The impact of hybridisation on the population structure of the Saker Falcon (Falco cherrug): genetic comparison between historical and recent populations

The main aim of the project is a genetic analysis of both recent and historical populations of the Saker Falcon (Falco cherrug) to assess the impact of hybridisation on the endangered wild populations. The historical populations of F. cherrug will be represented by individuals from museum collections. The drastic decline of European and North American falcon populations in the second half of the 20th century was caused by habitat fragmentation and the widespread use of DDT and other insecticides. New methods of artificial insemination initially developed to produce falcons for re-introduction programs soon were also applied to breed falcons in captivity for falconry, even allowing inter-crosses between different taxa of large falcons. As a consequence, the wild populations of F. cherrug are threatened through escaped hybrid falcons bred in captivity. The mere presence of escaped hybrids poses a nuisance to native falcons by disturbance at the nest, thus reducing their breeding success. Even more serious is the fact that interbreeding between escaped falcon hybrids and individuals from wild populations generates a continuous source of interspecific gene flow. The main part of the present project will be a genetic analysis based on microsatellite loci of present day F. cherrug populations and a comparison with the status before 1970 (prior to the introduction of artificial insemination techniques). Our aim is to find out whether the population decline in the 1960ies has caused a loss of genetic variability, and if introgression from other species as a consequence of intensive artificial hybridisation in falconry has taken place. Since individuals from different (remote) regions and related taxa are used for hybridisation, the material to be investigated must comprise a broader taxonomic as well as geographic range. Besides F. cherrug, the Gyrfalcon (F. rusticolus), the Lanner Falcon (F. biarmicus), the Lagger Falcon (F. jugger), the Prairie Falcon (F. mexicanus), and the Peregrine (F. peregrinus) will be investigated. Phylogenetic relationships among these species have not been clearly resolved so far. For the interpretation of the results it will be necessary to establish a molecular systematics of the taxa involved. Highly variable sections of the mt genome as well as nuclear introns will be used as molecular markers for this part of the project.

The project focused on hierofalcons, a group of large falcons comprising F. cherrug (saker falcon), Falco biarmicus (lanner falcon), Falco jugger (laggar falcon), Falco rusticolus (gyr falcon), and (according to some authors) Falco mexicanus (prairie falcon). The project comprised two major topics: (1) the phylogenetic and phylogeographic history of Hierofalcons and (2) the population genetics especially of F. cherrug with focus on its Central European distribution range. In this first comprehensive study of hierofalcons we used samples covering the whole distribution ranges of the four species including all described subspecies. In addition, samples of F. mexicanus were analyzed to determine its phylogenetic relationships. Different genetic markers (microsatellites as well as mitochondrial DNA sequences) were applied and the genetic patterns were compared to test hypotheses on population history and the possible role of Pleistocene climatic conditions. Another issue concerned hybrid falcons that have been produced artificially for falconry since the 1970ties. The question was whether escaped falcons affected the genetic composition of wild F. cherrug populations. Therefore, besides samples from contemporary populations of F. cherrug, historic samples from museum specimens were analyzed. The results of the DNA sequence analysis indicate that hierofalcons are very closely related. None of the four species is clearly differentiated or represents a monophyletic group in the genetic trees. Concerning F. mexicanus the sequence data shows that this species is more closely related to the peregrine (Falco peregrinus) than to the hierofalcons. Also in the microsatellite analysis no clear differentiation of hierofalcons was found and most of the variation was observed within species. The close relationships among hierofalcons suggest that the radiation of these species occurred rather recently (during or after the last glaciation). Based on our results we propose a scenario involving ancient interspecific hybridization and postulate an "Out of Africa" hypothesis for the evolution of the species group. The high intraspecific genetic diversity of F. biarmicus (which is widely distributed in Africa) implies an African origin of hierofalcons. The other species are supposed to be descendants of several waves of expansions into Eurasia and South Asia. Warm periods during the Pleistocene allowed a rapid colonization of vast ranges in the Palearctic accompanied by morphological and behavioural adaptation to new habitats. During cold phases suitable habitats and consequently the populations shrunk as survival was possible only in smaller favourable regions. In the course of such area shifts formerly isolated populations could have come into secondary contact facilitating hybridization. This could explain why the four species do not represent clearly differentiated genetic groups. Besides the presumed ancient hybridization events, our data indicate that recent hybridization occurs too. For some cases natural hybridization appears likely. Other cases of introgression (into Central European populations of F. cherrug and Scandinavian F. rusticolus populations) seem to be human induced: Gene flow from escaped falcons seems to be the most plausible explanation. Our results provide insights into the intraspecific genetic diversity of F. cherrug and contribute to the understanding of potential problems with uncontrolled introgression into wild populations.