Big apple

On August 14, 2003, my wife and I were returning from a trip to Hawaii.  It was a lovely vacation, but the return home was, to put it mildly, fraught with mishaps.  The most spectacular one occurred as we were descending into LaGuardia Airport in New York City.  It was late afternoon and I was watching the lights of the city zooming along below us, when, all of a sudden...

... the entire skyline went dark.

I nudged Carol and asked her to confirm that I was, in fact, seeing what I thought I was seeing.  The pilot landed the plane, but the jet bridges weren't working so we deplaned via a rolling ladder.  The entire airport was dark except for a few lights that were kept on by a generator.  Remember that this is a little less than two years after 9/11, so our immediate (and terrifying) thought was that it was a terrorist attack, but it turned out we'd gotten caught up in the Great Northeastern Blackout, which knocked out the electricity to a huge chunk of the northeastern United States and eastern Canada, and which apparently had been triggered by a software bug.

The upshot was we got stuck in the airport overnight with a bunch of other people who were also trying to get back to the Ithaca area, and one of these was a very nice woman who worked for the Apple Genomics Project at Cornell Orchards.  That evening she and I had a real Nerd-O-Rama about the ins and outs of plant genetics, which was a very peculiar way to make the best of a bad situation.

She and her team had a fascinating job -- going all over Europe, the Caucasus, Anatolia, and Central Asia looking for apple germ line -- basically, anything that can be used to reproduce an entire tree (seeds and cuttings being two of the most obvious examples).  They hired translators to accompany them, who asked locals to point out the best apple trees for various uses -- cooking, cider, making wine or vinegar, drying/preserving, or eating fresh -- and they took samples of germ line (along with copious notes) to bring home to the Orchards for growing and hybridizing.  Besides just looking for good fruit quality, they were also interested in finding strains that are resistant to pests and diseases.

The most diversity they discovered was in Kazakhstan and Uzbekistan, which is where apples originate.  ("American as apple pie" is about as inaccurate as you can get; apples not only aren't native to the United States, they were brought into North America in the mid-1600s by a Frenchman, Pierre Martin -- who settled in Nova Scotia.)  And some research out of the Max Planck Institute for the Science of Human History that appeared last week in Frontiers in Plant Science found that the spread of apples from their homeland, thousands of miles across Europe, was due to two factors; megafauna and the Silk Road.

[Image licensed under the Creative Commons Sandstein, Civni-Rubens apple, CC BY 3.0]

The modern apple is the result of hybridization between at least four wild species, followed by centuries of backcrossing and artificial selection.  Let apples cross-pollinate and plant the seeds, and you'll end up with something like a wild crabapple.  Originally, the bright fruits of apples were eaten by large herbivores like horses and wild cattle, and the seeds dispersed long distances, but with the disappearance of the huge herds that used to exist in central Asia, apple seeds were poorly dispersed.  (Apples aren't the only plants that got into trouble when their seed-disperser disappeared, something about which I wrote in more detail a couple of years ago.)  Fortunately for apples, though, their many uses were noted by humans, and when people moved -- especially along the Silk Road -- they took apple germ line with them, just as my Cornell researcher friend did a thousand years later.

The author, Robert Nicholas Spengler, writes:

Large fruits in Rosaceae [the family apples belong to] evolved as a seed-dispersal adaptation recruiting megafaunal mammals of the late Miocene.  Genetic studies illustrate that the increase in fruit size and changes in morphology during evolution in the wild resulted from hybridization events and were selected for by large seed dispersers.  Humans over the past three millennia have fixed larger-fruiting hybrids through grafting and cloning.  Ultimately, the process of evolution under human cultivation parallels the natural evolution of larger fruits in the clade as an adaptive strategy, which resulted in mutualism with large mammalian seed dispersers (disperser recruitment).

Current archaeobotanical evidence seems to suggest that apple domestication took place over a period of less than 100 generations, much less for the earliest morphological changes.  It seems feasible that rapid domestication through hybridization occurred in as little as one or a few generations, and most of the modern diversity in landraces is probably a recent phenomenon, through directed breeding.  Not only do protracted models of domestication fall short when discussing apples, the concept of a “center” of domestication is misleading. Genetic studies illustrate that wild apple populations across Europe and West Asia collectively contributed to the modern domesticated apple in a hybrid complex of species distributed across a continent and a half.

So that's something to think about next time you bite into a crisp apple -- you're enjoying a fruit that has roots reaching back millions of years, the current shape, color, and taste of which were created by megafaunal seed dispersers and the travel of human populations down the Silk Road.

