Dual Energy Computed Tomography for Diagnosis and Monitoring Attempted Medical Management of a Large Urate Urolith in a Desert Tortoise (Gopherus agassizii)

An estimated 29-year-old male, desert tortoise ( Gopherus agassizii ) under professional care presented for endoscopic liver biopsies as part of a diagnostic work-up for recurrent, profound anemia and hypoalbuminemia. Suspected cystoliths were identified during endoscopy but were not visible on contemporary radiographs. Dual-energy computed tomography (DECT) imaging confirmed the presence of a large urate urolith filling the majority of the bladder. Due to the recent clinical illness, the tortoise was considered a poor surgical candidate. Medical management consisting of urinary alkalinization with potassium citrate, vibration therapy, and daily warm water soaks was elected. Following institution of medical therapies, the tortoise began passing pieces of urate stone that were 0.25-2.0cm in diameter during daily soaks. A recheck DECT scan at two months indicated the urolith was approximately 1/3 the initial size, suggesting medical therapy was effectively treating the urolith. Unfortunately, after five months of medical therapy, the stone had increased in size again on the follow-up DECT scan. This case report suggests that medical management may be a potential option for large urate cystoliths in desert tortoises, though more research is needed to further refine effective therapeutics for such cases. The use of dual-energy CT imaging was essential in this case as it enabled confirmation of stone presence, identification of urolith composition, and monitoring of response to therapy.

Cytologic and Histologic Findings of Nephroblastoma in a Captive Desert Tortoise (Gopherus agassizii)

A 97-year-old, male, captive desert tortoise ( Gopherus agassizii ) had a 2 month history of lethargy. Imaging with ultrasound, X-ray, and computed tomography revealed a 10-cm-diameter mass in the caudal coelom. Fine needle aspiration revealed spindle and epithelial cell proliferations with formation of rosettes. Exploratory surgery was performed and the mass was removed and submitted for pathology. There was no evidence of metastasis on imaging or at surgery. Histology revealed a mass arising from and compressing the kidney. The mass was composed of primitive glomeruli, tubules, blastemal cells, and mesenchymal cells, features that are diagnostic for nephroblastoma. Tubules were reactive to cytokeratin and mesenchymal cells were reactive to desmin via immunohistochemistry; other immunohistochemical markers were either negative (i.e. S-100) or non-contributory (i.e. epithelial membrane antigen, myogenin, vimentin, and Wilms’ Tumor 1). This is the first report of nephroblastoma in a chelonian.

Comparing post-release cover and burrow use by differentially head-started Mojave desert tortoises in southern California

The effects of indoor rearing versus the conventional method of solely outdoor head-starting on post-release cover and burrow use of juvenile Mojave desert tortoises (Gopherus agassizii), a threatened endemic species, were investigated. We found that partially indoor-reared tortoises exhibited similar post-release behaviours when compared to both same-aged, but smaller, and similar-sized, but older outdoor-reared head-started tortoises, thus increasing the success and decreasing the costs of head-starting.

Individual heterozygosity predicts translocation success in threatened desert tortoises

Anthropogenic environmental modification is placing as many as 1 million species at risk of extinction. One management action for reducing extinction risk is translocation of individuals to locations from which they have disappeared or to new locations where biologists hypothesize they have a good chance of surviving. To maximize this survival probability, the standard practice is to move animals from the closest possible populations that contain presumably related individuals. In an empirical test of this conventional wisdom, we analyzed a genomic dataset for 166 translocated desert tortoises (Gopherus agassizii) that either survived or died over a period of two decades. We used genomic data to infer the geographic origin of translocated tortoises and found that individual heterozygosity predicted tortoise survival, whereas translocation distance or geographic unit of origin did not. Our results suggest a relatively simple indicator of the likelihood of a translocated individual’s survival: heterozygosity.

Head-started Agassiz’s desert tortoises Gopherus agassizii achieved high survival, growth, and body condition in natural field enclosures

We measured survival, growth, and body condition of 8 hatchling cohorts of desert tortoises Gopherus agassizii (living in predator-resistant outdoor pens in the Mojave Desert, California, USA) over 11 yr to evaluate head-starting methods. At 11 yr of age, 7 times as many of the first cohort had survived than if they had been free-living tortoises. Subsequent improvements in predator control, food and water supplementation, and pen structure increased survival from 7 to 10 times that under wild conditions in younger cohorts. Annual survival averaged 96%. Carapace length (CL) increased 6.95 mm yr-1, similar to that of free-living tortoises. Annual growth rates varied with calendar year (possibly reflecting food and water supply), age, cohort (year hatched), mother, and in 4 dry years, with crowding. Most of the first cohort grew to a releasable size (CL >100 mm) by their 9th year. Body condition indices remained high, indicating little dehydration despite droughts in 8 of the 11 years, because irrigation offered drinking opportunities. Head-started tortoises developed fully hardened shells (≥98% of adult shell hardness) earlier (10.1 vs. 11.6 yr), but at a larger CL (117 vs. 104 mm) than did free-living tortoises. Selective feeding in head-start pens decreased subsequent germination of favored wildflower species, apparently by reducing the natural seedbank. Consequently, we reseeded and irrigated each autumn to promote subsequent spring food supply. We irrigated in early summer to enable drinking and ensuing consumption of dry, dead plants and Bermuda grass hay, a supplement. These procedures can greatly improve juvenile survivorship, and increase numbers of hard-shelled, midsized juveniles to help augment wild populations.