MITOCHONDRIAL-DNA HYPERDIVERSITY AND VOCAL DIALECTS IN A SUBSPECIES TRANSITION OF THE RUFOUS-COLLARED SPARROW

The Rufous-collared Sparrow, Zonotrichia capensis, is widely distribut ed in neotropical America and shows extensive variation in its learned song. In northwestern Argentina it exhibits song dialects which map c losely onto the distribution of natural vegetation assemblages. To dat e, there is no evidence of a correlation between genetic (allozyme) va riation and dialects. However, recent genetic structuring produced thr ough philopatry and assortative mating by dialect is difficult to demo nstrate statistically with such protein-encoding nuclear genes. Theref ore, we assayed variation in more rapidly evolving mitochondrial DNA a long a 50 km transect, which spans three dialect boundaries between fo ur adjacent habitat-types (from similar to 1,800 m to similar to 3,000 m), using restriction fragment length polymorphism analysis. This rev ealed exceptional diversity (41 clones from 42 individuals), a level c omparable with DNA-fingerprinting, and higher than reported in any pas serine over such a small area to date. The degree of nucleotide diverg ence between the two main clusters of mtDNA haplotypes implies a separ ation time in excess of one million years. The mtDNA variability is no t related to song dialects; rather it is interpreted as a reflection o f secondary introgression between two well-differentiated subspecies w hose ranges about in this region.