Gemmell 1999). Leucocyte pro®les from T. vulpecula in captivity took several weeks to *.p<0.05. reach stable values 5Baker and Gemmell 1999). Seasonal Variation in Possum Haematology 71 Curiously, all our study animals showed neutrophilia, were observed for T. caninus 5Viggers and Lindenmayer as did a population from an earlier New Zealand study 1996). The change observed in the lymphocyte:neutro- 5Buddle et al. 1992), despite maintaining good condition phil ratio from approximately 1:2 in summer to 1:4 in and optimal haematocrit. Neutrophil:lymphocyte ratios winter may indicate environmental stress 5Baker et al. are species-speci®c and a high ratio is normal in T. 1998) although the cause is unknown. caninus 5Viggers and Lindenmayer 1996). We do not An increase in plasma glucose is linked to adrenal know whether these ratios are population-speci®c. cortisol secretion and stress in the brushtail possum T. Nonetheless, blood sampling from our study animals vulpecula 5Than and McDonald 1974) and occurred in following a three-year period of regular trapping and winter populations of T. caninus 5Barnett et al. 1979a). A sedation appears a reasonable protocol in view of the small but signi®cant increase in glucose occurred in lower and less variable values observed for haematocrit parallel with a reduction in plasma protein in our winter and WBC counts. We cannot be certain that haemato- possums. Total plasma protein was higher in Australian logical pro®les of possums in captivity correspond populations of T. vulpecula 5Presidente and Correa 1981) closely to those in wild, precapture animals. Accord- than in either our summer or winter animals and may ingly, we urge caution in interpretation of some earlier re¯ect water availaiblity. We have no evidence for observations that may include stress artefacts. changes in nutritional status through a seasonal shift from an exclusively folivore diet to one of signi®cant frugivory that might account for our seasonal plasma Seasonal Observations values of glucose and protein. Seasonal haematological adjustments to the blood- The use of paired observations to discriminate seasonal oxygen transport system that support altered metabolic differences in haemoglobin concentration, haematocrit, requirements in Australian marsupials are either absent and red blood cell count failed to show a seasonal effect. or weakly manifested in T. vulpecula in New Zealand. The New Zealand populations of T. vulpecula therefore Lower temperature and high winter rainfall are not differ from those in Australia 5Barnett et al. 1979a) and therefore signi®cant environmental stressors in habitats from other marsupials 5Shield 1971; Bradley 1990; of high nutritional quality and reduced competition Cleva et al. 1994; Viggers and Lindenmayer 1996) that where the condition index of possums remains high. show adjustments re¯ecting seasonal regulation of Brushtail possums in New Zealand have experienced oxygen transport capacity. A small but statistically an ecological release from several of the natural signi®cant reduction in red cell volumes 5MCV) and constraints that apply in Australia 5Clout and Ericksen increase in their size distribution 5RDW) occurred in the 2000). Favourable conditions in New Zealand include a winter populations of T. vulpecula, but are too small to lack of competitors, a reduced burden of parasites and be of physiological signi®cance. Reduced MCV in the predators, and relatively nutritious, palatable vegetation. marsupial quokka is associated with reduced seasonal In Australia, the generally low nutrient status of soils and food availability 5Shield 1971). Diet and foliage nutritive vegetation 5Attiwill and Leeper 1987) are important value have strong seasonal components that in¯uence factors limiting the abundance of arboreal herbivores performance of the ringtail possum 5Hume et al. 1996), 5Pausus et al. 1995). Foliage in Australian eucalypt but similar seasonal changes in New Zealand forests are forests is notoriously sclerophyllous, is low in nitrogen less evident 5Thomas and Ogden 1983; Williams