Phenotypic plasticity in Cassiopea ornata (Cnidaria: Scyphozoa: Rhizostomeae) suggests environmentally driven morphology

Abstract

This contribution investigates phenotypic plasticity in Cassiopea ornata Haeckel, 1880 from Guam, Micronesia. We collected C. ornata from two distinct habitats and used DNA barcoding for species identification. With this, we were able to document intraspecific phenotypic variation between populations that is likely reflective of distinct ecotypes rather than species-specific disparities. In particular, macromorphological characters, such as vesicle shapes and sizes, have been used as characters to discriminate among species of Cassiopea varied between populations. In addition, we uncovered differences in cassiosome structure and composition between populations that suggest differences in trophic modes across populations. Conducting a meta-analysis of a comprehensive cnidome dataset, we show that nematocysts may provide important information for species delineation and identification in Cassiopea, a suite of characters not fully exploited thus far. We interpret differences in vesicle and cassiosome morphology in conjunction with nematocyst size disparities as a reflection of environment-mediated shifts in trophic strategy (photo-autotrophy versus heterotrophy). Given the interest in Cassiopea as a model organism, the observations presented herein lay out a roadmap for studies that aim at linking environmental heterogeneity to phenotypic plasticity.