The threespine stickleback, Gasterosteus aculeatus, is a diverse superspecies that exists mainly in coastal temperate zones of the Northern hemisphere with a variety of life history modes. Past phylogenetic analyses of the populations of threespine stickleback have been completed using mitochondrial DNA (mtDNA) data. However, mitochondrial introgression has been observed in many fish species, including threespine stickleback, which causes phylogenetic studies using mtDNA to be false. Here, mitochondrial introgression refers to the movement of mitochondrial genes from one population to another population. Nuclear DNA (nDNA) was analyzed in this study to assess the validity of the mtDNA phylogenetic studies of Californian populations. Up to three nuclear loci containing a total of 41 single nucleotide polymorphisms (SNPs) were analyzed from five Californian populations of threespine stickleback and compared to stickleback from Pacific North America. Neighbor-joining trees were constructed and showed different relationships than found in the mtDNA-based study. Californian populations were found to be distinct from a British Columbian population and two different clades of Californian populations were found, including a Lost Lake/Shay Creek/Fillmore clade and a Holcomb Creek/williamsoni clade. These results, however, are inconclusive due to a large amount of intrapopulation variation at the sites assayed. Lost Lake seems to contain an unusually large amount of variation that makes it unique. Further study, though, must be completed to determine the validity of the these results and those from the previous mtDNA-based studies. Specifically, Shay Creek Stickleback may be confirmed as being closely related to Gasterosteus aculeatus williamsoni, which is already on the endangered species list or Lost Lake may be found to be another unique population. Conservation efforts may then be made to protect Shay Creek and/or Lost Lake Stickleback.
Frandsen, T. (2006). Using Nuclear DNA to Investigate the Phylogenetics of Californian Threespine Stickleback Populations (Undergraduate honors thesis, University of Redlands). Retrieved from http://inspire.redlands.edu/cas_honors/136