Ghosts of Evolution

December 18, 2013 3:49 PM

After a species goes extinct, in some cases its "ghost" may linger in the ecosystem it leaves behind in the form of evolutionary anachronisms.

Shit You Didn't Know About Biology: "Evolutionary Anachronisms" -- Avocados, osage-oranges and honey locusts [PDF] once relied on now-extinct megafauna for seed dispersal. Pronghorns might be (might be) as fast as they are so they can evade the Miracinonyx, or American cheetah, a genus that no longer hunts them.

Tetrapod Zoology: "The 'ghosts' of extinct birds in modern ecosystems" -- Flowers that seem adapted to extinct, Old World humming birds. Birds in New Zealand and lemurs in Madagascar that may still live in fear of large, extinct raptors. Plants in New Zealand that are still adapted to the Moa? Controversial.

You may be noticing the "mays" and the "seems" here, and that's because it's hard to make solid connections like this. As Darren Naish at TetZoo puts it:

On the one hand, it might be true that co-evolution with mostly lost megaherbivores is common and perhaps ubiquitous, given the state the world is in. On the other hand, it can be all too easy to jump to conclusions about perceptions of co-evolution and we often need to consider other possibilities: plants may grow tall, may grow weird or giant fruit, or may exhibit ‘defensive’ adaptations for reasons unrelated to the presence of their predators, for example, since plants have complex evolutionary interactions all their own. Indeed, some classic alleged examples of co-evolution that supposedly involve lost partners are now thought to be erroneous.

See also: The Ghosts of Evolution: Nonsensical Fruit, Missing Partners, and Other Ecological Anachronisms by Connie Barlow.

posted by brundlefly (11 comments total)

Obligatory XKCD.
posted by Doktor Zed at 4:09 PM on December 18, 2013 [12 favorites]

Cool post, although I think it was rather unkind of PBS to include the photo of the "bum" at the beginning of the clip.
posted by KokuRyu at 4:14 PM on December 18, 2013 [3 favorites]

Yeah, I agree.
posted by brundlefly at 4:15 PM on December 18, 2013 [1 favorite]

I had never considered that avocados evolved so that their seeds/pits would be defecated by a giant ground sloth.
posted by KokuRyu at 4:18 PM on December 18, 2013

I love this concept and hope it's true, especially the giant ground sloths and avocados, but I've seen some pretty determined squirrels hauling big plums and small Asian pears from the garden. A small avocado doesn't seem like much of a stretch for a squirrel or raccoon.
posted by Banish Misfortune at 4:30 PM on December 18, 2013

Gingkos and cycads are very cool trees.
posted by KokuRyu at 4:48 PM on December 18, 2013

A small avocado doesn't seem like much of a stretch for a squirrel or raccoon.

Most seeds will germinate more readily if the outer coat is cut or degraded. This happens mechanically through being abraded by the teeth of the animal eating the fruit, or chemically by passing through an animal's digestive system. That would be a stretch for a squirrel or raccoon.

A sulfuric acid bath or sandpaper are commonly used to prepare seeds with a hard outer coat for germination.
posted by peeedro at 4:50 PM on December 18, 2013 [1 favorite]

Here is an account of a botanist's search for the wild avocado from 1935:
"The more I have seen of these trees, the more I have come to feel that they may represent a truly indigenous form. Opposed to this belief is the relatively large size of the fruit (which suggests that they have been in cultivation, and at present are nothing more than escapes); and the very considerable range in size, form, proportion of edible pulp, and a few other characters, which variation in what we may term horticultural characteristics, also suggests that the trees are escapes. Indians have occupied this region for a long time. They have scattered seeds along the trails through these mountains, just as has been done in other parts of tropical America; and the avocado may have found, in this particular region, natural conditions so favorable that it has been able to grow and reproduce itself freely, until we have the small forests of avocados which today exist."

Maybe a ride's a ride from the avocado's standpoint, but God I wish we still had the sloths.
posted by Banish Misfortune at 7:23 PM on December 18, 2013 [3 favorites]

You get the same deal with cicadas, which are thought to reproduce in prime numbered sets of years so they're less likely to hit other animal's cycles. If they reproduced on a 15 year cycle instead of 13 or 17, they'd hit animals that reproduced on an appropriately synced 3-year and 5-year cycle. (Weirdly enough, I'm pretty sure I read about this in one of the weird scientific derails that Daniel Abraham is so fond of in one of the Black Sun's Daughter books.)
posted by NoraReed at 11:54 PM on December 18, 2013

I refuse to believe that New Zealand's divaricating shrub population was not evolved to poke out the eyes of giant moa because that's so cool. I suspect I would've made a crap biologist.
posted by Sonny Jim at 12:40 AM on December 19, 2013

But you could still make an excellent proponent for intelligent design from a Discordian perspective.
posted by NoraReed at 2:53 AM on December 19, 2013 [1 favorite]