Is It Time For New Tactics

Zebra mussels are a small, invasive mollusk (clam) that originated in Eastern Europe and first arrived in the U.S. in the mid-1980s. Although usually less than an inch in size as adults, they can rapidly spread under the right conditions. The larval stage of zebra mussels, called veligers, are nearly impossible to detect due to their small size, heightening the importance of the state’s new boat draining laws.

Zebra mussels are a fast growing problem for numerous waterways throughout the upper Midwest. Spreading all the way from their native home in the lakes of southern Russia and the Ukraine, this aquatic invasive species has even made its way to the shores of Lake Yankton and the Missouri River.

While prevention still remains the best method for trying to control the spread of these aquatic invaders, researchers at the University of Minnesota are exploring other methods to combat zebra mussels.

Michael McCartney, a zebra mussel expert in the aquatic invasive species department at the University of Minnesota, has been working since 2013 on various methods of preventing or slowing the spread of zebra mussels.

“I come from a background in molecular biology and genetics, and also in studying bivalve animals like mussels, specifically marine mussels,” McCartney said in an interview with the Press and Dakotan. “I first became interested in zebra mussels because they have a life cycle that is very similar to marine bivalves, and they actually came from marine ancestors.”

Since 2014, McCartney and his research team have been working non-stop on solving the growing zebra mussel issue that has affected many of the lakes and rivers in Minnesota.

“A lot of our research is mainly focused on control, but the rest of it is focused on prevention and figuring out how the mussels spread themselves around,” McCartney said. “We are trying to map the pattern of their spread across Minnesota.”

McCartney’s current projects include: the evaluation of the toxicity of low-dose molluscicide for zebra mussel veligers; genome sequencing and analysis for selecting target genes and strategies for genetic biocontrol; developing and testing a new molecular assay for early detection of zebra mussel veligers; creation of survey and monitoring protocols, and development of a research program for studying the effectiveness of zebra mussel pesticide treatment efforts; evaluating zebra mussel spread pathways and mechanisms in order to prevent further spreading; and estimating overland transport frequencies of invasive zebra mussels.

“The aquatic invasive species research center has a mandate from the state of Minnesota to work towards solutions for the zebra mussel problem, including figuring out methods of control,” McCartney said. “I’ve sort of taken a two-pronged approach when it comes to trying to control zebra mussels.”

The use of chemical treatments to neutralize zebra mussels in newly infested waters is one form of control that can be utilized depending on the size of the body of water and scope of the infestation.

 “The control work we’ve done with chemicals involves mainly helping the Minnesota Department of Natural Resources and other management groups in trying to figure out how to best treat bodies of water with chemicals after they become newly infested,” McCartney said. “We know that there are a whole set of chemicals that are harmful to zebra mussels, but the question is how do we most effectively use them while still having a positive impact on the elimination of zebra mussels and not harming other species in their natural habitats.”

The other prong of McCartney’s approach is something closer to what you might find in a science-fiction novel, and it is still a few years from becoming a reality. Genetic biocontrol, or altering the genetics of an organism to control its population, is gaining steam as a possible way of removing zebra mussels from waters without risking harm to other native plant and animal species.

“Genetic biocontrol grew out of two things,” McCartney said. “In part, it is a product of the research we’ve done to study the spread of zebra mussels. We had to develop all these genetic markers that we use, and some of them required that we actually go into the genome of the animal. Through that process, we found that the genome of the zebra mussels hadn’t been fully sequenced yet.”

 That was when McCartney and his group moved towards mapping the genome of the zebra mussels with help from the University of Minnesota genome research center. The research would become necessary in the development of future genetic biocontrol methods.

“I soon realized that a lot of the interest in sequencing the genome might be expendable to starting to look for some of the genetic information that we might actually use to control the animal,” McCartney said.

His group is currently trying to figure out the best ways to intervene in zebra mussels’ biological processes so that the population can be weakened.

