Most New Zealand grasshoppers live above the tree line, and are routinely frozen under the winter snow cap. They are globally unusual in that they survive winter in this torpor at all life stages – egg, nymph or adult, then reanimate when warmer weather returns. This allows multiplegenerations to be present at any one timeand for species lives to span up to three years (Batchelor, 1967; Hudson, 1970). In contrast many alpine species in other parts of the world overwinter only as eggs, resulting in an annual life cycle with synchronised generations (Batchelor, 1967). New Zealand species are also unusual in that they are sexually dimorphic; females being larger than males at maturity. In some cases (e.g. Brachaspis nivalis, Paprides nitidus, Sigaus australis, Sigaus piliferus and Sigaus villosus) this difference can be two-fold (Bigelow, 1967; Hudson, 1970). All species of the endemic New Zealand genera are flightless, have no ears and do not sing.
There are six genera of short horned grasshoppers (Orthoptera: Acrididae) in New Zealand: Alpinacris, Brachaspis, Locusta, Paprides, Phaulacridium and Sigaus; four of which are endemic to New Zealand. All four of these endemic genera may be found in the South Island of New Zealand, with only one species of the genus Sigaus found in the North Island and one species of the genus Paprides found on Stewart Island (Bigelow, 1967). Alpinacris, Brachaspis and Paprides are included in the acridid subfamily Cantantopinae (von Wattenwyl, 1893) (Eades et al., 2014). Sigaus, however, is currently placed in the subtribe Russalpiina in Catantopini (von Wattenwyl, 1893) (Key, 1993; Eades et al., 2014). Acrididae is a large family, containing some 10,000 species within a complex taxonomic classification system, and members of Catantopinae are found throughout Australia, Asia, Europe and Africa. Subtribe Russalpiina are restricted to New Zealand and the Australian island of Tasmania (Eades et al., 2014a).
Recent molecular work however has revealed disharmony between these morphologically described species and their genetic groupings (clades), with the taxonomy of Brachaspis and Sigaus being called into question. Sigaus australis is better treated as a complex with S. childi, S. homerensis, S. obelisci, and S. species-A. In fact there is little support for S. homerensis, S. obelisci or S. species-A; all three appear to be localised representations of the more widespread species Sigaus australis. Genetic mixture between S. australis and the rare microendemic S. childi has been demonstrated by genetic analysis (Trewick 2008, Dowle et al. 2014). Despite clear phenotypic differences, there is extensive gene flow between the two species where they occur in sympatry and this appears to an example of speciation with gene flow. A similar phenomenon may explain the rare, protected and morphologially distinctive microendemic Brachaspis robustus, which is genetically inseparable from B. nivalis (Trewick 2001). Current niche modelling, morphometric and molecular work will aid in distinguishing exact groupings and relationships within and between New Zealand endemic grasshoppers.
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