Data from: Functional consequences of morphologically plastic jaws in juvenile purple sea urchins

Morphological plasticity is a critical mechanism that animals use to cope
with variation in resource availability. During periods of food scarcity,
sea urchins demonstrate an increase in jaw length relative to test
diameter. This trait is thought to be reversible and adaptive by yielding
an increase in feeding efficiency. We directly test the hypotheses that
(1) there are reversible shifts in jaw length to test diameter ratios with
food abundance in individual urchins, and (2) these shifts alter feeding
efficiency. Purple sea urchins, Strongylocentrotus purpuratus, were placed
in either high or low food treatments for 3 months, after which treatments
were switched for 2 additional months. Measurements of jaw length to test
diameter ratios were significantly higher in low compared to high food
urchins, but this was due to test growth in the high food treatments.
Ratios of low food urchins did not change following a switch to high food
conditions, indicating that this trait is not reversible. Relatively
longer jaws were also not correlated with increased feeding efficiency. We
argue that jaw length plasticity is not adaptive and is simply a
consequence of exposure to high food availability, as both jaw and test
growth halt when food is scarce.