The eastern oyster, Crassostrea virginica, supplies major markets throughout the United States. In recent decades, t he species has been declining throughout most of its range including in the Gulf of Mexico, the largest producing region in the US. The SALT consortium is developing a breeding program to support commercial off-bottom harvests in the Gulf of Mexico with eastern oyster bred for improved performance in different salinity environments. The program is evaluating the effectiveness of a family selection approach where families are mixed at fertilization and reared communally until phenotyping.
In this work, 102 males and 102 females collected from 17 natural reefs from across the northern Gulf of Mexico between San Antonio Bay (Texas), and Cedar Key (Florida) were bred according to 51 non-overlapping 2 males x 2 females mini-factorial crosses to produce 204 families. Crosses were produced by strip spawning and in vitro fertilization between August 31 and September 3, 2020. F amilies produced on the same day were pooled after fertilization for larval culture. The protocol for setting larvae involved harvesting larval tanks daily during 4 days to capture pediveliger larvae as soon as an external foot was observed. Samples of the daily harvests of each setting group (16 spawning date x setting day combinations, 1,600 samples totals) were taken on October 10 (38-41 days post fertilization, dpf) for genetic analysis. All 16 fractions were then pooled for further nursery culture and another 1,600 spats were randomly sampled on December 7 (96-99 dpf) and their height, length, and width were recorded. Parents and all offspring were genotyped at 192 Single Nucleotide Polymorphism markers and pedigrees were reconstructed using a likelihood ratio approach.
Parentage analysis revealed that 96 sires and 80 dams contributed to the sampled offspring. Contributions of individual sires ranged from 0.07% to 5.93% while contributions of individual dams were from 0.07% to 7.00%. The estimate of heritability of (log transformed) height using a simple animal additive model was 0.26 ± 0.04. Length and width were strongly correlated to height (phenotypic and genetic correlations b etween height and length were rp = 0.89 and rg = 0.92 ± 0.02 respectively; correlations between height and wid th were rp = 0.77 and rg = 0.89 ± 0.04). Estimates of heritability of length and width analyzed with height as a covariat e were 0.36 ± 0.07 and 0.21 ± 0.04 , suggesting occurrence of genetic variation for both traits.