"It's the blending of ecological and evolutionary time," says Freeman, a Ph.D. candidate in the department of zoology. "It's an important development in the arms race between these crabs and these mollusks." Crabs prey on blue mussels by crushing their shells.
Freeman looked at the inducible defense – shell thickening – of blue mussels (Mytlius edulis) in the presence of two invasive crab species in New England, the Asian shore crab Hemigrapsus sanguineus and the green crab Carcinus maenas. While Carcinus was introduced to New England from Europe between 150 and 200 years ago, Hemigrapsus is a relative newcomer, arriving from Asia to New Jersey in 1988. While previous research had established that mussels recognize Carcinus, it had not be determined if they recognize Hemigrapsus. And, crucial to the design of Freeman's study, Hemigrapsus is not present north of mid-coast Maine.
"This set up a chance to look at populations that had been exposed to the predators for varying lengths of time," says Freeman. "We wanted to know, how is it that these mollusks can recognize a crab that is historically not present in North America?"
Freeman exposed mussels native to the northern – above mid-coast Maine – and southern New England to both Carcinus and the Hemigrapsus. Both populations thickened their shells when exposed to waterborne cues of Carcinus, but only the southern mussels – Freeman describes them as "more worldly" – expressed inducible shell thickening in the presence of Hemigrapsus.
"The mussel's inducible response to H. sanguineus reflects natural selection favoring the recognition of this novel predator through rapid evolution of cue specifity or thresholds," Freeman and Byers write.
Findings were consistent in two experiments over two years, one in a laboratory setting in Nahant, Mass., and one in the field at Woods Hole, Mass. "The consistency over two years and two sites really suggests an underlying robust mechanism," says Byers, who is Freeman's dissertation advisor.
While this sort of rapid evolutionary response to predators has been exhibited in some other species, all have been vertebrates. The blue mussel, which Freeman describes as the lab rat of marine biologists, is an invertebrate "that people assume is not very bright," he says. Yet his findings indicate that within the brief span of 15 years, it has evolved an inducible response to a new predator.
How do mussels evolve so quickly? In southern New England, the scientists say, mussels are prey to many crabs as well as other marine species. "When Hemigrapsus came along the mussels' wheels were well-greased to respond," says Byers. "That's our best guess."
Byers helps put the impact of the research in context. Because extensive data does not exist on invasive ecology, "there's a tendency to extrapolate any data you get on an invasive species. But here we show that the response from the prey differs over just a couple hundred kilometers."
And while its "real world" impact is not immediately obvious, Byers suggests that perhaps northern Maine and Canadian shellfishers might consider "beefing up the worldliness of their naïve mussel populations before the Hemigrapsus arrives," he says, suggesting that this could be done by mixing some of the responsive southern mussels into the naïve northern stocks. "Although 15 years is fast to evolve better defenses to your predator, it can be painfully long if you're a shellfisherman," Byers adds.
This paper is one chapter of Freeman's doctoral dissertation, which also explores how mussels respond to sea stars and to multiple predators. He anticipates completing his doctoral work by October 2006, when he will begin a post-doctoral position with UNH research associate professor Fred Short.
Freeman notes that there's one predator mussels will not need to defend themselves against: him. "I used to like them, before I started working with them for my dissertation," he says. "Not anymore."
Beth Potier | EurekAlert!
Despite government claims, orangutan populations have not increased. Call for better monitoring
06.11.2018 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig
Increasing frequency of ocean storms could alter kelp forest ecosystems
30.10.2018 | University of Virginia
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
16.11.2018 | Health and Medicine
16.11.2018 | Life Sciences
16.11.2018 | Life Sciences