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36
measurements of the large number of simultaneously maintained cultures in this study (as
many as 90 at a time). All well-acclimated replicates were kept in the same nutrient conditions,
and growth rate calculations were based on in-vivo data from the fluorescence of each
individual replicate measured relative to itself over time (Gilstad and Sakshaug, 1990; Chen and
Durbin, 1994; Wood et al., 2005; Ichimi et al., 2012, Kling et al. 2019). In-vivo fluorescence was
never used as a proxy to compare biomass across different light and temperature treatments;
however, in a pilot study with this isolate we did observe that fluorescence and cell count
increased linearly even across different light and temperature treatments (Figure S1).
These data were then used to calculate specific growth rates using GrowthTools
(DOI:10.5281/zenodo.3634918), an R package for calculating exponential growth rates for large
experiments. This package calculates growth rate as the slope of a regression line fit to the log
of these data (Wood et al. 2005). In order to assess growth rate response to light intensity for
this isolate, cultures acclimated to 16 °C were further acclimated to seven light intensities (15,
30, 50, 60, 70, 100, and 120 μmol photons / m2 * sec-1), followed by growth rate
measurements. In addition, we measured growth rate responses across a range of
temperatures in cultures acclimated to one of three light conditions (15, 30, and 50 μmol
photons / m2 * sec-1). For each light level, cultures were grown at 10 temperatures (2, 8, 12, 14,
16, 18, 20, 22, 24, 26 °C). GrowthTools (DOI:10.5281/zenodo.3634918) was used again to
calculate thermal performance curves (TPCs) using the Eppley-Norberg model (Norberg 2004;
Thomas et al. 2012). For the thermal curve done under 15 μmol photons / m2 * sec-1, 4 °C was
used as the lowest temperature instead of 2 °C.
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 41 |
| Full text | 36 measurements of the large number of simultaneously maintained cultures in this study (as many as 90 at a time). All well-acclimated replicates were kept in the same nutrient conditions, and growth rate calculations were based on in-vivo data from the fluorescence of each individual replicate measured relative to itself over time (Gilstad and Sakshaug, 1990; Chen and Durbin, 1994; Wood et al., 2005; Ichimi et al., 2012, Kling et al. 2019). In-vivo fluorescence was never used as a proxy to compare biomass across different light and temperature treatments; however, in a pilot study with this isolate we did observe that fluorescence and cell count increased linearly even across different light and temperature treatments (Figure S1). These data were then used to calculate specific growth rates using GrowthTools (DOI:10.5281/zenodo.3634918), an R package for calculating exponential growth rates for large experiments. This package calculates growth rate as the slope of a regression line fit to the log of these data (Wood et al. 2005). In order to assess growth rate response to light intensity for this isolate, cultures acclimated to 16 °C were further acclimated to seven light intensities (15, 30, 50, 60, 70, 100, and 120 μmol photons / m2 * sec-1), followed by growth rate measurements. In addition, we measured growth rate responses across a range of temperatures in cultures acclimated to one of three light conditions (15, 30, and 50 μmol photons / m2 * sec-1). For each light level, cultures were grown at 10 temperatures (2, 8, 12, 14, 16, 18, 20, 22, 24, 26 °C). GrowthTools (DOI:10.5281/zenodo.3634918) was used again to calculate thermal performance curves (TPCs) using the Eppley-Norberg model (Norberg 2004; Thomas et al. 2012). For the thermal curve done under 15 μmol photons / m2 * sec-1, 4 °C was used as the lowest temperature instead of 2 °C. |
