Regulation of developmental plasticity in spadefoot toad larvae and its phenotypic consequences

Amphibians have evolved the greatest diversity of reproductive modes across tetrapods. Within this diversity, a large fraction of anuran species maintains complex life cycles including a larval stage. In accordance with the diversity of microhabitats that anuran larvae have specialised in, we observe remarkable variation in tadpole size, shape and pigmentation across species. Inevitably, a lot of this phenotypic variation is the joint result of genomic variation and environmental induction. To understand to what extent such phenotypic variation in anuran larvae may be originated through developmental responses to environmental factors, we have experimentally exposed larvae of Western spadefoot toads (Pelobates cultripes) to factors affecting their growth, development and pigmentation: risk of predation, risk of pond drying, and varying background colour. Phenotypic responses to these factors individually resulted in altered size, body shape, pigmentation and time to metamorphosis, reproducing in a single experiment the range of phenotypic variation observed throughout the entire distribution range of the species. Moreover, when these factors were crossed, we observed interactive and at times conflicting phenotypic responses of the larvae, suggesting complex regulation of these developmental responses resulting in a fine-tuned adjustment to the local conditions experienced.