Macrogeographic Patterns of Morphometric and Genetic Variation in the Sage Sparrow Complex

We examined morphometric and genetic variation in 22 populations of three subspecies of the Sage Sparrow (Amphispiza belli belli, A. b. canescens, and A. b. nevadensis). The sum of squares simultaneous test procedure (SS-STP) demonstrated clear patterns of geographic change in six linear characters and in cube root of body mass. A UPGMA dendrogram and ordination plots using principal component analysis (PCA) and multidimensional scaling (MDS) defined two major groups of populations based on morphometric criteria: (I) those in the Coast Ranges and west slope of the Sierra Nevada (A. b. belli) plus those in the southern San Joaquin Valley and northern Mojave Desert (A. b. canescens), and (II) those in the Great Basin (A. b. nevadensis). Seventeen of 41 genetic loci scored (41.5%) were polymorphic. Genetic data identified the same two groups of populations delimited on morphometric grounds. Populations in group I were significantly less heterozygous than those of group II. Nei's genetic distances among populations of one taxon ranged from D̄ = 0.0007 (in A. b. nevadensis) to D̄ = 0.0015 (in A. b. canescens) and D̄ = 0.0019 (in A. b. belli). Intertaxon Nei's D̄ ranged from 0.0027 (A. b. belli vs. A. b. canescens) to 0.0056 (A. b. canescens vs. A. b. nevadensis) and 0.0077 (A. b. belli vs. A. b. nevadensis). An overall mean Fst value of 0.112 points to pronounced genetic structuring of the 22 populations. Sedentary populations are less panmictic than migratory populations. Gene flow is estimated at 2-4 immigrants per generation. Although intergradation is unknown, A. b. belli and A. b. canescens are genetically closely related. In contrast, A. b. nevadensis and A. b. canescens differ strongly on both morphologic and genetic grounds.