Conspecific Oophagy by Tadpoles: Conditions for Its Occurrence and Importance as a Source of Anuran Egg Mortality

The prevailing view of tadpoles as mostly herbivorous organisms is changing with multiple reports of carnivory and ontogenetic, spatial, and temporal changes in tadpole diet. One increasingly recognized aspect of tadpole diet is conspecific oophagy of living fertilized eggs. As reports of this behavior accumulate, patterns remain unanalyzed, and implications for population dynamics remain unexplored. We reviewed reports of conspecific oophagy by tadpoles and found that the behavior is taxonomically, phylogenetically, and regionally widespread, with reports worldwide, except Africa, and across 13 families. Additionally, we report the first observations of conspecific oophagy in threatened Chiricahua Leopard Frogs (Rana chiricahuensis). Conspecific oophagy is predominantly reported in species using ephemeral lentic environments, with cannibalistic tadpoles predominantly in advanced developmental stages (Gosner stages 31–38). We found that species engaging in conspecific oophagy share similar reproductive and larval traits, with a few intriguing outliers including R. chiricahuensis and other leopard frogs. We observed conspecific oophagy in R. chiricahuensis in the wild and assessed its effects by monitoring egg masses and evaluating the relative importance of conspecific tadpole abundance and size in predicting egg mass mortality. The size of nearby conspecific tadpoles was the only statistically significant predictor of egg mass survival. Our results underscore the importance of ontogenetic diet changes in tadpole development, which facilitate conspecific oophagy.