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

Abstract

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).

Global warming leads to habitat loss and genetic erosion of alpine biodiversity

“…Similar phylogeographic structure is known from other alpine animals in the Southern Alps (e.g. Hill et al, 2009;King et al, 2020;Trewick, 2001a;Trewick et al, 2000;Weston & Robertson, 2015), but these might reflect lineage sorting at different times (Trewick et al, 2011). The grasshoppers considered here each encompassed more than 10% sequence divergence (see also Trewick, 2001bTrewick, , 2008, which for comparison, is an order of magnitude greater than found in well-studied Chorthippus grasshoppers across Europe (e.g.…”

“…As high genetic diversity is indicative of large, persistent population size (Charlesworth, 2009; Morgan‐Richards et al, 2017), we can infer that the alpine adapted grasshoppers maintained dense populations through the Pleistocene. Similar high intraspecific diversity is known from other New Zealand alpine insects including wētā (King et al, 2020; Trewick et al, 2000) and stoneflies (McCulloch et al, 2009). Deep gene trees with major lineages of each grasshopper species in allopatry suggest long‐term extrinsic barriers partitioning large populations.…”

How did the toad get over the sea to Skye? Tracing the colonisation of Scottish inshore islands by common toads (Bufo bufo)

“…Notwithstanding phylogeographic evidence from other taxa for persistence in glaciated areas (e.g. King et al, 2020;Taylor, 1983), we therefore consider the hypothesis of relict populations surviving during the Loch Lomond Stadial to be rather unlikely.…”

Biodiversity in mountain soils above the treeline

“…For Australasian alpine taxa, a deeper phylogeographic structuring was shown compared to European and North American ones, possibly reflecting less intense glaciation and a higher availability of refuges during glaciation events (King et al, 2020). Colonisation processes in high alpine areas can be surmised by observing the colonisation of alpine land when glaciers retract (Koch & Kaufmann, 2010;Hågvar et al, 2020).…”

“…These species are mainly relicts of the last glaciations that survived in nunataks and other refugia offered by highly heterogeneous mountain topography (Brighenti et al ., 2021); in subsequent interglacial periods, these alpine invertebrates have expanded extensively (Hill et al ., 2009). For Australasian alpine taxa, a deeper phylogeographic structuring was shown compared to European and North American ones, possibly reflecting less intense glaciation and a higher availability of refuges during glaciation events (King et al ., 2020). Colonisation processes in high alpine areas can be surmised by observing the colonisation of alpine land when glaciers retract (Koch & Kaufmann, 2010; Hågvar et al ., 2020).…”