Tiny Hunters Along the Alpine Fault: Integrative Phylobiogeography Demonstrates High Geographic Structure in a Forest‐Dwelling Aotearoa Harvester Genus (Arachnida, Triaenonychidae: <i>Algidia</i>)

ABSTRACT Aim The archipelago of Aotearoa displays both high biodiversity and a dynamic geologic history, shaped by constantly shifting coastlines and the dramatic effects of glacial cycling on forest cover across the islands. This geographic history has important implications for the evolution of dispersal‐limited forest‐dwelling arthropods, such as Opiliones, which can help us reconstruct key past biogeographic events. In this study, we shed light on the evolutionary history of the triaenonychid genus Algidia Hogg, 1920 . Location The archipelago of Aotearoa|New Zealand. Time Period Late Cretaceous to the present‐day, with particular focus on events in the Oligocene onwards. Major Taxa Studied Algidia , Triaenonychidae, Opiliones, Arachnida. Methods We utilise an integrative phylobiogeographic approach, incorporating target enrichment sequence capture of ultraconserved elements, divergence dating, species delimitation and ecological niche modeling. Results Our genomic data in conjunction with divergence dating find evidence of high geographic structure and the influence of multiple key geologic events in the natural history of Aotearoa, including the origination and continuation of the Alpine Fault, marine transgression during the Oligocene and cycles of glaciation and orogeny that characterised the Pliocene and Pleistocene on the islands. Our results recover 10 putative species, including four that are undescribed. Paleoclimate modelling reflects geographic changes to Aotearoa's coastline which potentially underpin the modern distributions of Algidia , including land bridges in place of the current marine straits Raukawa Moana|Cook Strait and Te Ara‐a‐Kiwa|Foveaux Strait. Main Conclusions The phylogeny of Algidia indicates consistent northwards expansion, with the earliest diverging clade, A. homerica , located in Rakiura and southern Te Waipounamu, and subsequently diverging clades moving steadily northwards in their geographic distributions. Diversification of Algidia predates the Oligocene Marine Transgression, lending support to the now well‐established hypothesis that Aotearoa was not fully submerged during the Oligocene. The Alpine Fault seems to be an important feature explaining cladogenesis and diverging populations, including for species found across Raukawa Moana. However, other phenomena, including glaciation, orogeny or continental shifting, are also important explanatory factors in species distributions across Aotearoa.