Collembola

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 : 17-19

Collembola

Springtails, of the arthropod subclass Collembola, were the first Antarctic invertebrates to be described ( Carpenter 1902). Since their discovery, 17 continental and 25 maritime species representing 4 families having been recorded ( McGaughran et al. 2011), with almost two-thirds of all genera being endemic ( Stevens & Hogg 2003, 2006, Pugh & Convey 2008, Torricelli et al. 2010b). Phylogeographical work has mostly focused on springtails of continental VL (71.0– 78.5°S) in eastern Antarctica and on the peninsula. Three species are present in both continental and maritime regions: Cryptopygus antarcticus , Cryptopygus terranovus Wise, 1967 , and Kaylathalia klovstadi Carpenter, 1902 . What was once considered the sole circumpolar species, Friesea grisea Schaffer, 1891 (initially named Friesea antarctica Willem, 1901 ), has been taxonomically reassessed, resulting in the recognition of multiple species with smaller ranges, including Friesea propria Greenslade and Fanciulli, 2020 and Friesea gretae Greenslade and Fanciulli, 2020 ( Carapelli et al. 2020b, Stevens et al. 2021). F. grisea is now considered to be restricted to sub-Antarctic South Georgia alongside Friesea fantaba Greenslade, 2018 . An additional three species are found in continental southern VL (sVL): Antarcticinella monoculata Salmon, 1965 , Cryptopygus nivicolus Salmon, 1965 , and Gomphiocephalus hodgsoni Carpenter, 1908 ( Greenslade 2018, Collins et al. 2019). Taxonomic and phylogeographical studies have described local distributions and provided some insights into the ancient origins and restricted gene flow between populations arising from refugial survivors on the continent and other Antarctic regions.

Origins and refugia

Phylogeographical studies have improved theories of springtail origins, with a consensus being established of most taxa evolving from ancestors arriving on the continent ∼ 20 Ma, prior to the formation of the ACC ( Fig. 3 ; Stevens et al. 2006 a, Stevens & D’ Haese 2014). Several factors have promoted speciation, with several endemic species identified using molecular data, indicating more recent evolution ( Table I). Intermittent dispersal events from surrounding sub-Antarctic landmasses and inland refugia may have contributed to the allopatric speciation of populations separated by glaciers and other dispersal barriers ( Convey & Stevens 2007, McGaughran et al. 2011). Springtails show evidence of complex evolutionary histories, with certain species linked to ancient arrivals and others to more recent colonization events (Table II). The latter point to a series of post-glacial recolonization events followed by vicariant speciation. Significant divergence and a lack of shared haplotypes between continental and maritime springtail species suggest substantial dispersal barriers and long-term persistence in distinct refugia from which source populations remained separated following dispersal events ( Collins et al. 2019, 2020). Most studies found glaciers to be major dispersal barriers, restricting gene flow ( Stevens et al. 2006a, Bennett et al. 2016, Collins et al. 2019). This has led to the assumption of there being multiple refugia in glacial valleys throughout continental VL as the source for distinct haplotypes of C. terranovus ( Carapelli et al. 2017a) and K. klovstadi populations ( Fig. 4a ; Frati et al. 2001).

LGM = Last Glacial Maximum.

Several studies support the refugial theory and the potential for multiple source populations ( Marshall & Coetzee 2000, Fanciulli et al. 2001, Frati et al. 2001, Stevens & Hogg 2006, McGaughran et al. 2008). Evidence from the Friesea genus shows potential colonization by a common ancestor> 20 Ma (Miocene/Oligocene), with subsequent local speciation occurring and no haplotype sharing between the Antarctic Peninsula and VL regions ( Torricelli et al. 2010 b, Collins et al. 2019), nor between the Antarctic Peninsula and South Shetland Islands ( Torricelli et al. 2010a).

The northern VL (nVL) species K. klovstadi (formerly Isotoma klovstadi and of the Desoria genus) show divergences between subspecies that are geographically close to each other, further supporting multi-refugial sources ( Stevens et al. 2006 b, 2007, Stevens & D’ Haese 2016). The identification of different dominant haplotypes of K. klovstadi between the peninsular Adelaide, Lagoon and Killingbeck islands led to theories of separate lineages, with multiple refugial populations undergoing rapid evolution throughout the Pleistocene ( Fig. 4b ; Hawes et al. 2008). These patterns of distribution following refugial dispersal have also been observed on the Antarctic continent ( Carapelli et al. 2020a). Another study that supports the idea of multiple refugia maintaining isolated populations found lower-than-expected genetic distances between G. hodgsoni populations on the peninsula, indicating a scenario whereby dispersal from a singular refugial source was followed by minimal genetic admixing ( McGaughran et al. 2010c).

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.

Figure 4. a. Map of Victoria Land (VL) with major glacial features and compiled results from phylogeographical studies.Springtail geographical ranges are indicated by coloured lines on the left panel from McGaughran et al. (2008), with theorized dispersal routes to Ross Island from Stevens & Hogg (2003) and Collins et al. (2019, 2020). Dashed lines demarcate biotic boundaries used to define population groups, with symbols representing genetically distinct populations of springtails (yellow triangles),mites (red circles),nematodes (green circles) and rotifers and tardigrades (purple squares;sources:Barrett et al. 2006, Torricelli et al. 2010a, McGaughran et al. 2011, Convey et al. 2014, Brunetti et al. 2021b). b. Map of the Antarctic Peninsula (Graham Land), with theorized dispersal routes between springtail populations indicated by red arrows from McGaughran et al. (2010a). Symbols represent genetically distinct populations of midges (orange circles) and potential refugial locations (empty squares; sources: Torricelli et al. 2010a, Allegrucci et al. 2012, Convey et al. 2014, Velasco-Castrillón et al. 2014b, Carapelli et al. 2017b).