How Seedy Fruits Attract (Animal) Eaters

choi

I prefer to read the original material, but one scientific paper -- (2) below -- is not published in PRINT yet (only online) -- and in any event, are locked behind paywall. So I will rely on a NYT report (which merges the two papers in one report and whose rest you need not read).

(1) Nevo O et al, Fruit Scent as an Evolved Signal to Primate Seed Dispersal. Science Advances, 4: eaat4871 (which is number of the first page; published on Oct 3, 2018; full report).
http://advances.sciencemag.org/content/4/10/eaat4871

Introduction (section): "Here, we examine whether fruit scent evolved as a signal to seed dispersers [ie, lemurs and passerine birds mentioned immediately after] in 30 plant species of 15 families in Ranomafana National Park, Madagascar. As a group, the most important seed dispersers in Madagascar are the endemic lemurs ( [reference No] 21). Contrary to most other tropical systems, frugivorous birds are rare, and the system is divided between a large group of lemur-dispersal specialists and a minority of species that are fully or partially dispersed by passerine birds (21). 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. Like other primates, lemurs probably do not track the source of a scent to locate fruit crops, and the main function of olfaction in food acquisition is the identification that an individual fruit in a patch is ripe * * * For these reasons, our main prediction is that the fruits of species that specialize on lemur seed dispersal emit scents that can be used by the lemurs to recognize their ripeness [this report says their prediction turns out to be true] * * * 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)."

Note:
(a) There is no need to read the rest. The first author is based in Germany.
(b) lemur
https://en.wikipedia.org/wiki/Lemur
("are * * * primates endemic to the island of Madagascar. The word lemur derives from the word lemures (ghosts or spirits) from Roman mythology and was first used to describe a slender loris due to its nocturnal habits and slow pace")
(c)
(i) The English adjective passerine (where the "i" is pronounced the same as eye) is from Latin noun masculine passer sparrow.
(ii) No online dictionary defines "cathemeral" or corresponding noun, so I am clueless about its pronunciation.

cathemerality
https://en.wikipedia.org/wiki/Cathemerality
(d)
(i)
(A) cone cell
https://en.wikipedia.org/wiki/Cone_cell
(the graphic shows humans has three kinds of cone cells (blue, green and red) enabling him to see visible light (390-700nm).
(B) bird vision
https://en.wikipedia.org/wiki/Bird_vision
("Most birds are tetrachromatic [humans are trichromatic], possessing four types of cone cells" -- the accompanying graphic shows the fourth cone cell for UV light)

However, owls, being nocturnal, are the only birds that are color blind for all colors.
(ii) Five species of lemurs have received genetic testing for come pigments, and only one has retained both genes for both red and green, whereas the remaining four either loses color perception for either red or green.

In humans, genes for both red and green are in X-chromosome. Loss of either causes red-green color blindness -- the most common form of human color blindness (which is capable of yellow/blue perception)..
(e) In humans, olfactory bulb
https://en.wikipedia.org/wiki/Olfactory_bulb

is above the roof of nasal cavity, inside the cranial cavity (which holds the brain). The

------------------------------------------------------Oct 20
"owls, being nocturnal, are the only birds that are color blind for all colors."

I was mistaken. Owls' retinas have rod and few cones. Cones need bright light to see colors. Rods function in dim light to see black, white and shades of gray in between -- and these are what owls see. Though from physics point of view: "When light falls on an object, some of it is absorbed and some is reflected. The apparent color of an opaque object depends on the wavelength of the light that it reflects; eg, a red object observed in daylight appears red because it reflects only the waves producing red light [ie, wave of red light]. * * * An opaque object that reflects all wavelengths appears white; one that absorbs all wavelengths appears black. Black and white are not generally considered true colors; black is said to result from the absence of color, and white from the presence of all colors mixed together."  from the Web.

choi

(2)
(a) Nevo O et al, Frugivores and the Evolution of Fruit Colour. Biology Letters, _: _ (online publication Sept 26, 2018; abstract only)
http://rsbl.royalsocietypublishing.org/content/14/9/20180377
(b) Joanna Klein, Fruits Say 'Eat Me' to Animals; researchers find some plant adapted to appeal to eaters that spread their seeds. New York Times, Oct 16, 2018 (in the SienceTimes section).
https://www.nytimes.com/2018/10/ ... olor-evolution.html

Quote:

"In a similar way, many flowers [as opposed to fruits] tailor their petal shape, color, texture or nectar’s scent or flavor to attract often a single pollinating species. * * * But they've [biologists have] had questions about plants reproducing through seed dispersal. * * * Though traits like shape are easier to study, without proper tools to measure color and odor" it is more difficult

"The monkeys and apes in Uganda have tricolor vision like humans, and the birds have even better vision. But most lemurs in Madagascar can only see the blue-yellow spectrum — they’re red-green colorblind, and rely more on their strong senses of smell for many behaviors.

"They [biologists in these two papers here] found the colors of each fruit were optimized against their natural backdrops to meet the demands of the visual systems of their primary seed dispersers. In Uganda, fruits contrasting with foliage in colors on the red-green spectrum — say that red berry in a green cluster — popped for birds and monkeys whose eyes can see them.  But in Madagascar, fruit with blue-yellow contrasts — like those yellow berries — could be best detected by red-green colorblind lemurs (and some birds, too).