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35
Island Graduate School of Oceanography cell sorting facility using a BD FACSCalibur (San Jose,
CA, USA). Cells < 5 μm with chlorophyll a fluorescence were sorted into 96 well plates
containing natural seawater amended with nutrients following the recipe for F media diluted to
F/20 (Guillard 1975). The well plates were monitored over time, and when fluorescence was
detected in a well it was transferred to new media while gradually increasing nutrients to F/2
concentrations. Isolates were then switched to artificial seawater made according to the recipe
for Aquil medium (Sunda, et al. 2005). Stock cultures were maintained long-term at 4 °C under
30 μmol photons / m2 * sec-1. of cool-white fluorescent light, and diluted biweekly with fresh
medium.
Temperature and Light Assays
All culture work was done in climate controlled walk-in incubators on shelves holding
banks of cool white fluorescent lights. Light levels were verified with daily measurements using
a LI-250A light meter (LI-COR Biosciences, Lincoln, NE, USA) to ensure accurate and uniform
irradiance. Cultures were kept in triplicate 15ml polystyrene culture vials and temperature for
all experiments was set using a series of water baths, each with its own heating and cooling
element and thermostat. Replicates were kept in exponential phase by diluting cultures with
sterile media when biomass reached a predetermined threshold. Cultures were acclimated to
each combination of irradiance and temperature for two weeks.
After this initial acclimation period, growth rates were determined using daily
measurements of in vivo fluorescence on a Turner AU-10 fluorometer (Turner Designs Inc.,
Sunnyvale, CA, USA) for an additional seven to ten days. In vivo fluorescence was used as a
proxy for photosynthetic biomass, because it efficiently allowed us to make daily
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 40 |
| Full text | 35 Island Graduate School of Oceanography cell sorting facility using a BD FACSCalibur (San Jose, CA, USA). Cells < 5 μm with chlorophyll a fluorescence were sorted into 96 well plates containing natural seawater amended with nutrients following the recipe for F media diluted to F/20 (Guillard 1975). The well plates were monitored over time, and when fluorescence was detected in a well it was transferred to new media while gradually increasing nutrients to F/2 concentrations. Isolates were then switched to artificial seawater made according to the recipe for Aquil medium (Sunda, et al. 2005). Stock cultures were maintained long-term at 4 °C under 30 μmol photons / m2 * sec-1. of cool-white fluorescent light, and diluted biweekly with fresh medium. Temperature and Light Assays All culture work was done in climate controlled walk-in incubators on shelves holding banks of cool white fluorescent lights. Light levels were verified with daily measurements using a LI-250A light meter (LI-COR Biosciences, Lincoln, NE, USA) to ensure accurate and uniform irradiance. Cultures were kept in triplicate 15ml polystyrene culture vials and temperature for all experiments was set using a series of water baths, each with its own heating and cooling element and thermostat. Replicates were kept in exponential phase by diluting cultures with sterile media when biomass reached a predetermined threshold. Cultures were acclimated to each combination of irradiance and temperature for two weeks. After this initial acclimation period, growth rates were determined using daily measurements of in vivo fluorescence on a Turner AU-10 fluorometer (Turner Designs Inc., Sunnyvale, CA, USA) for an additional seven to ten days. In vivo fluorescence was used as a proxy for photosynthetic biomass, because it efficiently allowed us to make daily |
