Cryptic comments have an ambiguous, obscure or hidden meaning. In biology, cryptic species are outwardly indistinguishable groups whose differences are hidden inside their genes.

Two U-M EEB marine biologists have identified three cryptic species of tiny clams, long believed to be members of the same species, which have been hiding in plain view along the rocky shores of southern Australia for millions of years.

The unusual convergence of a climate-cooling event and the peculiarities of local geography caused the three cryptic species to split from a common ancestor more than 10 million years ago, the U-M researchers propose in a paper published in the April 2013 journal Molecular Ecology.

The U-M scientists conducted a genetic analysis after collecting thousands of the crevice-dwelling, rice grain-sized clams from hundreds of miles of southern Australia coastline over the past decade. Their findings provide insights about the forces that shape evolution and solve a puzzle that has stumped marine biologists for decades.

"This study provides important clues about how marine regional biotas can evolve, including our observation that these processes can involve major global climate change modulated by local geography," Jingchun Li, an EEB graduate student and lead author of the report.

Li conducted the research as part of her dissertation with co-author Professor Diarmaid O'Foighil, Li's adviser and director of the U-M Museum of Zoology.

"You cannot tell them apart physically, but their genes indicate that their evolutionary divergence predates that of humans from chimpanzees," O'Foighil said of the three clam groups, which are currently classified as members of the same species, Lasaea australis.

Read more to find out the answer to the riddle that has perplexed biologists for decades: How did these three distinct biogeographic provinces evolve along a continuous coastline?

U-M News Service press release

Caption: A closeup of L. australis clams from the southern Australia coast. Each clam is about the size of a rice grain. Photo by Denis Riek.