nocturnal [143]. While less is known about the sensory ecology of less studied
animals like hedgehogs, they possess very large main olfactory bulbs [144] and are
very likely to rely on fruit scent when possible.
Finally, seed dispersal by invertebrates is fairly common. The most
prominent invertebrate seed disperser is ants [145], which are attracted by fatty
acids [146] present on the elaiosome – a lipid-rich appendage which serves as
a reward and is functionally similar to fleshy fruits. Another invertebrate
which occasionally provides seed dispersal services is slugs [147, 148],
although neither their relative importance nor their reliance on scent has been
investigated.
3.2
Fruit Scent: A Cue or an Evolved Signal?
While the previous section considered only the animal side of the interaction, i.e.,
how different animals may use fruit scent to find and identify ripe fruits, there is
strong evidence that olfactory conspicuousness has evolved in some species to
promote seed dispersal. The first is convergent evolution across taxa which share
a dispersal vector. Comparing bat- and bird-dispersed figs, Hodgkison et al. [38]
found that bat-dispersed figs have converged to emit monoterpenes, although,
as they acknowledge, monoterpenes are not the dominant VOC class in a
few other bat-dispersed figs [40, 79]. More qualitatively, Nevo et al. [51]
found that ripe lemur-dispersed fruits are much more likely to emit aliphatic esters
than do sympatric bird-dispersed species. In both studies, the fact that species
which share a disperser at least partially converged in their ripe fruit scent
chemistry is an indication that there is some selective pressure exerted by these
seed dispersers.
A second line of evidence supporting the hypothesis that scent is an evolved
signal to seed dispersal comes from a handful of studies which looked at the
patterns of change in fruit scent upon ripeness and compared them between
sympatric species that rely on mammal and bird seed dispersers. Studying three
fig (Ficus spp.) species, Borges et al. [40] showed that at the dispersal stage, only
bat-dispersed figs had a unique scent which probably drives attraction of seeddispersing bats. Bat-dispersed fruits also tend to emit stronger scents than sympatric bird-dispersed fruits [25]. Taking a similar approach but going beyond the
Ficus model system, Nevo et al. [39] showed that in a system of four Neotropical
species, primate-dispersed fruits change their scent upon ripeness, while birddispersed species do not. This pattern was replicated on a much larger model
system in Madagascar, where it was shown that species which specialize on lemur
seed dispersal change their scent – qualitatively and quantitatively – significantly
more than sympatric bird-dispersed species [51]. The pattern that emerges from
these studies is that even though the ripening process is accompanied by much
biochemical activity which may affect fruit scent, the change in fruit scent upon
ripeness is much greater in species which interact with olfactorily oriented
mammals.
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O. Nevo and M. Ayasse
animals like hedgehogs, they possess very large main olfactory bulbs [144] and are
very likely to rely on fruit scent when possible.
Finally, seed dispersal by invertebrates is fairly common. The most
prominent invertebrate seed disperser is ants [145], which are attracted by fatty
acids [146] present on the elaiosome – a lipid-rich appendage which serves as
a reward and is functionally similar to fleshy fruits. Another invertebrate
which occasionally provides seed dispersal services is slugs [147, 148],
although neither their relative importance nor their reliance on scent has been
investigated.
3.2
Fruit Scent: A Cue or an Evolved Signal?
While the previous section considered only the animal side of the interaction, i.e.,
how different animals may use fruit scent to find and identify ripe fruits, there is
strong evidence that olfactory conspicuousness has evolved in some species to
promote seed dispersal. The first is convergent evolution across taxa which share
a dispersal vector. Comparing bat- and bird-dispersed figs, Hodgkison et al. [38]
found that bat-dispersed figs have converged to emit monoterpenes, although,
as they acknowledge, monoterpenes are not the dominant VOC class in a
few other bat-dispersed figs [40, 79]. More qualitatively, Nevo et al. [51]
found that ripe lemur-dispersed fruits are much more likely to emit aliphatic esters
than do sympatric bird-dispersed species. In both studies, the fact that species
which share a disperser at least partially converged in their ripe fruit scent
chemistry is an indication that there is some selective pressure exerted by these
seed dispersers.
A second line of evidence supporting the hypothesis that scent is an evolved
signal to seed dispersal comes from a handful of studies which looked at the
patterns of change in fruit scent upon ripeness and compared them between
sympatric species that rely on mammal and bird seed dispersers. Studying three
fig (Ficus spp.) species, Borges et al. [40] showed that at the dispersal stage, only
bat-dispersed figs had a unique scent which probably drives attraction of seeddispersing bats. Bat-dispersed fruits also tend to emit stronger scents than sympatric bird-dispersed fruits [25]. Taking a similar approach but going beyond the
Ficus model system, Nevo et al. [39] showed that in a system of four Neotropical
species, primate-dispersed fruits change their scent upon ripeness, while birddispersed species do not. This pattern was replicated on a much larger model
system in Madagascar, where it was shown that species which specialize on lemur
seed dispersal change their scent – qualitatively and quantitatively – significantly
more than sympatric bird-dispersed species [51]. The pattern that emerges from
these studies is that even though the ripening process is accompanied by much
biochemical activity which may affect fruit scent, the change in fruit scent upon
ripeness is much greater in species which interact with olfactorily oriented
mammals.
414
O. Nevo and M. Ayasse