Mitochondrial DNA Hyperdiversity and Vocal Dialects in a Subspecies Transition of the Rufous-Collared Sparrow

Abstract

The Rufous-collared Sparrow, Zonotrichia capensis, is widely distributed in neotropical America and shows extensive variation in its learned song. In northwestern Argentina it exhibits song dialects which map closely onto the distribution of natural vegetation assemblages. To date, there is no evidence ofa correlation between genetic (allozyme) variation and dialects. However, recent genetic structuring produced through philopatry and assortative mating by dialect is difficult to demonstrate statistically with such proteinencoding nuclear genes. Therefore, we assayed variation in more rapidly evolving mitochondrial DNA along a 50 km transect, which spans three dialect boundaries between four adjacent habitat-types (from ~ 1,800 m to ~-3,000 m), using restriction fragment length polymorphism analysis. This revealed exceptional diversity (41 clones from 42 individuals), a level comparable with DNA-fingerprinting, and higher than reported in any passerine over such a small area to date. The degree of nucleotide divergence between the two main clusters of mtDNA haplotypes implies a separation time in excess of one million years. The mtDNA variability is not related to song dialects; rather it is interpreted as a reflection of secondary introgression between two well-differentiated subspecies whose ranges abut in this region.