Oribatid mites show that soil food web complexity and close aboveground-belowground linkages emerged in the early Paleozoic

Ina Schaefer,Tancredi Caruso

doi:10.1038/s42003-019-0628-7

Ina Schaefer, Tancredi Caruso

Open Access

https://doi.org/10.1038/s42003-019-0628-7

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Abstract

The early evolution of ecosystems in Palaeozoic soils remains poorly understood because the fossil record is sparse, despite the preservation of soil microarthropods already from the Early Devonian (~410 Mya). The soil food web plays a key role in the functioning of ecosystems and its organisms currently express traits that have evolved over 400 my. Here, we conducted a phylogenetic trait analysis of a major soil animal group (Oribatida) to reveal the deep time story of the soil food web. We conclude that this group, central to the trophic structure of the soil food web, diversified in the early Paleozoic and resulted in functionally complex food webs by the late Devonian. The evolution of body size, form, and an astonishing trophic diversity demonstrates that the soil food web was as structured as current food webs already in the Devonian, facilitating the establishment of higher plants in the late Paleozoic.

Highlights

Terrestrial ecosystems above and below the ground are intricately linked by nutrient exchange between plants and soil-living decomposers[1]
Free-living species occur patchy in moist environments that are high in organic matter, or in ephemeral habitats, such as decaying logs, fungal fruiting bodies, dung, carrion or tree holes, and play a limited role in terrestrial soil food webs[5,29]
We included three prostigmatid mites as a outgroup taxon to Acariformes, but ignored non-mite chelicerate taxa as outgroups in this study, because we focused on trait evolution and divergence times of nodes and branches only within oribatid mites

Summary

Introduction

Terrestrial ecosystems above and below the ground are intricately linked by nutrient exchange between plants and soil-living decomposers[1]. To infer the development of soil food webs over geological times, oribatid mites are interesting as they have an outstanding fossil record among soil-living arthropods, ranging from the Devonian to more recent deposits in Miocene amber They are abundant as subfossils, especially from peat deposits, and are recognized as valuable indicators for palaeoenvironmental reconstructions[10,11]. The body plan of early acariform mites appeared suddenly in the fossil record without transitional characters linking them to earlier fossil chelicerates[20], but many fossils show striking resemblance to extant families and species, demonstrating morphological stasis for millions of years[12,20,21,22] This stasis suggests the existence of phylogenetic trait conservatism in this group, which is potentially very important. We aimed to analyze the evolution of variation in body size, form, and trophic strategies in relation to the increase in habitat complexity and availability of resources over geological time, and to test if major changes match with functional shifts in aboveground vegetation since the occurrence of vascular plants in the Late Silurian 425 mya

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