Láruson, Á. J. (2018). Genomics of the Globally Distributed Echinoid Genus Tripneustes (Doctoral dissertation).
Understanding genomic divergence can be a key to understanding population dynamics. As global climate change continues it becomes especially important to understand how and why populations form and dissipate, and how they may be better protected. To this effect, the globally distributed sea urchin genus Tripneustes has been highlighted as an ideal group for studying patterns of genomic divergence as the global distribution is split into two physically separated species (T. ventricosus in the Atlantic and T. gratilla the Pacific), and cryptic divergence in the absence of hard physical barriers has been suspected within each ocean. Molecular signatures of population divergence can be affected and skewed by a number of different biological realities. In the case of lower fitness of a heterozygous individual (underdominance), the degree as well as network shape of the connectivity between populations can determine wether rare alleles persist between populations, muddying population divergence signals, or are driven to fixation at one end of the population range while going extinct in the other, giving a signal of parapatric speciation. In order to address questions regarding the more nuanced molecular differences and broader evolutionary trajectories within the genus Tripneustes a draft transcriptome for the species T. gratilla was generated. In addition to showing an expansion in tumor suppressor genes when compared to the genome enabled sea urchin Strongylocentrotus purpuratus, and sex-specific gene expression differences in Sex determining Region Y-associated High Mobility Group box (SOX) genes, the transcriptome allowed for easy recovery of the full mitochondrial genome. Following isolation and sequence confirmation, the mitochondrial genome of T. gratilla was next compared to all previously published sea urchins mitochondrial genomes. A phylogenetic comparison validates the morphologically proposed superfamily Odontophora, with an estimated genesis of the group during the Eocene-Oligocene epoch transition. Estimates of selection via proportional non-synonymous to synonymous site substitution ratios suggest that purifying selection is the primary force acting on echinoid mitochondria.