Evol Ecol Res 9: 109-121 (2007)     Full PDF if your library subscribes.

Reduction in morphological plasticity in echinoid larvae: relationship of plasticity with maternal investment and food availability

Adam M. Reitzel1* and Andreas Heyland1,2

1Department of Zoology, University of Florida, Gainesville, FL 32611 and  2The Whitney Laboratory for Marine Biosciences, University of Florida, Saint Augustine, FL 32080, USA

Address all correspondence to Adam Reitzel, Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA.
e-mail: reitzel@bu.edu


Hypotheses: If phenotypic plasticity is costly or not beneficial to marine invertebrate larvae, then increased maternal investment into eggs should result in decreased plastic responses. If genetic assimilation is a mechanism for the evolutionary transition from planktotrophic to lecithotrophic larvae, then species with larger eggs will have reduced overall plasticity and growth trajectories similar to highly fed larvae from a species that exhibits plasticity.

Organisms: Larvae reared from three subtropical echinoid species, Mellita tenuis, Clypeaster subdepressus, and Leodia sexiesperforata, collected from the Gulf coast of Florida that differ in degree of maternal investment into eggs.

Methods: We reared larvae from each species at three food concentrations in laboratory cultures. We measured two larval structures (post-oral arm length and stomach size) on three occasions (1, 3, and 5 days after fertilization) and statistically compared these characters to determine: (1) within-species plastic responses to food environment and (2) between-species plastic responses to identical feeding treatments.

Results: Larvae of M. tenuis and C. subdepressus, the two species with smaller eggs, both expressed plasticity of larval arms (elongated arms under low food conditions) and stomachs (smaller stomachs under low food conditions) early in development, whereas L. sexiesperforata larvae only showed significant changes in stomach size on the last day of measurement in the highest food treatment. Comparisons among species showed that larvae developing from smaller eggs had a significantly higher plastic response to exogenous food than larvae developing from large eggs.

Keywords: larva, maternal investment, phenotypic plasticity, pluteus.

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