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 to be negatively correlated with genome size, which is possibly linked to average cell size. The correlation, already significant at the species level (rsp = -0.61, P < 0.0002), gradually strengthens as mean values for higher taxonomic levels (genera, families, and orders) are substituted in place of the species points (rgen = -0.65, P < 0.0002; rfam = -0.71, P < 0.0004; rord = -0.81, P < 0.008). This finding suggests that a sizeable part of the mammalian (above 25% of human) genome can be used for evolutionary adjustment of metabolic rate resulting from nucleotypic effect independently of body size. The total variance of mammalian genome-size values is found to be divided into two parts: 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 mainly at family (42%) and order (53%) levels. The only order for which there seems to be a necessary minimum of data for intraorder analysis (rodents) shows a not statistically significant correlation at the species level (rsp = -0.47; P < 0.09), significant at the genus level (rgen = -0.74; P < 0.04), and very high at the family level (rfam = -0.98; P < 0.03). The concept of ultimate (distant) characters consolidation is proposed. In birds, with average genome sizes 40% of those of mammals, and similarly narrower ranges both of genome sizes and of body-mass-corrected metabolic rates, the correlation was not significant. © 1995 The Society for the Study of Evolution.