SCLERACTINIA SOFT TISSUE SYSTEMATICS: USE OF HISTOLOGICAL CHARACTERS IN CORAL TAXONOMY AND PHYLOGENETIC RECONSTRUCTIONS

Robust phylogenetic reconstructions are critical to understanding the history of life on Earth. Furthermore, conservation managers can create priorities for sensitive species, given anthropogenic climate change, based on information from their phylogenetic diversity. A combination of molecular and morphological data sources is necessary to resolve many phyla at both higher and lower taxonomic ranks. Phylum Cnidaria is one such group in which molecular data has shown that the group is monophyletic, but more morphological studies are needed to resolve families. Cnidarians are of particular interest as they make up a large component of tropical coral reefs, which are in need of conservation.

Traditionally, studies of the stony coral order Scleractinia have focused on morphological characters from the hard skeletal. While useful, this alone has not yielded enough characters to differentiate all species. Additional characters for phylogenetic analysis can be found in the soft tissue. For this study, eight Pacific species of scleractinian corals were investigated for new characters. Former members of the family “Pectiniidae” were used as they have skeletal features that are challenging to characterize. Specimens were ordered from retail stores and housed in home aquaria. Specimens were decalcified, embedded in paraffin, cut into thin sections and stained with H&E; similar to medical histopathological studies. A total of 20 characters focusing on stinging cells and tissue layers were coded. Phylogenetic software then analyzed and produced a phylogenetic tree roughly equivalent to molecular or skeletal character based studies and trait origination could be mapped onto this new phylogeny.

Despite only using a small number of characters in comparison to much larger skeletal and molecular based studies, broad congruencies could be observed in the phylogenies. This suggests that histological characters are a valid taxonomic tool to use for reconstructing lineage histories of extant organisms. Histological preparation equipment is now common enough in most major universities that histological character addition to other morphological studies is possible. Thus, with a larger number of characters to work with, phylogeneticists can better resolve phylogenies and use this data to aid conservation managers.