CAREER: Mechanisms and drivers underlying thermal specialization patterns in elastic recoil and muscle powered movements

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This award is funded in part under the American Rescue Act of 2021 (Public Law 117-2). In addition, this project is jointly funded by the Physiological Mechanisms and Biomechanics Program in the Division of Integrative Organismal Systems in the Biological Sciences Directorate and by the Established Program to Stimulate Competitive Research (EPSCoR).The ability of an animal to perform well in its environment is central to accomplishing many of its most basic and important functions. Since those abilities--and the physical features of the animals that permit them--evolved slowly over thousands of generations, rapidly changing environments challenge the ability of animals to respond and adapt. A key feature of an animal’s environment is temperature, particularly for cold-blooded animals like chameleons, who rely on heat from the environment to warm their bodies to the best operating temperature while seeking ways to cool off when it gets too hot. To investigate how the temperature impacts a fundamental ability--the chameleon’s feeding with its projectile tongue--this project measures the range of environmental temperatures experienced by different species of African chameleons, how those different habitats correspond to differences in feeding performance, how differences in feeding are related to differences in the temperature sensitivity of the muscles and connective tissues of the tongue, and how those differences might have evolved. In addition, this research harnesses the charismatic nature of chameleons and the captivating visuals of high-speed video of their feeding to engage and educate a broad audience. In particular, these results will be integrated into education modules developed to address specific K-12 learning objectives in the biological and physical sciences. Specifically, as part of a curriculum enhancement resource developed to connect scientists to teachers and classrooms in rural and tribal communities in South Dakota, this research will result in free curriculum modules based on scientific research occurring in South Dakota’s higher education institutions that are aligned with the South Dakota Science Standards. In the process, this research will form a foundation for developing content for new curricula offerings at the undergraduate and graduate level through the development of novel laboratory modules, original case study materials, and new course offerings.Temperature exhibits strong effects on animal movement and performance through its effect on muscle contractile dynamics. Movements powered by the recoil of elastic tissues, however, respond differently to changes in environmental temperature than movements powered by muscle contraction directly. These systems and their underlying functional processes therefore may also experience different selection pressures relating to thermal specialization to their environment. This project will compare patterns of thermal specialization in two movement types: elastic recoil-powered tongue projection and muscle-powered tongue retraction in chameleons. These comparisons will focus on examining the thermal sensitivity of whole organism performance and the different underlying mechanistic processes involved in producing these movements (e.g., motor control, muscle contractile physiology, anatomical variation) in chameleons living in different thermal environments. Combining ecological work in the field and experimental work in the laboratory, this work will determine to what extent different types of movement undergo thermal specialization, at what mechanistic level thermal specialization occurs for both movement types, what environmental factors drive these patterns, the extent to which acclimation affects performance in both movements, and evolutionary trends in these patterns. In the process, this research will provide insight into how animals using different types of movement for critical ecological functions may respond to shifts in environmental conditions. These advancements in our understanding of adaptation to differing and changing environmental conditions, particularly temperature, will impact the fields of ecology, physiology, and evolutionary biology. In addition, the work includes broad outreach efforts, educational activities, and scientific presentations and publications, with research training for undergraduates, graduate students, and a postdoctoral researcher.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.