The Two Faces of Introgression in Conservation Biology

Introgression is an important biological process that has a major impact on the evolutionary potential of species. Admixed offspring from parental individuals of different species, or in other word evolutionarily distinct gene‐pools, may enable the exchange of genomic information between these two species without leading to genetic swamping. Here, we argue that conservation biologists must take into account both the adaptive and maladaptive consequences resulting from introgression by evaluating the biological and environmental context: past, present and future. Our argument is based on recent insights confirming species boundaries to be permeable, with scenarios suggesting increased permeability in the future. As a consequence, closely related species may form syngameons that enhance the evolutionary potential and resilience to environmental change by exchanging genetic information. Here, we focus on three aspects of introgression in applied conservation. Firstly, introgression between species in their native habitats may be considered as a natural strategy of these species to enhance their resilience to environmental change. Secondly, introgression between species, particularly native and nonnative, may rarely lead to genetic swamping but need to be monitored carefully to avoid the loss of the species identity of native threatened species. Thirdly, introgression between threatened and non‐threatened species need to be considered as unique opportunities to recover alleles that are already lost in the gene pool of highly threatened species experiencing the attraction of the extinction vortex, especially where admixed individuals already exist naturally. In summary, we are calling for the replacement of a static Linnean species concept by a species concept that considers species a dynamic gene pools with permeable boundaries enabling the exchange of genetic information, enhancing adaptive capacity without losing species integrity.