Genetic improvement of survival in Pacific oysters to the Tomales Bay strain of OsHV-1 over two cycles of selection

Authors: DIVILOV, KONSTANTIN - Oregon State University; SCHOOLFIELD, BLAINE - Oregon State University; CORTEZ, DANIEL - Hog Island Oyster Co; WANG, XISHENG - Oregon State University; FLEENER, GARY - Hog Island Oyster Co; JIN, LING - Oregon State University; Dumbauld, Brett; LANGDON, CHRIS - Oregon State University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2021
Publication Date: 9/15/2021
Citation: Divilov, K., Schoolfield, B., Cortez, D.M., Wang, X., Fleener, G.B., Jin, L., Dumbauld, B.R., Langdon, C. 2021. Genetic improvement of survival in Pacific oysters to the Tomales Bay strain of OsHV-1 over two cycles of selection. Aquaculture. 543. Article 737020. https://doi.org/10.1016/j.aquaculture.2021.737020.
DOI: https://doi.org/10.1016/j.aquaculture.2021.737020

Interpretive Summary: Pacific oysters are one of the most important products of the shellfish aquaculture industry on the West Coast of the United States. One important growing area is Tomales Bay, California where the industry experiences large oyster mortality events every year. These mortalities have been associated with the presence of Ostreid herpesvirus 1 (OsHV-1) and increased seawater temperature in this estuary. In order to initiate a selective breeding program for oysters that are more tolerant to OsHV-1, a set of oyster families were planted in Tomales Bay for three consecutive years. Survival data was used to select which families to mate and spawn in subsequent years. This is the first study to evaluate and successfully document increased survival to OsHV-1 in the U.S. and high surviving families will become valuable genetic resources for oyster growers in Tomales Bay. We also measured the accumulation of inbreeding due to selection in these stocks and demonstrated that continued genetic improvement in survival will likely be successful since no decrease in genetic variance was found. Results will be directly applicable to an expanded effort to develop oyster stocks that are resistant to other forms of this virus that pose a serious threat the this US West Coast industry.

Technical Abstract: Background Yearly mass mortalities of Pacific oysters in a major oyster-growing estuary on the West Coast of the United States (Tomales Bay, California, USA) present a constraint to shellfish aquaculture. These mortalities have been associated with the presence of Ostreid herpesvirus 1 (OsHV-1) and increased seawater temperature in the estuary. In order to develop oyster families that are more tolerant to OsHV-1 than current oyster stocks, one cohort was planted in Tomales Bay per year over a three-year period, two of which were selected based on survival data collected from previous cohorts. In this study, we investigate the amount of genetic gain, the change in genetic variance, and the accumulation of inbreeding due to selection for survival. Additionally, we examine the accuracy of breeding value prediction and the influence of the spatial distribution of oyster families in the field on genetic parameters. Results Survival breeding values increased 9.0 to 16.4 percentage points after two generations of selection with no decrease in genetic variance, but with a slight increase in inbreeding from 2.9% to 5.3%. Breeding value prediction accuracies ranged from 0.37 to 0.57, depending on the model and phenotypes used in their calculation. Significant spatial effects were present in phenotypes collected from all three cohorts, but they did not affect prediction accuracies. Conclusions Breeding oysters for increased survival to OsHV-1 in Tomales Bay was successful without limiting future selection efforts. The oysters developed in this breeding program are the first OsHV-1-tolerant oyster families in the United States and will be valuable to oyster growers as well as researchers trying to understand the genetic basis of OsHV-1 tolerance in Pacific oysters.