18 July 2012
Title:Extraordinarily rapid life-history divergence between Cryptasterina sea star species
Authors: Jonathan B. Puritz, Carson C. Keever, Jason A. Addison, Maria Byrne, Michael W. Hart, Richard K. Grosberg, and Robert J. Toonen
Journal: Proceedings of the Royal Society B
A new species of sea star which evolved only 6,000 years ago, during a period of rapid environmental change, has been discovered in Hawaii. This evolution of a new species, 100 times faster than that normally seen in the ocean, is described in Proceedings of the Royal Society B today.
Jon Puritz and his team at the Hawaii Institute of Marine Biology discovered that during this rapid period of evolution, one species changed from the ancestral form with separate sexes that release eggs into the water for fertilization. The new species, Cryptasterina hystera, lost the larval stage all together, and changed from having separate sexes to being hermaphroditic. This means that the species now has the potential to self-fertilize and carries juveniles internally until giving birth to live young. This shift in reproduction has dramatically reduced the genetic diversity of C. hystera to levels that are on par with many endangered species.
This drastic change in the reproductive system means that a distinct species has evolved; a process which usually takes hundreds of thousands to millions of years. 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 species may have the potential to adapt to future climate change.
Postdoctoral researcher, Jon Puritz who led the investigation 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.”
Understanding the processes that create and maintain biodiversity, such as when and how new species form, remains one of the greatest challenges facing biologists, conservation scientists, and managers today. These processes are especially obscure in the ocean, where many organisms have tiny juvenile larval stages that swim in the plankton for some time before settling into a largely sedentary adult. This larval stage has the potential to disperse over great distances and keep populations very well-mixed, thus decreasing the chance for speciation. On the other hand, larvae also have the opportunity to disperse great distances to colonize new habitats where they may adapt and perhaps even evolve into a new species. This process usually takes hundreds of thousands to millions of years.