Oligocene divergence of frogmouth birds (Podargidae) across Wallace’s line

Wallace’s Line demarcates the transition between the differentiated regional faunas of Asia and Australia. However, while patterns of biotic differentiation across these two continental landmasses and the intervening island groups (“Wallacea”) have been extensively studied, patterns of long-term dispersal and diversification across this region are less well understood. Frogmouths (Aves: Podargidae) are a relictual family of large nocturnal birds represented by three extant genera occurring respectively in Asia, “Sahul” (Australia and New Guinea), and the Solomon Islands, thus spanning Wallace’s Line. We used new mitochondrial genomes from each of the extant frogmouth genera to estimate the timeline of frogmouth evolution and dispersal across Wallace’s Line. Our results suggest that the three genera diverged and dispersed during the mid-Cenozoic between approximately 30 and 40 million years ago. These divergences are among the oldest inferred for any trans-Wallacean vertebrate lineage. In addition, our results reveal that the monotypic Solomons frogmouth (Rigidipenna inexpectata) is one of the most phylogenetically divergent endemic bird lineages in the south-west Pacific. We suggest that the contemporary distribution of exceptionally deep divergences among extant frogmouth lineages may be explained by colonisation of, and subsequent long-term persistence on, island arcs in the south-west Pacific during the Oligocene. These island arcs may have provided a pathway for biotic dispersal out of both Asia and Australia that preceeded the formation of extensive emergent landmasses in Wallacea by at least 10 million years.

Methods
Denovo generation of mitochondrial genomes from Toe Pad and Liver samples, combined with existing data compiled from GenBank.