Don’t judge a clam by its shell.
That’s what University researchers claim in an article published in February in the journal Molecular Ecology. A clam previously thought to belong to the same classification as an already-known species was found to have three markedly different genomes, despite identical appearances.
The species, Lasaea australis, is posited as the most common bivalve — a classification that includes clams, oysters, scallops and other marine mollusks — found along the southern Australian coastline; the site of an ongoing, 10-year-long, University project studying the diversification of Galeommatoidea, an order of saltwater clams.
Rackham student Jingchun Li, who conducted the research as part of her doctoral thesis, said intense sampling of the coastline and genetic analysis revealed that the species’ differentiation matched perfectly with three distinct areas.
Li added that other studies demonstrated different marine organisms followed the same pattern of differentiation along the coastline.
“This seems to be pretty common phenomenon for that coast, and nobody really had a good idea why that is,” Li said.
Li and her adviser Prof. Diarmaid Ó Foighil, director and curator for the Museum of Zoology, hypothesize that this speciation of L. australis occurred 12 to 13 million years ago.
“Changes in climate can change the tempo of (speciation), but that change is modulated by geography,” Ó Foighil said.
The water L. australis lived had uniform temperatures, Li said. However, a growing ice sheet, ushered in by climate change 12 to 13 million years ago, caused water temperatures in this middle province — along the Victoria province and Tasmania coast lines — to dip as low as three degrees Celsius. This temperature change could be significant for a marine organism’s survival.
Some clams adapted to survive in the cooler region in between two warmer regions. Unable to travel between the areas of different water temperatures, the clams began to diverge into the three species observed today.
Ó Foighil said this interplay of climate change and geography is a novel explanation for speciation.
“We have this major biogeographical mystery,” he said. “We have a contiguous coastline with three different biogeographical provinces.”
The third author of the study, Joong-Ki Park, was a graduate student under Ó Foighil when the project began. He is now an associate professor at Chungbuk National University in South Korea.
The next step in the study is to observe how biotic factors, or living organisms, play a role in speciation.
“If your habitat is another animal … how does that modulate your speciation?” Ó Foighil said. “The basic idea would be that once you add biotic hosts to it you go through more differentiation. If you have a lineage of little clams and they live on, say, the sea urchin and then the population starts living on the sea cucumber, you have separate gene pools that speciate more rapidly.”
Marine organisms are difficult to study; the ocean poses a challenge to collecting samples of underwater life and observing their interactions with other organisms.
Moreover, organisms are capable of dispersing over huge areas, making it difficult to study speciation. Ó Foighil offered an example of two snails in a backyard, they travel only a few meters in their lifetime and it’s likely they’re siblings. This proximity is not the case for their seafaring counterparts.
“The chances they’re siblings is almost zero,” Ó Foighil said. “Their parents may be hundreds of kilometers away.”
Difficulties aside, Li said the ongoing research is helpful in designing conservation areas.
“Before you might think, ‘Oh, they’re just one species, they’re the same,’” Li said. “If you want to protect … certain species or fauna of that coastline, you might take this into account this hidden diversity we can’t really see by eye.”
And though these clams are tiny, they could be vital in our interwoven ecosystem.
“Our life is highly affected by all of the biodiversity around us,” Li said. “Those clams you might think (are) just one clam but it’s really in a great marine community. Its own survival is affecting and being affected by everything around it.”