Wallacean and Melanesian islands promote higher rates of diversification within the global passerine radiation Corvides: Supplementary information

The complex island archipelagoes of Wallacea and Melanesia have provided
empirical data behind integral theories in evolutionary biology, including
allopatric speciation and island biogeography. Yet, questions regarding
the relative impact of the layered biogeographic barriers, such as
deep-water trenches and isolated island systems, on faunal diversification
remain underexplored. One such barrier is Wallace’s Line, a significant
biogeographic boundary that largely separates Australian and Asian
biodiversity. To assess the relative roles of biogeographic
barriers—specifically isolated island systems and Wallace’s Line—we
investigated the tempo and mode of diversification in a diverse avian
radiation, Corvides (Crows and Jays, Birds-of-paradise, Vangas, and
allies). We combined a genus-level dataset of thousands of ultraconserved
elements (UCEs) and a species-level, 12-gene Sanger sequence matrix to
produce a well-resolved supermatrix tree that we leveraged to explore the
group’s historical biogeography and effects of biogeographic barriers on
their macroevolutionary dynamics. The tree is well-resolved and differs
substantially from what has been used extensively for past comparative
analyses within this group. We confirmed that Corvides, and its major
constituent clades, arose in Australia and a burst of dispersal west
across Wallace’s Line occurred after the uplift of Wallacea during the
mid-Miocene. We found that dispersal across this biogeographic barrier
were generally rare, though westward dispersals were two times more
frequent than eastward dispersals. Wallacea’s central position between
Sundaland and Sahul no doubt acted as a bridge for island-hopping
dispersal out of Australia, across Wallace’s Line, to colonize the rest of
Earth. In addition, we found that the complex island archipelagos east of
Wallace’s Line harbor the highest rates of net diversification and are a
substantial source of colonists to continental systems on both sides of
this biogeographic barrier. Our results support emerging evidence that
island systems, particularly the geologically complex archipelagoes of the
Indo-pacific, are drivers of species diversification.