Cryptic clams: Biologists find species hiding in plain view

Mar 12, 2013
Map of Australia showing the three biogeographic provinces and sampling sites included in the U-M clam study. Map by Jingchun Li.

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

Two University of Michigan have identified three of tiny , long believed to be members of the same species, which have been hiding in plain view along the rocky shores of 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 to be published next month in the journal .

The U-M scientists conducted a 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 modulated by local geography," Jingchun Li, lead author of the report and a doctoral student in the U-M Department of Ecology and .

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

Map of Australia showing the three biogeographic provinces and sampling sites included in the U-M clam study. Map by Jingchun Li.

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

Australia's southern coastline is home to three evolutionarily distinct assemblages of known as biogeographic provinces. Each province contains hundreds of species of invertebrates, fish, algae and other organisms, and there are substantial differences between the species living in each province.

Here's the riddle that has perplexed biologists for decades: How did these three distinct biogeographic provinces evolve along a continuous coastline? The emergence of new species often begins when gene flow between populations is reduced or eliminated. This type of genetic isolation happened routinely throughout evolutionary history when populations became physically separated—when a new physical barrier such as a mountain or a river split the geographic range of a species, for example.

But what force could drive speciation along an unbroken coastline with no obvious barriers to gene flow?

The genetic analysis by Li and O'Foighil, which is backed by evidence from the fossil record, shows that the three cryptic clam species began splitting away from a 13 or 14 million years ago.

That's about the same time that a major climate-cooling event called the middle Miocene climate transition permanently lowered sea-surface temperatures in the southwest Pacific Ocean—including the southern coast of Australia—by 10.8 to 12.6 degrees Fahrenheit.

Li and O'Foighil propose that the cooling event partitioned Australia's southern coastline into three zones with a cool region, including the present-day southeastern state of Victoria and the island of Tasmania, flanked on either side by two relatively warm ones.

The emergence of three temperature zones created opportunities for local adaptation that isolated the organisms living within each zone. That isolation led, in turn, to the evolution of the three biogeographic provinces seen today, according to Li and O'Foighil.

In their study, Li and O'Foighil showed that each of the three cryptic clam species is found in only one of the three biogeographic provinces.

"I know of no other case where you start out with one marine biota, then a climate-change event results in the generation of three biotas from that one," O'Foighil said. "A key finding of the study is that relatively ancient climate-change events can shape marine biotas."

Explore further: Call for alternative identification methods for endangered species

Related Stories

Species detectives track unseen evolution

Jul 19, 2007

New species are evading detection using a foolproof disguise – their own unchanged appearance. Research published in the online open access journal, BMC Evolutionary Biology, suggests that the phenomenon of different animal ...

Reproductive isolation driving evolution of species

May 16, 2012

Evolution of species remains a hot topic since Darwin’s theory of natural selection. A European initiative addressed the issue of speciation from the viewpoint of reproductive isolation.

Ocean heatwave decimates vital seaweed habitat

Jan 22, 2013

The decimation of a seaweed that provides vital habitat for an interdependent web of marine species off the WA coast, as a consequence of a record ocean heatwave, has been revealed in a paper published in ...

Recommended for you

Plants with dormant seeds give rise to more species

1 hour ago

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Scientists tether lionfish to Cayman reefs

11 hours ago

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

baudrunner
5 / 5 (1) Mar 12, 2013
Someone needs to have a word with Jingchun Li. Is he getting paid for two maps?

More news stories

Plants with dormant seeds give rise to more species

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Researchers develop new model of cellular movement

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

Male monkey filmed caring for dying mate (w/ Video)

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

LinkedIn membership hits 300 million

The career-focused social network LinkedIn announced Friday it has 300 million members, with more than half the total outside the United States.

Magnitude-7.2 earthquake shakes Mexican capital

A powerful magnitude-7.2 earthquake shook central and southern Mexico on Friday, sending panicked people into the streets. Some walls cracked and fell, but there were no reports of major damage or casualties.

Sun emits a mid-level solar flare

The sun emitted a mid-level solar flare, peaking at 9:03 a.m. EDT on April 18, 2014, and NASA's Solar Dynamics Observatory captured images of the event. Solar flares are powerful bursts of radiation. Harmful ...