Evolution on islands has produced extraordinary forms of adaptations including flightless birds, such as the New Zealand Kakapo, and dog sized elephants, such as the extinct Sicilian Pygmy Elephant. Among the most noticeable environmental adaptations is island gigantism1. It describes the phenomenon of island species that are significantly larger than their closest mainland relatives. New Zealand has given rise to a number of such island giants, including birds as well as insects.
Here we use complete mitochondrial genome data to study the evolution of two extinct New Zealand island giants: Haast's eagle, the largest raptor in the world, and Eyles harrier, one of the largest Harriers in the world. Our comparative studies show that both species are closely related to much smaller Australasian species, confirming results from an earlier study on Haast's eagle2 and providing new evidence of a broader pattern in New Zealand birds of prey. Recent divergence times with their respective closest relatives in both cases suggest a rapid evolution of island gigantism, most likely in adaptation to the unique, mammalian predator free New Zealand ecosystem.
The study provides a foundation for investigations into the functional genomic basis of island gigantism and highlights the potential of state-of-the-art ancient DNA and high throughput sequencing technology for evolutionary studies of extinct organisms.