Metabolic, ventilatory, and hygric physiology of the gracile mouse opossum (Gracilinanus agilis).

Publisher: University of Chicago Press Country of Publication: United States NLM ID: 100883369 Publication Model: Print Cited Medium: Internet ISSN: 1537-5293 (Electronic) Linking ISSN: 15222152 NLM ISO Abbreviation: Physiol Biochem Zool Subsets: MEDLINE

Original Publication: Chicago, IL : University of Chicago Press, c1999-2023.

Body Temperature Regulation/*physiology ; Energy Metabolism/*physiology ; Opossums/*physiology ; Pulmonary Ventilation/*physiology ; Water Loss, Insensible/*physiology; Animals ; Basal Metabolism ; Body Temperature ; Brazil ; Oxygen Consumption/physiology

We present the first complete study of basic laboratory-measured physiological variables (metabolism, thermoregulation, evaporative water loss, and ventilation) for a South American marsupial, the gracile mouse opossum (Gracilinanus agilis). Body temperature (T(b)) was thermolabile below thermoneutrality (T(b) = 33.5 degrees C), but a substantial gradient between T(b) and ambient temperature (T(a)) was sustained even at T(a) = 12 degrees C (T(b) = 30.6 degrees C). Basal metabolic rate of 1.00 mL O2 g(-1) h(-1) at T(a) = 30 degrees C conformed to the general allometric relationship for marsupials, as did wet thermal conductance (5.7 mL O2 g(-1) h(-1) degrees C(-1)). Respiratory rate, tidal volume, and minute volume at thermoneutrality matched metabolic demand such that O2 extraction was 12.4%, and ventilation increased in proportion to metabolic rate at low T(a). Ventilatory accommodation of increased metabolic rate at low T(a) was by an increase in respiratory rate rather than by tidal volume or O2 extraction. Evaporative water loss at the lower limit of thermoneutrality conformed to that of other marsupials. Relative water economy was negative at thermoneutrality but positive below T(a) = 12 degrees C. Interestingly, the Neotropical gracile mouse opossums have a more positive water economy at low T(a) than an Australian arid-zone marsupial, perhaps reflecting seasonal variation in water availability for the mouse opossum. Torpor occurred at low T(a), with spontaneous arousal when T(b) > 20 degrees C. Torpor resulted in absolute energy and water savings but lower relative water economy. We found no evidence that gracile mouse opossums differ physiologically from other marsupials, despite their Neotropical distribution, sympatry with placental mammals, and long period of separation from Australian marsupials.

Date Created: 20090210 Date Completed: 20090601 Latest Revision: 20090220

20231215

10.1086/595967

19199558