Monday, December 16, 2013

Anachronistic Osage orange

I don't remember what we called them when I was growing up in Illinois (hedge apples?), but I do remember some mischievous boys throwing the fruit of the Osage Orange at our car as we drove by. "In the fall, Osage-orange trees hang heavy with bright green, bumpy spheres the size of softballs, full of seeds and an unpalatable milky latex. They soon fall to the ground, where they rot, unused, unless a child decides to test their ballistic properties," reads an article with the tantalizing title "The Trees That Miss the Mammoths." The article goes on to explain that fleshiness and aromatic properties of the fruit entice large animals to eat them, pass through the seeds they contain, and deposit them – along with natural fertilizer – away from the parent tree. This evolutionary strategy worked beautifully in the age of the mammoths. Giant ground sloths and gomphotheres, one of the elephant's many interesting ancestors, gobbled up the fruit of the Osage apples and facilitated their propagation. But today, with the extinction of most megafauna, scientists were left with the "riddle of the rotting fruit," which remained on the ground beneath the tree or rolled downhill, sometimes carried away by water. Tropical ecologist Dan Janzen of the University of Pennsylvania and paleoecologist Paul Martin of the University of Arizona developed the concept of ecological anachronisms, organisms which persist despite their outdated adaptations. The pace of evolution is slow, but the disappearance of mammoths (at the hands of humans, according to many) was quick. The article concludes, "For a tree that lives, say, 250 years, 13,000 years represents only 52 generations. In an evolutionary sense, the trees don’t yet realize that the megafauna are gone."

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