Are bivalves susceptible to domestication selection? Using starvation tolerance to test for potential trait changes in eastern oyster larvae

Abstract

20Conservation efforts are increasingly being challenged by a rapidly changing environment, 21 and for some aquatic species the use of captive rearing or selective breeding is an attractive option. 22 However, captivity itself can impose unintended artificial selection known as domestication 23 selection (adaptation to culture conditions). For most marine species, it is not known to what 24 degree domestication selection affects traits related to fitness in the wild. To test for domestication 25 selection in a marine bivalve, we focused on a fitness-related trait (larval starvation resistance) that 26 could be altered under artificial selection. Using larvae produced from a wild population of 27 Crassostrea virginica and a selectively bred, disease-resistant line we measured growth and 28 survival during starvation versus standard algal diet (control) conditions. Larvae from both 29 lineages showed a remarkable resilience to food limitation, possibly mediated by an ability to 30 uptake and utilize dissolved organic matter for somatic maintenance. Water chemistry analysis 31 showed dissolved organic carbon in filtered tank water to be at concentrations similar to natural 32 river water. We observed that survival in larvae produced from the aquaculture line was 33 significantly lower compared to larvae produced from wild broodstock (8 ± 3% and 21 ± 2%, 34 respectively) near the end of a 10-day period with no food (phytoplankton). All larval cohorts had 35 arrested growth during the starvation period and took at least two days to recover once food was 36 reintroduced before resuming growth. Phenotypic differences between the wild and aquaculture 37 lines suggest potential differences in the capacity to sustain extended food limitation, but this work 38 requires replication with multiple selection lines and wild populations to make more general 39 inferences about domestication selection. With this contribution we explore the potential for 40 domestication selection in bivalves, discuss the physiological and fitness implications of reduced 41 starvation tolerance, and aim to inspire further research on the topic. 43 oyster, physiology 44 4 64aquatic organims other than salmon, or its fitness consequences in the wild when it occurs. Here, 65 we hypothesize that larval starvation tolerance is a likely trait subject to domestication selection 66 and experimentally measure and compare this trait in wild and selected-strain oysters. 67Natural populations of the eastern oyster Crassostrea virginica are only a fraction of 68 historic densities, and are deemed functionally extinct in some regions of the northeastern U.S. 69[12]. The great ecological and economic value of oysters has prompted aggressive population 70 supplementation (= "restoration") programs in parts of its native range [13,14] and millions of U.S. 71 dollars have been spent to revive this once thriving ecosystem engineer [15]. Oyster restoration 72 approaches often include the hatchery production and planting of spat (juvenile oysters) on shell...