Sunday, November 22, 2015

Pumpkin Extinction?

Thanksgiving overload - REK
One more thing to be thankful for this Thanksgiving are the humans that saved pumpkins and squash from extinction.  An article in PNAS describes this close call and the role of both megafauna and their new biped enemies in saving them for us to eat.

Current science suggests that large fruits of the osage orange were spread following ingestion and defecation by megafauna.  Likewise the long bean pods of the Kentucky coffee tree and honeylocust contain hard shelled beans that require digestion to germinate, a perfect match for a mastodon or a 3 ton giant sloth.  Furthermore, the large honeylocust thorns may have evolved to protect against these giant mammals, as explained in Trees that Miss the Mammoths.

Cucurbita, large squash and pumpkins, were widespread in the New World and their seeds were found in mastodon dung as early as 30,000 years ago.  They grew in heavily browsed areas and were dependent on the dispersal of seeds by their mutualistic partners.  They contained cucurbitacins, some of the most bitter compounds found in plants.  The few remaining ancient species are distasteful to humans and existing mammals that have evolved more bitter taste receptor genes.  Without the megafauna browsing open spaces and dispersing their seed in dung, their survival was at risk.

Enter the humans who arrived around 13,500-14,500 years ago.  The bad news for Cucurbita was the extinction of megafauna with over hunting likely to have played a role.  The good news was human domestication of squash and gourds for food and containers dating as early as 10,000 years BPE led to the development of the pumpkin as we know it.  No precursor species is known to have survived.  See Popsci.com for more details.

We have now perfected a sweet tasting Cucurbita that we use in pies, coffee and even beer.  It is even tasty to deer and racoon.  Is that good or bad?.....it depends on whether you have two legs or four.

Thanks for the tip from our personal dendrologist, Dr. Matt Kaproth.

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