Phylogenetic patterns of plasticity: Insights from predator-induced embryos and tadpoles

Background/Question/Methods

Phenotypic plasticity is a ubiquitous phenomenon in nature. Over the past several decades, researchers have provided a tremendous number of insights regarding the ecology and evolution of plasticity of species across a wide range of taxa. However, we know relatively little about how these responses have evolved within a phylogenetic context. Ideally, one would need to conduct identical experiments on a large number of species within a taxonomic group. Doing so would allow assessments of phylogenetic signal for the traits and the trait plasticities of species, which can both constrain the evolution of the traits expressed in different environments. Further, one could examine patterns of plasticity in relation to the habitat breadth , with the expectation that species living across a wider breadth of habitats would evolve greater plasticity. In a large collaborative effort, we addressed these questions by conducting predator-induction experiments on amphibian embryos and predator- and competitor-induction experiments on amphibian tadpoles. Using 20 species of amphibians, we quantified traits that spanned life history, morphology, and behavior.

Results/Conclusions

The embryo experiments documented large difference in life history traits among species such as time to hatching, mass at hatching, and developmental stage at hatching.  After constructing a phylogeny of the amphibians, we found significant phylogenetic signal in these traits. Several species exhibited predator-induced plasticity in their life history traits and this plasticity did not exhibit any phylogenetic signal. The tadpole experiments also documented large differences in relative morphology and activity level. The morphological and behavioral traits exhibited significant phylogenetic signal. Plastic responses were widespread in the tadpoles including predator-induced increases in relative tail depth and decreases in activity. Once again, the plasticity of the morphological traits did not exhibit phylogenetic signal. However, the plasticity of tadpole activity was the one trait that did exhibit phylogenetic signal. This suggests that the plasticity of morphological traits is not constrained from evolving different magnitudes of plasticity whereas activity is somewhat constrained. Finally, our analysis of plasticity versus habitat breadth refuted the prediction that species spanning a wider range of habitats have evolved greater trait plasticity. Collectively, these results suggest that whereas species traits can be phylogenetically constrained, the plasticity of these traits may be quite easily modified over evolutionary time.