Location: Forage Seed and Cereal Research Unit
2019 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
The research in Objective 1 is concerned with improving performance of oyster larvae in hatcheries exposed to reduced carbonate saturation states, also known as ocean acidification (OA). OA disrupts oyster larval development at critical points, including when larvae first form a shell and when they settle and become attached as juveniles (spat). Shellfish hatcheries now treat their seawater by adding carbonate, but larval production is still inconsistent, so other factors associated with the incoming seawater, such as microbial flora and other inorganic and organic compounds, may also be important. All of these factors contribute to stress during periods of high energetic demands and increase mortality at these critical points.
Research was focused on resistance to oyster herpes virus (OsHV-1). Oysters from the mixed family experiment conducted at the Hatfield Marine Science Center in 2018, contrasting OA and non-OA conditions are being maintained in tidal flip-bags in Yaquina Bay, Oregon, at a non-OA impacted location, and in Willapa Bay, Washington, at a potentially OA-impacted location. Oysters have been thinned to remove slower-growing individuals and 200 of the largest oysters from each site will be genotyped in late summer/early fall 2019 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 separately planted in Tomales Bay, California, (an OsHV-1 infected bay) and Willapa Bay, Washington, 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.
A study on the effects of OA on larval oyster growth, survival and settlement as juvenile spat that was undertaken by Oregon State University researchers concluded in 2019. Significant differences in both the phenotypic and genetic responses of larvae derived from selectively bred Molluscan Broodstock Program (MBP) and “wild” broodstock from a naturalized population in Willapa Bay were found. Overall, larvae from MBP broodstock produced from 37 percent to 50 percent more spat than larvae from wild broodstock under both OA and ambient conditions. These results suggest that improvements in larval performance of MBP stocks have occurred over six generations of selection. Apart from the phenotypic effects of OA on larvae derived from these two stocks, bioinformatics analysis of DNA sequences suggested that larvae from wild stocks had about 26 percent more loci changing across developmental stages and more than twice the number of loci affected by acidified culture conditions, compared to larvae from MBP stocks. The affected loci were largely exclusive to each parental stock with little overlap, suggesting that development of universal markers for OA resistance in Pacific oysters will be complicated by stock specificity. 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.
Research is being conducted on improving resistance of Pacific Northwest (NW) oyster stocks to specific strains, termed microvariants, of OsHv1. Non-microvariant strains of OsHV-1 that already occur in Tomales Bay, California, are also of concern. Outbreaks of Pacific Oyster Mortality Syndrome (POMS) caused by new microvariants of the oyster herpes virus have become a global problem for Pacific oyster farmers, killing large proportions of juvenile and adult oysters in Ireland, New Zealand, Australia and France. Selective breeding efforts in France have been successful in increasing resistance to OsHV-1 after four generations of mass selection. This research seeks to develop similar resistant Pacific oyster broodstock in the U.S. to mitigate any potential negative economic impacts, should an OsHV-1 microvariant become established on the U.S. West Coast or the original variant spread beyond California. Disturbingly, the first report of an OsHV-1 microvariant on the U.S. West coast occurred in fall 2018. To address this issue and take advantage of pre-existing knowledge developed in France, where a microvariant is present, three-month old oyster spat from 70 bi-parental families raised in the MBP hatchery (Newport, Oregon) were shipped to the French Research Institute for Exploitation of the Sea (IFREMER, La Tremblade, France) in May 2018 for resistance testing. Genetic variation in mortality among families was found and accounted for 70 percent of the overall mortality variation. This is a very important result because it indicates that selection for resistance to OsHV-1 is possible and represents an important first step towards protecting the U.S. West Coast industry from economic impacts due to this potential threat. A subsequent lab experiment conducted at the University of Arizona with collaborators from the Universities of Maryland and Washington, showed a correlation of 0.5 between mortalities of a sub-set of the 70 families exposed to French and Australian OsHV-1 strains, suggesting that resistance to one microvariant strain will 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 out in Tomales Bay, California, in a field trial to observe mortality of these families under natural conditions. In late July 2018, after a mortality event had been reported, mortality data were collected and analysis of about 100 tissue samples from live and dying oysters indicated high OsHV-1 levels in dying oysters. The heritability for survival in this trial was found to be 0.5, and a genetic correlation of 0.3 was found between mortalities of the MBP families in Tomales Bay and the French lab trials, indicating that results from lab trials are moderately predictive of field mortalities.
In spring 2019, a new of cohort of families was produced by giving equal prioritization to yield and OsHV-1 resistance. About 50 MBP families, plus an additional 30 families provided from a private breeding program, were expected to be tested at IFREMER against the French OsHV-1 microvariant. Due to a separate disease crisis and unavailable space in France, these oysters will instead be challenged with the Australian OsHV-1 microvariant in New South Wales, Australia in 2019 and have also been planted in Tomales Bay to determine their resistance to OsHV-1 under field conditions.
Four “pods”, which refer to seed from an intermating of selected families for distribution to stakeholders, were created from the four most OsHV-1 resistant MBP families identified in 2018. These pods were produced at commercial hatcheries and millions of seed were distributed to MBP partners for future use as broodstock.
Accomplishments
