Reproductive investments of a small,arid zone tortoise Chersobius signatus: Follicle and egg development

We used ultrasonography and radiography to evaluate whether body size (BS), body condition (BC) and environmental factors influenced reproductive investments by Chersobius signatus in September 2000 and from September 2003 to November 2004. Follicle volume increased with increasing BS, BC and rainfall but decreased with increasing temperature. Egg volume averaged 8.8% of body volume, increased allometrically with BS, but was not affected by BC, rainfall or temperature and did not differ between first and second clutches. Most females produced at least one single-egg clutch per year, even when BC was low. Many females produced two, possibly more, clutches but some forfeited reproduction in some years. Females often retained large follicles from one season to the next with 18%–71% carrying pre-ovulatory sized follicles in different times of the year. Increasing temperatures likely influenced timing of first ovulations in August while decreasing water and food availability, linked with high temperatures, possibly terminated ovulations by November. The gravid season was short compared to other winter-rainfall tortoises in South Africa. We propose that the females' small bodies may constrain investments in eggs, resulting in low fecundity, which is countered by producing large hatchlings with high survivorship in an arid habitat.