Romantic Reunion of Two Fern Species After 60 Million Years Apart Stuns Plant Geneticists

A delicate woodland fern discovered in the mountains of France is the “love child” of two distantly-related groups of plants that haven't interbred in 60 million years, genetic analyses show. For most plants and animals, reuniting after such a long hiatus is thought to be impossible due to genetic and other incompatibilities between species that develop over time. Reproducing after such a long evolutionary breakup is akin to an elephant hybridizing with a manatee, or a human with a lemur, said co-author Kathleen Pryer, who directs the Duke University Herbarium. Led by Dr. Pryer and Dr. Carl Rothfels of the University of California, Berkeley, the study appears online on February 14, 2015 in the American Naturalist. The pale green fern was found growing wild on a forest floor in the Pyrenees and eventually made its way to a nursery, where researchers plucked several fronds and extracted the DNA to pinpoint its parentage. To their surprise, genetic analyses revealed that the fern was the result of a cross between an oak fern and a fragile fern -- two distantly related groups that co-occur across much of the northern hemisphere, but stopped exchanging genes and split into separate lineages some 60 million years ago. "To most people they just look like two ferns, but to fern researchers these two groups look really different," Dr. Rothfels said. Other studies have documented instances of tree frog species that proved capable of producing offspring after going their separate ways for 34 million years, and sunfish who hybridized after nearly 40 million years, but until now, those were the most extreme reunions ever recorded. "For most plant and animal species, reproductive incompatibility takes only a few million years at the most," Dr. Rothfels said.
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