P1-54 - Variable expression of food-conditioned phenotypic plasticity in feeding larvae of diverse echinoderms Steiner, BM*; Pernet, B; California State University, Long Beach; California State University, Long Beach firstname.lastname@example.org
Feeding larvae of echinoderms take two distinct forms: pluteus (echinoids, ophiuroids) and dipleurula (asteroids, holothuroids). Plutei fed low food rations often develop longer ciliary bands relative to body or stomach size than those fed high rations, but it is unclear how widespread phenotypic plasticity is in dipleurulae. Further, comparisons among taxa are difficult since prior studies vary in methods. Here we apply uniform methods to study phenotypic plasticity in larvae of echinoids, asteroids and holothuroids. For each species, larvae of four replicate families were reared at 0.25 larvae ml-1 and fed low (1000 cells ml-1 Rhodomonas lens) or high (6000 cells ml-1) food rations. We measured body length (BL), stomach area (SA), and the length of the feeding ciliary band (CBL) at three developmental stages. CBL was measured in three dimensions from stacks of images, a method not previously applied to dipleurulae. Within species, we compared the ratio of CBL/BL, and CBL/SA, between food rations. Plutei of two of three echinoids showed evidence of plasticity. Dipleurulae (bipinnariae) of the two asteroids showed no evidence of plasticity, but the dipleurula (auricularia) of the holothuroid did. We found no plasticity in pre-feeding stages of any species, though this has previously been documented for two of the echinoids we studied. The expression of plasticity in our study was surprisingly variable, sometimes not being detected even in species where it has been previously seen. This may be due to our moderate contrast in food levels. Prior studies have often used stronger contrasts in food level, sometimes including treatments with extremely low or even no food. Such extremely low food levels are probably relatively rare in nature, which raises questions about the frequency of expression of phenotypic plasticity in the field.