support [20]. In that, the study of fruit traits and seed dispersal has followed the much
more mature field of pollination ecology, in which the role of floral scent as a
pollinator attractant has been recognized for decades [20, 23, 30, 31].
Yet despite the growing body of knowledge and understanding of the role of fruit
scent as an attractor of seed dispersers, the number of studies that conducted
chemical characterizations of wild fruit scent is still low, and is based on a narrow
taxonomic coverage from only a few geographical regions, exclusively in the
tropics. Moreover, the focus on fruit scent as an animal attraction mechanism risks
downplaying other ecological roles which fruit scent may fulfill [16]. Thus, it is
important to remember that the field is still in its initial stages and that there are many
more open questions than definite answers [15].
This chapter will summarize the latest developments in the study of the ecology
and evolution of wild fruit scent. It will first examine what chemicals tend to
characterize fruit scent and describe the basic biochemical processes leading to
their synthesis. It will then examine how fruit scent is used as a food detection and
selection by various animals and present the supporting evidence for the adaptive
hypothesis of fruit scent. It will end with a discussion of other factors determining
fruit scent evolution, and conclude with recommendations for future studies.
2
Fruit Scent: Chemistry, Biochemistry, and Patterns of
Emission
2.1
Chemistry and Biochemistry
Fruits of wild and cultivated species emit complex mixtures that can comprise
dozens to hundreds of different VOCs [14]. Most of these belong to three prominent
chemical classes, terpenoids, fatty acid derivatives, and aromatic compounds [32,
33], although some fruits also contain rarer compounds such as amino acid derivatives [14, 15].
2.1.1 Terpenoids
Terpenoids are the most diverse group of plant secondary metabolites [34, 35]. They
are ubiquitous in leaves [13, 36] and flowers [30] and are also very common in
unripe and ripe fruits of both wild and cultivated species [15, 37–40]. The most
common volatile terpenoids are the C10 monoterpenes and C15 sesquiterpenes,
along with their homoterpene or oxidized derivatives [34, 36, 41, 42]. Among
many, common examples are limonene, α- and β-pinene, cis- and trans- β-ocimene,
and β-myrcene (monoterpenes); β-caryophyllene, α-copaene, and α-humulene (sesquiterpenes); and linalool (monoterpene oxide) (Fig. 1, 1–3).
Terpenoids are synthesized via two separate biosynthetic pathways and are a construct of two or three basic C5 (isoprene) units, which are then modified to create the end
product [35, 42]. The enormous diversity of plant terpenoids is a result of the latter
stage, in which a narrow range of precursors are transformed into thousands of different
end products by various members of the terpene synthase (TPS) family [42, 43 ].
17 Fruit Scent: Biochemistry, Ecological Function, and Evolution
405
more mature field of pollination ecology, in which the role of floral scent as a
pollinator attractant has been recognized for decades [20, 23, 30, 31].
Yet despite the growing body of knowledge and understanding of the role of fruit
scent as an attractor of seed dispersers, the number of studies that conducted
chemical characterizations of wild fruit scent is still low, and is based on a narrow
taxonomic coverage from only a few geographical regions, exclusively in the
tropics. Moreover, the focus on fruit scent as an animal attraction mechanism risks
downplaying other ecological roles which fruit scent may fulfill [16]. Thus, it is
important to remember that the field is still in its initial stages and that there are many
more open questions than definite answers [15].
This chapter will summarize the latest developments in the study of the ecology
and evolution of wild fruit scent. It will first examine what chemicals tend to
characterize fruit scent and describe the basic biochemical processes leading to
their synthesis. It will then examine how fruit scent is used as a food detection and
selection by various animals and present the supporting evidence for the adaptive
hypothesis of fruit scent. It will end with a discussion of other factors determining
fruit scent evolution, and conclude with recommendations for future studies.
2
Fruit Scent: Chemistry, Biochemistry, and Patterns of
Emission
2.1
Chemistry and Biochemistry
Fruits of wild and cultivated species emit complex mixtures that can comprise
dozens to hundreds of different VOCs [14]. Most of these belong to three prominent
chemical classes, terpenoids, fatty acid derivatives, and aromatic compounds [32,
33], although some fruits also contain rarer compounds such as amino acid derivatives [14, 15].
2.1.1 Terpenoids
Terpenoids are the most diverse group of plant secondary metabolites [34, 35]. They
are ubiquitous in leaves [13, 36] and flowers [30] and are also very common in
unripe and ripe fruits of both wild and cultivated species [15, 37–40]. The most
common volatile terpenoids are the C10 monoterpenes and C15 sesquiterpenes,
along with their homoterpene or oxidized derivatives [34, 36, 41, 42]. Among
many, common examples are limonene, α- and β-pinene, cis- and trans- β-ocimene,
and β-myrcene (monoterpenes); β-caryophyllene, α-copaene, and α-humulene (sesquiterpenes); and linalool (monoterpene oxide) (Fig. 1, 1–3).
Terpenoids are synthesized via two separate biosynthetic pathways and are a construct of two or three basic C5 (isoprene) units, which are then modified to create the end
product [35, 42]. The enormous diversity of plant terpenoids is a result of the latter
stage, in which a narrow range of precursors are transformed into thousands of different
end products by various members of the terpene synthase (TPS) family [42, 43 ].
17 Fruit Scent: Biochemistry, Ecological Function, and Evolution
405