One clear example of a Rule of Life is evolutionary convergence, the occurrence of the same or extremely similar adaptations in independent lineages of species on the Tree of Life. The recent discovery of a blind cavefish that walks and climbs waterfalls with a salamander-like gait and has evolved a robust pelvic girdle (a kind of hip) offers an extraordinary opportunity to study, in living fishes, a pivotal event in evolutionary history. That event, the vertebrate invasion of land, hinged on the evolution of fins to limbs that enabled the first vertebrates to walk on land. The fossil record of this transition is scarce, and extant fishes were thought to lack the morphological features necessary for studying the origin of quadrupedal walking. This research will provide a unique opportunity to understand, through phylogenetic analysis and mathematical and robotic modeling, the mechanism underlying a major event in the history of life: how fishes were able to transition to a terrestrial lifestyle and evolve into the tetrapods. The broader impacts of this project will promote teaching, training, and learning for high school students in diverse and underprivileged communities. The project will also provide opportunities for graduate and undergraduate research training and make important contributions to public science education. This project was co-funded by the Biology Directorate and the Physics of Living Systems Program in the Physics Division.
The proposed work will identify the genomic, morphological, and mechanical qualities that enable a fish to walk on land. Advancing previous work on the functional morphology and kinematics of terrestrial walking in the blind cave fish Cryptotora thamicola, the proposed research will examine the phylogenomic relationships, morphology, biomechanics, and walking performance from an evolutionary perspective among balitorid loaches. Genomic sequencing will determine convergent genetic markers known to be involved in pelvic girdle formation in other walking vertebrates. Morphological examinations will reveal how functional phenotypic adaptations can be formed by major genomic changes. A biorobotic model organism, validated through comparison with our experimental biomechanical data, will be used to take a modular approach to examining convergence and answering questions on the effect of pelvic morphology on walking performance in extinct fin-to-limb transitional forms and modern forms. The work proposed will discriminate the fundamental physical properties which are inherent to the transition to terrestrial walking from an aquatic form. The evolution of the terrestrial pelvic girdle was critical to the diversification of amphibians, reptiles, birds and mammals; the proposed work uses a convergent fish model to study the evolution of anatomical structures that support the vertebrate body against gravity and show how modulation of muscular control can produce a tetrapodal gait within a given range of skeletal morphologies. This research will inform scientific understanding of the mechanisms underlying the convergent evolution of morphological innovation, allowing development of a unifying principle for mass support in tetrapods based on the genomics, basic physics, and mechanics that define the pelvic girdle contribution to quadrupedal walking.
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.
