PHYSIOLOGICAL-CHANGES IN BRUSHTAIL POSSUMS, TRICHOSURUS-VULPECULA, TRANSFERRED FROM THE WILD TO CAPTIVITY

To determine the effect of relocation on the health of possums, the bo dy weights and hormone and immune responses of 11 male and 9 female br ushtail possums were monitored following transfer from the environs of Brisbane into an established breeding colony in Brisbane. The possums were monitored weekly for the first 20 weeks of captivity, and their immune responses assessed again 12 months after capture. Over the firs t 5 weeks of captivity, male possums lost a mean of 8.8% of their orig inal body weight, and females lost 15.3% over the first 6 weeks. Varia tion between individual possums was evident, and the 11 male possums c ould be divided into two groups, those that gained weight (number of a nimals, N = 4) and those that lost weight (N = 7) in captivity. Four m ales gained weight following capture, and their body weight after 20 w eeks of captivity was higher than at capture. The remaining seven male s lost weight over the 20 weeks following introduction into captivity, resulting in a lower weight at week 20 than at capture. All of the ni ne female possums lost weight and were slower to regain weight compare d to the males. Plasma cortisol concentrations did not vary greatly ov er the 20 weeks in male possums, and the mean plasma concentration of cortisol for the 11 male possums was 7.8 ng/ml (number of samples, n = 220). The female possums showed a different pattern. The concentratio n of cortisol for the nine female possums at week 1 was 34.0 ng/ml, wh ich was significantly higher than 13.3 ng/ml at week 20 (P < 0.016). N o significant variation in the mean concentration of plasma thyroxine of 5.7 ng/ml occurred in the 11 male possums over the 20-week period ( n = 220). The plasma concentration of thyroxine for the nine female po ssums was 2.5 ng/ml (n = 54) for the first 6 weeks. At week 6, an incr ease in the concentration of thyroxine occurred, and a peak concentrat ion of 6.9 ng/ml was reached at week 13. This increase correlated with the females regaining body weight. A low concentration of thyroxine i s often associated with stress, thus an increase in the concentration of this hormone, combined with an increase in body weight, may indicat e that these females had begun to adjust to their new environment. The seven male possums that lost weight following introduction into capti vity displayed a significantly higher concentration of cortisol (9.1 c ompared with 5.3 ng/ml P < 0.01), and a lower concentration of thyroxi ne compared to the four males that gained weight following capture (4. 7 compared with 7.3 ng/ml, P < 0.005). Over the 20-week period, the to tal number of white blood cells increased, and the number of neutrophi ls increased in both males and females. The proliferative response of lymphocytes from male possums to the T-cell mitogen, phytohaemagglutin (PKA) decreased significantly over the 20-week period (P < 0.002). In females an initial decrease in the reactivity of lymphocytes observed over the first 10 weeks was followed by an increase in this response over the remaining 10-week period. Twelve months following capture, th e white blood cell parameters of both males and females had returned t o similar levels to those of the first 1-5 weeks. The reactivity of ly mphocytes from male possums that had been in captivity for 12 months w as significantly higher than that of the first 20 weeks of captivity ( P < 0.005). Females that had been in captivity for 12 months displayed lymphocyte responses similar to those observed at weeks 16-20. The bo dy weight and hormonal results would suggest that female possums under go a more severe stress response than males immediately following thei r capture. In contrast, the immune response of males is lower than fem ales and is depressed for a longer period following capture. (C) 1998 Wiley-Liss, Inc.