5.12. Morphology and genetic variation may go hand in hand

Many species are divided into subspecies based on a limited number of morphological characteristics. According to Van Wagner and Baker (1990), Merilä et al. (1997), Mundy et al. (1997), Lucchini and Randi (1998), Barrowclough et al. (1999), and Holder et al. (2000) subspecies may also be distinguished by genetic variation, but the morphological classification and genetic differentiation may not be strictly comparable (Avise et al. 1992, Ball & Avise 1992, Seutin et al. 1995, Fry & Zink 1998, Questiau et al. 1998, Bensch et al. 1999).

The grey partridge subspecies may be determined on the basis of the plumage colour, even though it may, in some cases, depend on factors like soil consistency (Potts 1986). The grey partridge subspecies can be divided into two classes based on plumage colour. More dark/rufous-brown subspecies (P. p. hispaniensis, italica, armoricana, sphagnetorum) originate from the west, and paler/greyer subspecies (P. p. lucida, canescens, robusta) from the east. The nominate P. p. perdix may be considered an intermediate form. Relatively high amount of genetic variation (80.74 %) was associated with the plumage colour variation. Morphological patterns (plumage types among subspecies) also reflected in the neighbour-joining tree and genetic divergence in the rock ptarmigan (Holder et al. 2000). The NW German samples were from the assumed distribution area of P. p. sphagnetorum and the eastern Polish from the area of P. p. lucida (Potts 1986), but the mtDNA sequences were mainly identical with the basic western haplotype (VI). Two different haplotypes with a systematic difference of one/two nucleotides from the main western type were found in the wild population in Italy, and one different haplotype with one systematic deviant nucleotide came from the Pyrenees. In the distribution areas of the French subspecies, P. p. armoricana (FR1, FR2), the basic western haplotype together with four other closely related haplotypes were found. Pairwise comparisons revealed a significant difference between all other expected subspecies except between P. p. perdix and P. p. sphagnetorum. Genetic markers other than the control region, such as nuclear microsatellites, may be needed to examine the divergence at the level of morphological subspecies.

In addition to plumage colour disparities, grey partridge subspecies may have ecological, physiological and behavioural differences as well. Some of these can be considered as adaptations to the climatic conditions of their distribution area. In Finland, grey partridges have an extremely high clutch size with up to 24 eggs (Putaala & Hissa 1998). They are also known to form large winter flocks, where covey mixing is possible (Pulliainen 1965). The ambient temperature may be well below –30 °C, strengthened by an icy wind in the open fields. To avoid the freezing effects of frost and cutting wind, birds reduce heat loss by spending nights huddled together (Pulliainen 1965, Putaala et al. 1995). Finnish grey partridges are able to maintain their body temperature in ambient temperature as low as –52 °C (Hohtola et al. 1991). Additionally, they are able to dig through the snow cover for food. An ice layer on the snow, or snow cover > 50 cm may impede feeding (Siivonen 1957, Sulkava 1964). The easternmost populations of P. p. lucida may have hard weather movements, and even migration, and the long-winged easternmost subspecies P. p. robusta is known to migrate south in autumn (Potts 1986). Grey partridges from eastern Bulgaria, Finland, and Greece represented the eastern mtDNA type, which also seems to be adapted to geographically more extreme areas. The liver samples were from a study population in Greece, which inhabits a mountainous area about 1 km asl (B. Alexiou, pers. comm.).