Location: Forage Seed and Cereal Research Unit
2020 Annual Report
Objectives
The overall goal of this project is to improve stocks of Pacific oysters with desirable performance traits for U.S. West Coast hatchery and farm production under increasingly difficult environmental conditions of ocean acidification and the threat of the introduction of new, highly pathogenic variants of the oyster herpes virus (OsHv-1 µVar).
Objective 1: Determine the effects of selective breeding in Pacific oysters for improved larval performance in acidified seawater and resistance to oyster herpes virus (OsHV-1) through the addition of quantitative genetics expertise and development of genome-enabled strategies for breeding for disease resistance.
Subobjective 1A: Improve performance of oyster larvae in hatcheries exposed to ocean acidification (OA).
Subobjective 1B: Improve resistance of Pacific NW oyster stocks to microvariants of the oyster herpes virus OsHv1.
Approach
Utilize quantitative and molecular genetics techniques to improve the performance of Pacific oysters by 1) including larval traits (growth and setting success) in the selection index of the Molluscan Broodstock Program (MBP), and 2) including individual pedigreed oysters in the breeding program that are selected for high larval growth rates and settlement under potentially adverse commercial hatchery conditions. Collaborate with researchers in France and the Universities of Washington and Maryland to screen selected U.S. West Coast oyster stocks for resistance to new microvariants of the oyster herpes virus (OsHv-1 µVar) that have decimated Pacific oyster farms abroad. Estimate heritabilities of MBP families for resistance to OsHv-1 based on lab exposure experiments and use this information to develop effective breeding strategies to produce OsHv-1 resistant stocks of Pacific oysters for U.S. west coast farms.
Objective 1: Determine the effects of selective breeding in Pacific oysters for improved larval performance in acidified seawater and resistance to oyster herpes virus (OsHV-1).
Subobjective 1A: Improve performance of oyster larvae in hatcheries exposed to ocean acidification (OA). Research Goal: Implement breeding strategies to improve the survival and growth of Pacific oyster larvae in hatcheries that are dependent on sources of acidified seawater. Experimental Design: MBP stocks will be selected for improved larval performance in lab and commercial hatchery conditions. Unselected control populations will be maintained to assess the genetic improvement. Three changes to current MBP practices need to be implemented to meet these objectives: a) include performance traits for larval (hatchery) growth and settlement success in a modified MBP selection index to identify families with high breeding values (BLUPs) for both hatchery and on-farm traits. b) include individual pedigreed oysters as broodstock in the production of MBP’s cohorts that are selected from mixed families for high larval growth and settlement success under commercial hatchery conditions, as well as high growth rates at farm test sites. c) include randomly mated controls in MBP cohorts to determine the response to selection from one generation to the next.
Subobjective 1B: Improve resistance of Pacific Northwest oyster stocks to microvariants of the oyster herpes virus OsHv1. Research Goal: Prepare the U.S. West Coast oyster industry for a possible accidental introduction of a microvariant of OsHV-1 µVar by developing resistant oyster stocks. Experimental Design: a) In laboratory trials, determine the potential for selection for resistance to OsHV-1 µVar infection and compare results with exposure to the Tomales Bay OsHV-1 strain. b) Formulate optimal breeding strategies to develop OsHV-1 and OsHV-1 µVar resistant broodstock.
Progress Report
This is the final report for project 2072-31000-005-00D, "Genetic Improvement of Oyster Stocks for the Pacific Northwest," which terminated in December 2019. This project was merged with project 2072-63000-004-00D and replaced by new project 2072-63000-005-00D, "Improving the Sustainability and Productivity of Shellfish Culture in Pacific Estuaries." See the new project report for additional details.
Substantial results were realized over the life of this two-year bridging project, which sought to utilize quantitative and molecular genetics techniques to improve the performance of cultured Pacific oysters in the face of ocean acidification (OA) and the oyster herpes virus (OsHV-1) that are expected to or have already caused significant losses for the oyster aquaculture industry on the U.S. Pacific Coast.
Research was continued on OA in support of Sub-objective 1A. A study on the effects of OA on larval oyster growth, survival and settlement to become juvenile spat revealed that oyster larvae derived from selectively bred parents (Oregon State University Molluscan Broodstock Program (MBP), Newport, Oregon) produced from 37% to 50% more spat than larvae from “wild” broodstock collected in Willapa Bay, Washington, under both OA and ambient conditions replicated in the hatchery. These results suggest that improvements in larval performance have occurred over six generations despite no directed selection effort. Analysis of DNA sequences suggested that about 26% more loci changed expression levels across larval developmental stages in larvae from wild stocks compared to larvae from MBP stocks and wild stock larvae had more than twice the number of loci affected by OA. The affected loci however were shown to be mostly exclusive to each parental stock with little overlap, suggesting that development of universal markers for OA resistance in Pacific oysters will be complicated. Despite these differences, functional analysis revealed that the predicted genes associated with changes under OA conditions were linked to the structure and function of cellular membranes in both stocks. A second mixed family experiment followed both selectively bred families and wild oysters beyond the spat stage to harvest. Oysters were planted at a non-OA impacted site in Yaquina Bay, Oregon, and at a potentially OA-impacted location in Willapa Bay. Oysters were thinned to remove slower-growing individuals and 200 of the largest oysters from each site have been genotyped in order to identify families that produced the fastest growing individuals. This individual growth data will be combined with family yield and survival data for these same families that were separately planted in Tomales Bay, California, (an OsHV-1 infected bay) and Willapa Bay (a non-OsHV-1 infected Bay) in order to select broodstock that are faster-growing, more OA and OsHV-1 tolerant, and higher yielding for production of subsequent cohorts.
