Tectorial structures on the inner ear sensory epithelia of Proteus anguinus (Amphibia, caudata)

Abstract

The tectorial structures of the inner ear of the proteid salamander Proteus anguinus were studied with transmission and scanning electron microscopy in order to analyze the ultrastructure of the otoconial membranes and otoconial masses of the maculae and the tectorial membrane of the papilla amphibiorum. Both otoconial and tectorial membranes consist of two parts: (1) a compact part and (2) a fibrillar part that joins the membrane with the sensory epithelium. Masses of otoconia occupy the lumina above these membranes. There are two types of calcium carbonate crystals in the otoconial masses within the inner ear of Proteus anguinus. The relatively small otoconial mass of the utricular macula occupies an area no greater than the diameter of the sensory epithelium, and it is composed of calcite crystals. On the other hand, the enormous otoconial masses of the saccular macula and the lagenar macula are composed of aragonite crystals. In the sacculus and lagena, globular structures 2-9 m̈m in diameter were discovered on the lower surfaces of the otoconial masses above the sensory epithelia. These globules show a progression from smooth-surfaced, small globules to large globules with spongelike, rough surfaces. It is hypothesized that these globules are precursors of the aragonite crystals and that calcite crystals develop similarly in the utriculus. The presence of globular precursors in adult animals suggests that the formation of new crystals in the otoconial membranes of the sacculus and lagena of Proteus is a continuous, ongoing process.

Non-visual sensory physiology and magnetic orientation in the Blind Cave Salamander, Proteus anguinus (and some other cave-dwelling urodele species). Review and new results on light-sensitivity and non-visual orientation in subterranean urodeles (Amphibia)

“…In amphibians and in some other vertebrates there are two vertically oriented groups of hair cells in the saccular macula (Lewis et al 1985 ). Proteus has four groups of hair cells with diff erent orientation similar to the pattern in many fi shes (Bulog, 1989a(Bulog, , 1989bPopper 1977Popper , 1981. Th ese fi shes have developed a potential for sound source registration (Popper and Northcutt 1983 ).…”

Wandering outside of the Styx: Surface activity of an iconic subterranean vertebrate, the olm (Proteus anguinus)

“…The olm, Proteus anguinus , is one of the most iconic stygobionts. Except for a clade living in a handful of springs in southern Slovenia (the “black olm” described as Proteus anguinus parkelj Sket and Arntzen (1994)), olms are a complex of depigmented and blind salamanders, specialists of groundwaters (Balazs et al, 2020), that probably colonized caves 8–20 million years ago (Mya) (Bulog, 1994; Recknagel et al, in press; Trontelj et al, 2007). Olms are the largest troglobiont vertebrates in the world and the only stygobiont amphibians of the Palearctic (Balazs et al, 2020).…”

“…Olms are the largest troglobiont vertebrates in the world and the only stygobiont amphibians of the Palearctic (Balazs et al, 2020). They show impressive adaptations to underground life, including magnetic sensing that partially compensates for blindness (Bulog, 1994;Durand & Parzefall, 1987;Guillaume, 2002;Schlegel, 2008), low metabolic rates (Bizjak Mali et al, 2013), high tolerance for low levels of dissolved oxygen (Beale et al, 2016), and exceptional longevity (Vandel & Durand, 1970). Olms are also obligate paedomorphs, and their study can help in understanding the links between the evolution of paedomorphosis and adaptations to underground environments (Bonett et al, 2014(Bonett et al, , 2022.…”

History of research on Proteus anguinus Laurenti 1768 in Slovenia / Zgodovina raziskovanja človeške ribice (Proteus anguinus Laurenti 1768) v Sloveniji

“…After the World War II, cave fauna was researched at the Department of Biology (Biotechnical Faculty, University of Ljubljana) from 1950s (Sket, 1993A;Aljančič, in press), while proteus was more actively researched from the end of the 1960s, most markedly the functional morphology of proteus, by the Research group for comparative anatomy of vertebrates, led by Prof. Lilijana Istenič, with Aleš Sojar, Boris Bulog, Danilo Musar and associates; particular attention was put on adaptations of proteus to occasional hypoxic conditions of groundwater and lung breathing, accumulation of riboflavin in skin, and studies of inner ear sensory epithelia and mechanoreceptive lateral line system (selected studies: Istenič, 1971;Istenič & Sojar, 1974;Istenič & Zigler, 1974;Istenič, 1976;Istenič & Bulog, 1976;Istenič, 1979;Istenič & Bulog, 1979;Sojar, 1980;Istenič & Bulog, 1984;Bulog, 1989A;Bulog, 1989B), continued by Prof. Boris Bulog since 1989, with Danilo Musar, Lilijana Bizjak-Mali and Marjanca Kos, with numerous students and young researchers (Katarina Mihajl-Dobrovoljec, Gregor Aljančič, Petra-Maja Prelovšek, Marjeta Konec, and others). This research group determine proteus adaptations to its cave environment through advanced histological investigations of proteus morphology, such as the capacities of proteus sensory system (mechanoand electroreception, undeveloped eyes and pineal gland; orientation by Earth magnetic compass and hearing), in collaboration with German physiologist Prof. Peter A.…”