Hyperarid areas of the Atacama Desert are regarded as largely free of animals. However, results with extensive trap systems within B02 of CRC 1211 indicate that there is virtually no “death zone” without animals. Instead, we found a gradual transition from complex food webs via very simple food webs to extremely hyperarid habitats solely inhabited by Maindronia (Insecta: Zygentoma). We plan to use this information for defining the hyperarid core of the Atacama Desert from a biological perspective as a region characterized by the exclusive presence of Maindronia (no other animals). Abiotic variables within and outside the boundaries of this hyperarid core will be studied to determine the key factors responsible for the collapse of more complex food webs and, in turn, the disappearance of desert specialists such as tenebrionid beetles. Habitat characterization will be based on meteorological observations using the CRC implemented weather station network in northern Chile (A01, Z03), and existing paleoclimate data. Surface and subsurface sediment composition (mineralogy, salt content, grain-size, sediment structure) will be analysed in close collaboration with C04 and C09 for representative transects using standard techniques such as XRD, grain‑size determination, and ICP-OES. Analysis of sediment samples also includes the identification of layers containing microorganisms or dead organic remnants. These may serve as food and water source for the Maindronia, but are often difficult or impossible to detect in salt crusts by gene sequencing methods. Therefore, we plan to use SEM and molecular analyses such as GC-MS and NMR as primary detection tools. Our planned extensive grid sampling (25 x 25 km) across the Atacama Desert using trap systems, developed and deployed for such purposes in Phase 2, will not only provide sufficient information regarding the hyperarid core of the Atacama Desert, but will also be used to reconstruct spatially the different “layers of biodiversity” surrounding the hyperarid core. Based on the distribution and molecular analysis of desert arthropod communities, particularly tenebrionid beetles and Maindronia spp., we will further add temporal information on the evolution and migration history of selected taxa to track environmental changes in the past. This detailed information will then be used to postulate key determinants for the evolution of the desert specialists among insects and thus consolidate the knowledge we have accumulated over the entire duration of the CRC. The definition of the hyperarid core of the Atacama Desert based on biological data will be compared to definitions of it on a geological/geomorphic and meteorological perspective, using existing information and gained knowledge from the other CRC subprojects. Our interdisciplinary approach (biological vs geological perspectives) enables a better understanding of what hyperaridity means and what boundary conditions are crucial for biological life and/or geological and geomorphological processes.

Evolution, biogeography and genetic diversity of insects and their associated gregarine protists

Research areas: Evolution, Biodiversity, Phylogeny, Population Genetics

Principal investigator: Prof. Dr. Reinhard Predel, Prof. Dr. Hartmut Arndt

In B02 we study the evolution of insects and their endobiotic protists (gregarines) in the Atacama with a focus on desert specialists such as the hyperdiverse tenebrionid beetles (Tenebrionidae) and silverfish (Zygentoma). Tenebrionid beetles are generally regarded as theinsects best suited for desert colonization and show increasing species diversity with an increasing degree of aridity.

As was shown in phase 1, some silverfish species are in fact evenmore adapted to hyperarid conditions and the remarkable Gondwanan relict Maindronia was identified as the most xerophilic desert animal. A main goal of our subproject is to correlate, on different time scales, the geographical distribution of desert-adapted insects and their co-evolving gregarines with genetic differentiation. The specific adaptation to their hosts, their ability to form cysts as well as their adaptability to extreme conditions make gregarines ideal model organisms for studies of speciation processes and the speed of evolution of host and endobionts and to analyse effects of geological and behavioural separation. This unprecedented dataset will then be correlated with both ancient and present-day biotic and abiotic factors, especially to identify the key conditions that have led to today's diversity and exceptional endemism in the Atacama Desert.

On the younger time scale, we additionally study the colonization of selected transects in the Atacama with population genetic methods for selected species. Extensive data obtained in the first phase on insect distribution and habitat requirements have provided valuable information for hypotheses on survival, speciation and minimum requirements for the existence of animals at the dry limit, which we will test through experimental and/or long-term studies in regions with an increasing aridity level.

For all approaches, the Atacama Desert can be seen as a perfect area for the study of theevolution of life at the dry limit because of habitat fragmentation and the generally low biodiversity. All planned work will benefit greatly from synergies with other subprojects and collaboration with colleagues from Argentina, Peru and Chile.

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