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Fleshy fruits have evolved independently in more than half of extant angiosperm families (2), indicating that the need to offer an attractive reward to seed dispersers exerts a strong selection pressure on fruit traits.

Fruit traits that have been attributed to selection by seed dispersers include, among others, size (4, 10, 14), shape (15), and location and presentation on the branch (16). In addition, fruit color has been shown to respond to selection pressures by visually oriented frugivores, primarily birds (9, 11, 13). Fruit color has also been suggested to be an honest signal that allows birds to assess a fruit’s nutrient content (11). Fruit scent has long been suggested to play a similar role in mediating the interaction between plants and olfactorily oriented seed dispersers.

Only primate-dispersed fruits show a shift in their scent profiles upon ripeness (19) and that primates can use the scent of ripe fruits to identify them (20).


Many lemurs are nocturnal or cathemeral, and most or all individuals in all species are dichromatic, that is, red-green color blind (22). At the same time, they have relatively large main olfactory bulbs (23) and routinely use chemical cues for intraspecific communication (24), and some species have been shown to prefer more odorous fruits (25). It would thus appear that lemurs rely more on olfaction and less on vision during fruit selection.

Plants benefit from signaling that an individual fruit is ripe because (i) it reduces waste by allowing animals to identify and ignore unripe fruits and (ii) animals should be selected to prefer fruits that are easy to exploit;

All plant tissues, including unripe fruits, emit chemicals and thus have a scent, but we expect that to make ripe fruit more conspicuous in these species, ripe fruits would show a substantial shift away from unripe fruits in quantity (amount) and quality (chemical composition) of scent.

At the same time, fruits that do not specialize on olfactorily oriented lemurs and receive dispersal services from passerine birds, which, along with a lower number of olfactory receptor genes compared to lemurs (27, 28), have excellent color vision (22, 29) and tend to rely on visual cues (5, 9, 11), are expected to emit scents like all plant tissue. However, crucially, ripe fruits of these species are not expected to be under selection to be olfactorily conspicuous relative to unripe fruits. This expectation would parallel the observation that flowers that are bird-pollinated primarily rely on visual cues and emit only trace amounts of scent (30).

During focal animal observations, we recorded every interaction with an individual fruit as a single data point. For each individual fruit, we recorded the plant species and whether the animal sniffed the fruit before either ingesting or rejecting it. We defined “sniffing” as bringing the fruit to immediate proximity to the nostrils without biting it (see also movie S1).

The evolution of fruit scent as a signal for lemurs is yet another example of the coevolution of lemurs and plants in Madagascar. While it is likely that the lemurs’ unique set of sensory adaptations and long history of isolation from other frugivore guilds make this an extreme case, similar processes may have occurred in other tropical systems (19). It is therefore reasonable to assume that chemical interaction promoting the identification of ripe fruits is pertinent to frugivory and the sensory evolution of all primates, including humans.