Long-distance gene flow in a cooperative breeder detected in genealogies of mitochondrial DNA sequences.

Rates of gene flow among populations of cooperatively breeding birds have been inferred primarily from distributions of observed distances of dispersal from birthplace to place of first breeding. However, for most cooperative breeders, characteristics of geographic population structure and extent of realized gene flow as measured by genetic markers are not known. To estimate rates of gene flow in a cooperatively breeding bird, I conducted a continent-wide survey of DNA sequence diversity in the most variable part of the mitochondrial (mt) genome among 163 grey-crowned babblers (Pomatostomus temporalis) throughout Australia and Papua New Guinea. The variability found among 86 types of mtDNA was used to infer genealogical trees relating sequences within both eastern (P. t. temporalis) and western (P. t. rubeculus) babblers. The genealogies imply low but detectable levels of gene flow between populations separated by over 1000 km. In addition, they suggest that genes from unrelated migrants contribute to genetic diversity in 5 of 50 (10%) social groups, occasionally producing large (> 3%) intragroup sequence differences. However, on average, the fraction of sequence diversity apportioned among populations (Fst) and among social groups within populations (Fgs), was substantial for both P. t. temporalis and P t. rubeculus, implying a large opportunity for the spread of social behaviours in both lineages of babblers.