Application of microsatellite DNA markers to discriminate between maternal and genetic effects on scalation and behavior in multiply-sired garter snake litters

Incomplete knowledge of pedigrees sometimes limits the methods of estimating quantitative genetic parameters (heritability, genetic correlation) in nature and may result in estimates that are inflated by nongenetic sources of variation. North American garter snakes and their allies provide a model system for investigating evolutionary quantitative genetics, but estimates of quantitative genetic parameters in these snakes are mostly based on offspring-dam regression and full-sib analysis, methods that fail to discriminate between maternal genetic, maternal environmental, and direct genetic effects on traits of interest. Using data from the garter snake Thamnophis sirtalis, we demonstrate that microsatellite DNA markers can be used to identify full-sib sireships within litters in species that produce large numbers of offspring and in which multiple paternity is common. This allows estimation of quantitative genetic parameters using a maternal half-sib analysis in which sires are nested within dams. Six microsatellite DNA loci were scored for four wild-caught dams and their 73 offspring and revealed two full-sib sireships within each litter. Maternal half-sib analyses of scalation and behavior suggest that heritability may be lower and maternal effects larger than was previously thought.