Biology grad­uate stu­dent Meredith Doellman and fac­ulty researchers from Northeastern’s Marine Sci­ence Center in Nahant, Mass., have dis­cov­ered that a spe­cific species of snail has a much more com­plex evo­lu­tionary his­tory than pre­vi­ously thought.

Doellman worked with biology pro­fes­sors Geoff Trussell and Steve Vollmer and dis­cov­ered that a marine peri­winkle snail species, Lit­to­rina sax­atillis, has defied simple text­book clas­si­fi­ca­tions of spe­ci­a­tion — that is, the for­ma­tion of new and dis­tinct species in the course of evo­lu­tion — by com­bining two types of spe­ci­a­tion, an evo­lu­tionary strategy not seen before.

Allopatric spe­ci­a­tion occurs when two pop­u­la­tions become geo­graph­i­cally iso­lated and diverge over time; whereas another, and far less common type, sym­patric spe­ci­a­tion, occurs in the same geo­graph­ical loca­tion in or around the same stretch of time.

Our new wide-​​range under­standing of genetic rela­tion­ships among pop­u­la­tions of this snail pro­vides essen­tial con­text for this impor­tant model system in marine evo­lu­tionary ecology,” said Doellman, who received a pre-​​doctoral fel­low­ship from the National Sci­ence Foun­da­tion to pursue her focus in marine science.

Pro­fessor John Gra­hame from the Uni­ver­sity of Leeds in the United Kingdom col­lab­o­rated on the research, which was pub­lished ear­lier this year in the Pro­ceed­ings of the Royal Society of London, Bio­log­ical Series.

Researchers com­pared DNA sequences from sam­ples col­lected across the North Atlantic, including Ice­land, the United States and throughout Europe to infer the evo­lu­tionary his­tory of the snail species.

Among the dis­cov­eries, researchers found that what was once thought to be one snail species might actu­ally be dif­ferent snail species inhab­iting rocky shore­lines on both sides of the North Atlantic. “L. sax­atilis def­i­nitely needs to be rede­fined — it is prob­ably two species,” said Trussell. “This also means that within this group there is evi­dence for mul­tiple, repeated exam­ples of sym­patric speciation.”

The results of this study will surely change how researchers view the cre­ation of new species,” Vollmer said.

The study emerged as part of the National Sci­ence Foun­da­tion Research Coor­di­na­tion Net­work, “Coor­di­nating Research on the North Atlantic,” led by biology pro­fessor Clif­ford Cun­ningham of Duke University.