Variability of Sea Urchin Larvae: The Jar Effect

Abstract

A study of four-armed plutei (96 h post-fertilization) of a commercially valuable sea urchin, Strongylocentrotus intermedius (A. Agassiz, 1864), showed a significant variability of larvae morphology between technical replicates within a biological replicate. Of the three larval characters studied—length of body rod, length of post-oral arms, and length of body midline—the length of post-oral arms was found to be the most variable in terms of mean and variance values. The relative difference in the post-oral arm length varied from 0.002 to 9.3% between the technical replicates within a cross and considerably differed in 5 out of 20 biological replicates. In contrast, the relative difference in the mean body rod length between the technical replicates ranged within 0.06–4.7%, and the relative difference in the mean body midline length was within 0.12–10.22%. Only one biological replicate showed a statistically significant difference in the mean body midline length between the technical replicates, and none of biological replicates had statistically significant differences in the mean body rod length between their technical replicates. Our results have shown that the degree of variability differs among larval characters. These observations can help estimate the degree of variability in certain characters of sea urchin larvae to be taken into account when planning, analyzing, and interpreting results of experimental studies. This is critical when the expected effect of a treatment is small and can interfere with or masked by the variability in the characters under study.