Peering through the eyes of the Proteus

BioTechniques News
Georgia Bickerton

Researchers have produced x-ray-computed microtomography scans of the endangered Proteus anguinus an aquatic salamander – allowing scientists to study the unique evolutionary adaptations to its subterranean world.  

Charles Darwin described the species as a “wreck of ancient life”. They are carnivorous and tend to swallow their prey whole. They live where it is pitch black. But the adventurous scientist needn’t worry about lurking Grues. Instead, these ‘human fish’, more commonly known as ‘olms’, feed on the small crustaceans inhabiting the inky depths of the karst caves found in Central and Southeastern Europe.  

The colorless serpentine Proteus anguinus was believed to be a baby dragon in the 1600s, but in more recent times is still highly regarded for its sheer evolutionary tenacity. While most amphibians lose their gills as adults, the olm maintains a healthy set of gills and lungs throughout its potentially 100-year-plus lifespan – although the average olm only lives for a respectable 68 years.

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But the proteus is also incredibly rare and so researching their extraordinary evolutionary characteristics is extraordinarily difficult. This makes it incredibly fortunate, then, that international collaboration between scientists has produced detailed 3D reconstructions of the proteus’ head tissue using x-ray-computed microtomography scans of both juvenile and adult proteus heads. Scans allowed researchers to obtain information about the proteus’ fascinating vision-related developmental changes across their lifecycle. 

Samples were gathered from multiple sources, including the proteus’ close relations, the salamander and the axolotl. This allowed them to survey the numerous changes to form, shape and organ structure that the proteus has undergone throughout its evolutionary timeline. The data also allows for comparisons to be drawn between cave and surface-dwelling salamanders.  

Author Lucia Mancini (Elettra Sincrotrone Trieste; Italy) explained, “Thanks to the combined use of synchrotron and laboratory-based analyses, future studies could help to model the mechanisms of behavioral adaptation, to better understand the habitat use.” 

Proteus ancestors were surface-dwelling with functional eyes, but the evolutionary necessity for vision retention disappeared as they began living in subterranean environments, leading to the modern proteus’ incomplete visual organs. Those rudimentary eyes are present in a young proteus, but as they develop into adults, the eyes are lost. In place of vision, other sensory organs need to be developed to ensure survival. Researchers sought to better understand this evolutionary shift. Though this current research focusses on physical changes, the same data can also be used to study behavioral changes.  

“The data will allow us to study perceptive abilities through three-dimensional models and to research behavioral responses in relation to chemical cues, auditory frequencies or emission of signals,” elaborated author Edgardo Mauri (Speleovivarium Erwin Pichl; Trieste, Italy). 

The research benefits other researchers across the globe looking to develop their own projects due to its ease of access. This could save many people the immense effort of attempting to gather nigh on impossible-to-share physical samples of this endangered species. Researchers can access these 3D models and forego the experience of lurking beneath the karst caves of Europe; for there is not always a Proteus anguinus down there, in the dark, waiting to come out…  

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