Abstract

Broad-sense heritabilities and genetic correlations of maximal oxygen consumption (VO₂max), blood hemoglobin levels, and ventricle mass were estimated in a natural population of snakes. Traits were measured for six or fewer presumed full-sibling offspring from each of 45 wild-caught gravid garter snakes (Thamnophis sirtalis). VO₂max was highly reproducible between replicate trial days (r = 0.88). In an attempt to reduce maternal effects, correlations of each character with body mass, snout-vent length, age at testing, litter size, dam mass, and dam snout-vent length were removed by computing residuals from multiple-regression equations. These residuals were used in subsequent genetic analyses. Approximate coefficients of variation of residuals were 16% for VO₂max, 19% for hemoglobin level, and 13% for ventricle mass. Broad-sense heritabilities were highly significant for all characters [P < 0.0001; VO₂max heritability (h²) = 0.88; hemoglobin level h² = 0.63; ventricle mass h² = 0.41], suggesting that they could respond genetically to selection. Phenotypic correlations (r_P) among residual characters were significant only between VO₂max and ventricle mass (r_P = +0.27). VO₂max and ventricle mass exhibited a significant (broad-sense) genetic correlation of +0.64; this might facilitate the correlated evolution of these two traits in response to natural or artificial selection. Ventricle mass and hemoglobin level showed a significant environmental correlation of +0.43. Treadmill endurance crawling time (Evolution 42: 335-350, 1988) showed a weak but significantly positive r_P with VO₂max (r_P = +0.17).

Copyright 1990 the American Physiological Society