Picking Parents for the Best Traits

By Janet Krenn, Virginia Sea Grant

Think about the last baby you saw. Was it identical to its mother or father? Of course, it’s a trick question. Children’s characteristics are a combination of their two parents. The same goes for oysters.

With the help from National Sea Grant National Strategic Initiative funding, Virginia Institute of Marine Science (VIMS) Aquaculture Genetics and Breeding Technology Center (ABC) tested how well each oyster parent can pass down traits to their offspring. The results could improve Virginia’s oyster aquaculture industry, which generates more than $13 M in annual economic impact to the state.
ABC aquaculture geneticist Anu Frank-Lawale, one of the VIMS scientists involved in this study, sees this research as the key to putting oyster growers in the driver’s seat. 

“Right now the grower basically doesn’t have much he can control. He can’t control the salinity or the environment. What he can control is the kind of oyster he grows,” Frank-Lawale says. If a grower can use scientific fact to choose the oyster parents, the crop could benefit. Understanding the role of each parent is especially useful because, in aquaculture, oyster parents don’t contribute the same number of genes. 

Aquacultured oysters are triploid and have three sets of genes. Triploids come from mating an oyster with four sets of genes with a typical oyster with two sets of genes. When it comes time for these animals to reproduce, they each put half of their genes into the sperm or egg. Two sets of genes from the four-gene set parent combines with one set from the two-gene set parent, and you get triploid oyster babies (2+1=3). 

Triploid food is not uncommon in our food. Having an odd number of gene sets prevents plants and animals from reproducing. In the cases of bananas and seedless watermelon, which are triploid, triploidy is responsible for your seedless experience. In the case of triploid oysters, all of their energy goes into growth, and they reach market size faster. 

Now the industry is looking for oysters with traits in addition to disease resistance and fast growth, but breeding other traits into oysters is challenging. If it were a numbers game, you may expect that the parent giving one set of genes wouldn’t be very effective at passing down traits compared to the parent giving twice as many gene sets. 

The researchers are hoping it isn’t the case. Oysters with two gene sets are easier to selectively breed. It can take a few generations to get a trait consistently appearing in an oyster family with two gene sets. It can take dozens more for those with four. 
“If [offspring from] selected parents do better than the wild, then by selective breeding we can make the triploid better,” says Frank-Lawale. 

To test this, ABC mated oysters with four gene sets with two gene set oysters that were either wild or selected from a long line of oysters that ABC exposed to disease, mating the survivors to select for disease resistance. 

The team found that triploid oysters with a selectively bred parent survived better–“Hands down better,” says Frank-Lawale–than those mated with wild oysters. This gives the team confidence that other traits could be passed down from the typical two-gene parent to their triploid offspring.
Now the door is open for oyster geneticists like Frank-Lawale to select traits that could be beneficial and profitable for the industry: “These projects are really important because the industry’s at a cross road, and what’s amazing, is we’re basically helping chart the course.”

This is part 3 of a 3 part series. See also, Part 1 and Part 2