Persisting in a glaciated landscape: Pleistocene microrefugia evidenced by the tree wētā Hemideina maori in central South Island, New Zealand

Abstract

AbstractAimRepeated cycles of Pleistocene glaciation have influenced phylogeographic structure of taxa on New Zealand's South Island. Many taxa became restricted to refugia at either end of the island during glaciation, resulting in an area of low endemicity in central South Island. This area of low endemism is typified by the so‐called beech (or biotic) gap, where the absence of Nothofagus forest (and many other plant and invertebrate taxa) has been attributed to repeated glaciation. Some taxa, however, appear to have persisted in situ in localized refugia within the biotic gap. We test these alternative hypotheses in a large flightless alpine wētā (grasshopper).LocationSouthern Alps, South Island, New Zealand.TaxonHemideina maori Pictet & Saussure, 1891 (Orthoptera: Anostostomatidae).MethodsWe used phylogeographic analysis of mitochondrial cytochrome c oxidase I (cox1) and 25 nuclear DNA (nuDNA) markers to test for Pleistocene glacial microrefugia within the current montane South Island range of Hemideina maori.ResultsWe identified eight deeply differentiated mtDNA lineages with limited sharing of haplotypes among populations. Genetic differentiation assessed using nuDNA revealed a similar pattern, with three groups broadly corresponding to the deepest mtDNA splits. The central South Island region exhibits substantial endemic mtDNA diversity and a distinctive nuclear lineage.Main conclusionsThese results indicate that H. maori likely persisted in microrefugia within the biotic gap during glaciation. These deep lineages are estimated to have started diverging prior to the initiation of glaciation, up to 3 Ma. These results add to a growing number of Southern Hemisphere examples of deep phylogeographic differentiation in glaciated alpine regions compared to Europe and North America, probably reflecting less intense glaciation. We suggest that other Southern Alps species showing northern and southern clades alone are more montane than alpine, and were reliant on warmer habitat to the north and south during glacial eras. Thus, there are species‐specific responses to climatic processes, influenced by distinctive habitat requirements and physiological traits.