Cave Evolution

Abstract

Cave‐dwelling animals are fascinating because of the phenotypic extremes they frequently exhibit, such as a reduced vision and pigmentation. Equally interesting is the fact that irrespective of taxonomic position, organisms colonising the subterranean environment converge on highly similar phenotypic deficits and improvements. Thus, a predictable suite of morphological, physiological and behavioural changes evolve in response to low nutrient conditions of the subterranean environment. Despite several decades of enquiry, the precise genetic and molecular underpinnings of cave‐associated changes are only beginning to be elucidated through the use of high‐resolution contemporary molecular and genetic techniques. Regressive phenotypic changes, those traits that are lost in derived lineages, are particularly interesting since they evolve in the absence of obvious selective value to the organism. Continuing research utilising an increasing number of emerging cave‐dwelling models offers the exciting prospect of clarifying longstanding problems in contemporary evolutionary biology. Key Concepts Widespread convergence on cave‐associated (troglomorphic) characteristics is frequently attributed to the reduced nutrition and overall stability of the cave environment. Cave‐adapted organisms are excellent models for the study of regressive phenotypic evolution, that is. the loss of traits in derived organisms. The evolutionary mechanism(s) accounting for phenotypic loss in cave‐dwelling organisms (neutralism versus selection) remains unknown. Hybrid crosses between cave‐ and surface‐dwelling morphs demonstrate that numerous morphological changes associated with cave adaptation are recessive. Phenotypic analyses in experimental pedigrees have revealed that cave‐associated characteristics arise through both Mendelian (single locus) and complex (polygenic) patterns of inheritance. The cave environment is an attractive habitat given that over 50 000 cave‐limited species are known worldwide, distributed across broad taxonomic groups. Contemporary cave research has advanced significantly over the last decade thanks to integrative analyses combining developmental, genetic, genomic, behavioural, physiological and population‐level approaches. Genomic and transcriptomic techniques are providing new insights to the underlying genetic changes mediating cave evolution, and how genomes evolve in the subterranean habitat.

The cave beetle genus Anthroherpon is polyphyletic; molecular phylogenetics and description of Graciliella n. gen. (Leiodidae, Leptodirini)

“…Subterranean environments are considered to be extreme because of highly stable abiotic conditions and low nutrient availability. Species that have colonized these habitats evolve a somewhat predictable suite of morphological, physiological and behavioural characteristics (Gross, 2012;Trontelj et al, 2012), including eye degeneration, depigmentation, development of sensory organs, longer life cycles, lower metabolic rate, and body shape modifications (Racovitza, 1907;Vandel, 1964;Culver et al, 1990;Faille et al, 2009). This set of characteristics is known as 'troglobiomorphy' or 'troglomorphy' and organisms characterized by these features are often restricted to subterranean environment (troglobites).…”