Aquaculture of the eastern oyster occurs across a broad range of environmental gradients along the Atlantic and Gulf Coasts of the United States. Multiple breeding programs have been developed in pursuit of developing stocks with improved growth and yield across these variable conditions. However, field trials assessing the genetic lines developed in these programs typically measure size at discrete time points on oysters haphazardly sampled from replicate grow-out cages. Estimates of growth are then derived from the average size measured at each time point for each cage, masking the tremendous variability in the growth of individuals over time. Currently, it’s common practice for farmers to grade size classes and carry out large culling events on “slow growing” individuals. A better understanding of the within- and between-individual variation in oysters, and whether it results from genetic variation, environmental differences, or both, will not only reduce time and labor costs associated with grading and culling events, but contribute to the continued improvement of breeding programs.
We monitored individual growth of oysters from a single genetic cohort cultured in two Maine estuaries. Oysters were tagged in the spring (May) and shell height and whole weight was taken bi-weekly throughout one growing season (through October). We combined these measurements with monitoring of water quality parameters including chlorophyll-a concentration, temperature, turbidity, and salinity to assess individual phenotypic response. Present evidence of some growth phenotypes includes “fast” initial growers, and “slow” more consistent growers. By statistically identifying these growth phenotypes, we hope to better understand the variability in their response to changing environments.
Determining the underlying causes, mechanisms, and consequences of the capacity of a genotype to produce different phenotypes in response to environmental variation (phenotypic plasticity) and how this will contribute to the performance of stocks of the eastern oyster is crucial for the continued improvement of breeding programs. Additionally, by facilitating early identification of fast and slow growers, farmers can reduce time and labor costs associated with grading and culling events. Here, we explore several approaches to modeling individual growth to partition out phenotypic variation both within- and between-individuals and define fast and slow growth phenotypes.