Plant reproduction in the alpine landscape : reproductive ecology, genetic diversity and gene flow of the rare monocarpic "Campanula thyrsoides" in the Swiss Alps

Aims & Objectives
The work presented in this thesis forms part of a larger project “How patchy
habitat and isolation affect alpine plant life: genetic diversity, gene flow and mating
systems”, which includes the PhD studies of Patrick Kuss and the author under the
supervision of Professor Jürg Stöcklin.
This doctoral thesis investigates the consequences of the natural fragmentation
and patchiness of alpine landscapes on the life of alpine plant populations. The central
focus of the thesis is on the mating system, the role of inbreeding and/or outbreeding
depression, genetic diversity and geographic structure within and among populations
of the rare Alpine monocarpic perennial Campanula thyrsoides. The main objectives
and research questions addressed are:
• Is Campanula thyrsoides self-compatible (SI) and if not, does the SI system
break down with flower age? Do inbred C. thyrsoides offspring in the common
garden suffer from inbreeding depression?
• Do we find a distance related inbreeding depression (poorer reproducive
output) or outbreeding depression (increased reproductive output) in field
populations of C. thyrsoides following crosses of different crossing distances
(selfing, 1m, 10m, 100m and among distant populations)?
• How much genetic diversity exists within populations of C. thyrsoides and
how does it relate to population size and altitude? Has the natural habitat
fragmentation let to strong genetic differentiation and restricted gene flow
among populations of C. thyrsoides resulting in a pronounced geographic
structure?
Study species
In order to seek answers to our research questions, we choose to study a
yellow bellflower; Campanula thyrsoides. The choice was based on the information
that C. thyrsoides is a rare plant species, which is only found on calcarious soils
within the European Alps and adjacent mountain ranges (Aeschimann et al. 2005).
The plants selectiveness for carbonate bearing soils together with the fact that its
seeds are not adapted to long-distance dispersal (Tackenberg 2003) are the main
reasons for the isolation and small sizes of many of its populations. These population
characteristics, therefore, made C. thyrsoides a suitable study species. Another
important characteristic of C. thyrsoides, and one of the main reasons for its inclusion
in the study is because it is a monocarpic perennial which flowers once and
subsequently dies (Jäger 2000). Monocarpic plants species, which are more
commonly found in subtropical and tropical mountain systems (e.g. the giant rosettes
of Puya spp, Espeletia spp., Echium spp. etc., Smith & Young 1987; Young &
Augspurger 1991) are rare amidst the temperate alpine flora (for the Alps, see
Aeschimann et al. 2005). Monocarpy can promote genetic differentiation between
populations by reducing the effective population size due to a shorter generation time
and lower density of populations (Loveless & Hamrick 1984; Vitalis et al. 2004).
When studying the effects of population isolation and habitat fragmentation on
plant reproduction (e.g. mating system and inbreeding depression), it is, moreover,
ideal to study a Campanula species. Although most Campanula species are selfincompatible
and allogamous (Nyman 1993), both a break-down in the SI system with
flower age (Vogler et al. 1998) and an evolution towards complete self-compatibility
(Ægisdóttir & Thórhallsdóttir 2006) have been recorded.
Design
We studied the reproductive ecology and genetic diversity of Campanula
thyrsoides by firstly setting up pollination experiments in the common garden and in
the field and secondly by sampling leaf material in 32 field populations in
Switzerland. In the common garden study, we set up a pollination experiment in order
to study the breeding system of C. thyrsoides, including the consequences of selfing,
half-sibling crossings and outcrossing on reproductive output and seedling
performance. Moreover, field experiments in four populations were set up in the
Swiss Alps in order to study the effect of different crossing distances on reproduction
in C. thyrsoides and to see if evidence would be found of hidden inbreeding
depression or outbreeding depression following large-distance crossings compared to
within-population crossings. In addition, we studied the genetic diversity, gene flow
and geographical structure within and among 32 field populations of C. thyrsoides in
Switzerland, covering both large geographical and altitudinal ranges. The genetic
study was conducted using 5 co-dominant microsatellite markers. In addition, we
studied the genetic diversity in C. thyrsoides and two other alpine plants using random
amplified polymorphic DNA (RAPD) marker as well as studing the evolutionary
demography of C. thyrsoides.