Extreme Adaptation in Caves

Abstract

Cave adaptation leads to unique anatomical specializations in many taxonomic groups. As the role of vision is reduced or disappears in a subterranean environment, other specializations arise to allow the organism to successfully detect and interact with their environment. A suite of unique, convergent phenotypes associated with subterranean adaptation has emerged (termed troglomorphy), with reduction or loss of pigmentation and eyes being the most conspicuous. Two vertebrate groups that have successfully colonized and adapted to subterranean environments are cavefishes and cave salamanders. There are many shared troglomorphic anatomical characters shared between these two groups, and we describe herein the morphological traits that are unique to fishes and salamanders that are adapted to caves and other subterranean habitats. Troglobionts, animals strictly bound and adapted to underground habitats, are outcomes of not just regressive evolution, but also constructive adaptation. There are skeletal changes, such as broadening and flattening of the head, as well as hypertrophy of non-visual modalities. Cavefishes and salamanders have lost eyes and pigmentation, but also enhanced mechanosenzation, chemosenzation and, in some cases, electroreception. Both cavefishes and cave salamanders have become important models in the study of the ecology, behavior, and evolution of subterranean colonization and adaptation. However, our knowledge is primarily limited to a few taxa and many questions remain to be studied. Anat Rec, 303:15-23, 2020.

Cave‐adapted evolution in the North American amblyopsid fishes inferred using phylogenomics and geometric morphometrics

“…The convergent loss of complex traits can occur in extreme environments that impose harsh selection pressures such as caves (Trontelj et al. 2012; Soares and Niemiller 2020). Whether these traits are lost forever remains an important topic in evolutionary biology (reviewed by Porter and Crandall 2003 and Collin and Miglietta 2008).…”

“…2006) and eye structures/visual systems in many cave‐obligate organisms (Trontelj et al. 2012; Soares and Niemiller 2020).…”

“…Convergence on reductive traits in cave animals is apparent with pale forms devoid of pigment, the elongation of limbs, and loss of eyes (Poulson 1963; Hedin and Thomas 2009; Christiansen 2012; Pipan and Culver 2012; Trontelj et al. 2012; Soares and Niemiller, 2013, 2020). Additional morphological convergence, such as body shape convergence (e.g., dorsoventral head‐flattening and a duck‐bill‐like rostral flaring), has been noted in cave‐obligate vertebrates ranging from fishes to salamanders, but has not yet been quantified (Christiansen 2012; Fenolio et al.…”

“…Additional morphological convergence, such as body shape convergence (e.g., dorsoventral head‐flattening and a duck‐bill‐like rostral flaring), has been noted in cave‐obligate vertebrates ranging from fishes to salamanders, but has not yet been quantified (Christiansen 2012; Fenolio et al. 2013; Edgington and Taylor 2019; Soares and Niemiller 2020).…”

Extreme Anatomy: Gear for the Pioneer

“…One such niche lies hidden deep in caves where no light penetrates, resulting in a lack of plant life and thus a dearth of resources. Soares and Niemiller (this issue) describe unique features of fishes that occupy the dark world. Their unique phenotype, troglomorphy, includes features one might expect in deep, dark dwellers: reduction or loss of the eyes and dermal pigmentation.…”