Genetic introgression and female mate choice within the Calendulauda albescens/C. barlowi hybrid zone

Abstract

The hybrid zone between Calendulauda albescens and C. barlowi, located near the Orange River, contains a wide range of phenotypically intermediate individuals. This study examines the mitochondrial DNA of some of these individuals to determine if possible introgression is occuring from C. albescens to C. barlowi. Mitochondrial DNA from 13 lark individuals found in the C. albescens/C. barlowi hybrid zone was analysed. A 358 base pair cytochrome-b sequence was obtained. The neighbour-joining phylogenetic tree obtained revealed two distinct clades, a C. albescens and C. barlowi clade. The C. barlowi clade was supported with a bootstrap value of 100. The C. albescens clade contained individuals of intermediate morphology, as represented by their hybrid index scores, indicating that intermediates between the two species contain the mitochondrial DNA of only one species, C. albescens. These results point at introgression from C. albescens to C. barlowi, with female C. albescens choosing to mate with male C. barlowi.