“One weak point of zebra mussels is that they don’t do very well in water with low calcium concentrations,” McCartney said. “There are a lot of other native mollusks that do perfectly fine in bodies of water with those lower calcium concentrations, but not zebra mussels. That means the question we have to ask ourselves is, what makes zebra mussels susceptible to those low calcium levels in their genetic make-up and how can we exploit it?”

The other part of the equation that led McCartney and his group to pursuing biocontrol is the amount of new research being done on gene drives and inherited traits.

“I came up with the idea to biocontrol mussels, but it’s not something that just sprang into my head,” McCartney said. “One of the most attractive technologies for this is to use genetic elements that have their own tendency to be copied and inherited in populations. These gene drives, as they are called, are in the news a lot lately because of people’s interest in using them to control pest organisms like mosquitos and stopping the spread of things like the Zika virus. That’s what led me to think about using them to combat zebra mussels.”

While the altering of genes within an organism is a not an easy task and still far from becoming a reality, the process presents a very precise way to control invasive animal populations without endangering the existence of other animals in their native habitats. The biggest question for McCartney and his group, once they figure out which genes they are going to alter, is how to administer the alteration.

“I think a lot about how we can get these alterations into an animal,” McCartney said. “It’s kind of hard to explain the genetic constructs we use. They are packages of DNA and RNA that are linked together in clever ways and then inserted into an organism. The beauty of these constructs is that they are extremely specific. They are almost surgical in the way in which they can be used to go into the genome and alter a gene. The trick to the whole process is getting the altered DNA to be copied by the organism so that it passes into a line of cells that it will pass on to its offspring.”

Being able to specifically target and remove zebra mussels from a location that they have infested might sounds appealing on the surface, but there are a host of technical, legal and ethical issues that need to be considered.

“One of the big questions that we have to ask is, what do we do with a type of control like this that could get back to the native range of the animal?” McCartney said.

 Currently, zebra mussels are uncommon in their native range and very common in their invasive range in both Europe and North America.

“My opinion is that we have the ethical right to pursue methods to remove these animals from their invaded ranges because they are so damaging and don’t belong in those locations,” McCartney said. “If you eliminate zebra mussels from a lake, you are setting that body of water back four to five years before that species was present there. I think that is what we should do if we can. That ethic sits along the lines of trying to restore native systems and promoting conservation. “

Ultimately, the decision on whether to implement genetic biocontrol in zebra mussels is out of McCartney’s hands. While he and his researchers are able to offer input on the topic with scientific facts and their own personal observations, the decision will come from regulatory groups within the federal and state governments.

“It doesn’t matter what I think because the people making the decisions are going to be regulators, not scientists,” McCartney said. “We will certainly weigh in on the topic, but there are other people who should be evaluating our research. Our job is to just do the research and present the facts.”

There are still several roadblocks for McCartney and his researchers to overcome. It will likely be several years before all the necessary research and testing has been completed and the project gets the green light to be utilized in the field.

“The first set of challenges that we still have to overcome is the reality of how hard it is to do genetic research,” McCartney said. “We are working like crazy to map the zebra mussels’ genome. We still have about two to five years left before we have that completely mapped and select a gene to target. The second set of challenges is the technological challenge of figuring out how to put these alterations into the zebra mussel population. We will probably need help from the Game, Fish and Parks people for that. The third and final set of challenges involves the regulatory process and overcoming the ethical issues involved with genetic engineering.”

Due to the controversial nature of the research, McCartney anticipates there will likely be a real and legitimate challenge from the public when genetic biocontrol gets closer to becoming a reality.

“There is still plenty to be done, but I think we are doing the right thing,” he said. “There is a tremendous amount of interest in managing these invasive species. Not long ago, people thought it was a waste of time to try and control invasive species. They thought the only way to do it was through prevention, and that is still the first line of defense. But we also need to continue to pursue control as a method to help combat these species once they have invaded an area.”

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