NCBI offers a range of resources for studying the
nucleotide sequences,
proteins and
chemical compounds characterised to date and subsequent papers based from these findings. In particular nucleotide sequences, commonly in the form of DNA barcodes, originating from
Rhabdastrella globostellata allow for phylogenetic studies with surprising results. The use of
DNA barcoding to trace evolutionary history was first suggested and implemented by Herbert et al. (2003) as a method of constructing accurate phylogenies, without the limitation of reliable morphological traits.
Barcodes from the cytochrome c oxidase subunit I (COI) gene (partial sequence, mitochondrial in origin) (Cardenas et al., 2011) and the partial sequence for the large ribosomal DNA gene (LSU rDNA) (Nichols, 2005) are two published sets thus far for
R. globostellata. Both partial findings were a part of an attempt to formulate a molecular understanding of Demospongiae phylogeny and implement changes to current and historical phylogeny study methods. Due to the new findings being reported, molecular phylogeneticists are proposing a new system for classification following
PhyloCode, to present results independent of rank as clades (Nichols, 2005; Cardenas et al., 2011). This potentially allows for re-evaluation of the origin and evolution of the Porifera, showing unique links between species, genera, families and orders.
Mitochondrial genes have been extensively used in comprehensive evolutionary analyses due to their highly conserved coding through different species (Herbert et al., 2003; Amaral et al., 2007) and slow evolutionary rates (Nichols, 2005; Cardenas, 2010). Cytochrome c oxidase subunit I is a member of the cytochrome c oxidase complex, a key enzyme in aerobic metabolism (Castresana et al., 1994). Due to their conserved nature, COI genes serve well as an evolutionary tracking system or to find relatedness and method of separating closely related taxa (Cardenas, 2010; Amaral et al., 2007). The barcode of the large subunit ribosomal DNA gene is used in a similar manner, as published data indicates that the mitochondrial genes of sponges may evolve extremely slowly (Boury-Esnault & Sole-Cava, 2003; Cardenas, 2010). Caution is emphasised by authors, focusing on a single barcode set could give misleading results, hence the use of both COI and LSU rDNA genes is essential (Nichols, 2005; Cardenas et al., 2011). Researchers aim to find a true phylogenetic tree, an exercise that will take many revisions and careful examination of all available data.
The results of both Nichols (2005) and Cardenas et al. (2011) studies into the molecular phylogeny of Demospongiae and Astrophorida respectively, show a mass revision is needed in regards to grouping within certain families/clades. This revision though, is dependant on given data, discussed in terms of clades. Cardenas et al. (2011) in particular found that within the Astrophorida, and the family Ancorinidae especially, that certain genera displayed homoplasy and were in fact more closely related through molecular phylogenetics than previously thought. Results indicated the polyphyletic genera
Rhabdastrella (including
Rhabdastrella globostellata)
should be placed within the family Geodiidae, a move supported by biochemical findings for isomalabaricane triterpenes in
Rhabdastrella globostellata and
Geodia japonica (Clement et al., 2006; Cardenas et al., 2011). Further investigation is needed to resolve a problem as complex as untangling and aligning the phylogenetic tree of Astrophorida, using all genetic tools currently available.