Biology Reference
In-Depth Information
drastically reduce fitness [11,12]. Even for male flowers, however, pollinator
attraction is risky, as it may lead to infection by anther smut fungus that steril-
izes the flowers [13].
It has been known for a long time that floral traits like color, shape, size and
odor influence the behavior of flower visitors, but less is known about the relative
importance of these traits in different pollination systems [14,15]. Colorful floral
displays are often accompanied by fragrance, and both visual and olfactory signals
attract pollinators and serve as learning cues [16]. In many nocturnal pollination
systems, however, scent is thought to be of primary importance for pollinator at-
traction [16-18]. Floral signals in plants have a similar role in sexual reproduction
as mating signals in animals, although they act indirectly, through the behavior of
their pollinators. Thus, sexual dimorphisms in floral signals should evolve as a re-
sult of sexual selection, acting in concert with the neuronal and behavioral purge
of the pollinators. Therefore, the signature of sexual selection should be especially
pronounced in the signals that play a particular role in attraction of a given (guild
of ) pollinator(s).
We tested the prediction of higher attractiveness in male flowers by investigat-
ing floral signals and pollinator behavior in the perennial dioecious herb Silene
latifolia that is primarily pollinated by nocturnal moths [11,19-21]. This species
is an example of nursery pollination, as one of the main pollinators, the noctuid
moth Hadena bicruris, oviposits in female flowers where larvae feed on develop-
ing seeds. We investigated flower size, flower number and floral odor emission
in male and female S. latifolia plants. Further, we assessed the attractiveness of
individual flowers of both sexes using male and female Hadena bicruris moths in
a wind tunnel bioassay.
Results
Floral Odor
In both populations investigated, male flowers produced significantly more
odor than female flowers (Figure 1; Mean ± SE: Switzerland: males: 422.05
± 47.34 ng h
-1
, females: 202.56 ± 25.57 ng h
-1
; Spain: males: 134.19 ± 16.88
ng h
-1
, females: 81.56 ± 7.90 ng h
-1
). In the GLM, both sex and population
showed a significant effect and there was a significant interaction between sex
and population (Table 1; GLM: sex*population: F
1,555
= 11.252, P = 0.001),
indicating that the Swiss population differed more strongly among sexes than
did the Spanish population. The covariate flower diameter was not significant
(Table 1).
