Indeterminate Growth in Desert Tortoises

Indeterminate growth, although widely accepted in reptiles, has questionable supporting evidence. In turtles and tortoises, evidence for indeterminate growth is mixed depending on the species, population, and individual. Using a captive colony of desert tortoises, I explored three questions about adult growth: 1) Do tortoises experience growth at reproductively mature size classes? 2) For those adults that experience growth, is growth continuous throughout adulthood? 3) Are there differences in growth and size between males and females? I found that adult tortoises maintained growth potential past reaching sizes deemed sexually mature. Growth rate was strongly related to size. Larger individuals grew less than smaller ones, and the majority of individuals appeared to stop growth at some point during adulthood. Additionally, there was little difference in growth rate between males and females, although males did achieve larger sizes than females. In summary, desert tortoises appear to display a finite growth potential that is regulated by size, sex, and potentially age, but both sexes can grow well past sexual maturity.