José Ruiz Martín, University of Seville. Supervisors: Rocío Pérez-Barrales & Juan Arroyo. December 2017.
Summary:
The genus Linum L. includes about 250 species with
sub-cosmopolitan distribution. Linum species are highly diverse
in life forms, floral colours, pollination systems and arrangement of
sex organs. Particularly interesting are this last aspect, and Darwin
(The Different Forms of Flowers, 1877) already noticed this variation
and used it to formulate his ideas about the mechanisms that triggered
heterostyly. Linum species include monomorphism, approach
herkogamy, style dimorphism, distyly, and 3-D distyly, a putatively
derived form of style polymorphism (Armbruster et al. 2006. New Phytol
171: 581–590). To test if evolutionary transitions between stylar
conditions agree with existing hypotheses, it is crucial to have a solid
phylogenetic hypothesis for species and populations. Results of previous
research (McDill et al., 2009 Syst. Bot. 34: 386–405) concluded that
heterostyly in Linum seems a condition mostly restricted to the
Mediterranean Basin, but there have been reported cases of heterostyly
in other regions, such as the South African Cape Floristic Region, under
similar Mediterranean climate conditions.
Below are outlined the objectives of my thesis, which aim at testing
Darwin´s ideas on Linum species at different levels:
1. (i) To resolve the phylogenetic and phylogeographic relationships
among Mediterranean and South African species and populations ;(ii) to
characterize the style polymorphism of each species by measuring 30
flowers of each species per morph and thus determining the level of
herkogamy present in each population and species; (iii) to reconstruct
the ancestral character state of the flower polymorphism, and finally
(iv) to infer evolutionary transitions between the states of this
character in the phylogeny.
2. In a further step, I wish to examine the transitions of style
conditions among populations of the Linum tenuifolium aggr. in
the Mediterranean Basin. This group is represented by two distinct
species: L. tenuifolium L. (stylar monomorphic, herkogamous species) and
L. suffruticosum L. (distylous species, with a special 3-D reciprocal
herkogamy, supposedly derived from the former), although the latter
harbours much variation. All populations collected (125 pops: L.
tenuifolium (39 pops) & L. suffruticosum (86 pops)) will be included in
phylogenetic and phylogeographic analysis to disentangle the taxonomic
status and evolutionary relationships of the group. Once the
phylogenetic results are obtained, a chronology of the evolutionary
events in resolved clades will be performed using internal and external
calibration points.
3. Reproductive biology and stylar polymorphism in Linum
tenuifolium aggr. in natural conditions. This study aims at determining
the breeding systems of the species, including the possible
heteromorphic incompatibility system of stylar morphs. This study is
being undertaken in three different populations of the Iberian Peninsula
(Málaga, Guadalajara and Pyrenees).
4. After the preliminary field work around Mediterranean Basin some
collateral works are emerging. The recognition of a new heterostylous
species from Morocco, and the description of a new polymorphism in the
genus in a species from the Eastern Mediterranean, will be noteworthy
results. These results illustrate the value of conducting research in
biodiversity hotspots such as the Mediterranean Basin, as usually it
reveals new processes beyond taxonomical patterns.