and and phosphorus 5Attiwill and Leeper 1987; Cork 1996), Turnbull 1983). Further, haemoglobin values are higher and has high levels of phenolics, terpenoids and other for Australian possum populations living in peripheral chemical defences that limit the intake by possums of habit 5Barnett et al. 1979b) and for koalas exposed to any one species 5Freeland and Winter 1975) or low winter temperatures 5Cleva et al. 1994). individual tree 5Lawler et al. 1998). The range of dietary Altered metabolic requirements may alternatively be items consumed by Australian possums is much more supported by adjustments to blood oxygen af®nity which limited than that in New Zealand and is governed by the do not require an increase in oxygen-carrying capacity. capacity for detoxi®cation of compounds that are absent The red cell organic phosphate responsible for regulation or rare in the New Zealand ¯ora 5Dearing and Cork of haemoglobin±oxygen binding in marsupial erythro- 1999). In New Zealand forests a high proportion of plant cytes is 2,3-diphosphoglycerate 5Bland and Holland species are palatable 5Brockie 1992) and possum diets 1977; Isaacks et al. 1984). Unlike overwintering ground squirrels and woodchucks 5Harkness et al. 1974; include a wide variety of foliage 5Allen et al. 1997) and Maginniss and Milsom 1994), our possums showed no ¯eshy fruits 5Cowan 1990b). Overall, these favourable winter decrease in red cell organic phosphates that could factors combine to produce possums that are on average improve oxygen uptake. signi®cantly heavier than in their native Australia Adjustments in the leucocyte differential may re¯ect 5Cowan 1990a). challenges to the immune system in a generally robust immigrant population. Signi®cant increases of neutro- Acknowledgements. We thank Greg Wittmer and Steve Hicks of the Auckland Regional Council for ®eld advice; Michelle Baker, phils, monocytes, basophils, and eosinophils occurred in University of Queensland, and John Cross, University of Otago, for winter and may represent seasonal infectious, in¯am- advice on leucograms; Richard Jakob-Hoff, Auckland Zoo for matory, and detoxi®cation challenges. Similar increases veterinary advice. 72 R. M. G. Wells et al. References Dacie JV, Lewis SM 51984) Practical haematology 56th edn). Churchill Livingstone, Edinburgh Dawson TJ, Denny MJS 51968) In¯uence of the spleen on blood Agar NS, McAllan BM 51965) Red cell metabolism in a small volume and haematocrit in the brush-tailed possum 5Trichosurus dasyurid marsupial, the brown antechninus 5Antechinus stuartii). vulpecula). Aust J Zool 16:603±608 Comp Haematol Int 5:201±205 Dearing MD, Cork S 51999) Role of detoxi®cation of plant secondary Allen RB, Fitzgerald AE, Efford MG 51997) Long-term changes and compounds on diet breadth in a mammalian herbivore, Trichosurus seasonal patterns in possum 5Trichosorus vulpecula) leaf diet, vulpecula. J Chem Ecol 25:1205±1219 Orongorongo Valley, Wellington, New Zealand. NZ J Ecol 21:181± Ettinger SJ, Feldman EC 51995) Textbook of veterinary internal 186. medicine. WB Saunders, Philadelphia Andersen NA, Mesch U, Lovell DJ, Nicol SC 52000) The effects of Freeland WJ, Winter JW 51975) Evolutionary consequences of eating: sex, season, and hibernation on haematology and blood viscosity of Trichosurus vulpecula 5Marsupialia) and the genus Eucalyptus.J free-ranging echidnas 5Tachyglossus aculeatus). Can J Zool Chem Ecol 1:439±455. 78:174±181 Giacometti L, Berntzen AK, Bliss ML 51972) Hematologic Attiwill PM, Leeper GW 51987) Forest soils and nutrient cycles. parameters of the opossum 5Didelphis virginiana). Comp Biochem Melbourne University Press, Melbourne Physiol 43A:287±292 Baker ML, Gemmell RT51999) Physiological changes in the brushtail Grif®n JFT51989) Stress and immunity: a unifying concept. Vet possum 5Trichosurus vulpecula) following relocation from Armi- Immunol Immunopathol 20:263±321 dale to Brisbane, Australia. J Exp Zool 284:42±49 Hajduk P, Copland MD, Schultz DA 51992) Effects of capture on Baker ML, Gemmell E, Gemmell RT51998) Physiological changes in hematological