Effects of climate on oxygen consumption and energy intake of chromosomally divergent populations of the House Mouse (Mus musculus domesticus) from the island of Madeira (North Atlantic, Portugal)

We explored the effects of climatic variables (mean altitude, mean daily winter temperature, mean daily summer temperature, mean annual precipitation and days of precipitation per year) on energetic parameters (food intake and resting oxygen consumption) in six Robertsonian chromosomal races and hybrid populations of House Mice (Mus musculus domesticus) collected throughout the island of Madeira in the North Atlantic. Food energy intake and resting metabolism (oxygen consumption) were measured, in 59 non-reproducing adult males trapped in April-September 1998 and June 1999 and maintained in captivity for at least 3 weeks prior to measurements. Mean daily energy intake of Robertsonian mice varied between 25.3 kJ day(-1) in race S. Vicente (2n = 25-27) and 34.6 kJ day(-1) in race Achadas da Cruz (2n = 24-27), while in hybrids (2n = 22 x 2n = 40) it was 23.0 kJ day(-1). All races exhibited low resting rates of oxygen consumption compared with the predicted basal metabolic rates expected for Muridae, between 49.2% and 66.5% of the expected values. The main factor influencing both food energy intake and oxygen consumption was body mass, explaining 41% of the variation in food energy intake and 39% of the variation in resting oxygen consumption. Body mass was significantly related to the mean summer temperature at the sites where the mice were captured, but was unaffected by the chromosomal race or other biogeographical and climatic variables. There were no additional effects of these factors on resting oxygen consumption beyond the effect of body mass. Once the effects of body mass were removed, food energy intake was significantly correlated with the chromosomal race. The different environmental conditions experienced by the races may have favoured the physiological adaptation of mice to different habitats.