A 20-year record of captive breeding of a female Heosemys grandis revealed a tradeoff between egg size and clutch size across the years when she produced 2 clutches per breeding season. First clutches had few large eggs and second clutches had a large number of smaller eggs. Four F1 progeny from this founder female began their reproductive years with much smaller eggs; however, their eggs increased in size over successive years until they were the same size as those of the long-term breeder.