Three-month old oyster spat from 70 bi-parental families raised in the MBP hatchery were shipped to the French Research Institute for Exploitation of the Sea (IFREMER, La Tremblade, France) for resistance testing to the French microvariant of the ostreid herpes virus OsHV-1. The work advanced progress on Sub-objective 1B. Genetic variation in mortality occurred among families and accounted for 70% of the overall variation in mortality. This was a very important result because it indicated that selection for resistance to OsHV-1 was possible and represents an important first step towards protecting the U.S. West Coast industry from economic impacts due to this potential threat. A separate lab experiment conducted at the University of Arizona with collaborators from the Universities of Maryland and Washington, showed that mortalities in a sub-set of the 70 families exposed to French and Australian OsHV-1 virus strains was correlated. This suggested that resistance to one microvariant strain of the virus may provide resistance to other microvariant strains. The same 70 MBP oyster families that were tested as spat in the French and Arizona labs were planted in a field trial in Tomales Bay where a third less virulent OsHV-1 strain has been present since the 1980s. Oysters were sampled after a mortality event but a much weaker correlation was found between the mortalities of the families in Tomales Bay and those dying in French lab trials, indicating that results from lab trials are only moderately predictive of natural events.
A controlled laboratory experiment where Pacific oysters were injected with OsHv-1 was the first to show that mortality differed amongst viral strains, with aggressiveness of Tomales OsHV-1 less than the Australian microvariant and less than the French microvariant. Mortality was also not clearly related to the number of viral copies present. An additional laboratory experiment showed that multiple oyster species and stocks including Eastern oysters, Olympia oysters, Suminoe oysters, European flat oysters, Kumomoto oysters and Pacific oysters (Midoris, Inbreds, and MBP families) differed in their susceptibility to these three strains of OsHV-1. Preliminary results suggest a strong correlation amongst susceptibility to all three viral strains within individual stocks but that native West Coast Olympia oysters (Ostrea lurida) are the least susceptible to all three strains, while all other stocks, including East coast oysters (Crassostrea virginica), experienced variable but relatively high mortality.
Results of these first OsHV-1 disease trials were used to produce a second generation of MBP oyster families by giving equal priority to both OsHV-1 resistance and yield as desired traits. Disease trials could not take place in France due to import restrictions and that country's researchers' focus on a new disease, so trials were conducted in Australia. Results were variable but these oysters were also planted in Tomales Bay to determine resistance to the original OsHV-1 strain under field conditions. Pedigrees were examined and environmental effects were removed using controls to predict an approximate 9% increase in survival by generation for these MBP families subjected to the Tomales Bay viral strain.
The impact of this research was significant and immediate in that it provided direction to oyster breeding programs on the U.S. West Coast including MBP where breeding values are being quantified and used to increase resistance to OsHv-1 while attempting to maintain progress achieved for meat yield. This research suggests that breeding for resistance to OA is more challenging because oysters are most susceptible as larvae and most breeding programs don’t examine larval traits separately.
Accomplishments
1. Oysters bred for resistance to oyster herpes virus and acidified seawater. Scientists in Newport, Oregon, conducted breeding experiments to improve stocks of Pacific oysters with desirable performance traits for the U.S. West Coast including resistance to highly pathogenic variants of the oyster herpes virus (OsHV-1 µVar) and ocean acidification (OA). Seventy-one families of oysters from the Molluscan Broodstock Program (MBP) were screened for survival in a quarantine laboratory in France where they were exposed to the OsHV-1 µVar using a plate assay and also to the original OsHv-1 strain during a single mortality event in Tomales Bay, California. Survival was significantly higher for several of these families in each experiment indicating that selection for resistance to OsHV-1 is possible and results of these first OsHV-1 disease trials were used to produce a second generation by giving equal priority to both OsHV-1 resistance and meat yield. This represented an important first step towards protecting the U.S. West Coast industry from economic impacts due to this potential threat. Scientists also conducted two experiments to examine the effect of acidified seawater on oyster larvae in the hatchery. Larvae from adults selectively bred for yield as part of the MBP, produced on average more and larger oyster spat in ambient and acidified seawater respectively than did those from “wild” broodstock collected in Willapa Bay, Washington. This suggests there are genetic effects that confer resilience to stress from OA conditions, but breeding for resistance will be more challenging because oysters are most susceptible as larvae and current breeding programs don't examine larval traits separately.
