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 h ave been inferred primarily from distributions of observed distances o f dispersal from birthplace to place of first breeding. However, for m ost cooperative breeders, characteristics of geographic population str ucture and extent of realized gene flow as measured by genetic markers are not known. To estimate rates of gene flow in a cooperatively bree ding bird, I conducted a continent-wide survey of DNA sequence diversi ty in the most variable part of the mitochondrial (mt) genome among 16 3 grey-crowned babblers (Pomatostomus temporalis) throughout Australia and Papua New Guinea. The variability found among 86 types of mtDNA w as used to infer genealogical trees relating sequences within both eas tern (P. t. temporalis) and western (P. t. rubeculus) babblers. The ge nealogies imply low but detectable levels of gene flow between populat ions separated by over 1000 km. In addition, they suggest that genes f rom unrelated migrants contribute to genetic diversity in 5 of 50 (10% ) social groups, occasionally producing large ( > 3%) intragroup seque nce differences. However, on average, the fraction of sequence diversi ty apportioned among populations (F(st)) and among social groups withi n populations (F(gs)), was substantial for both P. t. temporalis and P t. rubeculus, implying a large opportunity for the spread of social b ehaviours in both lineages of babblers.