Natures wonders: attracting animals to eat fruit (Introduction)

by David Turell @, Tuesday, October 16, 2018, 15:09 (308 days ago) @ David Turell

It can be done by smell or color and help the plant to disperse seed as the animal defecates:

https://www.nytimes.com/2018/10/09/science/fruit-color-evolution.html?emc=edit_th_18101...

"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.

"So the researchers collected ripe and unripe fruits and foliage and analyzed their colors with a spectrometer. With a model based on the visual capacities of the seed-dispersing animals, they also determined who was most likely to detect different fruit colors contrasting against an assortment of backgrounds.

"They 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).

"In Dr. Nevo’s scent study, his team collected hundreds of ripe and unripe fruits from Ranomafana — about a third dispersed solely by visually challenged lemurs and the rest by other lemurs and the park’s few visually gifted birds. He suspected the lemur-eaten fruits would have a greater difference in odor after they ripened than the bird-eaten fruits.

"To find out, he extracted their odors using the “semi-static headspace technique.” Sealed in oven bags, chemical fruit odors built up and were then pumped out, trapped and analyzed.

"They confirmed that fruits dispersed solely by lemurs produced more chemicals and a greater assortment of compounds upon ripening. And in the wild, lemurs spent more time sniffing these same fruits with big differences in ripe versus unripe odors. To the researchers, this suggested the differences could signal, “I’m here. Eat me,” to creatures otherwise possibly unable to see them.

"These results may only be extreme, localized cases supporting the hypothesis that plants and seed-dispersers evolve together. But the researchers see additional clues in a relationship between forest elephants in the Uganda park and Balanites wilsoniana, a tree that might not be able to survive without them.

"When ripe, Dr. Valenta said she could detect the “fermented gym sock” odor of the tree’s large fruits for miles. Elephants — with huge noses and more olfactory receptor genes than any other known animal on Earth — gobble up the fallen fruits (they may make them feel tipsy too).

"Only elephants can swallow the fruits and defecate the equally large seeds whole. And this plant won’t reproduce unless it passes through an elephant’s gut, Dr. Valenta said. This type of mutual dependence is seen in well-established flower-pollinator relationships, but it’s rare to find in fruit-seed-disperser relationships.

***

"In other parts of the world, related birds of paradise plants produce red or yellow coated seeds easily detectable to birds. But in Madagascar, where traveler’s palm is native, the seeds are brilliant blue and particularly detectable to aye-ayes, a kind of rat-cat-bat-looking lemur with an enhanced capacity to detect ultraviolet light, according to Dr. Valenta.

***

"The seeds of many plants — the traveler’s palm likely included — also contain a laxative, urging whatever eats them to hastily expel them, undigested, “with a nice pile of runny fertilizer,” said Jonathan Drori, author of “Around the World in 80 Trees.”

"Aye-ayes and other lemurs are also pollinators, using their strength to open the palm’s sturdy nectar packages, ensuring the plant can produce seeds in the first place.

“'If something happened to those lemurs, those trees, at least in the wild, would become extinct,” Mr. Drori said."

Comment: Fascinating interdependence in the balance of nature, which is beautifully illustrated in this article. Note 'red in tooth and claw' is not involved. Lots of balance in nature is not competitive killing.


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