Widmer Alex

Mechanisms of habitat adaption in Silene dioica and S. latifolia (Caryophyllaceae)
Mechanismen der Habitatsanpassung von Silene dioica und S. latifolia

Project Number: CH-4828
Project Type: Dissertation
Project Duration: 03/01/2007 - 12/31/2010 project completed
Funding Source: SNSF ,
Leading Institution: ETH Zürich
Project Leader: Prof. Alex Widmer
Institut für Integrative Biologie (IBZ)
ETH Zürich
CHN G 21.1
Universitätstrasse 16
8092 Zürich
Phone: +41 (0) 44 632 21 74 ; +41 (0) 44 632 57 01
FAX: +41 (0) 44 632 14 63
e-Mail: alex.widmer(at)env.ethz.ch
http://www.peg.ethz.ch/

related to this project.
for which the project has a relevance.


Research Areas:
Biodiversity

Disciplines:
biology and medicine
environmental sciences

Keywords:
biodiversity, adaptation, reproductive isolation

Abstract:
Habitat adaptation allows species or populations to survive and reproduce in certain habitats but not in others. The evolution of such ecological differentiation has been identified as a major driver of divergence processes that can lead to reproductive isolation and speciation. In this thesis I contribute to the understanding of ecological divergence using several related studied on the naturally hybridizing campions Silene dioica and S. latifolia.


First, we investigated habitat differentiation between and within sites of Silene dioica and S. latifolia using AFLP banding patterns and vegetation relevés around individual plants. Only three putative early-generation hybrids were detected at natural contact sites. Silene dioica was found in moister, colder and less disturbed sites than S. latifolia. However, asymmetric habitat overlap was evident with contact sites found in intermediate conditions that were more similar to S. latifolia sites. Within contact sites, however, the micro-habitats of the two species did not differ making habitat-mediated selection against intermediate phenotypes of hybrids unlikely and suggesting that other reproductive barriers contribute to the rarity of early-generation hybrids.


Secondly, we studied responses to shade and drought stress in crosses between and within Silene dioica and S. latifolia to further understand ecological differences between the species and their hybrids. Responses to drought stress did not differ between cross types. Shade stress, in contrast, led to a reduced flowering incidence in Silene dioica and the hybrids but not in S. latifolia. Rapid flowering under stress conditions in S. latifolia could be an adaptation to higher disturbance in its habitat, whereas a delay of reproduction might be adaptive in the more predictable environment of S. dioica. While hybrids did not show a generally reduced stress tolerance in comparison to the two species, our results do suggest that S. dioica and hybrids may be excluded from highly disturbed and stressful habitats of S. latifolia due to their delayed flowering.


In a third study, we investigated whether habitat adaptation, phenological divergence or low performance of first- and second generation hybrids could act as reproductive barriers between S. dioica and S. latifolia. For this purpose we
transplanted Silene dioica, Silene latifolia as well as two classes of hybrids (F1 and F2) into six sites, three within natural populations of each species and assessed cumulative fitness and flowering phenology. We found clear evidence for habitat adaptation: in each habitat, the resident species had the highest fitness. Such habitat adaptation may limit possibilities for contact between the two species. Furthermore, flowering times of the two species overlapped only partially further reducing possibilities for mating. While first-generation hybrids performed intermediate between the two species, second-generation hybrids had a generally low performance that may be due to a disruption of epistatic interactions and further limit gene flow between the species. A stronger fitness reduction of S. latifolia in S. dioica habitats than vice versa and a longer flowering overlap of hybrids with S. latifolia than with S. dioica further suggest that reproductive barriers between S. dioica and S. latifolia lead to preferential gene flow from S. dioica into S. latifolia.
In a fourth part, we investigated mechanisms of habitat adaptation in more detail and analyzed the relative importance of survival, flowering and the production of an overwintering rosette in S. latifolia, S. dioica and hybrids in our transplant experiment (see above). Differences in survival were the main restriction to the establishment of one species in the other species habitat. F2 hybrids, however, had a generally lower flowering incidence than the other cross types. Production of an overwintering rosette was under positive selection within F2 hybrids in the S. dioica habitat and might be a key trait limiting the establishment S. latifolia and hybrids within the S. dioica habitat.


This thesis adds to the understanding of ecologically-mediated reproductive isolation between two cross-fertile species and shows the importance of combining several approaches including field observations and experimental crosses, as well as greenhouse and field experiments.

Leading questions:
  • Do the habitats of S. dioica and S. latifolia differ between sites and within contact sites, do the habitats overlap and are the species genetically differentiated between and within sites?

  • How do S. dioica, S. latifolia and their reciprocal hybrids differ in their fitness reduction under drought and shade stress and does the plastic response in leaf morphology differ between the two species and their hybrids?

  • Are Silene latifolia and S. dioica more fit in their respective habitat and how does the fitness of the different classes of hybrids compare with each other and with S. dioica and S. latifolia? Does flowering time of the species and their hybrids overlap?

  • Do S. latifolia, S. dioica and their hybrids differ in their survival and/or flowering between the contrasting habitats and is the production of an overwintering rosette a trait under selection in either of theses habitats?

    URL: http://e-collection.library.ethz.ch/eserv/eth:1652/eth-1652-01.pdf

    Publications:
    Favre, Adrien. 2010. Mechanisms of habitat adaptation in Silene dioica and S. latifolia (Caryophyllaceae). Dissertation, ETH Zürich.


    Last update: 12/29/16
    Source of data: ProClim- Research InfoSystem (1993-2024)
    Update the data of project: CH-4828

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