Reproduction in the red-cheeked mud turtle (Kinosternon scorpioides cruentatum) was studied in southeastern Mexico and Belize (Yucatan Peninsula) on the basis of museum and field-collected specimens. Adult females (mean carapace length [CL]  =  110 mm) were not significantly larger than adult males (mean CL  =  108 mm). Females matured at 100–105 mm CL and an estimated age of 9–10 years. Annual reproduction by females was apparently continuous for at least 10 months of the year (August–June), with the production of multiple annual clutches (possibly as many as 5) being typical and the number of clutches per year increasing with female size. Eggs exhibit diapause and embryonic estivation and apparently hatch in nature during the wet season (June–August) after up to 9 months in the nest. Modal clutch size was only 2 eggs (mean 2.2; range 1–4), and clutch size increased with female body size. Egg size averaged 31.5 × 16.6 mm and 5.5 g and did not vary with female body size. Relative egg mass (REM  =  mean egg mass × 100/[body mass − clutch mass]) averaged 2.3, was lower in larger clutches, and decreased with increased body size. Relative clutch mass (RCM  =  REM × clutch size) averaged 4.85, similar to that for the sympatric K. creaseri (4.5), the 2 lowest values reported for any studied Kinosternon population. RCM did not vary with female body size or clutch size. Females devote a relatively constant proportion of body mass to each clutch, and increases in reproductive output with size and age are apparently accomplished by increases in clutch size (but not egg size) and clutch frequency. This unusual suite of reproductive traits (small body size, small clutch size, production of up to 5 clutches per year, reduced relative clutch mass, and embryonic diapause and estivation) may have been instrumental in the success of this species at colonizing more of South America than any other Mesoamerican turtle genus or species and in less than 4 million years.

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