Ecological and evolutionary processes shape below-ground springtail communities along an elevational gradient

Aim Both ecological and evolutionary processes shape biological communities along elevational gradients. Compared to above-ground taxa, elevational patterns and processes of below-ground animals are little studied. Here, we investigated how environmental gradients across elevation may affect species divergence in the past and act as filters of contemporary assembly of soil detritivores via traits. We asked: (1) Are environmental filtering processes due to elevation, vegetation or microhabitat-related factors driving isotomid springtail community assembly across elevation; (2) did species divergences occur after mountain uplift; and (3) are there environmental factors related to species divergences in the past. Location Changbai Mountain, north-east China. Taxon Isotomidae, Collembola. Methods We collected isotomid springtails from 800 to 2150 m above sea level and reconstructed the phylogeny using mitochondrial genome sequencing. We inspected the body length, number of ommatidia and pigmentation, and determined their evolutionary patterns. We then derived community parameters using trait-based and metacommunity phylogenetic approaches and used linear mixed-effects models to identify environmental variables that allow predicting community trait and phylogenetic parameters. Results Isotomid springtails differed more in traits when co-occurring in environments with lower soil nitrogen, typically at higher elevations. Most communities exhibited phylogenetic clustering, but this pattern was not related to elevation or any environmental variables. These isotomid species mainly diverged in the Mesozoic with some divergence events associated with soil N and pH, as well as other factors covarying with the contemporary elevational gradient studied. The current communities comprised old phylogenetic lineages possessing traits that have undergone evolutionary drift. Main conclusions While environmental gradients act as filters for below-ground detritivores, evolution of traits preconditions their assembly. Species divergence likely resulted from filtering processes of past environments resembling the present day. Below-ground diversity in Changbai Mountain is mainly based on the persistence of old phylogenetic lineages, while recent speciation is of little importance.