Thu, Aug 05, 2021:On Demand
Background/Question/Methods
Genus Chelonibia is informally referred to as the “turtle barnacles,” with Chelonibia testudinaria historically subdivided into three species based on morphological differentiation and host affinity. The thin-shelled, high aspect barnacles that comprise crab and mollusk specialists were designated Chelonibia patula; specimens with deeply ridged tests and basal projections that are commensal with marine mammals of the Order Sirenia were designated C. manati; and the smooth, low-aspect barnacles affixed to any of the seven species of sea turtles were designated C. testudinaria. Recent attempts to reconcile morphological variation with molecular differentiation have presented conflicting results, and additional data are necessary to resolve the taxonomic relationship and investigate the degree of morphological variation among the Chelonibia. In this preliminary study, we measured 11 test and cirral attributes of 75 C. testudinaria specimens, 25 C. manati specimens, and seven C. patula specimens and conducted discriminant function analysis (DFA) to compare the three species. We also conducted scanning electron microscopy (SEM) of the captorial fan for C. testudinaria and C. manati to assess gross setal differences, and acquired measurements of 12 small-scale cirral attributes for inclusion in a separate, two-species DFA.
Results/Conclusions We found significant differences in cirrus length in each of the three terminal cirri, demonstrating a species-specific pattern. We also observed significant differences in shell conicity and ellipticity among all three species. Results of the three-species DFA resulted in distinct group clusters with 80.6 % of cases classified in accordance with expected species designation. Analysis of SEM images of cirral anatomy did not present setal type differentiation among the three species, although discriminant analysis of cirral attributes resulted in 94.7 % cases classified in their correct species group. Further, we found specimens with morphology and host origins that opposed expectation, presenting evidence against the currently held explanation of host-specific phenotypic plasticity among C. testudinaria specimens. Our study findings suggest that sufficient variation exists to separate C. testudinaria into subspecies based on quantitative measures of external attributes rather than the hosts from which barnacles are collected. Further study of molecular divergence of the Chelonibia is necessary, as taxonomic classification is essential for communicating science and informing policy to mitigate biodiversity loss, as well as benefitting conservation of endangered host species through precise categorization of associated epibiota.
Results/Conclusions We found significant differences in cirrus length in each of the three terminal cirri, demonstrating a species-specific pattern. We also observed significant differences in shell conicity and ellipticity among all three species. Results of the three-species DFA resulted in distinct group clusters with 80.6 % of cases classified in accordance with expected species designation. Analysis of SEM images of cirral anatomy did not present setal type differentiation among the three species, although discriminant analysis of cirral attributes resulted in 94.7 % cases classified in their correct species group. Further, we found specimens with morphology and host origins that opposed expectation, presenting evidence against the currently held explanation of host-specific phenotypic plasticity among C. testudinaria specimens. Our study findings suggest that sufficient variation exists to separate C. testudinaria into subspecies based on quantitative measures of external attributes rather than the hosts from which barnacles are collected. Further study of molecular divergence of the Chelonibia is necessary, as taxonomic classification is essential for communicating science and informing policy to mitigate biodiversity loss, as well as benefitting conservation of endangered host species through precise categorization of associated epibiota.