Electronic Supplement 4
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Organisms
Diversity & Evolution 4 (2004) Electronic Supplement 4 |
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Regine Claßen-Bockhoff, Thomas Speck, Enikö Tweraser,
Petra Wester, Sascha Thimm, Martin Reith:
The staminal lever mechanism in
Salvia L. (Lamiaceae): a key innovation for adaptive radiation?
print version: Org. Divers. Evol. 4(3): 189-205. 2004 (full article)
electr. suppl.:
Part 1. Figure 2 (Colour plate). pdf-format, 1 MB
Part 2. Figure 6 (Colour plate).
pdf-format, 330 KB
Abstract:
Floral key innovations play a significant role in the
discussion of adaptive radiation in plants. The paper brings together a brief
review of morphological key innovations in plants, elucidating their
evolutionary significance in flower-pollinator interactions, and new data on
Salvia, a genus being examined as an example for presumed adaptive
radiation. We hypothesize that the characteristic staminal lever mechanism
functions as a key innovation. It is defined as a functional unit including the
modification of stamens to lever-like structures, their reversible movement,
and the organization of the remaining floral structures involved in the process
of pollen transfer. We follow the assumption that structure and functioning of
the staminal levers play a major role in the process of pollen deposition on
the pollinator's body, and that minute changes of both their proportions and
their interactions with pollinators may have significant consequences for the
pollination system. The functioning of the staminal lever mechanism is tested
by field investigations, biomechanical experiments and pollination simulations.
First results are presented, and possible modes of allopatric and sympatric
speciation are discussed, based on morphometry of Salvia flowers and
pollinating insects as well as on the operating mode of the staminal lever
mechanism. Special attention is given to species-specific patterns of pollen
deposition on the pollinator's body. We assume that, depending on the precision
of the lever movement, sympatric Salvia species flowering during
overlapping periods and sharing the same pollinating species may be either
mechanically isolated from each other or able to hybridize. The latter may
result in speciation, as may spontaneous mutations influencing the
flower-pollinator interaction, e.g. by significant changes in morphometry of
the staminal lever system and/or other flower structures. As a consequence,
Salvia individuals may deposit pollen on a different part of the
pollinator's body, or even adapt to a new pollinator species, both resulting in
reproductive isolation from the parental population.
Key words: Functional morphology; Biomechanics; Pollination; Diversity; Speciation
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