Date of Graduation

5-2014

Document Type

Thesis

Degree Name

Master of Science in Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Alverson, Andrew J.

Committee Member

Douglas, Marlis R.

Second Committee Member

Silberman, Jeffrey D.

Keywords

Algae; Diatoms; Evolution; Life Cycle; Transcriptomics

Abstract

An organism's life cycle is the direct result of its evolutionary history and represents a fundamental aspect of its ancestry and ecology. Yet the process of linking alternating life-history stages has proven to be challenging, if not impossible in some cases. Diatoms (Bacillariophyceae) are no exception to this challenge, and their diversity of life stages and reproductive strategies add further challenges. A central focus of diatom research has been to unravel the evolutionary events that led to their extraordinary diversity, a line of inquiry that has been greatly aided by the availability of next-generation sequence data. Yet without proper taxonomic sampling, many fundamental questions have remained unresolved. Furthermore, the incorporation of data from outgroup lineages provides crucial insights into the ancestral state of a taxon. However the life cycle of the sister lineage to diatoms, the Bolidophytes, has also remained an enigma. Here, to address yet unresolved questions about the origin of the diatom life cycle, transcriptomes for Bolidomonas pacifica (Bolidophyceae) and two diploid diatoms, Leptocylindrus danicus and Hemiaulus sinensis (Bacillariophyceae) were sequenced and analyzed. A novel approach of quantifying the degree of heterozygosity across the genome was used to infer the ploidy in Bolidomonas, whose ploidy level is unknown. Lack of heterozygous alleles in Bolidomonas strongly suggests that it is a vegetatively haploid organism, and the presence of several meiosis-specific genes indicate that it is likely capable of sexual reproduction as well. These results suggest that Bolidomonas represents the haploid phase of a haplodiplonitic life cycle, in which silicified Parmaleans are the diploid phase.

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