Regulation and evolution of phenotypic plasticity: Insights from horned beetles

Plasticity, an individual’s ability to adjust its phenotype in response to environmental factors, is a ubiquitous property of developmental systems. Yet our understanding of the molecular mechanisms that regulate plasticity as well as their evolution is limited. I used a comparative RNAseq approach using onthophagine horned beetles to better understand the transcriptomic mechanisms underlying the development and evolution of nutrition-sensitive plasticity of horns. I investigated three species of beetles whose nutritional plasticity in horn growth ranged from the ancestral, moderately polyphenic state to the derived exaggerated polyphenic state, or alternatively, the secondary loss of nutrition responsiveness. I found that the regulation of polyphenic development is partly shared across species regardless of the degree of nutrition-sensitivity. Additionally, the evolution of polyphenism exaggeration involved recruitment of diverse genes, and secondary loss of morphological plasticity is paralleled by extensive loss of gene expression plasticity. By utilizing a comparative, unbiased, genome-wide assessment of gene expression plasticity this work provides comprehensive insights into the regulation and evolution of nutrition-responsive development.