This report documents the oyster conditioning (immune priming) trials conducted to evaluate the effects of parental PolyIC treatment on offspring performance. The study examined transgenerational immune priming in Pacific oysters (Crassostrea gigas) through controlled laboratory experiments and field outplant assessments. Results demonstrate complex, temperature-dependent effects on offspring survival, metabolic activity, and growth.
- Evaluate whether parental immune stimulation with PolyIC affects offspring performance
- Assess transgenerational immune priming effects across multiple developmental stages
- Measure impacts on survival, growth, and metabolic activity under various environmental conditions
- Broodstock treatment and spawning: 2024 (Point Whitney facility)
- Larval development: 0-14 days post-fertilization (Point Whitney)
- Setting phase: Shipped to Kona, Hawaii (November 2024)
- Juvenile growth monitoring: November 2024 - May 2025 (Point Whitney)
- Stress testing and metabolic assays: January - March 2025
- Field outplants: Multiple sites including Sequim Bay (June 2025)
Treatment Agent: Polyinosinic:polycytidylic acid (PolyIC) - a synthetic double-stranded RNA that mimics viral infection and stimulates immune response without causing actual pathogen exposure.
Broodstock Treatment:
- Treatment group: Adult breeding oysters immersed in PolyIC solution for 2 hours
- Control group: Adult oysters maintained under standard conditions without PolyIC exposure
- Timing: Treatment administered immediately before spawning to maximize potential for transgenerational effects
- Replication: Approximately equal numbers of parents contributed to each pooled treatment group
Spawning Protocol:
- Oysters spawned at Point Whitney using standard production workflow
- Pooled egg and sperm collected separately from Control and Treated broodstock
- Fertilization conducted independently for each treatment group
- Equal contribution from multiple parents per treatment to maintain genetic diversity
To reproduce this conditioning protocol:
- Select healthy broodstock oysters at reproductive maturity
- Divide into two groups (Control and Treated) with equal sample sizes
- Prepare PolyIC solution according to manufacturer specifications
- Immerse treated group in PolyIC solution for exactly 2 hours
- Maintain control group under identical conditions without PolyIC
- Following treatment, immediately spawn both groups using standard hatchery protocols
- Fertilize eggs with sperm from same treatment group (avoid cross-contamination)
- Pool gametes from multiple individuals within each treatment for genetic diversity
Initial Rearing (Days 0-3):
- Setup: 10,000 L tanks (n=1 tank per treatment)
- Feeding: Nano-pav and CC mix following production practices
- Age at first sampling: 3 days post-fertilization
- Screen size: 60 µm
- Replication: Larvae distributed into 1,000 L tanks (n=2-3 tanks per treatment)
Mid-stage Development (Days 3-8):
- Tank size: 1,000 L
- Replication: n=2-3 tanks per treatment
- Screen size at 8 days: 105 µm
- Survival rate: >90% for all larval groups
- Samples collected: RNA/DNA samples from each tank
Pre-settlement (Days 8-14):
- Screen size at 14 days: 240 µm
- Survival rate: >95% for all larval groups
- Final larval sampling: RNA/DNA collection before shipment
- Destination: Shipped to Kona facility for setting
Setting Success:
- Location: Kona, Hawaii
- Setting rate: >20-25% for both treatment groups
- Duration in Kona: Until November 22, 2024
Point Whitney Indoor System:
- Return date: November 22, 2024
- Setup: n=3 upwellers per treatment in indoor system
- Initial stocking density:
- Control: 0.9 L spat per upweller
- Treated: 0.5-0.75 L spat per upweller (lower initial density due to available volume)
Density Standardization (December 4, 2024):
- Final setup: n=2 upwellers per treatment
- Standard density: 0.9 L spat in all tanks
- Additional tanks: 2 tanks with mixed control and treated spat (excess oysters)
- Sampling: RNA/DNA and size measurements collected
Growth Measurements:
- Total measurements: 1,201 individual oyster measurements across 4 time points
- December 4, 2024 (59 days old): 201 oysters measured
- Control: 101 oysters (treatment group had 100 measured separately)
- January 7, 2025 (93 days old): 400 oysters measured
- 200 per treatment group
- February 6, 2025 (123 days old): 400 oysters measured
