Anticipatory plasticity: frog embryos respond to environmental cues by producing an adaptive phenotype at hatching

Developmental plasticity can occur at any life stage, but a context in which it might be crucial is when individuals that produce specific phenotypes early in development gain a competitive advantage at a later life stage. Here we asked if pre-hatching (embryonic) exposure to a nutrient-rich resource can impact hatchling morphology in tadpoles of Mexican spadefoot toads, Spea multiplicata. Induction of a distinctive carnivore morph can occur when a tadpole eats live fairy shrimp. We investigated whether cues from fairy shrimp, detected as embryos, determine hatchling morphology in a manner allowing individuals to take advantage of this nutritious resource. We found that hatchlings with embryonic exposure to shrimp were larger and had larger jaw muscles––traits that increase their ability to compete for shrimp. Thus, embryos can assess and respond to environmental cues by producing preemptive resource-use phenotypes. Such anticipatory plasticity may be an important but understudied form of developmental plasticity.