5.9. A deep divergence between the two lineages of the grey partridge

DNA technology provides with suitable markers to study the genetic structure of populations, species, and communities (Hewitt 2000). MtDNA was chosen because of several reasons: it is considered to be a marker that is evolving fast (Brown et al. 1979), and not recombining (Hayashi et al. 1985). It is also considered a neutral marker, which means that environmental factors do not affect it (Brown et al. 1979, but see Ballard & Kreitman 1995, Fry 1999). Further, it is only matrilinearly inherited (Wilson et al. 1985). These properties make mtDNA widely used in genetic studies on populations and subspecies (Shields & Wilson 1987b, Avise & Nelson 1989, Lucchini & Randi 1988, Tarr & Fleischer 1993, Kvist et al. 1998, 1999a,b, Uimaniemi et al. 2000), and also on phylogenetic relationships between species (Edwards & Wilson 1990, Crowe et al. 1992, Kvist et al. 1996, Randi 1996, Marshall & Baker 1997, Kimball et al. 1999, Gutiérrez et al. 2000, Randi et al. 1998, 2000, Ruokonen et al. 2000, Young et al. 2000). The control region, which is the most variable region of the avian mtDNA, is divided into three domains (Baker & Marshall 1997). Intraspecific variation in birds is commonly found in the domains I and III, the central domain (II) being most conserved (e.g. Wenink et al. 1993, 1994, Marshall & Baker 1997, Lucchini & Randi 1998, Uimaniemi et al. 2000, Young et al. 2000).

The mean nucleotide composition in the CR1 of the grey partridge was similar to several other bird species (Lucchini & Randi 1998, Holder et al. 2000, Uimaniemi et al. 2000). The amount of divergence (3.6 %) found in the CR1 between the basic eastern and western mtDNA lineages was of the same magnitude as the divergence between Sicilian and Alpine haplotypes of the rock partridge (Lucchini & Randi 1998). The Palaearctic lesser white-fronted goose also exhibited two main lineages, eastern and western, with a mean divergence of 2.0 % (Ruokonen et al., manuscript).

In this study substantial variation was found in the nucleotide diversity between populations. Low diversity areas have suffered large-scale environmental changes, and have been under severe hunting pressure. Of these, the Greek population has been bottlenecked during the last century (B. Alexiou, pers. comm.). The NW German population did not contain any variation at all in the CR1, which may result from a local population crash following the hard winters of 1978/79 and 1979/80, and from the continuous decrease in population size since 1991 (E. Strauss, pers. comm.). Close inbreeding may be expressed in the loss of genetic variation (O’Brien 1994b). In grey partridge, however, close inbreeding does not occur, because of differential dispersal of sexes, and the female mate choice from other than her own winter covey (Potts 1986). Extremely high nucleotide diversities together with high haplotype diversities, found in the Oulu region, Ireland and Bulgaria, can be explained by the finding of both mtDNA lineages in these populations.