Plasticity-first evolution (PFE) posits that novel features arise when selection refines pre-existing phenotypic plasticity into an adaptive phenotype. However, PFE is controversial because few tests have been conducted in natural populations. Here we present evidence that PFE fostered the origin of an evolutionary novelty that allowed certain amphibians to invade a new niche—a distinctive carnivore morph. We compared morphology, gene expression and growth of three species of spadefoot toad tadpoles when reared on alternative diets: Scaphiopus holbrookii, which (like most frogs) never produce carnivores; Spea multiplicata, which sometimes produce carnivores, but only through diet-induced plasticity; and Spea bombifrons, which often produce carnivores regardless of diet. Consistent with PFE, we found diet-induced plasticity—in morphology and gene expression—in Sc. holbrookii, adaptive refinement of this plasticity in Sp. multiplicata, and further refinement of the carnivore phenotype in Sp. bombifrons. Generally, phenotypic plasticity might play a significant, if underappreciated, role in evolutionary innovation.
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We thank W. Zhang and K. O’Donnell for assistance with animal care, A. Serrato-Capuchina for help collecting tadpoles, and K. Pfennig, I. Ehrenreich, C. Ledón-Rettig, D. Matute, C. Martin, R. Martin and A. Levis for comments on the manuscript. Funding was provided by the National Science Foundation grants DEB-1643239 and DEB-1753865.
The authors declare no competing interests.
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Levis, N.A., Isdaner, A.J. & Pfennig, D.W. Morphological novelty emerges from pre-existing phenotypic plasticity. Nat Ecol Evol 2, 1289–1297 (2018) doi:10.1038/s41559-018-0601-8
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