values and plasma cortisol levels in free-ranging brushtail possums, Trichosurus vulpecula, transferred from the wild koalas 5Phascolarctos cinereus). J Wildl Dis 28:502±506 to captivity. J Exp Zool 280:203±212 Harkness DR, Roth S, Goldman P 51974) Studies on the red blood cell Bamford J 51970) Estimating fat reserves in the brush-tailed possum, oxygen af®nity and 2,3-diphosphoglyceric acid in the hibernating Trichosurus vulpecula Kerr 5Marsupialia: Phalangeridae). Aust J woodchuck 5Marmota monax). Comp Biochem Physiol 48A:591± Zool 18:415±425 599 Barnett JL, How RA, Humprheys WF 51979a) Blood parameters in Hellgren EC, Rogers LL, Seal US 51993) Serum chemistry and natural populations of Trichosurus species 5Marsupialia: Phalan- hematology of black bears: physiological indices of habitat quality geridae) I. Age, sex, and seasonal variation in T. caninus and T. or seasonal patterns? J Mamm 74:304±315 vulpecula. Aust J Zool 27:913±926 Hume ID, Bladon RV, Soran N 51996) Seasonal changes in digestive Barnett JL, How RA, Humphreys WF 51979b) Blood parameters in performance of common ringtail possums 5Pseudocheirus pere- natural populations of Trichosurus species 5Marsupialia: Phalan- grinus) fed Eucalyptus foliage. Aust J Zool 44:327±336 geridae) II. In¯uence of habitat and population strategies of T. Innes J, Hay R, Flux I et al. 51999) Successful recovery of North caninus and T. vulpecula. Aust J Zool 27:927±938 Island kakapo Callaeas cinerea wilsoni population, by adaptive Bland DK, Holland RAB 51977) Oxygen af®nity and 2,3-dipho- management. Biol Conserv 87:201±214 sphoglycerate in blood of Australian marsupials of differing body Isaacks R, Nicol S, Sallis J, Zeidler R, Kim HD 51984) Erythrocyte size. Respir Physiol 31:279±290 phosphates and hemoglobin function in monotremes and some Bradley AJ 51990) Seasonal effects on the haematology and blood marsupials. Am J Physiol 246:236±241 chemistry in the red-tailed phascogale, Phascogale calura JakuboÂw K, Gromadzka-Ostrowska J, Zalewska B 51984) Seasonal 5Marsupialia: Dasyuridae). Aust J Zool 37:533±543 changes in the haematological indices in peripheral blood of Breuer K, Lill A, Baldwin J 51995) Haematological and body-mass Chinchilla 5Chinchilla laniger L.). Comp Biochem Physiol changes of small passerines overwintering in South-eastern 78A:845±853 Australia. Aust J Zool 43:31±38 Kean JM, Barlow ND, Hickling GJ 51999) Evaluating potential Brockie RE 51992) A living New Zealand forest. David Bateman, sources of bovine tuberculosis infection in a New Zealand cattle Auckland. 172 pp herd. NZ J Agric Res 42:101±106 Buddle BM, Aldwell FE, Jowett G et al. 51992) In¯uence of stress of Lawler IR, Foley WJ, Eschler BM, Pass DM, Handasyde K 51998) capture on haematological values and cellular immune responses in Intraspeci®c variation in Eucalyptus secondary metabolitoes the Australian brushtail possum 5Trichosurus vulpecula). NZ Vet J determines food intake by folivorous marsupials. Oecologia 40:155±159 116:160±169 Cleva GM, Stone GM, Dickens RK 51994) Seasonal changes in Maclean GS, Lee AK 51973) Effects of season, temperature, and haematocrit in captive koalas 5Phascolarctos cinereus). Aust J Zool activity on some blood parameters of feral house mice 5Mus 42:233±236 musculus). J Mamm 54:660±667 Clout MN, Ericksen K 52000) Anatomy of a disastrous success: the Maginniss LA, Milsom WK 51994) Effects of hibernation on blood brushtail possum as an invasive species. In: The brushtail possum: oxygen transport in the golden-mantled ground squirrel. Respir biology, impact and management of an introduced marsupial. Physiol 95:195±208 Landcare Research, Lincoln, New Zealand, pp. 1±9 Parsons RS, Atwood J, Guiler ER et al. 51971) Comparative studies on Clout MN, Sarre SD 51997) Model marsupial or menace? A review of the blood of monotremes and marsupials-I. Haematology. Comp research on brushtail possums in Australia and New Zealand. Wildl Biochem Physiol 39B:203±208 Soc Bull 26:168±172 Paterson BM, Morris RS, Weston J et al. 51995) Foraging and denning Cork SJ 51996) Optimal digestive