Microsatellite DNA markers, multiple paternity, and the inheritance of morphology and behavior in Butler's garter snake (Thamnophis butleri)

Variation in behavior can be the result of many environmental and genetic factors. Quantitative genetics has provided a contextual basis in which to study traits, such as behavior, that vary in a continuous manner. Estimating quantitative parameters with precision depends on complete knowledge of pedigrees. Molecular genetic techniques, such as microsatellite DNA markers, allow researchers to more accurately determine relatedness.

Garter snakes (Thamnophis) and other natricine snakes are suitable models for genetic studies due to the relatively large number of precocial offspring born to each dam. In addition, multiple paternity in Thamnophis litters is widespread. Thamnophis butleri, the subject of this thesis, is a threatened species in Wisconsin as a result of both human and genetic intrusion. The presence of morphological T. radix- T. butleri hybrids provides evidence that the parapatric species, T. radix, may be able to interbreed and genetically "swamp" T. butleri.

Preliminary studies found primers developed for T. sirtalis and Nerodia sipedon amplified T. butleri microsatellite DNA regions as well. Using this microsatellite information, I determined if multiple paternity was present in T. butleri. As expected, I found multiple paternity in 55% to 78% of the sample litters. In addition, I employed microsatellite allele distribution to deduce full and half-sibship with a litter.

Data was also collected on scale counts, body and head measurements, antipredator responses, and chemical extract and live prey preference. Disparity among litters, or dam effects, was determined using an analysis of variance. Several characteristics, such as body size, head size, number of ventral scales, propensity to strike and flee when confronted with threatening stimuli, and preference for live fish was found to vary among litters.

Dam variance could be the result of maternal genetic, maternal environmental or additive genetic effects. I performed a nested analysis of variance to establish sire-within-dam effects, which are a consequence of genetics only; therefore, the difference between dam and sire-within-dam variances is attributable to maternal environment. I found no sire-within-dam differences for any traits measured. Low sample size for the sire-within-dam analysis probably masked any true differences.