Monitoring health and reproductive status of olms (Proteus anguinus) by ultrasound

Abstract

The olm (Proteus anguinus) is a troglomorphic, neotenous amphibian with extraordinary life expectancy and unique adaptations that deserve further investigation. A low reproductive rate and habitat decline render it threatened by extinction. Establishing captive populations for maintenance and artificial breeding may one day become crucial to the species. Longitudinal, in-vivo assessment of inner organs is invaluable to our understanding of reproductive physiology, health, and behavior. Using ultrasound, we measured heart rate and assessed health and reproductive status of 13 captive olms at Zagreb Zoo. Heart rate averaged 42.9 ± 4.6 bpm (32–55 bpm), as determined via pulsed-wave Doppler at 4–12 MHz. By using frequencies of up to 70 MHz (ultrasound biomicroscopy), inner organs were visualized in detail. Assessment of the gastrointestinal tract provided insights into feeding status and digestive processes. Several subclinical pathologies were detected, including biliary sludge, subcutaneous edema, ascites, and skin lesions. Detection of skin lesions by ultrasound was more sensitive than visual adspection. Olms with ultrasonographically detected skin lesions tested positive for Saprolegnia and were treated. Three of the four affected individuals survived and subsequently tested negative for Saprolegnia. Sex was reliably determined; only one individual proved male. The reason for this extreme female-biased sex-ratio remains unknown. However, as most of the individuals were flushed from the caves by strong currents in spring, the sample may not be representative of natural populations. In female olms, different stages of ovarian follicular development were observed with diameters ranging between 0.1 and 1.1 mm. Results were confirmed by comparing ultrasound, necropsy, and histological findings of one dead specimen. In summary, ultrasound proved a valuable tool to support conservation and captive breeding programs by allowing non-invasive assessment of physiological parameters, clinical condition, and reproductive status in olms.

Ultrasound description of the coelomic cavity of the axolotl (Ambystoma mexicanum) in a healthy population: a pilot study

“…24 Hyperechogenic millimetric particles were found in the lumen of the gallbladder in 9 axolotls, which is consistent with images obtained in olm (Proteus anguinus). 41 Larger hyperechoic particles are reported in one axolotl and in case of cholelithiasis in giant ditch frog (Leptodactylus fallax). 18,45 As our axolotls display a normal clinical state, it remains di cult to a rm if hyperechogenic millimetric particles in gallbladder are physiological or pathological.…”

“…50 Other amphibians' kidneys (Proteus anguinus, Andrias davidianus and Dyscophus antongil) are located in caudal part of coelomic cavity. 25,41,51 In axolotls they were easily observed dorsally to the pelvic members. A central vessel was observed in all axolotls.…”

“…40 This increased heart rate could be explained by movements associated to contention or stress as previously shown in amphibian. 41,42 Therefore, we strongly advised to monitor heart rate at the beginning of experiment or clinical examination.…”

“…46 Gallbladder distension is also recognized as an ultrasonographic feature in cholelithiasis and cholecystitis, However physiological variation of gallbladder dimensions has been reported in olms and in mammals. 41,47 According to the organ's axis, this parameter showed signi cant differences, thus it has been chosen to not measure it in this study…”

Alternative Animal Models of Aging Research

“…As resources, specific cell populations may be interesting in the context of long-term genome maintenance, for example, the so-called cell clusters of the intestine, which represent slowly proliferating stem cells of intestinal epithelium (Bizjak Mali and Bulog, 2004). Establishing captive Proteus anguinus populations is important not only for studies of the mechanisms of aging, but also for preservation of this endangered species (Holtze et al, 2017). Other neotenic amphibians that demonstrate a longer lifespan compared to endotherms of similar body mass include the common mudpuppy (Necturus maculosus), a species of the sister evolutionary branch (Zhang and Wake, 2009) that has a predicted lifespan of 34 years, and as a more distant relative, the axolotl (Ambystoma mexicanum) that lives for about 20 years (Tacutu et al, 2018).…”