Fatty acid content in two nudibranch species phyllidia varicosa and phyllidiella pustulosa from east coast peninsular Malaysia

Abstract

The present study aimed to explore the molecular phylogeny, fatty acid composition, food preferences, and feeding ecology of the selected nudibranch species Phyllidia varicosa and Phyllidiella pustulosa from two locations: the coastal waters of Balok, Pahang and Bidong Island, Terengganu, Malaysia. A 16S rDNA marker was utilized to identify the studied species to the species level. 16S rDNA sequences of each studied species, P. varicosa and P. pustulosa, were aligned and applied to the examination of the phylogenetic relationships among them. The divergence of sequences was adequate to identify the samples to the species level with the assistance of the GenBank database and the BLAST tool. The studied species from the coastal water of Balok and Bidong Island are the same species and there is no possibility of new species arising. Analysis of the fatty acid composition of P. varicosa and P. pustulosa were analysed by gas chromatography-mass spectrometry (GC-MS), it was found that 15:0, 16:0, 17:0, 18:0, 18:1(n-9), 20:1(n-9) and 20:4(n-6) were predominant. Based on the univariate analysis, there was no significant difference in total saturated fatty acid (SFA). In contrast, there was a significant difference between species and site in total polyunsaturated fatty acids (PUFA) p < 0.05. Besides that, the univariate analysis of odd-chain branched fatty acids (OBFA) was significantly different between the species but not the site, and the total percentages of OBFA in Balok samples were noted to be higher than the sum of OBFA in Bidong Island samples. There was a significant difference between species but no significant differences in site and interaction in total of monounsaturated fatty acids (MUFA). Based on the pairwise analysis, the fatty acid composition between the same species but different sites was also significantly different p < 0.05. The overall fatty acid composition was significantly different. Statistical analyses were conducted in Primer V6 + PERMANOVA using Euclidean distance similarity matrices, and the data were visualized using PCO plot and showed the main fatty acids contributed to the main differences. Analysis of the fatty acid composition of the sponge prey was also carried out in order to assess the predator-prey relationships between P. varicosa species and its sponge prey. In both sponge species, the main saturated fatty acids were 16:0 and 18:0. The positional isomers of 18:0 were the most common in both species with 6.78% in Xestospongia vansoesti and 5.3% in Aaptos suberitoides. Two demospongic acids 5,9-25:2 and 5,9 -26:2 were detected. The characterization of 5,9 -25:2 was achieved based on the MS spectra to confirm the presence of demospongic acids in the nudibranch tissue and sponge species. As a conclusion, based on the fatty acid analysis and food preferences, the variation of nudibranch size between two different locations might come from different diet specificities.