Quantitative Genetics of Scale Counts in the Garter Snake Thamnophis sirtalis

Abstract

This study addresses the quantitative genetic basis of phenotypic variation and covariation for a series of meristic traits in the garter snake Thamnophis sirtalis fitchi (six head scale counts: loreals, supraand infralabials, preand postoculars, temporals; three body scale counts: ventrals, subcaudals, dorsal scale rows at midbody; two derived traits: umbilical scar size and position). Each trait was scored on approximately 540 offspring and their 47 dams captured in the wild while gravid. Correlations of the meristic traits with body mass at birth, dam's snout-vent length and body mass, litter size, and number of days each dam was held under laboratory conditions prior to giving birth were removed by computing residuals from multiple regression equations. Narrow-sense heritabilities (estimated by restricted maximum likelihood) of residuals were high for temporal scale counts (0.59), moderately large for ventral (0.29) and subcaudal scale counts (0.41), and low (in the range 0-0.12) for the other five traits. Probably as a consequence of the low statistical power of significance testing under restricted maximum likelihood, only the heritability for temporal scales was significantly