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Glacially induced bursts of speciation were thought to have occurred in both temperate ( 2, 4) and tropical latitudes ( 3, 5). Speciation was believed to have occurred primarily through habitat movements and fragmentation tied to global temperature fluctuations that accompanied the glacial advances. These cycles were originally proposed to have fragmented populations, resulting in speciation and the formation of much of today’s species richness ( 1– 5). Pleistocene climate cycles resulted in glaciation and the buildup of extensive ice sheets at temperate latitudes during periods of global cooling, followed by recession of ice sheets during brief interglacial periods. Our results support a fivefold increase in diversification rates during key glacial periods, comparable with levels observed in classic adaptive radiations, and confirm that at least some lineages distributed near glaciated regions underwent rapid ice age diversification.

Estimates of effective population size through time show a dramatic bottleneck during the last glacial cycle in all but one kiwi lineage, as expected if kiwi were isolated in glacially induced refugia.

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During this period, New Zealand was repeatedly fragmented by glaciers into a series of refugia, with the tiny geographic ranges of many kiwi lineages currently distributed in areas adjacent to these refugia. We found that 80% of kiwi diversification events date to the major glacial advances of the Middle and Late Pleistocene. By sampling across the geographic range of the five kiwi species, we discovered many cryptic lineages, bringing the total number of kiwi taxa that currently exist to 11 and the number that existed just before human arrival to 16 or 17.

Here, we used a genome-wide dataset of more than half a million base pairs of DNA to test for a glacially induced burst of diversification in kiwi, an avian family distributed within several hundred kilometers of the expanding and retracting glaciers of the Southern Alps of New Zealand. Molecular dating largely overturned the paradigm that global cooling during recent Pleistocene glacial cycles resulted in a burst of species diversification although some evidence exists that speciation was commonly promoted in habitats near the expanding and retracting ice sheets.

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