CAREER: Discovering how swimming shapes fin function and development: A multi-level approach to studying developmental plasticity

The water-to-land transition of tetrapods approximately 375 million years ago was one of the most significant evolutionary events in the history of life on Earth. This shift is marked by changes across the skeleton, including appendicular systems, as early tetrapods transitioned from swimming to walking. Research on how fins and limbs evolved in early tetrapods has focused almost exclusively on early developmental processes. This project therefore fills a major knowledge gap by targeting the role of developmental processes in juvenile fishes, specifically the impact of behavior, on shaping the adult skeleton. Understanding how juvenile behaviors contribute to the emergence of adult form is important for explaining broad patterns of biological diversity. Studying this process in fishes is critical for formalizing hypotheses about how the anatomy and physiology of tetrapod bone arose, and how mechanical forces contribute to the evolution of skeletal anatomy. Beyond its scientific contributions, this project will expand access to research experiences for undergraduate students at Pennsylvania State University through a “First-year Research-Intensive” course that places students directly into the scientific process from their first year of college. As part of this course, undergraduates will digitize kinematic videos and develop semi-automated tracking methods using Artificial Intelligence/Machine Learning-based software, leading to new AI/ML approaches incorporated into the lab’s research toolkit. The project will also partner with a local science education center to deliver hands-on evolutionary biology programming to thousands of K–5th grade students across Central Pennsylvania, with the goal of inspiring the next generation of scientists and making science more accessible to all. Several undergraduate and graduate research students, a technician, and a post-doctoral fellow will be supported, contributing to workforce development. This project tests the central hypothesis that the fins of fishes show adaptive responses to mechanical loading during development, and that the cellular and genetic mechanisms of these responses are homologous to those of tetrapod limbs. Three integrated research aims are pursued using two complementary fish models: the cichlid Satanoperca daemon and the zebrafish Danio rerio. Aim 1 examines how ecologically relevant foraging behaviors, specifically pelagic feeding and substrate winnowing, produce different patterns of pectoral fin use, and whether these differences alter the mechanical properties of adult fins, including their flexural stiffness. Three-dimensional high-speed kinematics, micro-computed tomography, and three-point bending tests are used to link behavior, anatomy, and biomechanical function. Aim 2 investigates the cellular mechanisms underlying behaviorally induced differences in fin skeletal growth, focusing on chondrocyte proliferation, maturation, and bone deposition in pectoral fin radials using confocal microscopy and fluorochrome labeling. Aim 3 characterizes the molecular basis of fin skeletal plasticity in zebrafish through bulk RNA sequencing across a developmental time series, followed by in situ hybridization to spatially resolve candidate mechanoresponsive genes and pathways. Together, these aims will establish the first integrated behavioral, cellular, and genetic framework for understanding developmental plasticity in fish fins, advancing our knowledge of how vertebrate skeletal diversity is generated and how early tetrapods came to live on land. 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: 2541874 | Program: 01003031DB NSF RESEARCH & RELATED ACTIVIT,01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Thomas Stewart | Institution: Pennsylvania State Univ University Park, UNIVERSITY PARK, PA | Award Amount: $1,212,537 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2541874 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2541874.html