Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)




Edmund D Brodie, Jr.


The genetics of colonization is understudied in salamanders but has large conservation implications as new habitats are formed or restored to their previous condition. The 1980 eruption of Mount St. Helens provided a natural experiment to study the genetic effects of a large infrequent environmental disturbance on two species of salamander, Taricha granulosa (Rough-skinned newt) and Ambystoma gracile (Northwestern salamander). Both these species breed in ponds, and are thought to exhibit high breeding site fidelity and low vagility. I designated three treatments based on the effects of the eruption: new ponds (created by the eruption, immigrants only), recovery lakes (in blast zone, survivors plus immigrants), and reference lakes (unaffected by eruption, assumed to represent pre-eruption genetic diversity measures). Salamanders took at least nine years to colonize the new ponds. I studied the population genetics of colonization and recovery using microsatellites and AFLPs (amplified fragment length polymorphisms) to measure genetic diversity, gene flow, and population substructure at Mount St. Helens National Volcanic Monument. Based on population genetics theory and the life history characteristics of these pond-breeding amphibians, I predicted that genetic diversity would be lower in newly colonized ponds compared to recovery or reference sites. I also expected significant levels of population substructuring. Finally, I predicted that because of their lower vagility and large number of neotenes, that A. gracile would have less gene flow and a greater degree of population substructuring than T. granulosa. My predictions were not supported by my data. There was no loss of genetic diversity in new or recovery populations in either species. There was no strong evidence for population substructure by either AMOVA, isolation by distance or principal components analysis. Gene flow (Fst) was high in both species. Taricha granulosa and A. gracile were found to be resistant to a large infrequent environmental disturbance. Loss of genetic variability in new populations cannot automatically be assumed. Predicting dispersal and colonization ability based on the broad category of pond-breeding amphibian is not always reliable.