25th Annual Meeting and Symposium of the
Desert Tortoise Council, April 21-24, 2000
Abstracts

Egg Follicles and Yolks of Sonoran Desert Tortoises (Gopherus agassizii)

Brian T. Henen^1,2, Roy C. Averill-Murray³ and Christopher M. Kluge^4
1Smithsonian Institution, National Zoological Park, Department of Zoological Research, 3001 Connecticut Avenue, Washington, D.C. 20008
²Desert Tortoise Conservation Center, Las Vegas, NV
^3,4Arizona Game and Fish Department, Nongame Branch, 2221 West Greenway Rd.,
Phoenix, AZ

There are many differences between desert tortoises of the Mojave and Sonoran Deserts, including aspects of tortoises reproductive biology. To develop a better mechanistic understanding of these reproductive differences, we used ultrasonography to measure the number and size of vitellogenic and atretic follicles, plus egg yolk width, in wild, female Sonoran tortoises during May, July, August and October 1999. As typified by desert tortoises, there was extreme individual and temporal variation in all of these measures. Vitellogenic follicles were large during May and July but appeared to be small and numerous in October. Atretic follicles were not detected until after the peak periods of oviposition (July) but then they were abundant. Egg yolks, and shelled or oviductal eggs, were most numerous in July. Body size effects were weak, having mild effects upon the size of vitellogenic follicles prior to and during peak oviposition times (May and July) but not affecting atretic follicle size or number. Although some relatively small females (<239 mm MCL) had vitellogenic follicles, these females did not produce shelled eggs. Smaller tortoises of the Sonoran and Mojave Deserts can produce eggs, so the smaller females may have had insufficient nutrients available (as body reserves and fresh food) in 1999 to convert their follicles into eggs.