P3-3 Sunday, Jan. 6 15:30 - 17:30 The contribution of morphological characteristics on the bouncing gait of sea stars: A cross-species comparison ETZEL, R*; KHORIATY, J; ELLERS, O; JOHNSON, AS; Bowdoin College; Bowdoin College; Bowdoin College; Bowdoin College firstname.lastname@example.org
While sea stars are known to exhibit a crawling gait, they also exhibit a bouncing gait, observed in at least five species of sea stars. This bouncing gait (periodic vertical motion with associated horizontal variation in speed) is characterized by coordinated movement of a sea star’s podia, or tube feet, and an overall increase in speed from the crawl. Here we focus on how the locomotion-relevant geometric scaling of individuals changes with size, and how various morphological differences (such as arm length, ambulacral area, animal density, and height) can inform differences in bouncing behavior between species. To study this, three species of sea star (Protoreaster nodosus, Asterias forbesi, Luidia clathrata) were filmed in recirculating seawater flow tanks using two cameras to provide paired views from the bottom and side. Tracker software was used to gather raw position and time data, which were processed using Mathematica to determine parameters such as maximum speed and bouncing frequency. We found P. nodosus and L. clathrata to be relatively dense sea stars with the ambulacral area from which podia emerge composing about 20% of their ventral surfaces, while A. forbesi is less dense, with an ambulacral area around 40%. P. nodosus is a tall sea star, while L. clathrata is flat and long-armed. With respect to locomotion, L. clathrata bounced at a higher frequency and attained speeds more than five times that of P. nodosus, while A. forbesi bounced at intermediate speeds and frequencies. Further, we found a positive correlation between maximum velocity and size for A. forbesi and P. nodosus, while L. clathrata’s velocity decreased with size. P. nodosus and L. clathrata both have scaling coefficients consistent with the inverted pendulum model, while A. forbesi does not.