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.