This study describes gonadal changes in lizards ( Uta stansburiana ) exposed to chronic low levels of γ radiation (1.5-10 R/day) under field conditions and attempts to evaluate endocrine involvement in these changes. Reproductive impairment in irradiated males is demonstrated during the breeding season by reduced testes weights and by seminiferous tubules devoid of germ cells. Ultrastructural morphology of Leydig cells, plasma testosterone levels, and developed accessory sex structures indicate normal steroidogenesis in such males; cytology of the pituitary gonadotropes and pituitary gonadotropin content indicate normal gonadotropin levels. These findings suggest that low levels of radiation affect the spermatogenic process directly, rather than through damage to the pituitary. Comparable irradiation causes complete resorption of ovarian tissue in some female Uta . The oviducts are atrophic and the pituitary gonadotropes hyperactive. Resemblance of gonadotropes to those of castrated animals and reduced pituitary hormone content suggest elevated levels of gonadotropin production, probably due to the absence of ovarian steroid feedback in affected animals. The continued mitotic activity of oogonia in adult reptiles and their limited number contribute to the vulnerability of germinal tissue in irradiated female lizards. Destruction of the germ cells is accompanied by resorption of all ovarian tissue including steroidogenic elements. Thus, in females as in males, radiation appears to damage gametogenesis rather than pituitary function.

Nevada↗

USGS1978

The status of the flat-tailed horned lizard, (Phrynosoma mcallii), at nine sites in Imperial and Riverside counties, California

No abstract available at this time

Report↗

USGS1977

Sterility among female lizards (Uta stansburiana) exposed to continuous gamma irradiation

A natural population of the lizard Uta stansburiana occupying a fenced 9-ha area in southern Nevada was exposed to essentially continuous γ irradiation from an artificial source between February 1964 and September 1973. Tissue doses were estimated using implanted lithium fluoride microdosimeters. Females became sterile as early as 11 months of age, but many were still fertile at ages of 20 months and a very few may have reproduced at 32 months. Dosimetry showed some females to be sterile after accumulated doses of around 500 rad, while others may have required 1000 or more rad. One female estimated to have received over 1200 rad was still reproductive. Irradiated females may pass through a state of half sterility, during which time they possess one functional ovary. Female U. stansburiana are sterilized at lower doses than the sterilizing dose (1500 rad) previously suggested for the leopard lizard, Crotaphytus wislizenii .

Nevada↗

USGS1976

The impact of off-road vehicles on a desert ecosystem

The effects of operating a 4-wheel drive truck in a 9-ha area of the Mojave Desert were evaluated. A truck was driven over the same 0.9-km track 21 times between November 1973 and May 1974. The vehicle was also driven randomly around the area (1.3 to 3.4 km) 17 times between December 1973 and May 1974.

Environmental Management↗

USGS1976