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Sea Urchin Evolution

Distant relatives become new species

Naos Island, Panama

A five-million-year-old urchin ancestor gave rise to two common lineages of sea urchins found today on either side of the Isthmus of Panama, according to new research by a Smithsonian scientist.

Is losing contact with relatives enough to become a new species or is moving into a new environment important too?  Staff scientist Haris Lessios enlisted sea urchin taxonomists and geneticists to find out. 

Species believed to have the same recent ancestor are grouped into a genus. Most sea urchin genera live either in tropical or in temperate seas. But one genus, Arbacia, includes species that span the two, making it the perfect candidate for their study.

Lessios and colleagues sequenced genes from species collected worldwide to discover that five million years ago, a single ancestor gave rise to two lineages in the temperate southeastern Pacific and one in the tropics. The latter was then isolated from the Atlantic by the rise of the land bridge connecting North and South America. Deep water in the mid-Atlantic separated two more species. 

Now they know that both separation from relatives and new environments are important. What selective pressures caused species to diverge is still unknown.

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