Metabolic, ventilatory and hygric physiology of the chuditch (Dasyurus geoffroii; Marsupialia, Dasyuridae)

Abstract

The chuditch is a large carnivorous dasyurid marsupial. Historically it had one of the widest geographical distributions of all marsupials, encompassing much of arid Australia, but it is now restricted to the mesic south-west of Western Australia. It is therefore of interest to determine if its physiology better reflects adaptation to its historically arid or present mesic habitat. The basic physiological parameters of the chuditch conform to other marsupials.Body mass of males (1385g) at an ambient temperature of 26.0°C, and increased at higher ambient temperatures due to panting and licking. Changes in wet thermal conductance largely reflected changes in evaporative heat loss, and dry thermal conductance increased at high ambient temperature due in part to posture change. Ventilatory parameters were consistent with metabolic demands in and below thermoneutrality, and suggested augmented evaporative heat loss above the thermoneutral zone. Chuditch had a high point of relative water economy of 22.6°C, indicating favourable water economy at even moderate ambient temperatures, due to its low evaporative water loss rather than high metabolic water production. Chuditch were physiologically more similar to marsupials from arid rather than mesic habitats, better reflecting their historical distribution than their current geographical range.

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

“…This pattern of T b consistency at lower T p 35Њ a T a and then hyperthermia at high T a is expected for a euthermic mammal (e.g., McNab 1980;Withers 1992) and is consistent with that observed for other species of dasyurid marsupial (e.g., Robinson and Morrison 1957;Nicol and Maskrey 1980;Dawson and Dawson 1982;Geiser 1986;Schmidt et al 2009;Cooper and Withers 2010). Many smaller dasyurid species are relatively thermolabile at low T a (Morton and Lee 1978;Dawson and Wolfers 1978;Withers andCooper 2009a, 2009b;Warnecke et al 2010), but dibblers maintained a constant T b below thermoneutrality and showed no tendency for torpor during experiments.…”

“…35Њ a This is the expected pattern from the Scholander-Irving model for an endotherm (e.g., McNab 1980;Withers 1992), reflecting the increased metabolic heat production required for thermoregulation of a constant T b at low T a , and it is typical of normothermic dasyurid marsupials (e.g., Nicol and Maskrey 1980;Geiser 1986;MacMillen and Dawson 1986;Schmidt et al 2009;Withers andCooper 2009a, 2009b;Cooper and Withers 2010;Warnecke et al 2010). The predicted T b from the relationship of Vo 2 with T a below thermoneutrality of 36.2ЊC was very similar to the measured T b (36.3ЊC), confirming the near conformity of dibblers to the Scholander-Irving model.…”

“…Similar use of a priori contrasts demonstrated the constancy of C wet and C dry at low T a but elevated values at high T a . This pattern is typical for endotherms in general (e.g., McNab 1980;Withers 1992) and for other dasyurid marsupials in particular (Schmidt et al 2009;Withers andCooper 2009a, 2009b;Cooper and Withers 2010;Warnecke et al 2010).…”

“…Such f R and V T changes are typical of similar-sized marsupials. Smaller species generally increase only f R and larger species only V T to increase V I at low T a (Hallam and Dawson 1993;Chappell and Dawson 1994;Schmidt et al 2009;Withers and Cooper 2009b;Cooper and Withers 2010;Warnecke et al 2010).…”

“…The dibbler's current distribution is restricted to three small islands near Jurien, Western Australia, and a few scattered mainland sites on the south coast of Western Australia, where it inhabits dense heath on sandy soils (Menkhorst and Knight 2004;Cronin 2008;Woolley 2008). We characterize body temperature, metabolic rate, thermal conductance, respiratory ventilation, evaporative water loss, and relative water economy over a range of ambient temperatures and then examine the various patterns of T a effects below and above thermoneutrality using a priori contrasts and MANOVAR (Rencher 2002), based on the typical responses of endotherms (e.g., McNab 1980;Withers 1992) and more specifically of other dasyurid marsupials (e.g., Dawson and Wolfers 1978;Morton and Lee 1978;Geiser 1986;Geiser and Baudinette 1988;Hallam and Dawson 1993;Larcombe 2002;Schmidt et al 2009;Cooper and Withers 2010;Warnecke et al 2010). We use polynomial contrasts to examine linear changes with T a , as might be expected for metabolic rate (MR), ventilatory variables including respiratory rate (f R ), tidal volume (V T ) and minute volume (V I ), and possibly evaporative water loss (EWL).…”