Genetic Aspects of Restoring Olympia Oysters and Other Native Bivalves: Balancing the Need for Action, Good Intentions, and the Risks of Making Things Worse

The ecology, evolution, impacts and management of host–parasite interactions of marine molluscs

“…Selective breeding programs, often aimed at accelerating growth or enhancing resistance to particular diseases, can result in reduced genetic variation among cultivated as compared to wild molluscan populations and in some instances may result in inbreeding depression (e.g., Bower, 1992;Evans et al, 2004;NRC, 2004a;Gaffney, 2006;Hare et al, 2006;Camara and Vadopalas, 2009;Hoffman et al, 2009;Hedgecock, 2011;Rohfritsch et al, 2013; in press also in this volume). This may render cultivated populations more susceptible to diseases for which they have not been selectively bred for resistance against.…”

“…As more molluscs are cultured across the globe, potentially without good genetic practices (inbreeding, small brood stock numbers), populations of wild molluscs, especially those that have significantly depressed population sizes, such as Ostrea lurida and O. edulis, may be affected by interbreeding with captively-bred populations that may lack local adaptations and genetic variability to respond to existing, let alone novel introduced diseases and parasites (discussed related Sections here, and in Gaffney, 2006;Camara and Vadopalas, 2009;Hedgecock, 2011; in press this volume).…”

“…As selectively bred and non-native molluscs have been increasingly adopted by aquaculture industries, there has also been interest in applying them to restoration projects (e.g., Allen et al, 2003;Arnold et al, 2005;Crane et al, 2013). The application of selective breeding and non-native species to aquaculture and restoration has been highly controversial, due to the mixed success of such approaches and their potential to produce major changes to aquatic food webs (e.g., Carlsson et al, 2006;Gaffney, 2006;Hare et al, 2006;Camara and Vadopalas, 2009). In this section, we review disease management strategies and, in keeping with the ecological focus of this review paper, discuss the direct and indirect ecological effects of these.…”

“…As disease epidemics have threatened the viability of molluscan aquaculture industries, they have increasingly turned to cultivation of animals selectively bred for disease resistance and rapid growth (e.g., Ragone Calvo et al, 2003;Dove et al, 2013;Degremont et al, in press this volume). Selective breeding programs in many instances take advantage of natural variation in the susceptibility of individuals to disease, and the heritability of this trait (discussed in Elston and Ford, 2011;Hedgecock, 2011;Camara and Vadopalas, 2009).…”

“…This may result in inbreeding depression, which lowers survivorship and fitness of the inbred individuals (e.g., Bierne et al, 1998;Launey and Hedgecock, 2001) and may diminish the genetic 'health' of wild populations if the selectively bred and wild oyster populations interbreed (Wang and Ryman, 2001). Further although the selectively bred line(s) may exhibit superior performance when exposed to a particular parasite for which resistance has been selectively bred, genotype by environment interactions may result in this line being sub-optimal under alternative 'environmental' or 'biological' conditions (e.g., Mallet and Haley, 1983;Rawson and Hilbish, 1991;Camara and Vadopalas, 2009;Hedgecock, 2011;Degremont et al, in press this volume). For example, Sydney rock oysters selectively bred for disease resistance appear to be less resilient to enhanced pCO 2 than wild oysters (Thompson et al, 2015).…”