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8
environmental DNA, but these metagenomically assembled genomes (MAGs) represent a
consensus sequence for a population rather than a distinct organism. Recent variations in
metagenomics such as the use of long read sequencing technologies or Hi-C linkage have
claimed to be able to resolve fine-scale diversity (Bickhart et al. 2019), but these techniques have
yet to be widely used. Single-cell genomics has been able to resolve coexisting strains in the
environment (Kashtan et al. 2014), but a limitation of this technique is that it often has difficulty
reconstructing complete genomes.
Despite these methodological challenges, intraspecific diversity has been observed to
differentiate strains into temperature-defined ecotypes as seen in picocyanobacteria (Kashtan et
al. 2014; Sohm et al. 2016; Lee et al. 2019), diatoms (Canesi and Rynearson 2016; Rynearson et
al. 2020), and picoeukaryotes (Schaum et al. 2013). There is also evidence that fine scale
diversity could be an intermediate step in major speciation events, as radiations into numerous
thermal niches have been suggested to play a key role in the evolutionary history of marine
phytoplankton. For instance, it has been hypothesized that just a handful of mutations in the
photosynthetic machinery of the marine picocyanobacterium Synechococcus are responsible for
its expansion into relatively cold, high latitude waters (Pittera et al. 2014, 2017). In a global
change context, fine-scale species- and strain-level rearrangements likely won’t affect
biogeochemistry as significantly as changes in interspecific diversity. However, intraspecific
microdiversity could instead be a source of potential thermal resilience if particular strains in a
population are already adapted to warmer temperatures.
Thesis Motivation
Anthropogenic CO2 is actively reshaping the world ocean. Rising temperatures, falling
pH, and new weather patterns are challenging life everywhere. A key question for scientists
studying marine biological systems is how communities of organisms will respond. This has
Object Description
| Title | Thermal diversity within marine phytoplankton communities |
| Author | Kling, Joshua David |
| Author email | Joshuakl@usc.edu;Joshuakl@berkeley.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Biology (Marine Biology and Biological Oceanography) |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2020-08-11 |
| Date submitted | 2020-08-11 |
| Date approved | 2020-08-11 |
| Restricted until | 2020-08-11 |
| Date published | 2020-08-11 |
| Advisor (committee chair) | Hutchins, David |
| Advisor (committee member) |
Levine, Naomi Heidelberg, John Ehrenreich, Ian |
| Abstract | Marine photosynthetic carbon fixation in the sunlit upper reaches of the ocean is almost entirely carried out by chlorophyll-containing, single-celled microorganisms, and is responsible for half of the net primary production on the planet. Because of this connection to the marine carbon cycle, it is essential to assess the responses of marine phytoplankton to global change. However, this work is challenged by the dazzling diversity of both eukaryotic and prokaryotic lineages which coexist in complex phytoplankton assemblages. My dissertation contributes to this effort by investigating how the diversity of phytoplankton influences their resilience to rising temperatures. In my first study, I used natural California coastal communities collected across three seasons to show that the phytoplankton assemblage as a whole was able to maintain growth well above typical temperature ranges. However, either steady or fluctuating temperatures exceeding the maximum threshold recorded in a decade-long observational dataset caused drastic rearrangements in the phytoplankton community, including the appearance of novel dominant species. My dissertation work also highlights that there are still unrecognized but environmentally-important taxa with bizarre and unexpected life histories and thermal responses, even in the most well-studied environments. In my second study, I characterized a recently isolated nanoplanktonic diatom from the Narragansett Bay Time Series that occupies a distinct low-light, low-temperature niche. This isolate demonstrated an unusual sensitivity to light, whereby its ability to respond to what should be favorable increases in temperature is constrained by light intensity. Six years of amplicon sequencing data from the time series site suggest that this diatom is a temperate wintertime/early spring specialist, and will likely not fare well in a warmer and more stratified future ocean. In addition to expanding knowledge of functional diversity at the species level, my work also examines the potential of intra-specific diversity to house hidden adaptations to rising temperatures. Natural microbial populations are composed of distinct individual strains, whose relative abilities to contribute to the success of the whole population in a changing environment have not been well-studied. In my third study, I compared the thermal responses of 11 strains of the marine unicellular cyanobacterium Synechococcus simultaneously isolated from a single estuarine water sample to explore this cryptic intra-specific diversity. Surprisingly, these nearly genetically-identical strains showed distinct low and high temperature phenotypes. This study indicates that strain-level variation could be a key yet understudied element in the responses of phytoplankton to global change. Together, these studies highlight that the diversity of marine phytoplankton at the species and individual level includes both functional variability and redundancy relative to temperature. We can expect community composition to change over time in a warming ocean, reflecting the increasing abundance of preadapted groups or individual strains; however, wherever there are winners there are also losers. Besides providing new insights into the contribution of diversity to climate resilience, this dissertation also highlights the need to expand our knowledge of functional thermal traits, especially for typically under-studied pico- and nanoplankton which are often only known from sequence data. |
| Keyword | thermal response; phytoplankton; community ecology |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Contributing entity | University of Southern California |
| Rights | Kling, Joshua David |
| Physical access | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-KlingJoshu-8915.pdf |
| Archival file | Volume13/etd-KlingJoshu-8915.pdf |
Description
| Title | Page 13 |
| Full text | 8 environmental DNA, but these metagenomically assembled genomes (MAGs) represent a consensus sequence for a population rather than a distinct organism. Recent variations in metagenomics such as the use of long read sequencing technologies or Hi-C linkage have claimed to be able to resolve fine-scale diversity (Bickhart et al. 2019), but these techniques have yet to be widely used. Single-cell genomics has been able to resolve coexisting strains in the environment (Kashtan et al. 2014), but a limitation of this technique is that it often has difficulty reconstructing complete genomes. Despite these methodological challenges, intraspecific diversity has been observed to differentiate strains into temperature-defined ecotypes as seen in picocyanobacteria (Kashtan et al. 2014; Sohm et al. 2016; Lee et al. 2019), diatoms (Canesi and Rynearson 2016; Rynearson et al. 2020), and picoeukaryotes (Schaum et al. 2013). There is also evidence that fine scale diversity could be an intermediate step in major speciation events, as radiations into numerous thermal niches have been suggested to play a key role in the evolutionary history of marine phytoplankton. For instance, it has been hypothesized that just a handful of mutations in the photosynthetic machinery of the marine picocyanobacterium Synechococcus are responsible for its expansion into relatively cold, high latitude waters (Pittera et al. 2014, 2017). In a global change context, fine-scale species- and strain-level rearrangements likely won’t affect biogeochemistry as significantly as changes in interspecific diversity. However, intraspecific microdiversity could instead be a source of potential thermal resilience if particular strains in a population are already adapted to warmer temperatures. Thesis Motivation Anthropogenic CO2 is actively reshaping the world ocean. Rising temperatures, falling pH, and new weather patterns are challenging life everywhere. A key question for scientists studying marine biological systems is how communities of organisms will respond. This has |
