MCHENRY, Matthew/J.: A TALE OF TWO TAILS: SWIMMING DYNAMICS IN LARVAE OF A COLONIAL (DISTAPLIA OCCIDENTALIS) AND A SOLITARY ASCIDIAN (CIONA INTESTINALIS)

The body shape of ascidian larvae is correlated with the performance of their swimming. The larvae of colonial species have enlarged trunks, shortened tails and a large body length compared to solitary species. Both solitary and colonial ascidians swim along helical trajectories, but the larvae of colonial species swim faster and with a larger helical radius. How do the morphological differences between the larvae of colonial and solitary species affect the dynamics of swimming such that they swim differently? I examined how the body shape, tail movement, and distribution of tissue mass affect the forces and moments generated by the bodies of larvae during swimming in the colonial species Distaplia occidentalis and the solitary species Ciona intestinalis. By recording the axial motion of the tail in 3D with high-speed video (500 fps), larvae of D. occidentalis were found to beat their tails with asymmetrical tail undulations that were not found in C. intestinalis. Using these kinematics and morphometrics of the body, I modeled the hydrodynamics of the swimming in these species using a blade element approach. The results of this model suggest that D. occidentalis generates moments by the asymmetrical motion of their tails that significantly influence both the speed and radius of the helical trajectory. Tissue density measurements suggest that C. intestinalis generates moments affecting swimming trajectory by the distribution mass in their tissues. These results suggest that hydrodynamics and mass distribution are mechanisms that are used differently by the larvae of solitary and colonial ascidians to swim helically.