Developmental polyphenism shapes juvenile behaviours and glucocorticoid regulation in spadefoot toads.

Developmental plasticity allows organisms to generate phenotypic variation in response to environmental cues, adaptively matching local conditions. The most striking plasticity is developmental polyphenism, where a single genotype produces two or more discrete morphs, each defined by a suite of integrated traits. However, few studies address how these suites can be decoupled, within or across life stages. To address this question, we collected polyphenic Spea tadpoles-which develop as omnivores or predatory carnivores depending on ecological conditions-from three ponds and reared them under common garden conditions to measure juvenile traits ('carry-over effects'). We found that developmental acceleration-a carnivore-associated trait-could be decoupled in response to hydroperiod. Tadpoles that did not accelerate development avoided, as juveniles, mortality and putatively maladaptive prey-capture behaviours seen in fast-developing tadpoles. Further, tadpoles that did accelerate development could decouple body condition from glucocorticoid regulation, recalibrating juvenile exploratory behaviour. While these carry-over effects depended on accelerated development, others, such as impaired juvenile locomotion, occurred regardless of developmental speed. Thus, while some carry-over effects are morph-dependent, others arise from interactions between morph and ecological context. Overall, our findings demonstrate that polyphenism leaves a lasting mark on later life, suggesting that carry-over effects can shape polyphenism evolution.