Introductions over introductions: the genomic adulteration of an early genetically valuable alien species in the United Kingdom.
Invasive alien species are a major cause of biodiversity loss. Nevertheless, non-native species can also contribute to conservation objectives. In 1673, the red-legged partridge (Alectoris rufa), a galliform native to southwest Europe, was introduced from France (A. r. rufa) into the UK for hunting purposes. Nowadays, hunters constantly supplement natural populations of A. rufa in its native range with stocks of captive-bred individuals. Such birds are usually genetically unscreened, and human-mediated hybridization with the exotic chukar (Alectoris chukar) has undermined genomic integrity of the species. Alectoris rufa in the UK has never been genetically investigated, and birds from East Anglian estates with no modern history of supplementation offer a potential genomic backup for the highly polluted native-range A. r. rufa. We genotyped modern and ancient (1824-1934) birds at the mitochondrial DNA (mtDNA) level to determine present and past kinship between East Anglian and native-range A. rufa. We used Short Tandem Repeats (STR) and Random Amplified Polymorphic DNA (RAPD) markers to identify A. rufa × A. chukar hybrids. The kinship of East Anglian birds with A. r. rufa was confirmed. No A. chukar introgression was found in ancient East Anglian A. rufa. Among modern partridges, we found birds with A. chukar mtDNA, and both STRs and RAPDs disclosed many A. rufa × A. chukar hybrids. While the genetic analysis pointed to the increase of diversity and decline of disparity over time within and among A. rufa populations, respectively, the conservation value of the resource historically introduced to the UK proved to have been quashed by three decades of recent releases of A. chukar and its A. rufa hybrids.