Oh, and we eventually did get back home.  Carol and I, our geneticist friend, and four other people finally decided to hire a limousine when it became obvious that (1) the power, and therefore the airport, was going to be out of commission for a long time, and (2) there wasn't a rental car to be had anywhere in the New York City area.  We figured that splitting the cost of a limousine all the way to Ithaca seven ways wasn't going to be much more than each of us separately hiring a rental car anyhow.  All was going well until the limousine overheated and died in the middle of nowhere in the Poconos, leaving us stranded by the side of the highway with all our luggage.

By then, even my new friend and I didn't feel much like talking about genetics.

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The disappearing elephant

Ever heard of gomphotheres?

They're a group of prehistoric megafauna related to modern elephants with some pretty wacky-looking dental adornments.  There was Cuvieronius:

[Image licensed under the Creative Commons DiBgd, Cuvieronius hyodon2, CC BY-SA 4.0]

And Stegatetrabelodon:

[Image licensed under the Creative Commons ДиБгд, Stegotetrabelodon11, CC BY-SA 4.0]

And strangest of all, Platybelodon:

[Image licensed under the Creative Commons Tim Bertelink, Platybelodon, CC BY-SA 4.0]

Illustrating that it's a good thing I'm not in charge of assigning scientific names, because I'd'a named this one Derpodon bucktoothii. 

In any case, these behemoths were once widespread across North America and Europe, but gradually died out during the Pliocene Epoch (5.3 to 2.6 million years ago), with the last species persisting a little way into the next epoch, the Pleistocene.  Probably for the best, actually.  I have a hard time keeping rabbits and woodchucks out of my vegetable garden, I'd just give up if I had to fend off these things as well.

Where it gets even more interesting is that these animals, like (literally) millions of others, had coevolved with other life forms.  Coevolution -- when the adaptations of one species effect the adaptations of an unrelated species -- can take two forms.  First, there's an evolutionary arms race, where a predator/prey relationship pushes both species to evolve (such as cheetahs and antelopes, where the fastest cheetahs catch the slowest antelopes, selecting both for greater speed).  The other is mutualism, where each of the two helps the other, like flowers that have adapted to specific pollinators, sometimes resulting in such dependence that neither species can survive without the other.

It's this latter type that happened with the gomphotheres.  They were major seed dispersers -- eating fruits of trees and shrubs, then defecating out the seeds (unscathed) after digesting the pulp.  Many of these plants still exist in North America and Europe, and all are united by having large, tough-skinned fruits, usually with hard or unpalatable seeds, and some sort of thorns or spikes on the branches to deter smaller animals from eating them.

There's only one problem -- as I mentioned earlier, all the gomphotheres have been extinct for millions of years.

So that leaves a bunch of plants without an efficient way of dispersing their seeds.  And we're not talking about exotic and unfamiliar plants, here.  If you look up evolutionary anachronisms, you'll see lots of names you recognize, including:

• Avocado (Persea americana)
• Papaya (Carica papaya)
• Cacao (Theobroma cacao)
• Custard apple (Annona spp.)
• Wild squash (Cucurbita pepo)
• Pawpaw (Asimina triloba)
• Osage orange (Maclura pomifera)
• Kentucky coffee tree (Gymnocladus dioicus)
• Honey locust (Gleditsia triacanthos)
• Devil's walking stick (Aralia spinosa)
• American persimmon (Diospyros virginiana)

Some of these, like cacao, Osage orange, and Kentucky coffee tree, have only prospered and/or expanded their range because humans intervened.  The last-mentioned, for example, was found only in a highly fragmented, restricted range in the south central United States when it was first cultivated by botanists and found to be a decent ornamental tree.  In the wild, the big, leathery pods -- like the fruit of a lot of these species -- simply fall to the ground when ripe and rot, the seeds nearly all failing to germinate.  Now it's planted throughout the eastern half of the United States, although given its poor germination rate even with help, the species will probably never be common.

Unless the elephants come back somehow.

This all illustrates a point I've made before -- the biosphere is a complex interwoven tapestry.  While change is inevitable -- and the extinction of the gomphotheres isn't the fault of humanity but (likely) the changing climate -- it behooves us to keep in mind that nothing on the Earth exists in isolation.  You can't pull out one thread without making the entire thing start to come unraveled.  And too many threads pulled out, the entire tapestry falls apart.

I can only hope we learn from what we've found out about the ebbs and flows of prehistory.  While we can't halt change, we need to do a far better job of protecting what we have.

Lest we go the way of the gomphotheres.

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