Re-examination of the effects of food abundance on jaw plasticity in purple sea urchins
Morphological plasticity is a critical mechanism that animals use to cope with variations 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 tested 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 collected and placed in either high or low food treatments for 3 months, after which treatments were switched for two additional months in La Jolla, CA (32.8674°N, 117.2530°W). 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 within the time frame of this study. 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.
We sincerely thank P. Zerofski for aquarium and experimental design support, T. Tunstall for help with data analysis, A. Rankin for assistance with animal care and measurements, M. McCowin for animal care assistance, and the insightful reviewers of this manuscript. This research was supported by a National Science Foundation Ocean Sciences Division Postdoctoral Broadening Participation Fellowship (OCE-PRF 1323837 to M. S. deVries), and the Marine Biology Research Division at Scripps Institution of Oceanography (to J. R. A. Taylor).
MSdV conceived of the study with input from SJW. MSdV and SJW designed the study with input from JRAT. SJW conducted the experiments and collected the data with help from MSdV. MSdV analyzed the data. MSdV wrote the manuscript but SJW wrote the methods section. JRAT had significant input in manuscript preparation. All authors contributed substantially to manuscript editing.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This research complied with animal welfare guidelines at the University of California, San Diego. The author declares no competing financial interests.
- Cavole LM, Demko AM, Diner RE, Giddings A, Koester I, Pagniello CMLS, Paulsen ML, Ramirez-Valdez A, Schwenck SM, Yen NK, Zill ME, Franks PJS (2016) Biological impacts of the 2013–2015 warm-water anomaly in the Northeast Pacific: winners, losers, and the future. Oceanography 29:273–285CrossRefGoogle Scholar
- Ebert T (1980a) Relative growth of sea urchin jaws: an example of plastic resourse allocation. Bull Mar Sci 30:467–474Google Scholar
- Ebert T (1996) Adaptive aspects of phenotypic plasticity in echinoderms. Oceanol Acta 19:347–355Google Scholar
- Fansler SC (1983) Phenotypic plasticity of skeletal elements in the purple sea urchin, Stongylocentrotus purpuratus. San Diego State University, San DiegoGoogle Scholar
- Leighton DL (1966) Studies of food preference in algivorous invertebrates of Southern California kelp beds. Pac Sci 20:104–113Google Scholar
- Ling SD, Scheibling RE, Rassweiler A, Johnson CR, Shears N, Connell SD, Salomon AK, Norderhaug KM, Pérez-Matus A, Hernandez JC, Clemente S, Blamey LK, Hereu B, Ballesteros E, Sala E, Garrabou J, Cebrian E, Zabala M, Fujita D, Johnson LE (2015) Global regime shift dynamics of catastrophic sea urchin overgrazing. Philos Trans R Soc B Biol Sci 370:1–10. https://doi.org/10.1098/rstb.2013.0269 CrossRefGoogle Scholar
- Meyer A (1987) Phenotypic plasticity and heterochrony in Chichlasoma managuense (Pices, Cichlidae) and their implcations for speciation in fishes. Evolution (NY) 41:1357–1369Google Scholar
- Mittelbach GG, Osenberg CW, Wainwright PC (1999) Variation in feeding morphology between pumpkinseed populations: phenotypic plasticity or evolution? Evol Ecol Res 1:111–128Google Scholar
- R Development Core Team (2014) R: a language and environment for statistical computing. R Found Stat Comput 1:409Google Scholar