Living in darkness: Exploring adaptation of Proteus anguinus in 3 dimensions by X-ray imaging

Abstract

Background Lightless caves can harbour a wide range of living organisms. Cave animals have evolved a set of morphological, physiological, and behavioural adaptations known as troglomorphisms, enabling their survival in the perpetual darkness, narrow temperature and humidity ranges, and nutrient scarcity of the subterranean environment. In this study, we focused on adaptations of skull shape and sensory systems in the blind cave salamander, Proteus anguinus, also known as olm or simply proteus—the largest cave tetrapod and the only European amphibian living exclusively in subterranean environments. This extraordinary amphibian compensates for the loss of sight by enhanced non-visual sensory systems including mechanoreceptors, electroreceptors, and chemoreceptors. We compared developmental stages of P. anguinus with Ambystoma mexicanum, also known as axolotl, to make an exemplary comparison between cave- and surface-dwelling paedomorphic salamanders. Findings We used contrast-enhanced X-ray computed microtomography for the 3D segmentation of the soft tissues in the head of P. anguinus and A. mexicanum. Sensory organs were visualized to elucidate how the animal is adapted to living in complete darkness. X-ray microCT datasets were provided along with 3D models for larval, juvenile, and adult specimens, showing the cartilage of the chondrocranium and the position, shape, and size of the brain, eyes, and olfactory epithelium. Conclusions P. anguinus still keeps some of its secrets. Our high-resolution X-ray microCT scans together with 3D models of the anatomical structures in the head may help to elucidate the nature and origin of the mechanisms behind its adaptations to the subterranean environment, which led to a series of troglomorphisms.

Request for an Opinion: conservation of the illegitimate prokaryotic generic name Proteus Hauser 1885 (Approved Lists 1980)

“…According to Rule 51b(5) of the ICNP, names that were validly published and not treated as later homonyms prior to 1 January 2001 are not affected and therefore the homonymy between the amphibian Proteus Laurenti, 1768 and Proteus Hauser 1885 is acceptable in prokaryotic nomenclature [5,6]. In this way, although the amphibian Proteus is in current usage in zoological nomenclature [7][8][9][10], only the earlier homonymy of the protozoan Proteus Müller, 1786 should be factored into the potential illegitimacy of Proteus Hauser 1885 (Approved Lists 1980).…”

Altered developmental programs and oriented cell divisions lead to bulky bones during salamander limb regeneration

“…To address the differences in skeletogenesis, we collected developing, postmetamorphic and regenerating limbs from the newt Pleurodeles waltl, and reconstructed cartilage and bone structures employing phospho-tungstic acid (PTA) enhanced micro-CT according to a published protocol 23,27 . The identification of the border between soft tissues, cartilage and bone was done according to our previously published approach allowing reliable segmentation of soft and stiff tissues in vertebrates, and specifically in salamander species 23,[28][29][30][31] . All samples were 3D-rendered, and subsequent segmentations of the skeletal parts were generated to analyze the regenerating structures (Fig.…”