Genetic differences between the endangered San Clemente Island loggerhead shrike Lanius ludovicianus mearnsi and two neighbouring subspecies demonstrated by mtDNA control region and cytochrome b sequence variation.

We investigated mtDNA sequence variation in five populations of the loggerhead shrike Lanius ludovicianus, representing four subspecies, including the San Clemente logger-head shrike L. l. mearnsi, a critically endangered California Channel Island endemic. Variability in 200 bp of control region and 200 bp of cytochrome b was extremely low, and defined four haplotypes. Strong structure was apparent among all three southern California subspecies, including L. l. mearnsi, with one haplotype predominating in each subspecies. Although potential levels of gene flow between L. l. mearnsi and neighbouring populations are low, mtDNA data support field observations that some shrikes visit the island during winter but do not stay to breed, and suggest that these birds come from the mainland. The similarity in haplotypes between populations from Saskatchewan, Canada and those in southern California suggests post-glacial northern range expansion of the species. Our results confirm the evolutionary distinctiveness of L. l. mearnsi and justify continuing efforts for its conservation.

Tandem repeats and heteroplasmy in the mitochondrial DNA control region of the loggerhead shrike (Lanius ludovicianus).

We report the presence of a 128 bp tandem repeat in the mitochondrial control region of the loggerhead shrike (Aves: Lanius ludovicianus). All individuals examined had either two or three copies of the repeat or were heteroplasmic for two and three copies. This is the first direct demonstration of a tandem repeat associated with heteroplasmy in the control region of a bird. A novel model for repeat duplication, which involves an inverted repeat located adjacent to the tandemly repeated sequence, is presented. Individuals with three repeats are absent from the endangered population of San Clemente loggerhead shrike in southern California, suggesting that the island endemic has a small effective population size and that there is insignificant gene flow from the adjacent mainland.