Comparison of Eggshell Mineral Content and Oviposition Success between Captive- and Wild-Bred Eastern Indigo Snakes (Drymarchon couperi)

Dystocia is well documented in captive eastern indigo snakes (Drymarchon couperi; EISs), and differences in plasma biochemical parameters have been noted between snakes that successfully oviposited versus those that had dystocia. The objectives of this study were to 1) measure 13 minerals in EIS eggshells from wild-bred and captive-bred snakes and 2) determine whether mineral content of EIS eggshells differed depending on the origin (wild-bred Georgia vs. wild-bred Florida vs. captive bred) and dystocia status (captive bred successfully hatched vs. dystocia) of the snakes. Four clutches of dried, previously hatched or surgically removed and stored eggshells were randomly selected for each EIS group, and three eggshells from within each clutch were randomly selected for analysis on a dry matter basis by spectroscopy. Differences were found between EIS origin groups for four minerals: manganese (F = 6.015, P = 0.006), selenium (F = 32.6, P < 0.001), potassium (F = 3.976, P = 0.026), and zinc (F = 3.316, P = 0.050). Significant differences in eggshell mineral composition were also determined for dystocia versus successfully oviposited captive-bred EISs for magnesium (F = 6.425, P = 0.016), phosphorus (F = 4.148, P = 0.016), and sodium (F = 5.287, P = 0.028). No significant difference in mineral content was found within clutch for any mineral. These findings suggest that differences in environment and diet may play a role in the mineral composition of EIS eggshells. Further research is needed to elucidate how these differences increase the risk of dystocia in captive EISs.