Keith Newgrain

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

SummaryWater turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass0.5 and mean values varied from 4.8 ml CO2 g−1h−1 (2.9 kJ g−1d−1) in autumn and winter, to 7.0 ml CO2 g−1h−1 (4.2 kJ g−1d−1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l−1 body water d−1 (122 ml kg−1d−1) to 1000 ml l−1d−1 (725 ml kg−1d−1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l−1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.

Studies on the carbohydrate content of milk of the crabeater seal (Lobodon carcinophagus)

1. The mean carbohydrate content of six samples of milk of the crabeater seal (a phocid), measured as total hexose, was 1.5 +/- 0.3% (w/v). Ultrafiltrates of the skim milk of these samples had a mean carbohydrate content of 1.9 +/- 0.2%. 2. Thin-layer chromatography of the ultrafiltrates showed that this carbohydrate consists mainly of various oligosaccharides of low chromatographic mobility; lactose and traces of free glucose and galactose were also detected. 3. These oligosaccharides consisted mainly of D-galactose and N-acetylhexosamine; L-fucose, D-glucose and sialic acid were additional minor components. 4. The mean lactose content of the ultrafiltrates, determined by a specific enzymic method, was 0.021 +/- 0.007% (w/v); this is similar to the levels which have been reported for the milk of otariids.

Milk composition in an American marsupial (Monodelphis domestica).

1. Twenty one sequential milk samples from an American marsupial (Monodelphis domestica) were analyzed. 2. The solids fraction was relatively low initially (10% w/w) and then increased to about 30% at mid-lactation where it remained until lactation ceased. 3. During the first 50 days of lactation the relative proportions of protein, fat and carbohydrate were 36, 28 and 34%, respectively, of the solids fraction. 4. Sodium and magnesium concentrations were constant; however levels of potassium and magnesium varied substantially. 5. The milk of M. domestica exhibits a similar pattern of quantitative and qualitative changes to that seen in Australian marsupials.

Energetics and water flux of the marbled velvet gecko (Oedura marmorata) in tropical and temperate habitats

Abstract The gecko Oedura marmorata was studied in two different climatic zones: the arid zone of central Australia and in the wet-dry tropics of northern Australia. Doubly labelled water was used to measure field metabolic rate (FMR) and water flux rates of animals in the field during the temperate seasons of spring, summer and winter, and during the tropical wet and dry seasons. FMRs were highest in the tropical wet season and lowest in the temperate winter. The geckos in central Australia expended less energy than predicted for a similarly sized iguanid lizard, but geckos from the tropics expended about the same amount of energy as predicted for an iguanid. Water flux rates of geckos from the arid zone were extremely low in all seasons compared to other reptiles, and although water flux was higher in tropical geckos, the rates were low compared to other tropical reptiles. The standard metabolic rates (SMRs) of geckos were similar between the two regions and among the seasons. Geckos selected higher body temperatures (Tbs) in a laboratory thermal gradient in the summer (33.5°C) and wet (33.8°C) seasons compared to the winter (31.7°C) and dry (31.4°C) seasons. The mean Tbs selected in the laboratory thermal gradient by geckos from the two regions were not different at a given time of year. The energy expended during each season was partitioned into components of resting metabolism, Tb and activity. Most of the energy expended by geckos from central Australia could be attributed to the effects of temperature on resting lizards in all three seasons, but the energy expended by tropical geckos includes a substantial component due to activity during both seasons. This study revealed variability in patterns of ecological energetics between populations of closely related geckos, differences which cannot be entirely attributed to seasonal or temperature effects.

Estimation of the Milk Intake of Sucklings by Means of 22Na

Pups of dingoes and domestic dogs were injected with 22NaCl and rates of sodium turnover were derived. These rates were highly correlated with rates of milk consumption; however, isotopically based estimates of sodium intake were consistently lower than actual sodium intake by about 20%. Even so, we believe that milk consumption by pups can be estimated reliably using sodium turnover. The advantages of the 22Na turnover technique over tritiated water turnover and gravimetric techniques are discussed.

