Phylogeny-based species delimitations and the evolution of host associations in symbiotic zoanthids (Anthozoa, Zoanthidea) of the wider Caribbean region

Abstract

Zoanthusids are marine cnidarians with simple morphologies that challenge our ability to delineate species. Phylogenetic analyses of internal transcribed spacer (ITS) sequences are consistent with six morphologically described species from the wider Caribbean region, and reveal four additional species that were not previously recognizeaid. Histological examinations of unidentified species reveal cryptic Isozoanthus and Edwardsiidae (Actiniaria) species. Observations of Zoanthusids in situ reveal geographic distributions that range from regional to trans-Atlantic. ITS and 16S data are consistent with hypotheses of paraphyly in some higher taxa of Zoanthusids; however, the clades of Zoanthusids recovered in both analyses can largely be defined by their host associations, thereby supporting phylogenetic conservatism in Zoanthusid–host association evolution. The single clear example of a Zoanthusid switching hosts was accompanied by a compensatory loss of endosymbiosis, which maintained the match in photosynthetic symbioses between Zoanthusids and sponge hosts.