Cell size is positively correlated between different tissues in passerine birds and amphibians, but not necessarily in mammals

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.

Growth rate and thermoregulation in reared king quails (Coturnix chinensis)

Growth rate was investigated in king quails between 1st and 60th day of life. Gompertz growth constants were 0.075 in males and 0.056 in females. Colonic temperature (Tb) was measured in quails divided into four age groups (1-3, 7-10, 16-19, and 44-59 days old) in ambient temperatures set separately for each group. Metabolic rate was measured only in 44-59-day-old birds. The mean value of the thermoneutral body temperature (Tb at TNZ) in the active phase in the youngest quails was 39.0 degrees C. In 44-59-day-old quails, the resting metabolic rate in the thermoneutral zone (RMR at TNZ) was on average 9.44 mW g(-1) (1.66 cm3 O2 g(-1)h(-1)), without sex-specific differences. No such differences were found in this age group neither in Tb at TNZ, nor in minimal thermal conductance (Cmin). However, differences were found in the rate of metabolic heat production below the thermoneutral zone, even when mass-independent units were used. The maximum metabolic rate (Mmax) in 2-month-old males was 34.08 mW g(-1) (5.98 cm3 O2 g(-1)h(-1)), while in females 29.73 mW g(-1) (5.21 cm3 O2 g(-1)h(-1)). Heat-stressed 44-59-day-old quails elevated their Tb to as much as an average 44.1 degrees C in Ta of about 45 degrees C. The obtained growth model and a gradual development of the body temperature regulation mechanism in king quails followed the known strategy of development, typical for precocial birds. The sexual size dimorphism in the studied quails did not result in differences in thermoregulation parameters between the sexes, except for the rate of metabolic rate below thermoneutral zone.

Energy metabolism and thermoregulation in hand-reared chukars (Alectoris chukar)

Metabolic rate and colonic temperature were measured in chukars between 1st and 108th day of life (divided into six age groups: 1-3-days old, 1, 2, 3, and 4-weeks old and 3.5-months old) in ambient temperatures set separately for each group and ranging from -12 to 41 degrees C. The Gompertz growth constant for growing chukars (0.042) was close to the value obtained in earlier study for the grey partridge. Similarly as in other species of Galliformes, newly hatched chukar chicks had lower T(b) at TNZ (39.5 degrees C) than that found in older birds (41.3 degrees C in 4-weeks old). The body temperatures taken at TNZ in 2-weeks old chicks and older fitted neatly within allometrically predicted limits of body temperatures for adult birds. The values of RMR at TNZ followed closely a biphasic pattern, with the second phase correlating strongly with the body mass. The value of metabolic scope (the level of metabolic efficiency) for the youngest group was high (3.2) and exceeded the values obtained in earlier studies for other gallinaceous species, including the grey partridge. The obtained values of minimum wet thermal conductance for growing chukar chicks exceeded the predicted values by approximately 40% but the slopes of both lines were very similar. In chukars, the key stage in the expression of fully developed thermoregulatory capacities comes immediately after the first week of life (maintaining somewhat constant body temperature, evident drop in the value of RMR at TNZ and minimal thermal conductance). The model of gradual development of thermoregulation which could be derived from the experiments on chukar chicks was characteristic for typical precocial birds.