Rapid spread of invasive genes into a threatened native species

Abstract

When introduced or cultivated plants or animals hybridize with their native relatives, the spread of invasive genes into native populations might have biological, aesthetic, and legal implications. Models suggest that the rate of displacement of native by invasive alleles can be rapid and inevitable if they are favored by natural selection. We document the spread of a few introduced genes 90 km into a threatened native species (the California Tiger Salamander) in 60 years. Meanwhile, a majority of genetic markers (65 of 68) show little evidence of spread beyond the region where introductions occurred. Using computer simulations, we found that such a pattern is unlikely to emerge by chance among selectively neutral markers. Therefore, our results imply that natural selection has favored both the movement and fixation of these exceptional invasive alleles. The legal status of introgressed populations (native populations that are slightly genetically modified) is unresolved by the US Endangered Species Act. Our results illustrate that genetic and ecological factors need to be carefully weighed when considering different criteria for protection, because different rules could result in dramatically different geographic areas and numbers of individuals being protected.conservation | California Tiger Salamander | genetics | hybridization | Ambystoma

Toward a genome-wide approach for detecting hybrids: informative SNPs to detect introgression between domestic cats and European wildcats (Felis silvestris)

“…Even so, when two populations are subjected to different selective pressures, some levels of selection are expected to cause divergence in different parts of their genomes. Native California tiger salamanders (Ambystoma californiense) provide an excellent example of the benefit of SNPs in uncovering patterns of admixture (Fitzpatrick et al, 2010). These authors were able to determine that only 3 out of 68 studied markers spread rapidly into native genomes, whereas the other 65 showed little evidence of introgression beyond the region where introductions of non-native barred tiger salamanders (A. tigrinum mavortium) occur.…”

“…In some areas, where taxa boundaries are probably maintained and wildcat populations less fragmented, introgression may be minimal (for example, Pierpaoli et al, 2003;Kitchener et al, 2005;Lecis et al, 2006). However, in particular historical or ecological conditions, widespread admixture might produce hybrid swarms, likely leading to the genetic extinction of the wildcat parental populations (Allendorf et al, 2001;Beaumont et al, 2001;Brumfield, 2010;Fitzpatrick et al, 2010). European wildcats have apparently experienced both extremes.…”

The origin of tiger salamander (Ambystoma tigrinum) populations in California, Oregon, and Nevada: introductions or relicts?

“…Using nuclear SNP markers we have recently identified the first known hybrid individual between these two taxa in Santa Barbara County, CA, approximately 15 km from the sampled Lompoc Valley populations (JR Johnson and HB Shaffer, unpublished data). The spread of non-indigenous genes through native populations of A. californiense in the Salinas Valley has occurred broadly and rapidly (Fitzpatrick and Shaffer 2007;Fitzpatrick et al 2009) and raises many conservation concerns regarding the management and protection of the A. californiense in the face of hybridization (Ryan et al 2009;Fitzpatrick et al 2010). Given that contact and hybridization have just occurred in the Santa Barbara/Lompoc region, it is critical to take measures to eliminate these populations and prevent the spread of individuals/haplotypes out of the Lompoc Valley into the range of the endangered Santa Barbara distinct population segment.…”

“…Hybridization is an often-overlooked consequence of biological invasions because it occurs more rarely and is more difficult to detect than the effects of competition and predation. But the effects of genetic invasions can be great (Allendorf et al 2001), and there are now several examples of the negative effects of hybridization with non-indigenous amphibian taxa (Arntzen and Thorpe 1999;Storfer et al 2004;Holsbeek et al 2008;Ryan et al 2009;Fitzpatrick et al 2010).…”

Is Australia ready for assisted colonization? Policy changes required to facilitate translocations under climate change.

“…The legal status of hybrids, for instance, is not always clear. Under current Australian or United States legislation hybrids of threatened species may not have the same legal protection as the pure-bred entities (Walker et al 2009;Garnett et al in press), yet sometimes a small number of genes of introduced organisms can move far in advance of detectable phenotypic change (Fitzpatrick et al 2010). In this case, the legal status of introgressed populations (natural populations with novel genes from a related taxon) of a threatened species is unresolved.…”