Using A Priori Contrasts for Multivariate Repeated-Measures ANOVA to Analyze Thermoregulatory Responses of the Dibbler (Parantechinus apicalis; Marsupialia, Dasyuridae)

Abstract

Physiological studies often involve the repeated measurement of individuals over a range of ordered categorical conditions, for example, varying ambient temperature. We illustrate here the use of a priori contrasts for multivariate repeated-measures ANOVA by analyzing the thermal responses of various physiological variables for a small marsupial, the dibbler (Parantechinus apicalis). Our analyses showed that dibblers conform closely to the Scholander-Irving model of endothermy. Body temperature was constant at low air temperatures, was 36.3 ± 0.24°C at thermoneutrality (30°C), and increased at 35°C. Metabolic rate decreased with increasing ambient temperature to a basal rate of 0.619 ± 0.036 mL O(2) g(-1) h(-1) at 30°C; it extrapolated closely to thermoneutral body temperature. Increased oxygen demand at lower ambient temperature was met by increased respiratory minute volume, achieved by increased respiratory frequency and tidal volume; oxygen extraction was constant at about 19%. Evaporative water loss and wet and dry thermal conductance increased markedly at high ambient temperatures but not sufficiently to maintain constant body temperature. Relative water economy was similar to that of other small marsupials, increasing linearly at lower air temperatures with a point of relative water economy of 20.3°C. We conclude that a priori contrasts provide a statistically appropriate and powerful analysis that can be used routinely to statistically describe the pattern of response of physiological variables to a categorical factor and are especially useful for repeated-measures ANOVA designs common to many physiological studies.