The evolution of fern vascular architecture

A central goal of biology is to understand how and why diverse structures evolve. This highlights a long-standing question: do new forms arise mainly because natural selection directly favors them, or because they emerge indirectly as a consequence of how organisms grow and develop? Tackling these questions requires knowledge of how new forms originate and their fitness implications. This project uses ferns, an ecologically important and evolutionarily persistent group of plants, to address this fundamental problem by exploring the evolution of vascular architecture (the set of tubes that move water and nutrients). Ferns are a powerful system for this work because they have evolved some of the most diverse vascular systems on Earth. The project tests two leading, and potentially complementary, explanations for this diversity: that vascular patterning evolved as a direct adaptation to drought (the Drought-Driven Hypothesis) versus that it reflects developmental linkage with changes in overall plant growth (the Ontogenetic Hypothesis). By integrating physiology, development, and large-scale evolutionary analyses, the project will clarify the unresolved problem of how developmental mechanisms generate new anatomical variation and how selection acts on this new form. Understanding these mechanisms advances fundamental knowledge about how plant form evolves, while also improving the scientific basis for anticipating how plants may respond to drought - fundamental to agricultural productivity. Moreover, this work can help influence broader processes from agricultural crop breeding to artificial intelligence, both of which operate under evolutionary frameworks. The project also strengthens public engagement with science through widely disseminated educational videos, which transparently document the research process and its findings. This will occur by creating and sharing short, engaging videos through Let’s Botanize, an educational organization focused on plant science communication. By making complex botanical science accessible and story-driven, this outreach will spark curiosity and connect broader audiences with how research unfolds. This project is organized into three integrated aims. Aim 1 tests the Drought-Driven Hypothesis by quantifying whole-plant vulnerability to drought-induced embolism across leaves, rhizomes, and roots. Anatomical traits will be quantified for each species, linking hydraulic function to vascular construction across three scales: architectural (vascular bundle arrangement), histological (tissue organization and connectivity), and cellular (conduit size and wall traits). Aim 2 tests the Ontogenetic Hypothesis by examining whether variation in stelar morphology covaries with whole-plant developmental traits (e.g., rhizome diameter, internode length, phyllotaxy, leaf area) across a broad comparative dataset (>300 fern species). This will combine traditional histology with non-destructive micro-computed tomography (microCT) to capture 3D vascular networks, and it will leverage AI-based image segmentation to rapidly quantify vascular features from large image datasets. Aim 3 places the results from Aims 1 and 2 into macroevolutionary frameworks using phylogenetic comparative methods and climate data from species occurrences to evaluate how hydraulic function and development scale up to explain macroevolutionary patterns. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2552957 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Jacob Suissa | Institution: University of Tennessee Knoxville, KNOXVILLE, TN | Award Amount: $567,696 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2552957 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2552957.html