Mechanisms of Plant Evolution
Special topic:
speciation in Lamiaceae
Special topic: speciation in the Lamiaceae
Dracocephalum
(Dragonhead) – a genus of
35 almost identical species
The Lamiaceae challenge
•Lamiaceae are around 7000 species that
are often distinct in secondary compounds
•Many species of Lamiaceae are crossfertile and hybrids are very common
•Morphology is often very similar,
taxonomy is very difficult and still
unresolved („Lamiaceae are the disgrace of
plant taxonomy“)
What is a species in this context?
Special topic: speciation in the Lamiaceae
One postman, many letters – Salvia pollination
•Lamiaceae are very species rich. Many
species occur sympatrically. How to
prevent hybridisation?
•Lamiaceae flowers are zygomorph and
rich in scents and patterns. They are
pollinated by specialised and intelligent
Hymenoptera
as
Bombus
spec.
(bumblebee).
•Is speciation in the Lamiaceae maintained
by specific pollinators?
Pollination in Salvia. A lever mechanism deposits pollen onto the
abdomen of the pollinator. The style grows later. In the receiving flower,
the style takes up the pollen from the site, where it was deposited in the
donor flower. Length of anthers and stamina are genetically linked.
Special topic: speciation in the Lamiaceae
One postman, many letters – Salvia pollination
Burgenland
Niederösterreich
S. pratensis
S. austriaca
S. pratensis
Conclusion: no propagation barreer by
temporal difference
S. verticillata
•Pollinators are the same!
Conclusion: no propagation barreer by
specific pollinators
S. nemorosa
S. aethiopis
•Flowering time of different species
overlaps!
S. glutinosa
Sympatric species of Salvia. In Austria 6 species occur in the same region.
Flowering times and pollinators overlap. Gene flow across species
boundaries must be maintained by different mechanisms.
•Due to close relationship all Salvia
species should hybridise, such that there
is no speciation barreer
•How is speciation maintained?
Special topic: speciation in the Lamiaceae
One postman, many letters – Salvia pollination
4
3
1
5
6
Burgenland:
1 – S. pratensis
2 – S. austriaca
3 – S. nemorosa
4 – S. aethiopis
2
Bombus terrestris
3 14
Niederösterreich:
1 – S. pratensis
5 – S. verticillata
6 – S. glutinosa
Multipurpose-Pollinator. Sympatric species of Salvia deposit pollen at
different sites of the abdomen. Since length of stylum and anthers are
genetically coupled, the stylum will pick up the pollen from the right site.
This creates a propagation barreer.
•Stamina geometry is species specific as
well as length of stylum.
•For each species of Salvia the stylum
touches the site, where the pollen had
been deposited in the donor flower.
•A pollinator (such as Bombus terrestris)
can transmit pollen from different Salvia
species, but at different sites of the
abdomen
•The stylum takes up the „right“ pollen,
because it is at the „right“ site.
Special topic: speciation in the Lamiaceae
Morphology precedes genetics: the Dragonhead case
D. ruyschiana
•small changes in flower morphology
generate different mechanism for
pollination specificity
•this will lead to reproductive channelling
of subclades
model of pollination in D. ruyschiana (M. Sci. Stefanie Calin)
D. ruyschiana
D. moldavica
Flower of D. moldavica (Dipl. Julia Völker)
Phylogenetic tree of Dracocephalum
(Ph.D. Thomas Horn)