Super-fast evolution of sea stars

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How quickly does it take for a new species to evolve in the ocean? Hundreds of thousands of years? Millions? Usually it does — but researchers at the University of Hawaii have discovered two sea stars that evolved into separate species in what could have been as little as 6000 years!

The closely related cushion stars, Cryptasperina pentagona and C. hysteria, look identical to one another, but live in different areas on the coast of Australia, with C. hystera living on a few beaches and islands at the far southern end of C. pentagona's range.

And their sex lives are very different indeed. C. pentagona has separate sexes that release sperm and eggs into the water for fertilisation. The larvae float around in the plankton for several months before they settle and develop into adult sea stars.

The new species, Cryptasterina hystera, lost the planktonic larval stage altogether, and changed from having separate sexes to being hermaphroditic (organisms that have both sexes). This species now carries juveniles internally until they give birth to live young, and has the potential to self-fertilise.

This shift in reproduction has dramatically reduced the genetic diversity of C. hystera to levels that are on par with many endangered species. Additionally, populations of this species are genetically different among tide pools only meters apart from each other. This rapid speciation in response to environmental change means that some may have the potential to adapt to future climate change.

Postdoctoral researcher, Jon Puritz led the investigation, and when asked about the recent discovery said: "This rate of speciation is nearly a hundred times faster than we normally see in the ocean, and to have it coupled with such a drastic change in life history is really spectacular. It seems like evolution in life history traits may be a particularly fast pathway to speciation."

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