Collecting eco-evolutionary data in the dark: Impediments to subterranean research and how to overcome them

Abstract

(1) Caves and other subterranean habitats fulfill the requirements of experimental model systems to address general questions in ecology and evolution. Yet, the harsh working conditions of these environments and the uniqueness of the subterranean organisms have challenged most attempts to pursuit standardized research(2) Two main obstacles have synergistically hampered previous attempts. First, there is a habitat impediment related to the objective difficulties of exploring subterranean habitats and our inability to access the network of fissures that represent the elective habitat for the so-called “cave species.” Second, there is a biological impediment illustrated by the rarity of most subterranean species and their low physiological tolerance, often limiting sample size and complicating lab experiments.(3) We explore the advantages and disadvantages of four general experimental setups (in-situ, quasi in-situ, ex-situ, and in-silico) in the light of habitat and biological impediments. We also discuss the potential of indirect approaches to research. Furthermore, using bibliometric data, we provide a quantitative overview of the model organisms that scientists have exploited in the study of subterranean life.(4) Our over-arching goal is to promote caves as model systems where one can perform standardised scientific research. This is important not only to achieve an in-depth understanding of the functioning of subterranean ecosystems but also to fully exploit their long-discussed potential in addressing general scientific questions with implications beyond the boundaries of this discipline.

Global distribution of microwhip scorpions (Arachnida: Palpigradi)

“…This bias is well-exemplified by 'deepest habitats' (Mammola, 2020), such as the bottom of the sea and the deep subsurface biosphere at depths of kilometers into the Earth's crust. De facto, organisms inhabiting these difficult-to-access habitats are likely to be less known compared to those living at the surface (Ficetola et al, 2019;Guerra et al, 2020;Mammola, Lunghi, et al, 2020;Pipan et al, 2020).…”

Refining sampling protocols for cavefishes and cave crayfishes to account for environmental variation

“…Cavefishes and cave crayfishes are typically surveyed by 1-3 people walking, crawling, or snorkeling slowly upstream in caves while recording the number of organisms observed (e.g., Graening et al , 2010Bichuette and Trajano 2015;Behrmann-Godel et al 2017). Stygobiotic organisms (groundwater obligates, Sket 2008) may go undetected during visual surveys due to similar environmental factors as surface aquatic environments (e.g., water depth, turbidity), but also because researchers can only access limited portions of the underground ecosystem and accessible areas are often difficult to traverse (Mammola et al 2020). Additionally, the biology of cave organisms (e.g., low density due to k-selected life history and uneven distributions within caves) makes them difficult to detect (Mammola et al 2020).…”

“…Stygobiotic organisms (groundwater obligates, Sket 2008) may go undetected during visual surveys due to similar environmental factors as surface aquatic environments (e.g., water depth, turbidity), but also because researchers can only access limited portions of the underground ecosystem and accessible areas are often difficult to traverse (Mammola et al 2020). Additionally, the biology of cave organisms (e.g., low density due to k-selected life history and uneven distributions within caves) makes them difficult to detect (Mammola et al 2020). Several cave surveys may be needed to detect stygobionts; thus, estimates of species occupancy and richness are skewed toward commonly sampled locations (Culver et al 2004;Krejca and Weckerly 2008).…”