Paradox lost: genetic diversity and the success of aquatic invasions

There is mounting evidence that reduced genetic diversity in invasive populations is not as commonplace as expected. Recent studies indicate that high propagule vectors, such as ballast water and shellfish transplantations, and multiple introductions contribute to the elimination of founder effects in the majority of successful aquatic invasions. Multiple introductions, in particular, can promote range expansion of introduced populations through both genetic and demographic mechanisms. Closely related to vectors and corridors of introduction, propagule pressure can play an important role in determining the genetic outcome of introduction events. Even low-diversity introductions have numerous means of avoiding the negative impact of diversity loss. The interaction of high propagule vectors and multiple introductions reveal important patterns associated with invasion success and deserve closer scrutiny. There is mounting evidence that reduced genetic diversity in invasive populations is not as commonplace as expected. Recent studies indicate that high propagule vectors, such as ballast water and shellfish transplantations, and multiple introductions contribute to the elimination of founder effects in the majority of successful aquatic invasions. Multiple introductions, in particular, can promote range expansion of introduced populations through both genetic and demographic mechanisms. Closely related to vectors and corridors of introduction, propagule pressure can play an important role in determining the genetic outcome of introduction events. Even low-diversity introductions have numerous means of avoiding the negative impact of diversity loss. The interaction of high propagule vectors and multiple introductions reveal important patterns associated with invasion success and deserve closer scrutiny. The occurrence, in the same population, of individuals from multiple genetically distinct sources. These sources are typically geographically separated native populations of a species, though they can also be temporally distinct samples from the same geographic population or even populations of closely related species. Note that observation of admixture in this sense does not require direct observation of intermediate genotypes, although the generation of such genotypes is the expectation for admixture between populations of the same species. Severe reduction in the demographic size of a population. The geographic route along which introduced propagules are conveyed. Invasion of a species or non-native genotype that goes undetected, often because of morphological similarity with a native or previous invasion; typically resolved by molecular techniques. Loss of genetic diversity in a population established by a small number of individuals. Transfer of genetic material from one population to another, also referred to as migration. A dilemma in invasion biology: how do newly founded populations overcome low genetic diversity and expected low evolutionary potential, typically associated with extinction risk, to become established outside of their native range? The breeding of individuals from genetically distinct populations (either within or between species), resulting in genotypes with novel combinations of alleles. The reduction of fitness caused by mating between relatives. The establishment of a non-indigenous species An introduced species that has become established outside of its native range and is likely to cause ecological or economic harm. The time between the introduction and establishment of a non-indigenous species. The reduction of fitness of hybrids. A condition in which a heterozygote has higher relative fitness than either homozygote, also known as heterozygote advantage. A measure of the number of viable individual non-native organisms introduced to a recipient environment. Equal to the product of inoculum size (the number of propagules released with a single introduction event) and number of introduction events. The physical conveyance responsible for moving introduced propagules from source to recipient environments.