Biology Reference
In-Depth Information
Morphology
Flower number was higher in male plants compared to female plants in both
populations (flowers plant
-1
± SE: Switzerland males 7.74 ± 0.53, Switzerland fe-
males 5.26 ± 0.50, Mann-Whitney U-test: U = 2887, P < 0.001; Spain males 8.63
± 0.54, Spain females 4.67 ± 0.19, Mann-Whitney U-test: U = 8908, P < 0.001).
Flower diameter was significantly smaller in male flowers than in female flowers
in both populations (mean flower diameter ± SE: Switzerland males 2.51 ± 0.03,
Switzerland females 2.60 ± 0.03, t-test: t = 2.017, df = 193, P < 0.05; Spain males
2.67 ± 0.02, Spain females 2.84 ± 0.02, t = 5.405, df = 351, P < 0.001).
Moth Behavior
Most flower-naïve pollinator moths chose male flowers in their first approach to
S. latifolia, suggesting higher attractiveness of male flowers compared to female
flowers, however the preference was only significant for male moths. Of the 25
male moths tested, 6 chose female and 19 male flowers (Chi
2
= 6.76, df = 1, P =
0.009). Of the 31 unmated females tested, 11 chose female and 20 male flowers
(Chi
2
= 2.61, df = 1, P = 0.11).
Discussion
Floral traits that increase pollinator attraction are expected to evolve under stron-
ger pollinator-mediated selection in male plants because males compete for polli-
nator visitation whereas females are usually limited by resources other than pollen
[1,3-5]. For female plants, and especially in nursery pollination systems, attrac-
tiveness to pollinators is risky because it is linked to seed predation [11,12]. Con-
sistent with theoretical expectations of sexual selection on floral attractiveness,
we found that individual male flowers were more attractive to naïve pollinators,
especially to male moths. The likely reason for this is the significantly higher emis-
sion of floral scent per flower in male versus female flowers.
In many dioecious plant species, males produce larger or more flowers than
females [3,10,22-24]. Plants with increased floral display usually receive higher
numbers of visits by pollinators [25-28]. In S. latifolia, male flowers are smaller
than female flowers, but male plants produce more flowers than females, suggest-
ing a trade-off between flower size and number [29]. Silene latifolia pollinators
prefer plants with larger floral displays [13]. Therefore, the increased number of
flowers found on male S. latifolia plants enhances the attractiveness to pollina-
tors [29,30]. However, as yet it was not clear whether the increased attractiveness
of male plants is simply a function of the higher number of flowers, or whether
