Plasticity and variation of cirral attributes in Chelonibia spp. barnacles

Prior studies suggest that many species of intertidal Balanomorph barnacles exhibit plastic responses to wave action and variable rates of water flow, with this environmental variability intrinsic to shaping the morphology of feeding cirri. However, this idea has not been quantitatively demonstrated in barnacles of the family Coronulidae, which exhibit obligatory epibiotic life-history patterns as adults. If the recent single-species classification of Chelonibia testudinaria continues to be upheld, the species represents a cosmopolitan and highly diverse life history with settlement on sea turtles, manatees, dugongs, and crustaceans. This species is therefore exposed to a wide variety of environmental conditions, including changes in ecosystems, water flow, pressure, and salinity. While spatial distribution of C. testudinaria on loggerhead turtle ( Caretta caretta ) carapaces—and therefore areas of variable flow—presents some evidence for potential plasticity in epibiotic cirri, interhost comparisons are lacking. To determine if morphology differs significantly by host, we conducted discriminant function analyses (DFAs) with twelve cirral measurements from barnacle specimens collected from both sea turtle and manatee hosts. Overall, we show greater than 94% discrimination in the classification of original grouped cases and cross-validated grouped cases in generalized and stepwise discriminant models. While plasticity remains evident within the Chelonibia genus, our data provide evidence contradictory to the currently accepted hypothesis that this plasticity is dependent upon, and strongly correlated with, host association. Therefore, we suggest that the single-species designation of the Chelonibia testudinaria complex be reevaluated.