Meeting Abstract
Phenotypic plasticity helps animals cope with drastic environmental changes, and plastic responses can sometimes be reversed when conditions are restored. Field studies on the purple sea urchin, Strongylocentrotus purpuratus, have suggested that changes in food abundance elicit a reversibly plastic response in the morphology of the Aristotle’s lantern (feeding apparatus). Specifically, jaw size relative to body size increases when food abundance is low. This response, however, has only been observed at the population level. To test whether this relationship holds in individual juvenile urchins, we divided 90 purple sea urchins into two food treatments for six months. In the high food treatment, urchins had constant access to kelp. In the starvation treatment, urchins were only given kelp every 12-14 days for 24 hours. After three months, 30 animals were subsampled to assess the relationship of jaw length to test diameter and gonad weight to body size (gonadal index). Treatments were then switched for the remaining 60 animals. At three months, both the test diameter and gonadal index of the starved animals were significantly lower than the animals given constant food. Yet, the ratio of jaw length to test diameter was significantly higher in starved individuals, confirming field observations. Increased jaw size implies that individuals allocate greater resources to feeding morphology, which may improve feeding efficiency during food scarcity. It is predicted that this trait is reversibly plastic within individuals and that jaw length will therefore decrease after previously starved animals have been held in high food conditions for three months. The ability to alter relative jaw size depending on resource availability may have contributed to the success of this kelp forest consumer.
