In
several genera within the Brassicaceae family quite a few evolutionary
tendencies can be observed, which are possibly involved in speciation. “Key
innovations” such as polyploidisation, breakdown of self-incompatibility or
the reduction or total loss of petals are common trends within the family.
Especially because those partly strong variations appear in wild populations,
they hint a powerful tool for investigating so called “speciation genes”.
Such
a naturally occuring variation of the shepherd´s purse Capsella bursa-pastoris defined through an abnormal development of
floral organs is the centre of our studies. This variation was first described
in the early 19th century and is characterized by petals transformed into
stamina. Developing a second whorl of stamina instead of petals leads to a
decandric flower shape.
|
|
|
|
|
|
|
|
|
Wildtype flower |
|
Decandric flower |
Yet
we only know a few habitats of this Capsella
variation, such as in Rheinhessen, Ostwestfalen-Lippe and Russia, but of
course we want more.
Fieldstudies
and climate chamber progenies apparently revealed no lack of fitness in spite
of the intense phenotypic aberration in contrast to the wildtype. For this
reason a promising model system seems to have been identified, which is going
to be studied and established from molecular level up to field biology within
this project.
In
our studies we focus especially on the chromosomale localisation of the
presumable singular locus which is responsible for the loss of petals. Our
test population is a crossing, in which one parent shows a distinct decandric
phenotyp. Via selfing a F2-mapping generation was obtained
(University of Jena). Several molecular markersystems, such as AFLPs, RAPDs,
microsatellites and isozyme are used. Conducting a linkage analysis with these
markers, we aim to generate a linkage map to the Arabidopsis
thaliana genome. Our cooperation partners in Jena are trying to clone the
possible locus, using a combination of candidate gene approaches and map based
approaches.
Using
molecular markers, further investigations will be carried out to reveal
whether the decandric variation of yet known habitats has arised once or
several times independently .
Extensive
isozym analysis of more than 300 individuals from at least 15 sub-populations
of wildtype and decandric plants from Rheinhessen are being used for detecting
outcrossing rates. These rates are calculated from allel frequencies via
F-statistic. As an experimental approach to analyse outcrossing rates and
pollination biology we are planning a fieldstudy in the botanical garden of
Osnabrueck.
Effects
of the decandric flower concerning pollination biology are being investigated
in additional fieldstudies at the University of Jena, assisted by further
cooperation partners in Halle.
|