Todd Becker

Date of Award


Document Type


Degree Name

Master of Science (MS)




In this study, I examined genetic population structure in spadefoot toads (Scaphiopus bombifrons) living in western North Dakota. Spadefoct toads have a very unique life history among amphibians. They are generally limited to being active only during nocturnal wet periods. Because of this, and other factors such as philopatry, it is expected that migration and dispersal rates should be relatively low. I hypothesize that this low rate of movement, along with fairly short dispersal distances when individuals do move, should lead to the structuring of genetic variation at relatively fine scales.

Five microsatellite loci were used to examine population structure at 9 temporary breeding ponds. Distances between ponds ranged from <500m to 14 km. The data showed evidence of significant genetic variation occurring between ponds even at the shortest interpond distances.

A strong heterozygote deficiency was observed for 4 out of the 5 microsatellite loci, suggesting that inbreeding may be occurring in the system. A pattern of isolation by distance was also observed but was not statistically significant. High Fst and Rst values at short interpond distances deviated from the pattern predicted by isolation by distance, and may be driven by stochastic processes such as drift, bottlenecks, and founder events.