Detecting introgressive hybridisation in rock partridge populations (Alectoris graeca) in Greece through Bayesian admixture analyses of multilocus genotypes

The nominal subspecies of rock partridge (Alectoris graeca graeca) is widely distributed in Greece, where populations are declining due to over-hunting and habitat changes. Captive-reared chukars (A. chukar) have been massively released throughout the country, raising fear that introgressive hybridisation might have disrupted local adaptations leading to further population declines. In this study we used mtDNA control-region sequences and Bayesian admixture analyses of multilocus genotypes determined at eight microsatellite loci, to assess the extent of introgressive hybridisation in 319 wild rock partridges collected in Greece. A neighbour-joining tree split the mtDNA haplotypes into three strongly supported clades, corresponding to rock, red-legged (A. rufa) and chukar partridges. We did not detect any case of maternal introgression. In contrast, admixture analyses of microsatellite genotypes identified from four to 28 putative hybrids (according to different assignment criteria), corresponding to 1.2-8.8% of the samples, which were widespread throughout all the country. Power and limits of admixture analyses were assessed using simulated hybrid genotypes, which revealed that a small number of markers can detect all first and second generation hybrids (F-1 and F-2), and up to 90% of the first generation backrossess. Thus, the true proportion of recently introgressed rock partridges in Greece might be ca. 20%. These findings indicate that introgressive hybridisation is widespread, suggesting that released captive-bred partridges have reproduced and hybridised in nature polluting the gene pool of wild rock partridge populations in Greece.