Energy allocation for reproduction in a marsupial arboreal folivore, the common ringtail possum (Pseudocheirus peregrinus)

Abstract

This study examines the annual energetics of a small folivorous marsupial, Pseudocheirus peregrinus. Particular attention was given to the energy and time allocated to reproduction by the females. Daily energy expenditure was measured directly using the doubly labelled water technique. Energy transferred to the young via the milk was estimated from information on milk composition and production. There was no significant seasonal variation in the energy expenditure or water influx of males or females. The mean daily energy expenditure of a 1-kg non-lactating adult ringtail possum was 615 kJ day or 2.2 times standard metabolic rate. Females showed significant changes in daily energy expenditure according to their reproductive status. Without the burden of lactation the total annual energy expenditure of an adult female was estimated as 212.4 MJ kg year. The total annual energy expenditure of a female rearing two young was 247.5 MJ kg year, with the late stage of lactation constituting the most energetically expensive period accounting for 30% of the total yearly energy expenditure during 24% of the time. Total metabolisable energy allocation during reproduction (22 MJ kg) was similar to estimates available for other herbivores, although, the peak metabolisable energy allocation during lactation (759 kJ day) was lower than values available for other herbivores. The total energy requirement for reproduction (metabolisable energy plus potential energy exported to young via milk) suggests that the ringtail possum also has a relatively low overall energy investment in reproduction. It is suggested that the lactational strategy of the ringtail possum has been selected in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet and/or to prolong the mother-young bond. The strategies a female ringtail possum may employ to achieve energy balance when faced with the energy demands of reproduction are discussed.

Development of thermoregulation in the sugar glider Petaurus breviceps (Marsupialia: Petauridae)

“…Nagy & Suckling (1985) observed no difference between the metabolic rates of non-lactating and lactating female sugar gliders with one and two young, all estimated to be only a few weeks old. These results are in agreement with several other mammals studied during pregnancy and lactation, in which additional energetic costs for the mother were observed only in the latter half of lactation (Kenagy, Sharbaugh & Nagy, 1989;Munks & Green, 1995;Green, Merchant & Newgrain, 1997). This pattern of energetic cost to the mother during lactation can be explained by the rates of energy consumption of the developing young.…”

Sex in a material world: why the study of sexual reproduction and sex-specific traits should become more nutritionally-explicit

“…Preliminary support for this idea comes from Krockenberger and colleagues (1998), who suggested that the low daily production and low protein/lipid content of female koala milk is an adaptation to the low protein/lipid content of their specialized diet of Eucalyptus foliage. Similar reductions in maternal investment in lactation appear in other folivorous marsupials (Munks and Green 1995), but more work is needed to consider this hypothesis within a broader phylogenetic context.…”

The limit to the distribution of a rainforest marsupial folivore is consistent with the thermal intolerance hypothesis

“…Observations of water flux in wild Pseudocheirids indicate that all rely on free water to meet part of their water requirements (Foley et al 1990;Goudberg 1990;Munks and Green 1995). This is also likely to be true for P. archeri.…”

“…An average-sized individual (1,170 g) P. archeri is predicted to require 172 ml d -1 of water (Nagy and Bradshaw 2000). To satisfy predicted water requirements from foliage alone, an average-sized individual of P. archeri would have to consume 65-82 g d -1 DW foliage (assuming a water content of 65-70% for preferred foliage : Goudberg 1990;Jones and Krockenberger, unpublished data; and 20 ml d -1 metabolic water production: Munks and Green 1995;Foley et al 1990). Adjusted for mass this is up to 70% higher than intake rates for other pseudocheirids (Foley et al 1990;Marsh et al 2003b), and may not be feasible.…”

“…Given that the limited evidence shows no reproductive seasonality in this species (Krockenberger, unpublished data), it is feasible that lactating females are exposed to hot, dry conditions. This potential vulnerability assumes that extra water intake by lactating females is exported in milk and is not available for evaporative cooling, as in common ringtail possums, Pseudocheirus peregrinus, where close to 90% of the increased water intake at peak lactation is exported in milk (Munks 1990;Munks and Green 1995). However, if lactating females increase foliage water intake for the energetic requirements of milk production by more than what they export in milk, then lactating female P. archeri would not be as vulnerable to impacts of heatwave events.…”