Ecological and evolutionary concerns in freshwater bivalve relocation programs

Relocation of native freshwater bivalves has been used as a conservation tool primarily for restorative or supplemental reasons and to remove populations from the immediate impacts of construction projects. Though the presence of indigenous bivalves was most often used as an indicator of suitable habitat to receive relocated animals, subtle ecological and evolutionary differences between communities may have preculuded successful relocation. We discuss the importance of maintaining genetic diversity within and among populations, the potential for spread of disease causing pathogens and parasites, and suggest approaches that could lead to improved relocation success, with the ultimate goal of maintaining the evolutionary lineages of freshwater bivalve species. Conservation efforts should strive to ensure that genetic variation is preserved to maintain the potential for future evolutionary change, and intervene as little as possible when managing the genomes of threatened species. However, when relocations are deemed necessary, every precaution should be taken to minimize the effects of gene drift and inbreeding depression by providing sufficiently large effective population sizes. Those involved in relocations should also exercise vigilance to avoid the pitfalls of outbreeding depression resulting from mixing divergent evolutionary lineages and the potentially catastrophic consequences of introduced pathogens. In addition, relocation attempts to supplement population size and maximize genetic diversity of historically small populations may lead to the loss of critical adaptive features including the relationship established with the parasitized host(s). Management efforts that focus on the protection of existing populations, and the discovery and protection of new populations of threatened taxa, may represent a more realistic conservation strategy than the creation of populations of unknown ecological and evolutionary potential.