Researchers recently scanned the heads of blind cave salamanders to learn how the species’ dark, aquatic environment shaped its senses. Using X-ray micro-computed tomography, they were able to map the internal layout of the olm’s cranial structures, including the brain, olfactory organs, ears, facial muscles, and the remnants of eyes. What they found was weird, even by salamander standards.
Proteus anguinus (called the olm or the proteus) is a slender, foot-long aquatic salamander native to southern Europe. The earliest written accounts of the animal, by a 17th-century Slovenian naturalist, indicated that people thought olms were the offspring of dragons. The pale salamander can live up to a century. It has an elongated head and very small arms; if you squint, the olm looks like a super-smooth snake. Its bizarre features are the result of troglomorphism—the way cave-dwelling creatures adapt to life in perpetual darkness.
Olms aren’t entirely blind. The larvae are actually born with eyes, which regress shortly after the animals hatch. Adult olms’ vestigial eyes remain photosensitive, though they are beneath the skin—if you shine a light near an olm, it would likely flee. While they don’t have much in the way of vision, the olm’s other senses, particularly smell and hearing, are quite sharp.
The team scanned the heads of the olm and one of its relatives, the endearing axolotl, at different stages of development, in order to compare their divergent anatomies. The larval and juvenile olm scans revealed remnant eyes, but the vestigial eyes and optic nerves of the adult specimen were likely too faint to appear in the scans. The olm’s olfactory cavities are elongated compared to the surface-dwelling axolotl’s, a sign that the blind salamander’s sense of smell improved as its sight declined. Other senses of the olm, like its electrosensitivity and its ability to detect pressure changes in water, require further examination.
One mystery the olm brain scans didn’t reveal much about was the animal’s capacity for regeneration. Like the axolotl, the olm is able to regrow body parts, an ability that makes these salamanders an intriguing subject of study for the future of human medicine.
The 3D models will allow scientists to “research behavioral responses in relation to chemical cues, auditory frequencies or emission of signals,” said study author Edgardo Mauri, a researcher at the Speleovivarium Erwin Pichl in Trieste, in a press release. The new paper is published today in GigaScience. The three-dimensional models are publicly accessible, to further the study of the olm’s morphology down the road.
The axolotl’s genome was first completed in 2019, but far less is known about the olm. The researchers hope these detailed new X-ray scans will help to show how this cave salamander’s regenerative ability may differ from its surface-dwelling relative.