strategies for arboreal herbivorous patterns of brushtail possums, and their possible relationship to mammals in contrasting habitat types: Why koalas and colobines contact with cattle and the transmission of bovine tuberculosis. NZ are different. Aust J Ecol 21:10±20 Vet J 43:281±288 Cowan PE 51990a) Brushtail possum. In: King CM 5ed) The handbook Pausas JG, Braithwaite LW, Austin MP 51995) Modelling habit of New Zealand mammals. Oxford University Press, Auckland, pp quality for arboreal marsupials in the south coastal forests of New 67±98 South Wales, Australia. Forest Ecol Management 78:39±49 Cowan PE 51990b) Fruit seeds and ¯owers in the diet of possums Presidente PJA 51982) Common brushtail possum Trichosurus Trichosurus vulpecula in lowland podocarp/mixed hardwood vulpecula: maintenance incaptivity, blood values, diseases and forest, Orongorongo Valley, New Zealand. NZ J Zool 17:549±566 parasites. In: Evans DD 5ed) The management of Australian Cowan PE 51996) Possum biocontrol: prospects for fertility mammals in captivity. Zoological Board of Victoria. Melbourne, regulation. Reprod Fertil Dev 8:655±660 pp. 55±66 Cross JP, Mackintosh CG, Grif®n JFT51994) Haematological Presidente PJA, Correa J 51981) Haematology plasma electrolytes and reference values for farmed red deer 5Cervus elaphus) in New serum biochemical values of Trichosurus vulpecula 5Kerr) Zealand. Comp Haematol Int 4:76±85 5Marsulialia: Phalangeridae). Aust J Zool 29:507±517 Seasonal Variation in Possum Haematology 73 Sarre SD, Aitken N, Clout MN, Ji W, Robins, J, Lambert D 52000) Thomas GM, Ogden J 51983) The scienti®c reserves of Auckland Molecular ecology and biological control: the mating system of a University. I. General introduction to their history, vegetation marsupial pest. Mol Ecol 9:723±733 climate, and soils. Tane 29:143±161 Schmitt LH, Bradley AJ, Kemper CM et al. 51989) Ecology and Viggers KL, Lindenmayer DB 51995) The use of tiletamine physiology of the northern quoll Dasyurus hallucatus 5Marsupialia: hydrochloride and zolazepam hydrochloride for sedation of the Dasyuridae) at Mitchell Plateau Kimberley Western Australia. J mountain brushtail possum, trichosurus caninus 5Phalangeridae: Zool 5Lond) 217:539±558 Marsupialia). Aust Vet J 72:215±216 Sealander JA 51964) The in¯uence of body size, season, sex, age and Viggers KL, Lindenmayer DB 51996) Variation in hematological and other factors upon some blood parameters in small mammals. J serum biochemical values of the mountain brushtail possum, Mamm 45:598±616 Trichosurus caninus Ogilby 5Marsupialia: Phalangeridae). J Wildl Shield J 51971) A seasonal change in blood cell volume of the Dis 32:142±146 Rottnest Island quokka, Setonix brachyurus. J Zool 5Lond) Wells RMG 51993) The evolution of haemoglobin function: 165:343±354 adaptations for exercise. In: PMcN Hill 5ed) Exercise ± the Snyder GK 51971) In¯uence of temperature and hematocrit on blood physiological challenge. Confernece Publishing Ltd., Auckland, pp viscosity. Am J Physiol 220:1667±1672 119±129 Suarez GP, Arevala F, Caballero et al. 51991) Seasonal variations in Wenberg GM, Holland J, Sewell J 51973) Some aspects of the hematological values and heart weight in two small mammals, a hematology and immunology of the hibernating and non- mouse Apodemus sylvaticus, and a vole Pitymys duodecimostatus. hibernating woodchuck 5Marmota monax). Comp Biochem Physiol Acta Theriol 35:201±208 46A:513±521 Than KA, McDonald IR 51973) Adrenocortical function in the Williams CK, Turnbull HL 51983) Variations in seasonal nutrition, Australian brush-tailed possum Trichosurus vulpecula 5Kerr). J thermoregulation and water balance in two New Zealand Endocrinol 58:97±109 populations of the common brushtail possum, Trichosurus Than KA, McDonald IR 51974) Metabolic effects of cortisol and vulpecula 5Phalangeridae). Aust J Zool 31:333±343 corticotrophins in the Australian brush-tailed opossum, Trichosurus Wolk E, Bogdanowicz W 51987) Hematology of the hibernating bat: vulpecula 5Kerr). J Endocrinol 63:137±147 Myotis daubentoni. Comp Biochem Physiol 88A:637±639