animals to detect and identify them and that animal behavior has in turn exerted
selection pressures on some fruits to become olfactorily conspicuous. At the same
time, much more is required to fully understand the selection pressures and constraints which shape the diversity of wild fruit aroma.
An aspect which clearly lags behind chemical characterization, but is equally
important to answer both ecological and evolutionary questions, is behavioral
essays. As discussed above, many studies examined either scent-based fruit
foraging and selection or fruit scent chemistry, but only a handful [37–39, 46,
51] did both. Yet even as it becomes clear that several groups of animals rely on
fruit scent, many questions remain open – most of them can only be addressed
through systematic behavioral essays of the kind that has become ubiquitous in
insect chemical ecology [157]: To what aspects of fruit scent do they respond?
What information they seek? On which odorants they rely? Behavioral studies are
also paramount to answering the question whether and to what extent frugivorous
birds use fruit scent. It is a common assumption that they do not, or at least do so
substantially less than mammals [39, 40, 51]. While there is evidence suggesting
that this assumption is to some extent true, it should be verified and rigorously
tested in behavioral tests.
Behavioral tests with vertebrates are particularly challenging: wild population
densities are low, many animals avoid interactions with humans, and their intelligence and ability to learn complicate many experimental designs which have worked
well with invertebrates. Some of these challenges can be met in more controlled
experiments with captive animals, which are in turn hindered by the fact that captive
animals are in some cases not good representative of wild behavior. Thus,
a combination of wild and captive approaches is probably necessary to address
many of the questions regarding the use of scent by animal seed dispersers.
Comparative studies of fruit scent would benefit greatly from an increased
standardization in the field, which could allow syntheses based on the results of
studies conducted by different groups and in different locations. At the moment, the
use of different techniques renders most comparison between studies very unreliable
[15]. Yet a global comparative approach is crucial to pinpoint the multiple selection
pressures and constraints which resulted in contemporary patterns of scent released
by fruits. At the same time, it is also important not to forgo higher-resolution studies
of individual species or narrow lineages, which are more suitable for integrating
factors like the biochemistry of fruit scent and other functions it may fulfill.
The contrast between higher-scale lack of phylogenetic signal [38, 51] and its
absence in lower scales [38] and the fact that both should be studied in the context
of the biochemical pathways behind fruit scent [153] demonstrates this point. We are
in hope that further integration in the field would take these steps so that the next
decade will be at least as fruitful as the previous one.
Acknowledgments ON was funded by the German Science Foundation (Deutsche Forschungsgemeinschaft; grant nr. 2156/1-1) while working on this chapter. Dr. Kim Valenta and Prof. Colin A.
Chapman were heavily involved in data collection in Uganda, which was used for some of the
unpublished results cited here.
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O. Nevo and M. Ayasse
selection pressures on some fruits to become olfactorily conspicuous. At the same
time, much more is required to fully understand the selection pressures and constraints which shape the diversity of wild fruit aroma.
An aspect which clearly lags behind chemical characterization, but is equally
important to answer both ecological and evolutionary questions, is behavioral
essays. As discussed above, many studies examined either scent-based fruit
foraging and selection or fruit scent chemistry, but only a handful [37–39, 46,
51] did both. Yet even as it becomes clear that several groups of animals rely on
fruit scent, many questions remain open – most of them can only be addressed
through systematic behavioral essays of the kind that has become ubiquitous in
insect chemical ecology [157]: To what aspects of fruit scent do they respond?
What information they seek? On which odorants they rely? Behavioral studies are
also paramount to answering the question whether and to what extent frugivorous
birds use fruit scent. It is a common assumption that they do not, or at least do so
substantially less than mammals [39, 40, 51]. While there is evidence suggesting
that this assumption is to some extent true, it should be verified and rigorously
tested in behavioral tests.
Behavioral tests with vertebrates are particularly challenging: wild population
densities are low, many animals avoid interactions with humans, and their intelligence and ability to learn complicate many experimental designs which have worked
well with invertebrates. Some of these challenges can be met in more controlled
experiments with captive animals, which are in turn hindered by the fact that captive
animals are in some cases not good representative of wild behavior. Thus,
a combination of wild and captive approaches is probably necessary to address
many of the questions regarding the use of scent by animal seed dispersers.
Comparative studies of fruit scent would benefit greatly from an increased
standardization in the field, which could allow syntheses based on the results of
studies conducted by different groups and in different locations. At the moment, the
use of different techniques renders most comparison between studies very unreliable
[15]. Yet a global comparative approach is crucial to pinpoint the multiple selection
pressures and constraints which resulted in contemporary patterns of scent released
by fruits. At the same time, it is also important not to forgo higher-resolution studies
of individual species or narrow lineages, which are more suitable for integrating
factors like the biochemistry of fruit scent and other functions it may fulfill.
The contrast between higher-scale lack of phylogenetic signal [38, 51] and its
absence in lower scales [38] and the fact that both should be studied in the context
of the biochemical pathways behind fruit scent [153] demonstrates this point. We are
in hope that further integration in the field would take these steps so that the next
decade will be at least as fruitful as the previous one.
Acknowledgments ON was funded by the German Science Foundation (Deutsche Forschungsgemeinschaft; grant nr. 2156/1-1) while working on this chapter. Dr. Kim Valenta and Prof. Colin A.
Chapman were heavily involved in data collection in Uganda, which was used for some of the
unpublished results cited here.
418
O. Nevo and M. Ayasse