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7
(Engelen et al. 2015; Delmont and Eren 2018; Lee et al. 2019), and it is still largely unknown
how much functional diversity exists across the breadth of observed phylogenetic diversity.
Relatively little work has been done to explore the present range of thermal responses
currently existing in natural phytoplankton populations, and few data exist describing how
resilient current phytoplankton assemblages are to thermal stress (Shade et al. 2012; Irwin et al.
2015). For instance, there are fundamental uncertainties about threshold temperatures that can
cause large shifts in community composition. Also unknown are the scales at which diversity is
ecologically relevant. Communities contain multiple functional groups (diatoms, cyanobacteria,
etc,), and diversity at this level is obviously important, with rearrangements of these groups
having major ecological consequences. However, multiple coexisting species (interspecific
diversity) exist within these functional groups. In particular, many pico- or nanoplankton have
not been directly studied in the lab, or are just now being recognized for their important roles in
the marine environment (Ichinomiya et al. 2016; Leblanc et al. 2018).
Recently, differences between lineages or strains within a species complex (intraspecific
diversity) have been suggested to also be relevant to functional diversity, despite a high degree of
genomic similarity. This area has been largely understudied, because of methodological
limitations. At this taxonomic level morphology usually cannot be used to differentiate between
strains, and even molecular techniques may have difficulty detecting this fine scale diversity.
Recently though, some studies resolving amplified marker genes into amplicon sequence variants
(ASV) have been able to detect distinct ecotypes between sequences differing by as little as a
single base pair (Eren et al. 2013). Such single base pair differences in conserved marker genes
can however mask a great deal of genomic dissimilarity in functional genes. Whole-DNA
shotgun sequencing approaches such as metagenomics can reconstruct whole genomes from
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 12 |
| Full text | 7 (Engelen et al. 2015; Delmont and Eren 2018; Lee et al. 2019), and it is still largely unknown how much functional diversity exists across the breadth of observed phylogenetic diversity. Relatively little work has been done to explore the present range of thermal responses currently existing in natural phytoplankton populations, and few data exist describing how resilient current phytoplankton assemblages are to thermal stress (Shade et al. 2012; Irwin et al. 2015). For instance, there are fundamental uncertainties about threshold temperatures that can cause large shifts in community composition. Also unknown are the scales at which diversity is ecologically relevant. Communities contain multiple functional groups (diatoms, cyanobacteria, etc,), and diversity at this level is obviously important, with rearrangements of these groups having major ecological consequences. However, multiple coexisting species (interspecific diversity) exist within these functional groups. In particular, many pico- or nanoplankton have not been directly studied in the lab, or are just now being recognized for their important roles in the marine environment (Ichinomiya et al. 2016; Leblanc et al. 2018). Recently, differences between lineages or strains within a species complex (intraspecific diversity) have been suggested to also be relevant to functional diversity, despite a high degree of genomic similarity. This area has been largely understudied, because of methodological limitations. At this taxonomic level morphology usually cannot be used to differentiate between strains, and even molecular techniques may have difficulty detecting this fine scale diversity. Recently though, some studies resolving amplified marker genes into amplicon sequence variants (ASV) have been able to detect distinct ecotypes between sequences differing by as little as a single base pair (Eren et al. 2013). Such single base pair differences in conserved marker genes can however mask a great deal of genomic dissimilarity in functional genes. Whole-DNA shotgun sequencing approaches such as metagenomics can reconstruct whole genomes from |
