IntroductionThe house mouse is an ubiquitous species which forms many subspecies by crossing synanthropic forms with the original wild ones. U nder favourable climatic conditions, the house mouse may return to the wild, away from hum an settlements (particularly on islands where predators are lacking) (Pucek 1984).In Central Europe, two synanthropic subspecies of the house mouse occur. In the western part of the range M. musculus domesticus Rutty, 1772 is found whereas in Eastern Europe, up to Scandinavia to the north, and Elbe river to the west -M. musculus musculus Linnaeus, 1758. The latter is less associated with hum an settlements and moves easily into natural locations. The two subspecies form hybrids in the border zone o f their ranges (Pucek 1984).The mice of M us musculus musculus from Poland and Bulgaria were obtained from similar habitats (cultivated fields close to hum an settlements), although still different in respect to climatic conditions e.g. average annual air tem perature. In Poland it was lower (7.7°C) than in Bulgaria (9.7°C).M us spretus (Lataste, 1883) is distributed throughout Portugal and M editerranean region (Spain, southern France, northern Africa) (Orsini et al. 1982). In southern [209] France M us spretus occurs in dry warm locations (average annual tem perature 14.7°C) close to salt lakes and unwatered vineyards.The inform ation about physiological param eters is available mainly for laborato ry strains of Mus musculus (Bratke and Górecki 1968, Górecki and Krzanowska 1970, 1971. The data on wild populations of M. musculus are patchy (Pearson 1947, M okriyevich 1966, Bashenina 1977.The aim of this study was to determine basic physiological param eters (m etabo lism rate and therm oregulation) in wild representatives of genus M us and to find if there is any geographical variation between animals living in natural habitats under rem arkably different climatic conditions. Material and methodsThe ResultsThe body weight in mice used in experiments differed significantly. The lowest body weights were noted in M. musculus from Dziekanów (average 13.2 g ± 2.9 SD), the highest -in M. spretus (21.8 g ± 1 .8 SD) while average body weights in Mus musculus from K ostinbrod was 18.6 g ± 3 .0 SD (/?<0.01 and /?<0.05).The lowest value of metabolism rate in therm oneutral zone was assumed to approxim ate the basal metabolism rate (BMR). In M. musculus from Dziekanów such value was obtained at 32°C (Fig. 2).The intensity of therm oregulation was calculated in % per °C. It was lowest in M. spretus (4.0% per °C) while the values for two groups of M. musculus were 6.3 and 7.2% per °C (Dziekanów, Kostinbrod).The param eters o f regression equations of therm oregulation are given in Table 1. The slope coefficients for the range of ambients used in this study differed statistically significantly from each other. The "a " coefficients in these equations differed between two groups of M. musculus and between M. spretus and M. musculus from Dziekanów. Am bient tem p eratu re /°C / Thermoregulation i...