Tuesday, November 24, 2015

Be Thankful for Pumpkins

(Credit: Ginny via Flickr, 2008)

As families around the United States begin their Thanksgiving feast, they should be particularly grateful for the pumpkin. According to a study published last week in the journal Proceedings of the National Academy of Science, this beloved squash survived extinction only through domestication by humans thousands of years ago.

Over 10,000 years ago, ancient ancestors of the squash genus Cucurbita were broadly distributed across the New World, living alongside large mammals, like ground sloths and mammoths. By modern times, however, wild Cucurbita species were very rare compared to their more common domesticated relatives. This discrepancy prompted researchers in the United States and England to examine 91 genomes of plants in the genus Cucurbita, encompassing 72 species or subspecies of modern wild and domestic plants, as well as 19 ancient archaeological samples.

Analysis of the plants’ sequences provided evidence for multiple domestication events in the New World, including a previously unknown domestication in northeastern Mexico. The distribution of ancient species revealed that many more wild Cucurbita plants existed around the beginning of the Holocene than now. Researchers found that the sudden disappearance of wild Cucurbita coincided with the die-off of megafaunal species in the Americas.


Large herbivores, like mastodons, ate the bitter-tasting Cucurbita and dispersed seeds through their droppings. Smaller mammals, however, do not seem to have the same ability to digest these plants. Without aid from megafauna to spread their seeds, the wild Cucurbita species disappeared quickly from the landscape and many went extinct. Luckily for Pumpkin Spice Latte and pie lovers alike, ancient people of the New World bred these plants into sweeter and more palatable varieties. Ancient and modern specimens showed ecological upheaval which could have wiped out the Cucurbita genus, but careful cultivation ensured the survival of the pumpkin.


References:
Kistler, L., et al. (2015, November 16). Gourds and squashes (Cucurbita spp.) adapted to megafaunal extinction and ecological anachronism through domestication. PNAS doi:10.1073/pnas.1516109112



Glossary

Holocene
A geological epoch that began around 11,700 years ago and continues to present day. This epoch comes after the Pleistocene and is characterized by the current warm period and the growth of the human species in population and impact around the world.
megafauna
Large animals with adults growing to over 45 kg. Ancient and extinct megafauna include mastodons , woolly mammoths, and giant ground sloths. Modern day megafauna include great white sharks, ostriches, elephants, and blue whales.

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