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After 60 million years apart, two fern genera form hybrid in the mountains of France

The speciation clock ticks more slowly for ferns

University of Chicago Press Journals

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IMAGE: Cystocarpium roskamianum is a recently formed hybrid between two parents that last shared a common ancestor approximately 60 million years ago. view more

Credit: Harry C. Roskam

In an article published in the March 2015 issue of The American Naturalist, a team of researchers report on a fern from the French Pyrenees that is a recently formed intergeneric hybrid between parental lineages that diverged from each other approximately 60 million years ago.

The hybrid fern--×Cystocarpium roskamianum--was found growing wild in the mountains of France and is sterile, but can reproduce itself vegetatively and grows well in cultivation.

Rothfels et al.'s finding that two fern lineages are still able to hybridize after nearly 60 million years of divergence is surprising evidence for an extraordinarily deep hybridization event--one that is roughly akin to an elephant hybridizing with a manatee, or a human with a lemur.

As populations become separate, their members are thought to lose the ability to interbreed relatively quickly, usually within a few million years. This process--the evolution of reproductive isolation--is critical for the formation of new species, and understanding the rate at which it evolves is of great interest.

That a species of oak fern (Gymnocarpium) could cross with a fragile fern (Cystopteris) to produce a viable hybrid after such a long time apart suggests that ferns may evolve reproductive incompatibilities much more slowly than most animals or flowering plants. If a slower "speciation clock" for ferns is true, it might explain why there are only around 10,000 fern species on Earth today, compared with around 300,000 species of flowering plants, without any need to invoke competitive advantages of flowering plants per se.

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Carl J. Rothfels, Anne K. Johnson, Peter H. Hovenkamp, David L. Swofford, Harry C. Roskam, Christopher R. Fraser-Jenkins, Michael D. Windham, and Kathleen M. Pryer, "Natural Hybridization between Genera That Diverged from Each Other Approximately 60 Million Years Ago." The American Naturalist Vol. 185, No. 3 (March 2015), pp. 433-442. http://www.jstor.org/stable/10.1086/679662

Since its inception in 1867, The American Naturalist has maintained its position as one of the world's premier peer-reviewed publications in ecology, evolution, and behavior research. Its goals are to publish articles that are of broad interest to the readership, pose new and significant problems, introduce novel subjects, develop conceptual unification, and change the way people think. AmNat emphasizes sophisticated methodologies and innovative theoretical syntheses--all in an effort to advance the knowledge of organic evolution and other broad biological principles.

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