Testing the ‘caves as islands’ model in two cave-obligate invertebrates with a genomic approach

Abstract

Caves offer selective pressures that are distinct from the surface. Organisms that have evolved to exist under these pressures typically exhibit a suite of convergent characteristics, including a loss or reduction of eyes and pigmentation. As a result, cave-obligate taxa, termed troglobionts, are no longer viable on the surface. This circumstance has led to a "caves as islands" model of troglobiont evolution that predicts extreme genetic divergence between cave populations even across relatively small areas. An effective test of this model would involve (1) common troglobionts from (2) nearby caves in a cavedense region, (3) good sample sizes per cave, (4) multiple taxa, and (5) genome-wide characterization. With these criteria in mind, we used RAD-seq to genotype an average of ten individuals of the troglobiotic spider Nesticus barri and the troglobiotic beetle Ptomaphagus hatchi, each from four closely located caves (ranging from 3-13 km apart) in the cave-rich southern Cumberland Plateau of Tennessee, USA. Consistent with the caves as islands model, we find that populations from separate caves are indeed highly genetically isolated. In addition, nucleotide diversity was correlated to cave length, suggesting that cave size is a dominant force shaping troglobiont population size and genetic diversity. Our results support the idea of caves as natural laboratories for the study of parallel evolutionary processes.

Integrating landscape ecology and the assessment of ecosystem services in the study of karst areas

“…It has sometimes been assumed that caves are isolated elements because populations of cave-adapted organisms can be extremely isolated (Culver 1970;Snowman et al 2010;Balogh et al 2020), although there is growing evidence of extensive gene flow between karst systems (Buhay and Crandall 2005). Cave entrances are critical for human access, they typically occur as a chance intersection of an evolving underground environment with the surface (Culver and Pipan 2019) and represent only a small portion of a cave system.…”

Exploring the homogeneity of terrestrial subterranean communities at a local spatial scale

“…Ecologists and evolutionary biologists have frequently compared caves to islands (Culver, 1970;Snowman et al, 2010;Esposito et al, 2015;Fattorini et al, 2016;Balogh et al, 2020). In fact, from the perspective of a specialised subterranean Correspondence: Stefano Mammola, Molecular Ecology Group (MEG), Water Research Institute (IRSA), National Research Council (CNR), Verbania Pallanza, Italy.…”