Much More Than a Grain of Salt: LSU Research Group Manipulates Sodium to Understand Ecology and Evolution of Plant-Animal Interactions

When you think of sodium, you may think of table salt or the delicious Cajun cuisine found in southern Louisiana. From the gumbo, jambalaya and étouffée, there's no shortage of sodium in the Deep South. But outside of the kitchen, an LSU research group is exploring sodium's unusual role in food webs.

Dr. Luis Santiago-Rosario (currently a National Science Foundation postdoctoral fellow at the University of Minnesota), current LSU LAGNiAppE post-doc Ana Salgado, current LSU PhD student Diego Paredes-Burneo and Professor Kyle Harms published in November 2023 results from some carefully controlled hydroponic experiments to better understand the interrelationships among animals, plants and the substrates from which the plants obtain nutrients.

During Santiago-Rosario's time as a PhD student at LSU, he manipulated sodium concentrations in sunflower host plants and found that butterfly larvae that consumed low-sodium plant tissue cannibalized their siblings to get the sodium they needed but otherwise failed to obtain from their diets.

"In terms of sodium, there is a mismatch between what plants and animals need," he said. "Our plants took up and incorporated into their tissues however much sodium was in the substrate, which meant that caterpillars experienced a limitation when reared on the low-sodium plants. They then overcame the limitation by eating their siblings!"

Santiago-Rosario defended his PhD two years ago under Harms. The published paper was a part of his dissertation as he took a deep dive into the ecology of sodium and how it affects animal and plant development and their interactions.

"With some hardcore searching and working to figure it out, he found just the right butterfly species, figured out how to collect it in the wild in Texas, how to rear it in the lab, and then how to very carefully manipulate the amount of sodium in the plants," said Harms.

The group found that sodium uptake can have important consequences for herbivores and their population demographics, an important message as researchers continue to study the ecology and evolution of plant-animal interactions.

"Getting a little bit of knowledge in a small controlled system like we've done, sets the stage for many next steps to learn about these interactions in other species and in the field, especially on our human-dominated and changing planet," said Santiago-Rosario.

Harms added that his former student made a lasting legacy in the Biological Sciences Department.

"Luis in many ways was very much a model PhD student while he was here," said Harms. "I mean he did all sorts of things way beyond the outstanding research for his PhD. For just one example, he had a lasting influence as a two-term BioGrads President who seriously emphasized diversity, equity, and inclusion in our department."