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

Aim: Repeated 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). Location: Southern Alps, South
Island, New Zealand Taxon: Hemideina maori Pictet & Saussure, 1891
(Orthoptera: Anostostomatidae) Methods: We used phylogeographic analysis
of mitochondrial cytochrome c oxidase I (cox1) and twenty-five nuclear DNA
(nuDNA) markers to test for Pleistocene glacial microrefugia within the
current montane South Island range of Hemideina maori. Results: We
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 conclusions: These 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 phyleogeographic differentiation in glaciated
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.