Nutrition has been hypothesized as an important constraint on brain evolution. However, it is unclear whether the availability of specific nutrients or the difficulty of locating high-quality diets limits brain evolution, especially over long periods of time. We found that dietary nutrient content predicted brain size across 42 species of butterflies. Brain size, relative to body size, was associated with the sodium and nitrogen content of a species’ diet. There was no evidence that host plant apparency (measured by plant height) was related to brain evolution. The timing of diet shifts across species varied from 3.5 to 90 million years ago, but nutritional constraints did not lessen over time as species adapted to a diet. Although nutrition was linked to overall brain volume, there was no evidence that nutrition was related to the relative size of individual brain regions. Laboratory rearing experiments confirmed the underlying assumption of most comparative studies that the majority of interspecific trait variation stems from genetically based differences across species rather than developmental plasticity. This study highlights a novel role of sodium and nitrogen in brain evolution, which is additionally interesting given current anthropogenic change in the availability of these nutrients.
Bibliographical noteFunding Information:
We are grateful Supra Khare, Rhea Smykalski, and Sam Collins for help with brain sectioning and imaging. Laura Wagner and Megan Decook helped with brain dissections and weighing for the laboratory rearing experiments. We are indebted to Art Shapiro, Dan Papaj, Mike Reese, Jaret Daniels, Sandy Koi, Katy Prudic, and Jeff Oliver for help collecting specimens. Dean Hansen, Steve Kohler, Virginia Scott, Jeff Marcus, Kyle Johnson, Ann and Scott Swengel, Ron Huber, Robert Dana, Joel Kingsolver, and Dave Biesboer provided valuable assistance locating field sites and butterflies. Cedar Creek LTER, Cloquet Forestry Center, O'Leno State Park, Fairchild Botanic Garden, and Custer National Forest gave permission for insect collecting. Andrew Warren allowed the use of photos in figures. Sarah Hobbie and Simon Laughlin gave valuable insights into the design and interpretation of the study. Editorial comments and insights from two anonymous reviewers greatly improved the manuscript. This study has been supported by the TRY initiative on plant traits (http://www.try-db.org). This work was supported in part through a Grant-in-Aid of Research and a McKnight Land Grant Professorship from the University of Minnesota. The Snell-Rood laboratory was supported in part through NSF IOS-1354737; EMS was supported in part by an NSF postdoctoral fellowship (#1306627). The TRY initiative is currently supported by DIVERSITAS/Future Earth and the German Center for Integrative Biodiversity Research (iDIv) Halle-Jena-Leipzig.
- Brain size
- evolutionary stoichiometry
- mushroom bodies
PubMed: MeSH publication types
- Journal Article