NUCLEOTYPIC EFFECT IN HOMEOTHERMS - BODY-MASS-CORRECTED BASAL METABOLIC-RATE OF MAMMALS IS RELATED TO GENOME SIZE

The body-mass-corrected rate of basal metabolism in mammals is found t o be negatively correlated with genome size, which is possibly linked to average cell size. The correlation, already significant at the spec ies level (r(sp) = -0.61, P < 0.0002), gradually strengthens as mean v alues for higher taxonomic levels (genera, families, and orders) are s ubstituted in place of the species points (r(gen) = -0.65, P < 0.0002; r(fam) = -0.71, P < 0.0004; r(ord) = -0.81, P < 0.008). This finding suggests that a sizeable part of the mammalian (above 25% of human) ge nome can be used for evolutionary adjustment of metabolic rate resulti ng from nucleotypic effect independently of body size. The total varia nce of mammalian genome-size values is found to be divided into two pa rts: within genera (43%) and taxonomic levels higher than order (57%), with no tangible variance being added between these taxonomic levels; whereas the body-mass-corrected rate of basal metabolism varies mainl y at family (42%) and order (53%) levels. The only order for which the re seems to be a necessary minimum of data for intraorder analysis (ro dents) shows a not statistically significant correlation at the specie s level (r(sp) = -0.47; P < 0.09), significant at the genus level (r(g en) = -0.74; P < 0.04), and very high at the family level (r(fam) = -0 .98; P < 0.03). The concept of ultimate (distant) characters consolida tion is proposed. In birds, with average genome sizes 40% of those of mammals, and similarly narrower ranges both of genome sizes and of bod y-mass-corrected metabolic rates, the correlation was not significant.