Genetic divergence between willow grouse (Lagopus lagopus L.) and rock ptarmigan (Lagopus mutus L.) and the genetic structure of Scandinavian grouse populations

Abstract

Allozyme variability was studied at 23 loci in 424 willow grouse (Lagopus lagopus L.) and 46 rock ptarmigan (Lagopus mutus L.), from eight and two Scandinavian localities, respectively. Average heterozygosity (H) and the proportion of polymorphic loci (P) for both the willow grouse (H=7.6%, P=24%) and the rock ptarmigan (H=3.9%, P=15%) are close to those reported for other avian species. The two species share alleles at all loci studied, and the genetic distance (D: Nei 1972. Am. Nat. 106: 283–292) between species (D=0.046) is very small, supporting the general concept of a small amount of divergence between avian species. In contrast, the amount of differentiation between populations within the species (willow grouse D-0.0035, rock ptarmigan D=0.0009) is of the same magnitude as that observed between non-avian vertebrate species in the same geographical area (deglaciated within the last 10,000 years). Thus, there are no indications that bird populations of these two species differentiate at a much lower rare than do other vertebrate populations. Significant allele frequency heterogeneity was found in willow grouse between island and mainland populations as well as among closely located island populations. Island populations further showed a significant reduction in the amount of genetic variability. the genetic heterogeneity among populations may be related to climatic differences between mainland and island areas resulting in a shift to a more sedentary breeding behavior of island populations. However, the results did not indicate a general genetic subdivision between island and mainland populations, as has been suggested on the basis of the morphological differentiation between populations.