can also vary between individual plants of the same species and even between
individual flowers of an inflorescence. In Cimicifuga simplex (Ranunculaceae),
two of the three subspecies do not produce odor and are pollinated by bees, while
the third one emits methyl anthranilate and isoeugenol, which specifically attract
butterflies for pollination [155, 156]. Similarly, the fragrant C. breweri is pollinated
by moths, whereas other species of Clarkia are not fragrant and they are selfcompatible, pollinated by oligolectic bees [154].
3.3
Odor Dynamics and Presentation
The release process of odors by flowers can be highly complex, exhibiting different
patterns of dynamic emission and chemical composition of volatile compounds.
The composition and amount of volatiles emitted may vary depending on the
stage of floral development or the time of the day (some plants emit volatiles during
the day, while others emit them at night) [157]. For example, Stephanotis floribunda
has a peak of emission of linalool and methyl benzoate around midnight, while
the emission of 1-nitro-2-phenylethane reaches the highest levels in the morning
[158, 159]. Nicotiana sylvestris emits phenylpropanoids at night, while the emission
of terpenoids does not oscillate [160]. In general, specific daytime emission of
odor compounds accurately correlates with pollinator activity. Plants that mainly
emit odor during the day are predominantly pollinated by bees, bumblebees, and
butterflies, whereas flowers that mainly emit odor at night are pollinated by moths
and bats [161]. This emission of daytime or nighttime odor appears to be regulated
by light intensity and/or temperature. However, a circadian clock is involved in
Cestrum nocturnum, Nicotiana suaveolens, N. sylvestris, Rosa hybrida, Antirrhinum
majus, and S. floribunda allowing a precise time of emission independent of
environmental signals [157]. The complex regulation of scent emission is related
to the morphology, anatomy, and cellular characteristics of the osmophore [162].
In some flowers in which anthesis occurs at a given time of day, other processes must
occur simultaneously with scent release in order to ensure pollination, such as the
precise time of nectar and pollen presentation, thermogenesis, and/or movement
of organs [153, 163, 164]. Floral scents are particularly important in flowers
with nocturnal anthesis, where olfactory signals attract pollinators over long distances [153].
3.4
Evolution of Osmophores and Floral Odor
Floral scent emission is clearly affected by environmental factors, such
as temperature, irradiance, and air humidity [165–167], as well as biotic processes,
such as pollination and herbivory [168–175]. Hence, the high environmental
plasticity of floral scent is likely to deflate estimates of floral scent heritability.
On the other hand, it is often argued that the observation of a low heritability
could be caused by genetic variation having been depleted by strong selection
726
E. D. Tölke et al.
individual flowers of an inflorescence. In Cimicifuga simplex (Ranunculaceae),
two of the three subspecies do not produce odor and are pollinated by bees, while
the third one emits methyl anthranilate and isoeugenol, which specifically attract
butterflies for pollination [155, 156]. Similarly, the fragrant C. breweri is pollinated
by moths, whereas other species of Clarkia are not fragrant and they are selfcompatible, pollinated by oligolectic bees [154].
3.3
Odor Dynamics and Presentation
The release process of odors by flowers can be highly complex, exhibiting different
patterns of dynamic emission and chemical composition of volatile compounds.
The composition and amount of volatiles emitted may vary depending on the
stage of floral development or the time of the day (some plants emit volatiles during
the day, while others emit them at night) [157]. For example, Stephanotis floribunda
has a peak of emission of linalool and methyl benzoate around midnight, while
the emission of 1-nitro-2-phenylethane reaches the highest levels in the morning
[158, 159]. Nicotiana sylvestris emits phenylpropanoids at night, while the emission
of terpenoids does not oscillate [160]. In general, specific daytime emission of
odor compounds accurately correlates with pollinator activity. Plants that mainly
emit odor during the day are predominantly pollinated by bees, bumblebees, and
butterflies, whereas flowers that mainly emit odor at night are pollinated by moths
and bats [161]. This emission of daytime or nighttime odor appears to be regulated
by light intensity and/or temperature. However, a circadian clock is involved in
Cestrum nocturnum, Nicotiana suaveolens, N. sylvestris, Rosa hybrida, Antirrhinum
majus, and S. floribunda allowing a precise time of emission independent of
environmental signals [157]. The complex regulation of scent emission is related
to the morphology, anatomy, and cellular characteristics of the osmophore [162].
In some flowers in which anthesis occurs at a given time of day, other processes must
occur simultaneously with scent release in order to ensure pollination, such as the
precise time of nectar and pollen presentation, thermogenesis, and/or movement
of organs [153, 163, 164]. Floral scents are particularly important in flowers
with nocturnal anthesis, where olfactory signals attract pollinators over long distances [153].
3.4
Evolution of Osmophores and Floral Odor
Floral scent emission is clearly affected by environmental factors, such
as temperature, irradiance, and air humidity [165–167], as well as biotic processes,
such as pollination and herbivory [168–175]. Hence, the high environmental
plasticity of floral scent is likely to deflate estimates of floral scent heritability.
On the other hand, it is often argued that the observation of a low heritability
could be caused by genetic variation having been depleted by strong selection
726
E. D. Tölke et al.