Concern over hybridization risks should not preclude conservation interventions

Abstract

Conservation interventions such as assisted migration and genetic alterations are controversial in part because, through unintended hybridization events, they may imperil native species. Threats could stem from hybrid offspring having altered fitness or from genetic swamping due to extensive introgression of non-native genes. Over the last 40 years, papers discussing hybridization increasingly use value-laden terminology (e.g., “genetic contamination”). Such terms presume that any amount of hybridization equates to harm, but this perspective is at odds with modern evolutionary theory's recognition of hybridization as a creative force that can accelerate evolution or spur adaptive breakthroughs. To assess the evidence undergirding perceptions of hybridization threats, we examined the IUCN's Global Invasive Species Database (GISD). Of 870 invasive species, the GISD identified 35 as potentially threatening endemic taxa via hybridization. For each of these 35 species, we assessed the quality of data that the GISD cited pertaining to hybridization. Direct evidence for hybridization was cited for only 16 species, and there was neither direct nor indirect evidence demonstrating reduced fitness of hybrid offspring for 18 species. In our era of rapid environmental change, it is time to examine hybridization case-by-case and not to presume that hybridization always presents a threat to biodiversity, but rather, to consider it as a potential pathway to species survival.