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stronger excitement of olfactory receptors, a form of supernormal stimulation
found in floral mimicry systems [35].
Interestingly, the higher attractiveness of male flowers was less pronounced in
female moths, which showed no significant preference for male flowers. Female
moths need to find flowers for oviposition, besides nectar consumption for en-
ergy supply. Because only female flowers are optimal sites for larval development,
female moths are expected to evolve preference for female flowers, and especially
so after mating. It would be interesting to test in future experiments behavioral
preferences of unmated vs. mated females. This situation represents an interest-
ing example of sexual conflict, both in the plant and its pollinator [36]. In the
moths, male preference of stronger odor emission acts against female interests, i.e.
preference of female flowers, at least after mating. In the plant, the stronger odor
emission for increased pollen export should be selected against in female plants
that are probably not limited in reproductive success by pollen income and should
avoid the attraction of seed predating female moths.
Conclusion
In conclusion our study confirms the predictions by sexual selection theory that
male flowers should be more attractive to pollinators than female flowers. This
result was not obvious in this plant species, as male are smaller than female flow-
ers, however, the floral scent is decisive for attractiveness in this pollination sys-
tem. We suggest that taking into account the pollinators' sensory and behavioral
ecology will likely give a better picture on sexual and natural selection acting on
floral signals, and thus lead to a better understanding how flowers evolve under
pollinator-mediated selection.
Methods
(a) Plant Material and Odor Collection
For volatile collection, S. latifolia plants from seeds collected in two populations
(Leuk, Switzerland, n = 25; Ribes de Fraser, Spain, n = 4) were grown in a com-
mon garden setup in a green house. Floral odor of 555 S. latifolia plants (Switzer-
land: 79 males and 123 females, Spain: 217 males and 136 females) was collected
in May at night, between 9 p.m. and 7 a.m. by headspace sorption as described
in [18]. We used only newly opened flowers for odor collection. All floral odor
samples were stored in sealed glass vials at -20°C for subsequent gas chromato-
graph (GC) analysis.