|Nutritional and genetic adaptation of galliform birds: implications for hand-rearing and restocking|
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When examining the geological time chart, the most interesting period concerning the grey partridge is the Quaternary period, which is divided into two epochs, namely the Pleistocene (1.7–0.01 Myr BP) and the Holocene (0.01 Myr BP – present). The northern hemisphere ice sheets have varied in size for at least the last 2.5 Myr. About 100 000 year cycles of glacial-interglacial periods have forced species to evolve as a response to changes in climate and biosphere (Webb & Bartlein 1992, Hewitt 1999), with series of bottlenecks and expansions in population size and range (Hewitt 1996, 1999, 2000). The last European, so-called Weichselian, glaciation started ca. 120 000 years ago. It lasted about 100 000 years, having its coldest period ca. 18 000–20 000 years ago. At that time ice covered the entire northern Europe southwards to the Pyrenees, the Alps, and the Balkans (Webb & Bartlein 1992). Glaciations caused a series of bottlenecks that species had to survive (Hewitt 1996, 1999, 2000), but even during the coldest periods, some southern parts of Europe and the easternmost parts of the continent provided several plant and animal species with suitable habitats to survive (Taberlet et al. 1998, Hewitt 2000). According to Mourer-Chauviré (1993) a primitive form of the grey partridge, Perdix palaeoperdix, was a characteristic species from the Lower to Middle Pleistocene in western Europe. Perdix perdix has inhabited Europe from the Late Pleistocene on (Tyrberg 1998).
After the last glaciation the northern regions of Europe were recolonised from the Iberic and the Balkanic refuges, but the Alpine barrier isolated the Italian lineages (Taberlet et al. 1998, Hewitt 1999, 2000, see also Bilton et al. 1998). In the grey partridge the western mtDNA lineage was found primarily in England, France, Germany, Austria, and Poland. The possible refuge areas for this lineage were considered to be the Iberic and the Italic refuges. The two Italian haplotypes found in the wild birds may be remains of this Italic refuge. In contrast to this, at least the great bustard Otis tarda populations were reported to follow the biogeographic model of Bilton et al. (1998), with the Mediterranean Peninsula as a geographical isolate, and a non-Iberian source of European mainland populations (Pitra et al. 2000).
In the western populations the nucleotide diversity values showed a south-north oriented cline from the Pyrenees to Poland. This may follow the grey partridge postglacial recolonisation route from the Iberian refuge to Central Europe (Hewitt 1996, 2000, Merilä et al. 1996, 1997). Non-continental populations (England and Ireland) deviated from this cline. These populations included some unique haplotypes, which may be remainders of historical introductions on the Isles (Westerskov 1958). Among the eastern populations no clinal variation was detected. The Balkanic and the easternmost (Caucasian) refuges (Taberlet et al. 1998, Hewitt 2000) may be considered as the two potential refuge areas for the eastern lineage. This is supported by the finding of the eastern lineage mtDNA from Kazakhstan and Russia in addition to Bulgarian, Finnish and Greek samples. However, more Russian samples would be needed to draw final conclusions about this recolonisation route.
The 2 %/Myr mutation rate gave a divergence time of 1.1 Myr (i.e. in early Pleistocene) for the two lineages. This is, in general, earlier than the average phylogenetic subdivision time for several avian species (Shields & Wilson 1987a, Wenink et al. 1993, Lucchini & Randi 1998, Kvist et al. 1999b, Uimaniemi et al. 2000). The 20.8 %/Myr mutation rate gave a divergence time of 173 000 years (i.e. in late Pleistocene), which in turn refers to a clearly later subdivision (VI). Because of this ambiguity the use of divergence time estimates is questionable, and may require a calibration of the molecular clock for each genus separately (Ruokonen & Kvist 2001, manuscript).