The Chthamaloidea (Balanomorpha) present the most plesiomorphic characters in shell plates and cirri, mouthparts, and oral cone within the acorn barnacles (Thoracica: Sessilia). Due to their importance in understanding both the origin and diversification of the Balanomorpha, the evolution of the Chthamaloidea has been debated since Darwin's seminal monographs. Theories of morphological and ontogenetic evolution suggest that the group could have evolved multiple times from pedunculated relatives and that shell plate number diminished gradually (8 → 6 → 4) from an ancestral state with eight wall plates surrounded by whorls of small imbricating plates; but this hypothesis has never been subjected to a rigorous phylogenetic test. Here we used multilocus sequence data and extensive taxon sampling to build a comprehensive phylogeny of the Chthamaloidea as a basis for understanding their morphological evolution. Our maximum likelihood and Bayesian analyses separate the Catophragmidae (eight shell plates and imbricating plates) from the Chthamalidae (8-4 shell plates and no imbricating plates), but do no support a gradual reduction in shell plates (8 → 6 → 4). This suggests that evolution at the base of the Balanomorpha involved a considerable amount of homoplasy.
|Number of pages||6|
|Journal||Molecular Phylogenetics and Evolution|
|State||Published - Oct 2012|
Bibliographical noteFunding Information:
Specimens collected by us were identified by YA, A.J. Southward and J. Buckeridge. Samples were also provided and identified by B.K.K. Chan, R. Hayashi, A. Biccard and D. Jones. This research was supported by the following grants: PTDC/BIA-BEC/098553/2008 to MP-L, YA and JTH; NSF DEB-0236135 to KAC and MP-L; the US–Israel Binational Science Foundation (BSF) 2004-239 to YA and KAC; Israel Science Foundation (ISF) 574/10 to YA and the Danish Natural Science Foundation, the Carlsberg Foundation, the Scandinavian Sasakawa Foundation and the European Union COBICE and SYNTHESYS programs to JTH. We are very thankful to Philippe Lemey for his help with the beta version of BEAST used in this study. S. Zilinsky (BIU) helped with the lab work.
- DNA sequences
- Shell plates