Depending on environmental conditions, tadpoles of the Spea genus can switch from omnivores to predaceous carnivores that display cannibalism similar to post-metamorphic feeding behavior. The switch has long been attributed to heterochrony, or the developmental shift in the timing of gene-expression. However, Ledón-Rettig (2021) tested this hypothesis against an alternative that a novel pattern of gene expression is behind the ecological behavioral shift. She quantified RNA expression in two morphotypes of Spea bombifrons at two points in their development, tadpole and juvenile, and found that gene expression of tadpoles were more similar to each other than the gene expression of juveniles, which were also more similar to each other than to tadpoles. However, predaceous tadpoles also expressed a different suite of genes than omnivorous tadpoles lending support to the alternative hypothesis of a novel pattern of gene expression. These findings do not discount a role for heterochrony, but provide evidence of the potential for multiple routes to novel behaviors.