Parental investment in male and female offspring by the Peregrine Falcon, Falco peregrinus

Abstract There is general theoretical agreement that parents should alter offspring sex ratios in response to the relative costs of producing and raising sexually dimorphic male and female offspring. Among raptors females are often much larger than males, yet there is little skew in nestling sex ratios at the population level. The food intake of male and female Peregrine Falcon, Falco peregrinus, nestlings was compared in order to investigate parental resource allocation to their highly size-dimorphic offspring. Intake of seven broods was measured by (i) counting the mouthfuls nestlings received during a feeding bout, and (ii) by monitoring their turnover of tritiated water, which was combined with the results of an earlier study of four broods. Despite significant differences in size, there was no significant difference in the daily food intake of male and female nestlings for about the first 21 days of the nestling period, after which time growth of males slowed. Females continued to grow and by the end of the nestling period their total weight and food intake exceeded those of males by 45% and 25%, respectively. We argue that many apparent discrepancies between studies on gender differences in food intake can be explained in part by the section of the nestling period that was monitored: any differences may not be apparent until the latter part of the nestling period. The crude growth efficiency of females was greater than that of males. It is concluded that female nestlings require a greater amount of food than do males, but because of greater growth efficiency, they need less than expected on the basis of body mass. A similar pattern was apparent in an interspecific comparison—the difference in food intake between the sexes of the more dimorphic species was less than expected on the basis of direct proportionality. In Peregrine Falcons, there was gender overlap in total food intake over the nestling period. Other studies show that individual nestlings in large broods consume less food than those in smaller broods. Together, these results indicate a wide range of variation in intake for successful growth. Lastly, resource allocation patterns in Peregrine Falcon nests seemed largely determined by sibling interactions. The closest nestling to the adult female during a feeding bout received the most food and no individual monopolised this position, regardless of gender or relative size or age. We propose that a regular supply of large prey to Peregrine Falcon nestlings makes dominance hierarchies unnecessary.

Intake of milk by suckling echidnas (Tachyglossus aculeatus)

Estimation of milk intake in the sucklings of three captive echnidnas, Tachyglossus aculeatus, and in one living in its natural habitat were made by determination of sodium turnover rate and sodium content of the milk. The mean rate of sodium influx of the sucklings was 2.48 +/- 1.31 mmol/kg X day. The daily rates of milk consumption and growth rates were variable with a mean weight increment of 0.41 +/- 0.10 g for each ml of milk consumed. There is a wide disparity in growth rates of echidna young that is related to differences in the body weights of the mothers.

Milk composition in the North American opossum (Didelphis virginiana)

The composition of milk samples collected from captive opossums (Didelphis virginiana) was determined at various intervals during lactation. The milk solids increased from 9% at week one to a maximum of 34% at 11 weeks post-partum. There were changes in the relative proportions of protein, lipid and carbohydrate at different stages of lactation. Lipid represented the greatest fraction of the solids except for a period at mid-lactation when there was a peak in protein concentration. The concentrations of sodium, potassium and magnesium were relatively constant, 41 +/- 4, 35 +/- 11 and 9.2 +/- 1.6 mmol respectively, although calcium increased from 13 +/- 5 mmol at week one to a peak of 112 +/- 35 mmol at 9 weeks.

Estimated feeding rates and energy requirements of gentoo penguins, Pygoscelis papua, at Macquarie Island

SummaryWater and sodium turnovers of 6–7 week old gentoo penguin chicks and breeding adults were measured using isotopically labelled water and sodium. Influx rates for chicks averaged 188 ml·kg-1·day-1 and 13.9 mmol·kg-1·day-1 for water and sodium, respectively. Chicks consumed an estimated 228 g·kg-1·day-1 fresh food or 886 kJ kg-1 day. These values correspond to 761 g·day-1 or 2945 kJ·day-1 for a gentoo chick mid-way through the growth period. Flux rates for adults attending chicks ranged from 199 to 428 ml·kg-1·day-1 for water and from 15 to 36 mmol·kg-1·ay-1 for sodium.

Efficacy of the tritiated water and 22Na turnover methods in estimating food and energy intake by emperor penguins Aptenodytes forsteri

The accuracy of the tritiated water (HTO) and sodium-22 (22Na) turnover methods as estimators of dietary water and sodium intake was evaluated in emperor penguins fed separate diets of squid and fish. Emperor penguins assimilated 76.2% and 81.8% of available energy in the squid and fish diets, respectively. Both isotopes had equilibrated with body water and exchangeable sodium pools by 2 h after intramuscular injection. The tritium method yielded reliable results after blood isotope levels had declined by 35%. On average the tritium method underestimated water intake by 2.9%, with a range of-10.3% to + 11.1%. The 22Na method underestimated Na intake on average by 15.9% with the errors among individuals ranging from -37.2% to -1.8%. Discrepancies with 22Na turnover were sign ficantly greater with the squid diet than the fish diet. The results confirm the reliability of the tritium method as an estimator of food consumption by free-living emperor penguins (provided seawater and freshwater ingestion is known) and support the adoption of the 22Na method to derive an approximation of seawater intake by tritiated emperor penguin chicks and by tritiated adults on foraging trips of short duration.