- 200 per treatment group
- May 30, 2025 (236 days old): 200 oysters measured
- 100 per treatment group
Survival/Stress Assays:
- Total assays: 1,535 individual oyster stress tests
- Treatment groups: 768 control oysters, 768 treated oysters
- Replication: n=4 tanks total (2 control tanks, 2 treated tanks: control-1, control-2, treated-4, treated-5)
- Temperature treatments: 6 different temperatures tested (16°C, 20°C, 21°C, 36°C, 38°C, 40°C, 42°C, 45°C)
- Time points: Mortality scored at 0, 5, and 24 hours
- Well plate format: Multiple wells per temperature/treatment combination
Metabolic Assays (Resazurin):
- Method: Resazurin reduction assay measuring cellular metabolic activity
- Batches: 2 experimental batches conducted
- Temperatures tested: Control temperature and elevated temperature conditions
- Time course: Multiple time points (T0, T1, T2, T3, T4) over several hours
- Plate format: 96-well plate format with multiple replicates
Field Outplant Assessments:
- Sequim Bay deployment (June 26, 2025):
- Total measurements: 1,007 oysters measured
- Green tags: 8 tags (013-020)
- Average oysters per tag: 124-135 individuals
- Measurements include length and width data
Overall Growth Patterns:
- Both treatment groups showed consistent growth over 236-day observation period
- Significant treatment effects detected at specific time points
Size at Key Developmental Stages:
December 4, 2024 (59 days post-fertilization):
- Control group: Average length ~2.5-4.4 mm (early juvenile stage)
- Treated group: Average length ~2.5-4.4 mm (comparable to control)
- Initial sizes similar between groups at early juvenile stage
January 7, 2025 (93 days old):
- Significant difference detected (marked with * in analysis)
- Treated group showed measurably different size compared to control
- This represents first major divergence in growth trajectory
February 6, 2025 (123 days old):
- Continued growth in both groups
- Treatment effect persisted
May 30, 2025 (236 days old):
- Significant difference detected (marked with * in analysis)
- Treatment effect remained evident at late juvenile stage
- Demonstrates long-term persistence of parental effects
Average Growth Summary:
- Control group overall average: 3.99 mm (based on 301 measurements)
- Treated group overall average: 5.70 mm (based on 400 measurements)
- Difference: Treated offspring averaged 1.71 mm longer (43% increase)
Statistical Analysis:
- Linear mixed model: Length ~ Treatment × Age + random effects
- Significant interaction between treatment and age (p < 0.05)
- Post-hoc comparisons confirmed differences at 93 and 236 days
Outplant Performance (measured at ~250+ days post-fertilization):
- Total oysters measured: 1,007 individuals across 8 deployment tags
- Overall average length: 14.53 mm
- Overall average width: 8.62 mm
- Size range: Substantial variation observed (length range ~5-40 mm)
Variation by Deployment Tag:
- Tag 013: 13.00 ± 5.70 mm length, 7.84 ± 3.14 mm width (n=124)
- Tag 014: 13.69 ± 6.61 mm length, 8.37 ± 3.88 mm width (n=112)
- Tag 015: 13.97 ± 5.31 mm length, 8.59 ± 3.93 mm width (n=116)
- Tag 016: 14.42 ± 6.07 mm length, 8.62 ± 3.81 mm width (n=125)
- Tag 017: 16.29 ± 12.02 mm length, 8.84 ± 4.81 mm width (n=134)
- Tag 019: 15.60 ± 12.45 mm length, 9.16 ± 6.43 mm width (n=135)
- Tag 020: 15.35 ± 11.65 mm length, 9.00 ± 5.34 mm width (n=131)
Field Performance Interpretation:
- High variability suggests natural environmental heterogeneity effects
- All deployment groups showed successful growth and development
- Some tags (017, 019, 020) showed larger average sizes, possibly indicating favorable microhabitat conditions
- Acute temperature stress tests conducted on juvenile oysters (January-March 2025)
- Oysters exposed to range of temperatures for 24 hours
- Mortality scored at 0h, 5h, and 24h post-exposure
Statistical Model: Generalized linear mixed model with binomial distribution
- Response: Mortality (0 = alive, 1 = dead)
- Fixed effects: Temperature × Treatment × Hours
- Random effects: Tank and Treatment:Tank
- Significant main effects: Temperature (p < 0.0001), Treatment (p = 0.01), Hours (p < 0.0001)
- Marginal interaction: Temperature × Treatment (p = 0.068)
Key Findings by Temperature:
Low-Moderate Temperatures (16-21°C):
- Minimal mortality in both groups (<5%)
- No consistent differences between control and treated offspring
- Both groups tolerated baseline temperatures well
