We examined cell size correlations between tissues, and cell size to body mass relationships in passerine birds, amphibians and mammals. The size correlated highly between all cell types in birds and amphibians; mammalian tissues clustered by size correlation in three tissue groups. Erythrocyte size correlated well with the volume of other cell types in birds and amphibians, but poorly in mammals. In birds, body mass correlated positively with the size of all cell types including erythrocytes, and in mammals only with the sizes of some cell types. Size of mammalian erythrocytes correlated with body mass only within the most taxonomically uniform group of species (rodents and lagomorphs). Cell volume increased with body mass of birds and mammals to less than 0.3 power, indicating that body size evolved mostly by changes in cell number. Our evidence suggests that epigenetic mechanisms determining cell size relationships in tissues are conservative in birds and amphibians, but less stringent in mammals. The patterns of cell size to body mass relationships we obtained challenge some key assumptions of fractal and cellular models used by allometric theory to explain mass-scaling of metabolism. We suggest that the assumptions in both models are not universal, and that such models need reformulation.

Cell size plays a role in body size evolution and environmental adaptations. Addressing these roles, we studied body mass and cell size in Galliformes birds and Rodentia mammals, and collected published data on their genome sizes. In birds, we measured erythrocyte nuclei and basal metabolic rates (BMRs). In birds and mammals, larger species consistently evolved larger cells for five cell types (erythrocytes, enterocytes, chondrocytes, skin epithelial cells, and kidney proximal tubule cells) and evolved smaller hepatocytes. We found no evidence that cell size differences originated through genome size changes. We conclude that the organism-wide coordination of cell size changes might be an evolutionarily conservative characteristic, and the convergent evolutionary body size and cell size changes in Galliformes and Rodentia suggest the adaptive significance of cell size. Recent theory predicts that species evolving larger cells waste less energy on tissue maintenance but have reduced capacities to deliver oxygen to mitochondria and metabolize resources. Indeed, birds with larger size of the abovementioned cell types and smaller hepatocytes have evolved lower mass-specific BMRs. We propose that the inconsistent pattern in hepatocytes derives from the efficient delivery system to hepatocytes, combined with their intense involvement in supracellular function and anabolic activity.

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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...