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

Abstract

Water 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 mass and mean values varied from 4.8 ml CO gh (2.9 kJ gd) in autumn and winter, to 7.0 ml CO gh (4.2 kJ gd) 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 body water d (122 ml kgd) to 1000 ml ld (725 ml kgd). 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. 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.

Does high growth rate of juvenile house mice with prolonged access to ripening grain and free water drive population outbreaks?

“…Many authors have speculated about the likely importance of ripening grain in the development of mouse plagues (Bomford 1987a,b;Mutze 1991;Mutze et al 1991;Tann et al 1991;White 1993White , 2002Krebs et al 2004;Jacob et al 2007), but this study is the first to demonstrate clearly the nutritional superiority of ripening grain over mature grain for growing juvenile mice.…”

“…Litter sizes and field metabolic rates of house mice in non-irrigated cereal crops in southeastern Australia are highest in mid spring when grain is ripening, and significantly lower during summer when grain is dry and mature (Bomford 1987a;Mutze 1991;Mutze et al 1991;Singleton et al 2001;Jacob et al 2007). By contrast, in irrigated rice crops grown within the same region, maximum litter sizes appear 4-5 months later, at the end of summer, again corresponding with availability of ripening grains (Bomford 1987a).…”

“…Mice generally breed and increase in numbers from spring to early autumn, and populations decline in winter or early spring (e.g. , Bomford 1987a;Singleton 1989;Mutze 1991;Mutze et al 1991;Singleton et al 2001;Ylönen et al 2003).…”

Are mice calorically restricted in nature?

“…These two field studies did reach remarkably similar results for field metabolic rate, however. Furthermore, one of the studies - Mutze et al (1991) -was exceptionally thorough, sampling a total of 59 animals at different times of the year, during both breeding and non-breeding seasons. During some sampling periods, energy use was as high as 12.4 kJ day −1 (g 0.568 ) −1 or higher than laboratory mice under any conditions measured.…”

“…Geographical locations of these studies were southern California, southern Australia and a sub-Antarctic island (Nagy, 1987;Rowe-Rowe et al ., 1989;Mutze et al ., 1991). Metabolic rate measurements were typically made over a 2-to 2.5-day time interval in both sexes during both breeding and non-breeding seasons (Table 1).…”