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).