Doctor of Philosophy (PhD)
Sodium plays a crucial role in organismal performance, trophic-level interactions, and eco-evolutionary dynamics. For plants, sodium impacts osmoregulation, growth, and water uptake. For animals, sodium is essential influencing osmoregulatory processes, muscle and neural development, and blood regulation. My dissertation aims to disentangle why sodium mismatch affects resource-consumer interactions and its influence on morphological and behavioral plasticity. First, I identified how sodium impacts plant performance and sodium accumulation strategies. I initially focused my research on understanding how increasing substrate sodium affects plant growth and tissue sodium accumulation strategies in controlled settings using a systematic review approach. I found that saltier plants reflected saltier substrates, even across crop and non-crop species, regardless of species identity. However, responses in plant growth showed phylogenetic conservatism across the taxa studied.
I aimed to describe how the phytochemical landscape of sodium forms across a heterogeneous landscape. I performed field collections of widespread plant genera, along with adjacent soil, across the southern United States. Based on the results, environmental sodium correlated with plant sodium concentrations, contrasting with other cations which are at strict homeostatic levels across plant tissues. These findings suggest that plant sodium concentrations are highly dependent on environmental conditions and that plants lack the ability to homeostatically control sodium in their tissues. We can deduce that plant sodium concentrations result from complex interactions with the environment and that herbivores experience substantial variation in dietary sodium across their range
To then link the influence of plant tissue sodium variation to herbivore performance and behavior, I exposed larvae of the bordered patch to common sunflower plants grown hydroponically across increasing treatments of substrate sodium. The findings from this experiment demonstrate how plants with high sodium concentrations reduce herbivore survivorship and extend developmental time, potentially due to imposed physiological stress. In plants grown in no-addition conditions, 25% of larvae were eaten by their siblings, demonstrating the first instance where variation in dietary sodium influences cannibalistic behavior. These findings show the importance of sodium for animal development and performance and how two extremes in the plant sodium concentration negatively affect herbivore fitness.
Santiago-Rosario, Luis, "Sodium Mediates Developmentally Plastic Responses in Plants and Herbivores" (2022). LSU Doctoral Dissertations. 5850.
Harms, Kyle E.