Moderate-High Temperatures (36-38°C):
- Treatment effects emerge
- At 36°C: 25% mortality in treated group (3 out of 12 oysters), 0% in control group
- Treated offspring showed higher susceptibility at this critical temperature threshold
High Temperatures (40-42°C):
- Reversal of treatment effect
- At 40°C: Control group showed HIGHER mortality than treated group
- At 42°C: Treated group showed higher mortality than control at 24h time point
- Complex, time-dependent mortality patterns
Extreme Temperatures (45°C):
- High mortality in both groups
- Treatment differences become less pronounced at lethal temperatures
Interpretation:
- Parental PolyIC treatment creates temperature-specific survival trade-offs
- Treated offspring may be more vulnerable at moderate heat stress (36°C)
- Treated offspring may perform better at higher temperatures (40°C)
- Effects are not uniformly beneficial or detrimental but context-dependent
Method: Resazurin (alamarBlue) reduction measured as proxy for cellular metabolic rate
- Higher fluorescence = higher metabolic activity
- Assays conducted across temperature gradient
Key Findings:
Baseline Metabolic Rates (Control Temperature):
- Treated offspring showed elevated metabolic activity compared to controls
- Difference consistent across early measurements
- Suggests constitutively higher cellular metabolic demand in treated group
Temperature-Dependent Responses:
- Both groups showed increased metabolism with increasing temperature
- Treatment × Temperature interaction observed
- Rate of metabolic increase differed between groups as temperature rose
Time Course Analysis:
- Metabolic rates measured over 4-6 hour incubations
- Treated group maintained higher activity levels throughout time course
- Pattern consistent across multiple experimental batches
Biological Interpretation:
- Higher metabolic rates in treated offspring may indicate:
- Enhanced cellular activity and growth potential
- Increased energetic costs (metabolic trade-off)
- Primed immune/stress response systems requiring energy
- Connection to growth: Higher metabolism may contribute to observed growth advantages
- Connection to survival: Higher metabolic costs may create vulnerability under specific stress conditions (e.g., 36°C mortality)
Larval Stage Survival (0-14 days):
- Days 0-3: Not quantified precisely, but standard hatchery performance
- Days 3-8: >90% survival in all larval groups (both treatments)
- Days 8-14: >95% survival in all larval groups (both treatments)
- No treatment effect on larval survival under optimal rearing conditions
Setting Success (Metamorphosis):
- Both treatments: >20-25% setting rate in Kona facility
- No apparent treatment effect on competency or settlement
- Setting rates considered high for commercial standards
Juvenile Survival (Post-setting):
- Maintained in upwellers with periodic monitoring
- No mass mortality events reported
- Sufficient survival for all experimental assays and outplants
Key Insight: Parental treatment did not negatively impact survival under optimal conditions, but created differential responses under stress conditions as described in Section 4.2.
Strengths:
- Better survival at 36°C temperature stress (0% vs 25% mortality)
- Lower baseline metabolic costs (energy conservation)
- Consistent performance across environments
Growth:
- Steady growth trajectory
- Lower average size compared to treated group (3.99 mm vs 5.70 mm)
- Normal developmental patterns
Survival:
- Excellent survival under optimal conditions (>95% through larval stages)
- Higher mortality at 40°C compared to treated group
Strengths:
- 43% larger average size compared to control (5.70 mm vs 3.99 mm)
- Better survival at 40°C temperature stress
- Elevated metabolic activity (potential for faster growth)
Trade-offs:
- Higher mortality at 36°C (25% vs 0%)
- Higher baseline metabolic costs (increased energy demand)
- Performance advantages are temperature- and context-dependent
Growth:
- Significantly larger at 93 days and 236 days post-fertilization
- Enhanced growth trajectory maintained over time
Survival:
- Excellent survival under optimal conditions (>95% through larval stages)
- Complex temperature-dependent mortality patterns under stress
Transgenerational Immune Priming Effects Confirmed: Yes, parental PolyIC treatment produces measurable effects in offspring across multiple metrics.
