Some animals, such as hibernating mammals, combine both systems: they are homeotherms
in the spring and summer, but with the arrival of winter, they fall into the slumber of hibernation and their body temperature matches that of their environment.
Ecological energetics of homeotherms
: a view compatible with ecological modelling.
Birds are homeotherms
, having the ability to maintain their body temperature within a narrow range.
Of the "rules" that have been formulated to explain the effects of temperature or latitude on growth or size, one of the best known is Bergmann's rule, describing increased size of homeotherms
as an adaptive response of body surface: volume ratio to low temperatures (Vermeij 1978).
These studies have uncovered large differences in BMR between homeotherms
of similar size.
The association is absent, or negative among homeotherms, however, possibly because of their comparatively large offspring (Peters 1983, Roff 1992).
Similarly, terrestrial homeotherms at temperate latitudes also demonstrate an inverse relationship between body size and rates of population turnover (Fenchel 1974, Peters 1983).
The basal metabolic rate of homeotherms is known to depend mainly on body mass, but in mammals, more than 20% of total variance of mass-specific rate not explained by body mass can remain (e.g., McNab 1986, 1988a).
However, the body-mass-corrected nucleotypic effect can be observed even in homeotherms, at least in mammals.
He argued that the large carnivorous reptilian ancestors of mammals were inertial homeotherms
. McNab suggested that as the body size of these animals decreased over evolutionary time (as indicated by the fossil record), selection acted to increase mass-specific resting metabolic rate, thus preserving the ability to maintain relatively high and constant body temperatures.
He hypothesized that because homeotherms are more developmentally stable, and generally experience their habitat in a more fine-grained manner than poikilotherms (Levins, 1968), they might differ in genomic properties such as allelic composition, dosage compensation, or epistatic interactions and thereby in the way heterozygosity and/or changes in environmental conditions interact to influence developmental stability and/or morphology (Selander and Kaufman, 1973; Handford, 1980).
Hence, to increase statistical power and to provide another test of the heterozygosity-morphological variability relationship in homeotherms, herein we use a new and greatly enlarged data set to examine the relationship between heterozygosity and morphological variance among individual Z.