Acari

Ross, Giles M., Rymer, Paul D., Cook, James M. & Nielsen, Uffe N., 2025, Phylogeography of Antarctic soil invertebrate fauna reveals ancient origins, repeated colonization and recent evolution, Antarctic Science (Cambridge, England) 37 (1), pp. 13-30 : 21

Acari

The Acari , or mites, are the most diverse faunal group in terrestrial Antarctica ( Pugh 1993) . Current tallies number 105 species consisting of 5 continental, 22 maritime and 78 sub-Antarctic species, of which ∼ 70 are endemic ( Convey 2011, McGaughran et al. 2011). The biogeography of several mite species has been surveyed on the sub-Antarctic islands ( Mortimer et al. 2011) and Maritime Antarctica, with limited evidence of biogeographical patterns on the continent; despite evidence of structured distributions in VL ( Collins et al. 2023), most distributions remain unverified using molecular approaches.

Origins and refugia

First described from the Belgica expedition of 1897–1899 ( de Man 1904), continental mites have some of the earliest links to a pre-Gondwanan lineage ( Fig. 3 ). Several species appear to have ancient origins, including members of the oribatid mite genus Maudheimia Dalenius and Wilson, 1958 (> 100 Ma; Marshall & Coetzee 2000) and the prostigmatid mite genus Stereotydeus Berlese, 1901 mites (> 10 Ma; Stevens & Hogg 2006). While some mites have an ancient origin, it is difficult to ascribe all Antarctic taxa as having ancient lineages (Table II). Molecular analyses have shown that vicariant speciation was prevalent during interglacial periods in mites ( Stevens & Hogg 2006), similar to observed patterns in springtails ( McGaughran et al. 2008). There is evidence of local refugia with oribatid and prostigmatid mites persisting during glacial maxima, and most Antarctic mites appear to have dispersed from glacial refugia and coastal habitats ( Marshall & Coetzee 2000).

Dispersal effects on broad-scale and regional distribution Despite their ability for long-distance dispersal, the little overlap between continental and maritime populations demonstrates strong geographical barriers limiting dispersal among geographical regions ( Convey et al. 2014). However, there is evidence of some dispersal within regions. For example, a study of eight members of the genus Halozetes Berlese, 1916 in Maritime Antarctica and the sub-Antarctica islands found frequent dispersal events between the sub-Antarctic islands among H. belgicae and populations of the mite genus Alaskozetes Hammer, 1955 between 6 and 10 Ma, as well as a rare case of wind- or water-borne dispersal from northern peninsular refugia to surrounding islands ( Table I; Mortimer et al. 2011).

Restrictions to dispersal and mixing of populations, evident from a lack of shared haplotypes and gene flow, may also indicate recent colonization of the sub-Antarctic islands and continent ( Mortimer et al. 2011, Convey et al. 2014). Limited ranges and high endemism have been shown in peninsular populations of H. belgicae and Alaskozetes antarcticus Michael, 1903 , with further evidence of multiple refugial sources (Table II; Van Vuuren et al. 2018). Additionally, contemporary distribution patterns conform with the limited short-range dispersal ability of mites, linked to their low desiccation tolerance ( McGaughran et al. 2010a). Beyond this, molecular studies on the short-range dispersal of mites are limited.

Despite thorough biogeographical investigation ( Block & Starý 1996, Marshall & Coetzee 2000, Collins et al. 2023), knowledge on the phylogeography of Antarctic mites is limited. However, studies have revealed restricted distributions of several mite species ( Van Vuuren et al. 2018), with diverse prostigmatid communities in inland oases ( Lawley et al. 2004, Brunetti et al. 2021b). Phylogenetic support for their ancient lineages, combined with evidence of recent evolution linked to refugial dispersal, can be clarified through targeted sampling. This would overcome the data deficiency for these important decomposers and support arguments for their use of refugia and long-range dispersal as explanations of their diverse contemporary distribution.

Figures

Figure 3. Graphical timeline of invertebrate groups and earliest indications of endemic Antarctic lineage. Ages are based on mean estimated origins from molecular dating studies in Continental Antarctica alongside main regional geological events over a logarithmic timeline; 1 Ga = 1000 Ma (adapted from Convey 2010). ACC = Antarctic Circumpolar Current; Ka = thousand years ago; LGM = Last Glacial Maximum; Ma = million years ago.