Thermoregulation in Juvenile Red Kangaroos (Macropus rufus) after Pouch Exit: Higher Metabolism and Evaporative Water Requirements

Abstract

, T. J. (2001). Thermoregulation in juvenile red kangaroos (Macropus rufus) after pouch exit: higher metabolism and evaporative water requirements. Physiological and Biochemical Zoology, 74 (6), 917-927. Thermoregulation in juvenile red kangaroos (Macropus rufus) after pouch exit: higher metabolism and evaporative water requirements AbstractThe population dynamics of red kangaroos (Macropus rufus) in the Australian arid zone is tightly linked with environmental factors, which partly operate via the survival of juvenile animals. A crucial stage is the young-atfoot (YAF) stage when kangaroos permanently exit the pouch. We have examined the thermal biology of YAF red kangaroos during ages from permanent pouch exit until weaning. Over a wide range of environmental temperatures (ambient temperature [T-a] -5 degrees to 45 degreesC), YAF red kangaroos had a mass-specific metabolism that was generally twice that of adults, considerably higher than would be expected for an adult marsupial of their body size. The total energy requirements of YAF red kangaroos were 60%-70% of those of adult females, which were three times their size. Over the same range in T-a, YAF red kangaroos also had total evaporative water losses equal to those of adult females. At the highest Ta (45 degreesC), differences were noted in patterns of dry heat loss (dry conductance) between YAF red kangaroos and adult females, which may partially explain the relatively high levels of evaporative cooling by YAF. By weaning age, young kangaroos showed little change in their basal energy and water requirements (at T-a 25 degreesC) but did show reduced mass-specific costs in terms of energy and water use at extremes of T-a (-5 degrees and 45 degreesC, respectively). In their arid environment, typified by unpredictable rainfall and extremes of T-a, young red kangaroos may need to remain close to water points, which, in turn, may restrict their ability to find the highquality forage needed to meet their high energy demands. ABSTRACTThe population dynamics of red kangaroos (Macropus rufus) in the Australian arid zone is tightly linked with environmental factors, which partly operate via the survival of juvenile animals. A crucial stage is the young-at-foot (YAF) stage when kangaroos permanently exit the pouch. We have examined the thermal biology of YAF red kangaroos during ages from permanent pouch exit until weaning. Over a wide range of environmental temperatures (ambient temperature [T a ] Ϫ5Њ to 45ЊC), YAF red kangaroos had a mass-specific metabolism that was generally twice that of adults, considerably higher than would be expected for an adult marsupial of their body size. The total energy requirements of YAF red kangaroos were 60%-70% of those of adult females, which were three times their size. Over the same range in T a , YAF red kangaroos also had total evaporative water losses equal to those of adult females. At the highest T a (45ЊC), differences were noted in patterns of dry heat loss (dry conductance) between YAF red kangaroos and adult femal...

Bioenergetics and inter-individual variation in physiological capacities in a relict mammal – the Monito del Monte (Dromiciops gliroides)

“…Evaporative water loss (EWL) -the rate of water loss from the body due to evaporation -is an important variable related to the resistance to dehydration in vertebrates, which in small endotherms could be of crucial relevance to survival (Anderson et al, 1997;Hayes et al, 1998;Maloney and Dawson, 1998;Munn and Dawson, 2001;Wang and Wang, 2000;Williams and Tieleman, 2000). The repeatability of this trait was studied by Hayes and colleagues (Hayes et al, 1998; see also Hayes and Jenkins, 1997), who found up to 65% repeatable variation.…”

Ventilation patterns in red kangaroos (Macropus rufusDesmarest): juveniles work harder than adults at thermal extremes, but extract more oxygen per breath at thermoneutrality

“…At this 'in-out' stage, the young kangaroo is still unable to maintain deep body temperature (T b ) for long periods, regularly returning to the pouch for warmth and safety Dawson, 1995). By 230-250·d, thermoregulation is well developed (Munn and Dawson, 2001) and the young kangaroo permanently leaves the pouch, becoming a young-at-foot (YAF; mass 4-5·kg). YAF red kangaroos forage in association with their mothers but also continue to take milk by putting their head into the pouch to access the same teat used during pouch-life.…”

“…It is not for another 100·days or so that the YAF is fully weaned, at around 360·d and weighing 10-11·kg Dawson, 1995). Once young kangaroos have permanently left the mother's pouch they face the same environmental challenges as adults, but their smaller body size and high-energy requirements for growth (Munn and Dawson, 2001;Munn and Dawson, 2003) potentially impact on their ability to meet such thermal challenges.…”

“…Munn and Dawson showed that the energy and water requirements of YAF red kangaroos differ from those of adults (Munn and Dawson, 2001;Munn and Dawson, 2003). For example, at thermoneutral ambient temperatures (T a ) around 25°C, YAF red kangaroos had absolute rates of oxygen consumption (ml·min -1 ) that were 58% that of mature, nonlactating females, despite being only 30% of maternal body mass.…”

“…For example, at thermoneutral ambient temperatures (T a ) around 25°C, YAF red kangaroos had absolute rates of oxygen consumption (ml·min -1 ) that were 58% that of mature, nonlactating females, despite being only 30% of maternal body mass. To maintain heat balance at cold T a s, at -5°C, the absolute oxygen consumption (ml·min -1 ) of YAFs increased to 68% that of mature females (Munn and Dawson, 2001). In addition, YAF also had high water requirements at high T a (~45°C), where juvenile kangaroos evaporated 2.5-times more water per unit body mass than mature females.…”