Global distribution modelling of a conspicuous Gondwanian soil protist reveals latitudinal dispersal limitation and range contraction in response to climate warming
Authors: Bruni Estelle P. , Rusconi Olivia , Broennimann Olivier , Adde Antoine , Jauslin Raphaël , Krashevska Valentyna , Kosakyan Anush , Armynot du Châtelet Eric , Alcino João P. B. , Beyens Louis , Blandenier Quentin , Bobrov Anatoly , Burdman Luciana , Duckert Clément , Fernández Leonardo D. , Gomes e Souza Maria Beatriz , Heger Thierry J. , Koenig Isabelle , Lahr Daniel J. G. , McKeown Michelle , Meisterfeld Ralf , Singer David , Voelcker Eckhard , Wilmshurst Janet , Wohlhauser Sebastien , Wilkinson David M. , Guisan Antoine , Mitchell Edward A. D. 
Published: October 2023

Aim

The diversity and distribution of soil microorganisms and their potential for long‐distance dispersal (LDD) are poorly documented, making the threats posed by climate change difficult to assess. If microorganisms do not disperse globally, regional endemism may develop and extinction may occur due to environmental changes. Here, we addressed this question using the testate amoebaApodera vas, a morphologically conspicuous model soil microorganism in microbial biogeography, commonly found in peatlands and forests mainly of former Gondwana. We first documented its distribution. We next assessed whether its distribution could be explained by dispersal (i.e. matching its climatic niche) or vicariance (i.e. palaeogeography), based on the magnitude of potential range expansions or contractions in response to past and on‐going climatic changes. Last, we wanted to assess the likelihood of cryptic diversity and its potential threat from climate and land‐use changes (e.g. due to limited LDD).

Location

Documented records: Southern Hemisphere and intertropical zone; modelling: Global.

Methods

We first built an updated global distribution map ofA. vasusing 401 validated georeferenced records. We next used these data to develop a climatic niche model to predict its past (LGM, i.e. 21 ± 3 ka BP; PMIP3 IPSL‐CM5A‐LR), present and future (IPSL‐CMP6A‐LR predictions for 2071–2100, SSP3 and 5) potential distributions in responses to climate, by relating the species occurrences to climatic and topographic predictors. We then used these predictions to test our hypotheses (dispersal/vicariance, cryptic diversity, future threat from LDD limitation).

Results

Our models show that favourable climatic conditions forA. vascurrently exist in the British Isles, an especially well‐studied region for testate amoebae where this species has never been found. This demonstrates a lack of interhemispheric LDD, congruent with the palaeogeography (vicariance) hypothesis. Longitudinal LDD is, however, confirmed by the presence ofA. vasin isolated and geologically young peri‐Antarctic islands. Potential distribution maps for past, current and future climates show favourable climatic conditions existing on parts of all southern continents, with shifts to higher land from LGM to current in the tropics and a strong range contraction from current to future (global warming IPSL‐CM6A‐LR scenario for 2071–2100, SSP3.70 and SSP5.85) with favourable conditions developing on the Antarctic Peninsula.

Main Conclusions

This study illustrates the value of climate niche models for research on microbial diversity and biogeography, along with exploring the role played by historical factors and dispersal limitation in shaping microbial biogeography. We assess the discrepancy between latitudinal and longitudinal LDD forA. vas, which is possibly due to contrast in wind patterns and/or likelihood of transport by birds. Our models also suggest that climate change may lead to regional extinction of terrestrial microscopic organisms, thus illustrating the pertinence of including microorganisms in biodiversity conservation research and actions.