Meeting Abstract

P1-53   -   Echinoid larvae express food-conditioned morphological plasticity at ecologically relevant culture densities Nilsson, P*; Pernet, B; California State University, Long Beach; California State University, Long Beach peter.nilsson@student.csulb.edu

The feeding larvae of many echinoids develop longer postoral arms relative to body size when food is sparse but shorter arms when food is abundant, a response thought to adaptively adjust feeding ability. However, Kacenas & Podolsky (2018) found that larvae of the sand dollar Dendraster excentricus only exhibited this food-conditioned plasticity when reared at the high larval densities typical of laboratory cultures; when reared at a lower density more representative of field observations of plankton, larvae did not exhibit this plastic response. This suggests that phenotypically plastic responses to food abundance – a major focus in larval biology for the past three decades – may actually be rare in nature. We replicated Kacenas & Podolsky’s study and extended it to a lower culture density as well as to a second echinoid, Lytechinus pictus. Larvae of D. excentricus developed longer postoral arms relative to body size when fed the lower food ration at all culture densities, though these differences were not significant for the lower density in one experiment. Larvae of L. pictus likewise developed relatively longer postoral arms at lower food rations, though these differences did not reach statistical significance at any culture density. Consistent with prior work demonstrating phenotypic plasticity, postoral arm length appeared to be negatively correlated with stomach length in all of our experiments. That the feeding larvae of echinoids can exhibit plasticity of feeding structures even at very low culture densities suggests that this plastic response may occur in nature, where larval densities are generally thought to be extremely low.