Geography
Overall, the geographic origin of analysed populations correlated with molecular phylogeny (Figs 2–5). Specifically, clade A comprises in the vast majority Palaearctic populations (35/40; 87%) with a small fraction of Afrotropical (4/10; 10%) and a single Nearctic population. Clade B consists of mostly Palaearctic populations (18/23; 78%), with two Afrotropic, two Australian and a single Oriental population. Clade C is composed of African populations, belonging to two realms: Afrotropic (28/31; 90%) and Madagascan (3/31; 10%). Clade D groups eight populations, with seven belonging to the Australian realm (87%) and a single Oriental population (13%). Clade E consists of populations representing multiple realms, but all except one (Milnesium bohleberi US.065/species #57) come from a tropical or a subtropical climate: Oriental (7/21; 33%), Neotropic (6/21; 29%), Panamanian (3/21; 14%), Afrotropic (3/21; 14%), Oceanian (1/21; 5%) and Nearctic (1/21; 5%). Finally, clade F consists of three Afrotropical populations. The correlation between the geographic origin and phylogeny is also reflected by the results of the RASP analysis (SM.04), which suggest that all clades except one (clade E) originated in a single realm. Specifically, clades A and B originated in the Palaearctic (99% support), clades C and F in the Afrotropic (99% support), and clade D in the Australian realm (97% support). Only clade E has a mixed origin, with 45% and 44% probability for the Oriental and Neotropic origin, respectively. Thus, even though the two most ‘basal’ lineages have been collected in the Oriental realm, the mixed origin of the remaining species gives the clade the pantropical character (Figs 2, 5).
There are a total of 11 species (17% of all species delineated in our dataset), collected exclusively in a different zoogeographic realm than the majority of species in a given clade (Figs 2–4 and Table 4). Such species are termed here as ‘inclusion species’ and they suggest plausible ancient LDD events: a preliminarily delineated speciesMilnesium sp. nov. US.071 (species #16), from the Nearctic, embedded in the chiefly Palaearctic clade A (Fig. 3); Milnesiumsp. nov. MY.025 (putative species #19), from the Oriental realm, andMilnesium sp. nov. UG.006 (putative species #23), from the Afrotropic realm, both embedded in the mainly Palaearctic clade B (Fig. 3); Milnesium matheusi MG (species #33) and Milnesium wrightae MG (species #46), from the Madagascan realm, both embedded in the overwhelmingly Afrotropic clade C (Fig. 4); Milnesium sp. nov. ID.947 (putative species #53), from the Oriental realm, embedded in the chiefly Australian clade D (Fig. 4). Given that clade E (Fig. 5) consists mainly of a mixture of Oriental and Neotropic lineages, the identification of ‘inclusion species’ is not straightforward in contrast to the remaining major clades which all have a clearly defined geographic origin. Thus, depending whether the Oriental or the Neotropic is assumed as the realm chiefly characterising the clade, species of the other origin could be considered as ‘inclusions’. To overcome this problem, we decided to identify ‘inclusion species’ as lineages that differ in geographic origin from their closest ‘basal’ relatives. Thus, given that the most ‘basal’ lineage comprises an Oriental species (#62), the following species were classified as ‘inclusions’:Milnesium sp. nov. BR.007 (putative species #61) found in the Neotropic; Milnesium bohleberi US.065 (species #57) from the Nearctic, making it stand out not only geographically but also by climate type; putative new species #56 represented by two populations from the Afrotropic; putative new species #55 represented by five populations from South America; and a preliminarily delineated new species #54 represented by six populations from Far East Asia (see Table 4 and Fig. 5 for details).
Among the 27 species represented by more than one population in our data set, 20 (74%) species were found in a single zoogeographic realm and 7 (26%) species were recorded from more than one realm (Figs 3–5 and Table 5). Such species with wide geographic ranges, termed here as ‘widespread species’, signify recent LDD events: Milnesium tardigradum (species #1) and Milnesium berladnicorum (species #3), both present in the Palaearctic and the Afrotropic (both in clade A; Fig. 3); Milnesium inceptum (species #26), found in the Palaearctic, Afrotropic and the Australian realm (clade B; Fig. 3); a preliminarily delineated new species #40 recorded from the Madagascan and Afrotropic realms (clade C; Fig. 4); putative new species #54 found in the Oriental and the Oceanic realm (clade E; Fig. 5); putative new species #55 present in the Neotropic and the Panamanian realm (clade E; Fig. 5), and putative new species #58 found in the Neotropic and the Afrotropic (clade E; Fig. 5).