A comprehensive approach to detect hybridization sheds light on the evolution of Earth’s largest lizards

Hybridization between species occurs more frequently in vertebrates than
traditionally thought, but distinguishing ancient hybridization from other
phenomena that generate similar evolutionary patterns remains challenging.
Here, we used a comprehensive workflow to discover evidence of ancient
hybridization between the Komodo dragon (Varanus komodoensis) from
Indonesia and a common ancestor of an Australian group of monitor lizards
known colloquially as sand monitors. Our data comprise >300 nuclear
loci, mitochondrial genomes, phenotypic data, fossil and contemporary
records, and past/present climatic data. We show that the four sand
monitor species share more nuclear alleles with V. komodoensis than
expected given a bifurcating phylogeny, likely as a result of
hybridization between the latter species and a common ancestor of sand
monitors. Sand monitors display phenotypes that are intermediate between
their closest relatives and V. komodoensis. Biogeographic analyses suggest
that V. komodoensis and ancestral sand monitors co-occurred in northern
Australia. In agreement with the fossil record, this provides further
evidence that the Komodo dragon once inhabited the Australian continent.
Our study shows how different sources of evidence can be used to
thoroughly characterize evolutionary histories that deviate from a
treelike pattern, that hybridization can have long-lasting effects on
phenotypes, and that detecting hybridization can improve our understanding
of evolutionary and biogeographic patterns.