green, commercial ripe, and tree ripe. In most cases, the latter two were similar,
indicating that the shift in scent occurs abruptly and only when the seeds are mature
[76]. In snake fruits (Salacca edulis), the prominent acids and alcohols increase more
gradually during maturation, but ester emission skyrockets abruptly around the time
the fruits become softer and mature [77]. Taken together, this is exactly the pattern
expected in cases where fruit scent is used by animals to find or identify ripe fruits
[37, 38, 46, 78], as plants are expected to be selected to begin attracting them only
after the seeds are viable. This is similar to the patterns of floral scent emission,
which tend to peak when the flowers become ready for pollination [49]. Yet while
many wild fruits exhibit a rapid maturation process (Nevo, personal observation),
it is rarely known whether wild fruits are climacteric.
2.2.2 Circadian Rhythm
In flowers, emission of VOCs can be constant or change rhythmically over the 24 h
cycle, often the case in plants pollinated by nocturnal animals [30, 49]. Diel variation
in fruit scent is far less investigated, and data are available for only two fig species
from India. Mature syconia of Ficus benghalensis, a species dispersed by both
diurnal birds and nocturnal bats, change their scent over the 24-h cycle: day VOC
emissions are dominated by sesquiterpenes and fatty acid derivatives, while night
emissions are substantially poorer in sesquiterpenes and contain more aliphatic
esters and aromatic compounds [79]. In contrast, mature Ficus racemosa syconia
do not show day-night differences in their scent profiles [79], even though they
do show diel cycle variance in earlier stages of their development [69].
It is unknown whether fruits or mature syconia of other species alter their scent
over the 24-h cycle. Yet it is likely to be common given the prevalence of this
phenomenon in flowers [30, 49] and the fact that fruits tend to be more generalist
than flower, i.e., they interact with a wider range of animal mutualists [80] and thus
more likely to interact with diurnal, cathemeral, and nocturnal frugivores.
For example, species like Ficus maxima are dispersed by both bats [38] and diurnal
primates [81]. Bats and primates use their sense of smell differently: bats can rely on
olfactory cues to detect and locate fruits [82], while primates do so only for selection
over short distance [78]. Therefore, this and other similar species are excellent
candidates to examine whether fruits
1 are selected to emit different olfactory signals
at different times of the day.
3
Fruit Scent and Seed Disperser Attraction
The role of fruit scent as an attractant of vertebrate seed dispersal vectors has been
the main focus of most work on fruit VOCs in recent years [20], although the idea
that fruit scent is used by olfactorily oriented frugivores is decades old. Early works
have integrated it into the framework of the Dispersal Syndrome Hypothesis,
1
Including mature fig syconia, which are functionally equivalent.
17 Fruit Scent: Biochemistry, Ecological Function, and Evolution
409
indicating that the shift in scent occurs abruptly and only when the seeds are mature
[76]. In snake fruits (Salacca edulis), the prominent acids and alcohols increase more
gradually during maturation, but ester emission skyrockets abruptly around the time
the fruits become softer and mature [77]. Taken together, this is exactly the pattern
expected in cases where fruit scent is used by animals to find or identify ripe fruits
[37, 38, 46, 78], as plants are expected to be selected to begin attracting them only
after the seeds are viable. This is similar to the patterns of floral scent emission,
which tend to peak when the flowers become ready for pollination [49]. Yet while
many wild fruits exhibit a rapid maturation process (Nevo, personal observation),
it is rarely known whether wild fruits are climacteric.
2.2.2 Circadian Rhythm
In flowers, emission of VOCs can be constant or change rhythmically over the 24 h
cycle, often the case in plants pollinated by nocturnal animals [30, 49]. Diel variation
in fruit scent is far less investigated, and data are available for only two fig species
from India. Mature syconia of Ficus benghalensis, a species dispersed by both
diurnal birds and nocturnal bats, change their scent over the 24-h cycle: day VOC
emissions are dominated by sesquiterpenes and fatty acid derivatives, while night
emissions are substantially poorer in sesquiterpenes and contain more aliphatic
esters and aromatic compounds [79]. In contrast, mature Ficus racemosa syconia
do not show day-night differences in their scent profiles [79], even though they
do show diel cycle variance in earlier stages of their development [69].
It is unknown whether fruits or mature syconia of other species alter their scent
over the 24-h cycle. Yet it is likely to be common given the prevalence of this
phenomenon in flowers [30, 49] and the fact that fruits tend to be more generalist
than flower, i.e., they interact with a wider range of animal mutualists [80] and thus
more likely to interact with diurnal, cathemeral, and nocturnal frugivores.
For example, species like Ficus maxima are dispersed by both bats [38] and diurnal
primates [81]. Bats and primates use their sense of smell differently: bats can rely on
olfactory cues to detect and locate fruits [82], while primates do so only for selection
over short distance [78]. Therefore, this and other similar species are excellent
candidates to examine whether fruits
1 are selected to emit different olfactory signals
at different times of the day.
3
Fruit Scent and Seed Disperser Attraction
The role of fruit scent as an attractant of vertebrate seed dispersal vectors has been
the main focus of most work on fruit VOCs in recent years [20], although the idea
that fruit scent is used by olfactorily oriented frugivores is decades old. Early works
have integrated it into the framework of the Dispersal Syndrome Hypothesis,
1
Including mature fig syconia, which are functionally equivalent.
17 Fruit Scent: Biochemistry, Ecological Function, and Evolution
409