Climate
Milnesium populations were found in all five main climate
categories, with the largest number of populations found in the
temperate climate (49/127, 39% pops.; clades A–E). Except the smallest
clade (F), which represents a single climate category, all other clades
comprise species that were found in multiple (three to four) climate
types (Figs 3–5). Species representing both arctic and cool climate
were present exclusively in clades A and B, those dwelling in dry
climate were present in clades A and C–F, and the tropical climate was
recovered in clades B–E. Specifically, clade A includes populations
found in the following climate types: cool (21/40, 52%), dry (10/40,
25%) temperate (8/40, 20%), and arctic (1/40, 3%). Clade B comprises
populations mainly from cool climate (10/23 44%), with an equal number
of species collected in temperate and arctic climates (each 6/23, 26%),
and a single tropical population. Clade C groups populations mainly from
temperate climate (23/31, 74%) and four populations from dry and
tropical climate (13% each). Clade D consist chiefly of populations
found in dry climate (5/8, 63%), with an addition of temperate (2/8,
25%) and tropical type (1/8, 12%). In clade E, the majority of
populations represent tropical climate (11/21, 52%) with additional
populations dwelling in temperate (9/21, 43%) and single in dry
climate. Finally, clade F consists of populations originating from dry
climate. The RASP analysis (SM.05) showed that lineages within the main
six clades are generally correlated with particular climate types, which
is evidenced by high supports of the ‘ancestral’ states: 89% and 88%
support for cool climate for clades A and B, temperate for clades C, D
and E (with 98%, 94% and 84% support, respectively), and dry climate
for clade F (97% support).
In the aspect of the EiE hypothesis, it is particularly interesting to
compare climate types in which widespread species dwell with climate
types dominating in their respective clades. On the other hand,
‘inclusion species’, assuming that they represent ancient LDD events,
are less important in relation to the EiE hypothesis, because they had
considerable amounts of time to adapt to different climate conditions.
Thus, out of 28 non-singleton species (i.e. species represented by more
than one population in our dataset), 13 were found in more than one
climate type (46%). Except M. tardigradum (species #1), whose
populations dwell in three different climate types (cool, temperate and
dry), the remaining 12 species were found in two climate types (species
#2, #3, #6, #8, #13, #18, #20, #26 #28, #40, #55 #58),
representing six combinations of climate types: temperate+cool (spp.
#2, #6, #8, #26), tropical+temperate (spp. #28, #40, #55),
dry+cool (spp. #3, #13), dry+temperate (sp. #58), temperate+arctic
(sp. #18), and cool+arctic (sp. #20). Thus, four possible climate type
pairs were absent (tropical+dry, tropical+cool, tropical+arctic and
dry+arctic). Importantly, however, the missing pairs concern mostly the
climate types in which the lowest numbers of species were found, i.e.
arctic (8) and tropical (18) climate, whereas all combinations with the
most sampled type (temperate) were present.