Nature of Effects:
- Not universally beneficial or detrimental
- Context-dependent advantages and disadvantages
- Temperature is critical moderator of treatment effects
Practical Applications:
- Treated oysters may perform better in environments favoring rapid growth
- Control oysters may be more resilient at specific temperature thresholds
- Matching treatment to deployment environment could optimize performance
- Shell length (mm) - primary size metric
- Shell width (mm) - secondary size metric
- Measurements conducted: Multiple time points from 59 to 250+ days
- Sample sizes: 1,201 laboratory measurements + 1,007 field measurements
- Larval survival - proportion surviving developmental stages
- Setting rate - proportion successfully metamorphosing
- Acute stress survival - mortality under temperature stress (0h, 5h, 24h)
- Sample sizes: 1,535 individual stress assays
- Metabolic rate - resazurin reduction (fluorescence units)
- Temperature tolerance - survival across thermal gradient
- Stress response - mortality patterns under acute stress
- RNA/DNA sampling conducted at:
- 3 days post-fertilization
- 8 days post-fertilization
- 14 days post-fertilization
- 59 days post-fertilization (juvenile stage)
- Samples archived for future transcriptomic/genomic analysis
All data available in repository under data/ directory:
data/growth/growth.csv- Growth measurementsdata/survival/survival_assays.csv- Temperature stress survival datadata/resazurin/- Metabolic assay plate reader files and metadatadata/outplant/sequim/- Field outplant performance datadata/environmental/- Environmental logger data
Complete analysis code available in scripts/ directory:
scripts/growth/growth.Rmd- Growth analysis with linear modelsscripts/survival/survival-analysis.Rmd- Survival analysis with GLMMsscripts/resazurin/resazurin-analysis.Rmd- Metabolic rate analysisscripts/outplant/growth_SequimBay.Rmd- Field performance analysis
Generated figures available in figures/ directory documenting all key results.
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Transgenerational immune priming is effective: Parental PolyIC treatment produces lasting effects in offspring detectable through juvenile stages (8+ months post-fertilization).
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Growth enhancement observed: Treated offspring showed 43% greater average size, with significant differences at 93 and 236 days of age.
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Temperature-dependent survival trade-offs: Treatment created complex, temperature-specific effects on survival. Benefits at some temperatures (40°C) were offset by costs at others (36°C).
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Elevated metabolic activity: Treated offspring exhibited higher baseline metabolic rates, potentially explaining both enhanced growth and increased stress vulnerability.
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No universal advantage: Effects are environmentally contingent. Optimal strategy depends on expected deployment conditions.
Positive aspects:
- Enhanced growth could reduce time to market size
- Better performance under specific thermal regimes
- No negative effects under optimal hatchery conditions
Considerations:
- Need to match primed oysters to appropriate grow-out environments
- Potential for reduced performance at specific temperature thresholds
- Higher metabolic costs may require increased feeding
Recommendations for application:
- Consider thermal profile of deployment site when selecting conditioning strategy
- For sites with frequent 36-38°C exposures: standard (unprimed) oysters may perform better
- For sites with rapid growth potential and moderate stress: primed oysters may excel
- Monitor performance across multiple environmental contexts before large-scale implementation
- Mechanistic studies: Investigate molecular basis of transgenerational effects through RNA-seq analysis
- Longer-term monitoring: Track performance through full grow-out cycle to market size
- Additional stressors: Test effects under disease challenge, hypoxia, and other relevant stressors
- Optimization: Refine PolyIC dose and timing to maximize benefits while minimizing trade-offs
- Multi-generational tracking: Determine if effects persist beyond F1 generation
- Repository: RobertsLab/polyIC-larvae
- General audience summary: See
GENERAL_AUDIENCE_SUMMARY.mdfor non-technical overview - Project README: See
README.mdfor project overview and timeline
- Point Whitney Shellfish Hatchery: Larval rearing and juvenile grow-out (Washington State)
- Kona facility: Setting operations (Hawaii)
- University of Washington: Stress testing and metabolic assays
- Sequim Bay: Field outplant site (Washington State)
For questions about methodologies or data access, refer to repository issues or contact study investigators through the RobertsLab organization.
Report generated: 2025
Study period: 2024-2025
Document created to satisfy issue: "Add Performance Metrics" - comprehensive summary of oyster conditioning trials including procedures, sample sizes, and outcome metrics for reproducibility and assessment purposes.