Evolutionary history of Aotearoa New Zealand's extinct mātuhituhi | bush wren

The reconstruction of ecosystem responses to past climate change has historically focused on large vertebrates. In contrast, small vertebrates with potentially stricter habitat preferences have been neglected in ancient DNA studies despite their potential utility as proxies for inferring geographic and temporal changes in habitat. Aotearoa New Zealand's acanthisittid wrens are a speciose group of tiny perching birds, including the mātuhituhi | bush wren (Xenicus longipes ssp.). Despite its relatively recent extinction in the 1970s, very little is known about this enigmatic bird. Here we sequence mitochondrial genomes and nuclear ultra conserved genomic elements from 32 historical bush wren specimens to reconstruct their evolutionary history. We also genetically sex specimens and reanalyse their plumage to reconstruct aspects of bush wren plumage variation. Our analyses suggest North and South Island bush wren populations diverged 2.6 million years ago when narrowing and closure of Plio-Pleistocene seaways allowed colonisation of new habitats, followed by rapid glaciation-driven diversification of South Island populations 470,000-94,000 years ago. Genetic sexing allowed an accurate reconstruction of ontogenetic, sexual, and geographic variation in plumage. Our multidisciplinary data supports recognition of North and South Island populations as separate species, and the description of a new subspecies X. longipes perditus subsp. nov. This research shows how ecosystems can buffer against the impacts of climate change up to an ecological tipping point, which has important lessons for conservation management in a fast-changing world.