Universität zu Köln

Pietsch, Tobias ORCID: 0000-0002-6701-9238 (2023). Investigation of population dynamics, ecological traits and molecular phylogeny of bacterivorous chrysomonads. PhD thesis, Universität zu Köln.

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Abstract

The recognised high biodiversity of planktonic microbes in the absence of a comparable high variability of limiting conditions has fascinated scientist and is known as the “paradox of plankton”. The high number of species which coexist in aquatic ecosystems at the same time contradicts the principal of competitive exclusion and requires further investigations to understand the mechanisms allowing the coexistence of multiple species on a limited number of resources. In the last decades empirical and theoretical studies provided some explanations to solve this issue as for instance environmental variability, spatial patchiness, competition or selective predation. Most of these studies focused on environmental and biotic interactions of species and did not consider potential intrinsic mechanisms originating from a single population itself. The aim of this study was to investigate growth related differences within a single species population and their potential influence on complex nonlinear population dynamics favouring the coexistence of relatively similar species. Bacterivorous chrysomonads were chosen as a model group because they are essential and dominant bacterivorous in aquatic food webs. Phylogenetic studies revealed an unexpected high biodiversity of morphologically mostly indistinguishable species which classifies this group as an interesting model group to study mechanisms allowing their coexistence. Ten isolated strains were phylogenetically described and different growth-related traits were compared. Three of the isolated bacterivorous chrysomonads have a mixotrophic nutrition while the others are heterotrophs. For the comparison of traits, the mixotrophic species Chlorochromonas danica (SAG strain) was also included. The phylogenetic analysis revealed that only three of the ten investigated strains could be assigned to known species of which one (Ochromonas vasocystis) needed to be redescribed (Poteriospumella vasocystis comb. nov.). One strain could only be identified on the genus level. The remaining six strains could not be assigned to known species and were morphologically and phylogenetically described as new species (Pseudapoikia anjascherwassiae gen. nov., Vivaspumella atacamiensis gen. nov. sp. nov., Chlorospumella boenigkii gen. nov. sp. nov., Atacamaspumella andiensis gen. nov. sp. nov., Poteriospumella maldiviensis sp. nov.). The trait comparison of those strains, including C. danica, showed that cell size and size range of ingested bacteria overlap for all investigated strains of chrysomonads while growth rate and dynamics differed to a notable extent. This was not only due to different nutritional strategies (mixotrophy, heterotrophy) but also due to species-specific differences which could not be explained by the other investigated traits. Bacteria-free and well controlled single-species chemostat systems with two mixotrophic species were established to investigate intrinsic nonlinear dynamics and a continuous-time model was developed to study intracellular processes and their potential cause for nonlinear dynamics in those single-species systems. For the investigation of clonal trait differences as putative source for nonlinear population dynamics, an individual based model was developed and the coexistence of different traits was studied under natural temperature fluctuation. The time series analysis of single-species chemostat experiments resulted in nonlinear population dynamics under well controlled and stable experimental conditions with indications of chaos-like dynamics. The continuous-time model was able to explain those nonlinear dynamics in single-species systems by considering the cell cycle as a complex intracellular process. For the first time it was shown that individuality and intrinsic aperiodic dynamics have to be considered for explaining the coexistence of species and genotypes. Moreover, the individual based model allowed the coexistence of clonal traits which differed in their temperature related resource uptake because they responded differently under natural temperature fluctuation causing nonlinear dynamics of the whole population. The results of the study point to the great significance to consider not only differences among species to explain their coexistence but also to consider differences within a population of a single species on the clonal and individual level to estimate effects on population dynamics.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Pietsch, Tobias tobias.pietsch@alumni.uni-koeln.de orcid.org/0000-0002-6701-9238 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-744213
Date:	2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language Chrysomonads UNSPECIFIED Chrysophytes UNSPECIFIED Population dynamics UNSPECIFIED Intrinsic nonlinear dynamics UNSPECIFIED Phylogeny UNSPECIFIED Ecological traits UNSPECIFIED
Date of oral exam:	7 June 2023
Referee:	Name Academic Title Arndt, Hartmut Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/74421