Doctor of Philosophy (PhD)
In this study, 23 molecular lineages within the species-rich sea star genus Leptasterias subgenus Hexasterias section Camtschatica and an outgroup Leptasterias polaris were examined for patterns of mtDNA nucleotide sequence variation and evolution. Two separate regions of the mitochondrial genome were sequenced. The first region (549-bp) spanned the partial 3' ends of the 12s rRNA and 16s rRNA genes, complete tRNAs for glutamic acid and threonine, and complete putative control region. The second region (1644-bp) spanned approximately 85% of the 3' end of the cytochrome oxidase subunit I gene, complete tRNA for arginine and approximately 85% of the 5' end of the nicotinamide adenine dinucleotide dehydrogenase subunit 4L gene. Methods utilizing a non-phylogenetic approach, such as principal components and log-linear analyses, indicated that nucleotide composition varied by gene or gene region, with no obvious clustering of structurally or functionally similar genes. Intra-haplotypic nucleotide sequence variation within the 23 molecular lineages was minor (less than 1%), even from geographically distant locations. Phylogenetic-based analyses using maximum likelihood indicated that there were differences in transition and transversion rate ratios (b/a, mean value = 0.1241) and proportion of invariable sites (I, mean value = 0.7049) for the different domains analyzed. The ratio of non-synonymous substitutions to synonymous substitutions (dN/dS, mean value = 0.0416) was estimated separately by maximum likelihood for between-species and within-species branches, but no significant differences were found. Results of this study reinforce previous findings that the 23 molecular lineages consistently form five phylogenetically distinct groups which are proposed to represent separate species or species complexes.
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Hrincevich, Adam Wayne, "Patterns of nucleotide substitution within and among mitochondrial gene regions in sea star (Leptasterias spp)" (2002). LSU Doctoral Dissertations. 3963.