MCA: Spinal neuron diversity related to the evolution of a novel motor behavior

Movement is essential to nearly every aspect of life, yet scientists still do not fully understand how the nervous system evolves to produce new and increasingly complex behaviors. This project investigates that question by studying an unusual group of frogs that perform an elaborate "foot-flagging" display—a dramatic hind-limb movement used for communication that has evolved independently multiple times. These frogs provide a rare ‘natural experiment’ that will enable us to discover how similar behaviors evolve through changes in the nervous system. The research focuses on the spinal cord, a critical part of the nervous system that controls movement in all vertebrates, including humans. Previous findings show that foot-flagging frogs possess substantially more spinal nerve cells involved in coordinating hind limb movement than closely related species that do not perform this display. This project will identify the genes and specific cell types that are associated with the evolution of this novel movement. By comparing multiple species, the research will reveal whether evolution repeatedly arrives at similar biological solutions or uses different mechanisms to achieve the same outcome. Understanding how spinal circuits change over evolutionary time will advance fundamental knowledge about neural development and the organization of spinal circuits across vertebrates. Because the basic architecture of the spinal cord is remarkably conserved across species, insights gained from this work have the potential to inform other research on movement disorders and spinal cord function. The broader impacts of this work focus on building research collaborations and strengthening the nation's scientific workforce. The project supports a mid-career investigator to expand their skills in cutting-edge imaging and computational analysis. This project will also provide hands-on research training for undergraduate students and will develop freely available educational resources that will expand access to computationally-intensive bioinformatic research techniques for students and faculty. This project advances NSF’s priorities in Biotechnology. Evolutionary modifications in the spinal cord are thought to be key drivers of behavioral innovation, but what specific neural circuit modifications contribute to novel movements remains unclear. Preliminary data indicate that foot-flagging frogs – species that have evolved an elaborate hind limb display – have approximately twice as many lumbar spinal interneurons as non-foot-flagging frogs. The project will characterize whether these additional interneurons represent distinct molecular and anatomical subtypes using immunohistochemical markers and light sheet microscopy. It will also use RNA sequencing to compare gene expression profiles between lumbar and brachial spinal cords in foot-flagging frogs and non-foot-flagging relatives, identifying convergent transcriptional signatures associated with independently evolved foot-flagging behavior. By combining these approaches, this project aims to identify neural circuit modifications and genetic mechanisms that contribute to the evolution of specialized motor behaviors. The results may reveal generalizable mechanisms of neural circuit evolution that extend beyond foot-flagging frogs to other species exhibiting unique movement patterns. Importantly, this award supports a mid-career investigator to expand their research toolkit, gain expertise in advanced microscopy, anatomical mapping, and bioinformatic analysis that will enable their lab to address research questions that were not previously possible. 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.