Relationships among functional traits in experimental microcosms of the protist Tetrahymena thermophila


First Edition

Thèse présentée en vue de l'obtention du grade de docteur en sciences et technologie. Read More

Functional traits are phenotypic traits that affect organism's performance and shape ecosystem-level processes. However, estimating functional diversity as a measure of biodiversity remains difficult in practice. One of the main challenges is to choose which phenotypic traits should be considered functional and measured, since effort and money are limited. As one way of dealing with this, Hodgson et al. (1999) introduced the idea of two types of traits, with soft traits that are easy and quick to quantify, and hard traits that are directly linked to ecosystem functioning but difficult to measure. If a link exists between the traits, then one could use soft traits as a proxy for hard traits for a quick but meaningful assessment of biodiversity. However, this is usually limited by two factors : (1) traits must be tighly connected to allow reliable prediction of one using the other ; (2) the relationship between traits must be monotonic and linear to be detected by the most commonly used statistical techniques (e.g. linear model, PCA). Following that logic, my aim during this thesis was to test the presence of such relationships by focusing on six functional traits of the protist species Tetrahymena thermophila. In the first experiment, I tested the presence of these relationships using linear and non-linear relationship detection methods in a stable environment. Then, in the second experiment, I tested how these relationships were varying along two environmental gradients using similar detection methods. Both times, the traits were proved to be rather independent, indicating that each represents a distinct aspect of functional diversity for this organism, and a high number of non-linear relationships and patterns between the traits were detected, highlighting the need to be careful about what statistical techniques one uses to estimate relationships between traits.


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Specifications


Publisher
Presses universitaires de Louvain
Author
Nils Svendsen,
Set
Language
French
Onix Audience Codes
06 Professional and scholarly
Title First Published
08 March 2024

Paperback


Publication Date
08 March 2024
ISBN-13
9782390614463
Illustrations
1 bibliography
Extent
Absolute page count : 214
Code
106724
Dimensions
16 x 24 cm
Weight
80 grams
List Price
27.00 €
ONIX XML
Version 2.1, Version 3

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Contents


Contents
General introduction ................................................................................................1
1.A / The concepts of biodiversity and ecosystem functioning..............................1
1.B / The BEF framework ......................................................................................3
1.C / A glimpse of BEF early history.....................................................................5
1.D / The beginning of functional ecology.............................................................7
1.E / Functional ecology up to this day ................................................................10
How to estimate and analyze functional diversity: a summary of current
knowledge and practices........................................................................................15
2.A / The qualitative selection of functional trait.................................................15
2.A.1 / A definition of functional trait .............................................................15
2.A.2/ The different problems when selecting functional traits.......................17
2.A.3 / Phylogeny as proxy for functional diversity ........................................21
2.B / The quantification of functional diversity ...................................................23
2.B.1 / Abundance matters...............................................................................23
2.B.2 / The intraspecific trait variation ............................................................25
2.C / The environmental context ..........................................................................28
2.C.1 / Environmental filtering ........................................................................28
2.C.2 / What makes species coexist? ...............................................................31
2.C.3 / The role of phenotypic plasticity..........................................................35
2.C.4 / Expanding the local pattern to bigger scales........................................36
2.D / We live in a multivariate world...................................................................41
2.D.1 / Do not forget interactions ....................................................................41
2.D.2 / Interactions between traits ...................................................................43
2.D.3 / Other examples of traits' multidimensionality.....................................47
2.D.4 / Traits are not the only things to be multivariate...................................48
2.E / The statistical framework ............................................................................52
2.E.1 / Examples of different biases that one might encounter........................52
2.E.2 / The soft/hard framework ......................................................................54
2.E.3 / The framework's underlying assumptions ...........................................55
Microcosms & model organisms ...........................................................................61
3.A / About the usefulness of microcosms...........................................................61
3.B / The aim of the thesis, and the model organism Tetrahymena thermophila.64

3.C / Tetrahymena thermophila genetics and reproduction..................................68
3.D / The selection of T. thermophila’s functional traits......................................74
3.D.1 / Morphology – Easy traits.....................................................................75
3.D.2 / Movement – Intermediate traits...........................................................80
3.D.3 / Growth rate – The first hard trait .........................................................83
3.D.4 / Oxygen consumption – The second hard trait......................................86
3.D.5 / Expected relationships between traits..................................................94
Relationships between functional traits in an optimal environment..................97
4.A / Introduction .................................................................................................97
4.B / Methods.......................................................................................................98
4.B.1 / Culture conditions & experimental design ...........................................98
4.B.2 / Trait measurements............................................................................100
4.C / Results.......................................................................................................103
4.C.1 / Pairwise model for local pattern.........................................................103
4.C.2 / Multivariate analysis for global pattern..............................................106
4.C.4 / The intraspecific and intrastrain variability within functional traits in
T. thermophila................................................................................................114
4.C.5/ Trait change between mother and experimental cultures....................117
4.D / Discussion .................................................................................................120
Relationships between functional traits along an environmental gradient .....125
5.A / Introduction ...............................................................................................125
5.B / Methods.....................................................................................................131
5.B.1 / Culture conditions..............................................................................131
5.B.2 / Trait measurement..............................................................................132
5.C / Results.......................................................................................................137
5.C.1 / The impact of the environments on the traits.....................................137
5.C.2 / Pairwise model analysis.....................................................................142
5.C.3 / Multivariate analysis..........................................................................150
5.C.4 / Difference in the wave pattern along the temperature gradient..........156
5.C.5 / Traits changes between the different cultures ....................................160
5.D / Discussion .................................................................................................162
General discussion ................................................................................................167
References .............................................................................................................175