Niche Conservatism Drives the Elevational Diversity Gradient in Major Groups of Free-Living Soil Unicellular Eukaryotes

Abstract

Ancestral adaptations to warm and humid climates drive the biogeographical and macroecological patterns of numerous multicellular organisms. Recent evidence suggests that this niche conservatism may also be shaping broad-scale diversity patterns of soil unicellular organisms, although empirical evidence is limited to Acidobacteria and testate amoebae. Herein, we tested the predictions of this hypothesis for ve major soil protist groups (Bacillariophyta, Cercomonadida, Ciliophora, Euglyphida and Kinetoplastida), separately, as well as combined, along an elevational gradient in Switzerland. We found support for the predictions of this hypothesis in all protist groups, including decreasing diversity and increasing geographical ranges towards high and cold elevations (Rapoport effect); correlations between diversity and temperature (species-energy effect); and communities phylogenetically structured by competition (phylogenetic overdispersion) at warm-humid sites and habitat ltering (phylogenetic clustering) at cold-humid sites. Mid-domain null models con rmed that these ndings were not the result of stochastic processes. Our results therefore suggest that soil protists exhibit evolutionary constraints to warm and humid climates, probably linked to an ancestral adaptation to (sub)tropical-like environments, which limits their survival in exceedingly cold sites. This niche conservatism possibly drives their biogeographical and macroecological patterns both at the local (e.g., temperature, humidity gradients along elevation gradients) and more global (e.g., latitudinal gradients) spatial scales.

Landolt Indicator Values in Modern Research: A Review

“…A wide sample of 324 pastures in the northwestern Italian Alps was surveyed, and comprehensive vegetation and soil surveys were carried out [89]. The scientists traced the phylogenetic signal for this niche conservatism in the highly related and functionally contrasting groups of common soil protists (Bacillariophyta, Cercomonadida, Ciliophora, Euglyphida and Kinetoplastida) along the humid but increasingly cold altitude gradient in Switzerland [90]. Cold range limits of Carex curvula (Cyperaceae) and Nardus stricta (Poaceae) were defined on acidic soils of high-altitude habitats in the European Alps [91].…”

Filling gaps in the diversity and biogeography of Chilean millipedes (Myriapoda: Diplopoda)

“…We used a range interpolation approach to standardise species richness and reduce the effects of spatial sampling biases (McCain 2009;Fernández et al 2022). Range interpolation assumes that species have continuous latitudinal ranges between their lowest and highest latitudinal occurrences.…”

“…Possibly the need for warm, humid climates is a phylogenetically conserved trait in millipedes (Kadamannaya et al 2009;Cooper 2022b); i.e. they have evolutionary constraints that prevent them from adapting to new climates (Wiens et al 2010;Fernández et al 2022). Of course, this does not mean that there are no millipedes adapted to live in harsh climates.…”

Contemporary issues, current best practice and ways forward in soil protist ecology

“…In addition, manipulative experiments and subsequent sequencing analyses have revealed potential protist keystone species and communities linked to changes in plant performance and ecosystem functions (Guo et al, 2022; Jiang et al, 2020). Also, many studies have appeared on responses of protists to changes in land management or other anthropogenic factors (Reczuga et al, 2020; Wu et al, 2022) and ecological gradients at the regional to local scale (Fernandez et al, 2022; Mazel et al, 2022; Singer et al, 2018).…”