DOI: 10.57778/pvh5-xp09
title: Costs of induced defenses dissipate by maturity for diploid and triploid oysters

description: These data include oyster morphological characteristics of diploid and triploid oysters cultured as "single seed". Oysters were nursed with and without predator cues (caged blue crabs, controls of no cues) for one month before being raised at Auburn University's experimental farm in Grand Bay AL following standard aquaculture procedures. Subsets of oysters were assessed periodically until maturity for shell strength, shell size, shell dry weight and soft tissue dry weight using a Kistler force sensor and drying oven. Oyster somatic tissue mass, reproductive tissue mass, and gonadosomatic index were also measured at maturity and shortly prior to maturity. 
description: Oysters are phenotypically plastic, and rearing juvenile oysters, Crassostrea virginica, with predator cues causes them to grow stronger shells that increases survivorship in the field. However, induced defenses (e.g., shell hardening in oysters) are often associated with cost-benefit trade-offs, and the extent the increased shell strength persists into adulthood and alters the growth of somatic and reproductive tissues remains unknown. We raised diploid oysters (used in reef restoration) and triploid oysters (used in aquaculture) with and without predator cues for one month before placing individuals on an oyster farm to grow to market size. Oyster shell characteristics, soft tissue mass, and reproductive investment were measured periodically over one year of culture and compared across treatments. Both diploid and triploid oysters had significantly stronger and smaller shells than controls at the end of their nursery period. However, while diploid shells became 15 % stronger and 17 % smaller than controls, triploid shells became 28 % stronger and 23 % smaller. Additionally, triploid oysters exposed to predator cues returned to the size of controls faster and maintained their shell strength differences longer than diploids. Differences in soft tissue mass between treatments mirrored the patterns exhibited in shell size and weight with greater initial physiological costs and faster recovery for triploid individuals. There was no significant difference in somatic or reproductive tissue mass between induced and control oysters of the same ploidy after seven months in the field. Triploid oysters were 15–110 % larger than diploids depending on the characteristic measured at maturity. Additionally, there was a significant interaction between treatment and ploidy because induced triploids had marginally greater growth than their control counterparts while induced diploids had marginally less growth than controls. These findings demonstrate that physiological costs of oysters reacting to predators in early life stages are minimal by the time individuals reach maturity. Early exposure to predator cues is a promising tool for improving oyster survivorship in restoration and aquaculture operations, especially in regions with high predation pressure. Data were collected by Dr. Benjamin Belgrad, Dr. Lee Smee, Dr. Jessica Lunt, Mr. Carter Lin, Mrs. Christa Russell, and Ms. Randi Cannon.