Abstract
The biodiversity assessment of different taxa of the genus Caulerpa is of interest from the context of morphological plasticity, invasive potential of some species and biotechnological and pharmacological applications. The present study investigated the identification and molecular phylogeny of different species of Caulerpa occurring along the Indian coast inferred from tufA, rbcL, 18S rDNA and ITS rDNA nucleotide sequences. Molecular data confirmed the identification of 10 distinct Caulerpa species: C. veravalensis, C. verticillata, C. racemosa, C. microphysa, C. taxifolia, C. sertularioides, C. scalpelliformis, C. serrulata, C. peltata and C. mexicana. All datasets significantly supported the sister relationship between C. veravalensis and C. racemosa var. cylindracea. It was also concluded from the results that the specimen identified previously as C. microphysa and C. lentillifera could not be considered as separate species. The molecular data revealed the presence of multiple lineages for C. racemosa which can be resolved into separate species. All four markers were used to ascertain their utility for DNA barcoding. The tufA gene proved a better marker with monophyletic association as the main criteria for identification at the species level. The results also support the use of 18S rDNA insertion sequences to delineate the Caulerpa species through character-based barcoding. The ITS rDNA (5.8S-ITS2) phylogenetic analysis also served as another supporting tool. Further, more sequences from additional Caulerpa specimens will need to be analysed in order to support the role of these two markers (ITS rDNA and 18S insertion sequence) in identification of Caulerpa species. The present study revealed the phylogeny of Caulerpa as complete as possible using the currently available data, which is the first comprehensive report illustrating the molecular phylogeny and barcoding of the genus Caulerpa from Indian waters.
Highlights
The siphonous green algal taxa, those belonging to the genus Caulerpa, poses considerable difficulty in taxonomic identification at the species level due to the phenotypic plasticity in diagnostic characters
Two specimens of C. veravalensis (C10 & C23) resembling the specimen described by Thivy and Chauhan [10] were selected for molecular analysis
There is a strong resemblance of these specimens to the description of C. racemosa var. laetevirens f. laxa by Børgesen [65] and with C. racemosa var. cylindracea f. laxa described by Coppejans et al [66]
Summary
The siphonous green algal taxa, those belonging to the genus Caulerpa, poses considerable difficulty in taxonomic identification at the species level due to the phenotypic plasticity in diagnostic characters. Duraiswamy [8,12,13] prepared a comprehensive account of Caulerpa describing 21 taxa from the Indian shores based on morphological, cytological, anatomical and secondary metabolites (caulerpin, caulerpicin and β-sitosterol). These studies largely consisted of collections made from the southern part only. The biodiversity assessment study from the Gujarat coast reported the occurrence of 14 species including five varieties and three forms [14]
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