Multi-Gene Analysis, Morphology, and Species Delimitation Methods Reveal a New Species of <i>Melanothamnus</i>, <i>M. coxsbazarensis</i> sp. nov. (Rhodomelaceae, Ceramiales), for the Marine Red Algal Flora from Bangladesh
2025
Md. Ariful Islam | William E. Schmidt | Mohammad Khairul Alam Sobuj | Shafiqur Rahman | Suzanne Fredericq
Some <i>Melanothamnus</i> species have been documented growing epiphytically on other algae in seaweed aquaculture farms as fouling organisms. Such turf-forming <i>Polysiphonia</i>-looking algae were collected from a small (<1.0 km<sup>2</sup> area) <i>Agarophyton tenuistipitata</i> (Gracilariaceae, Gracilariales) farm on the east coast of the Bay of Bengal and examined for their taxonomy. DNA was extracted from silica gel-preserved specimens, and plastid-encoded <i>rbc</i>L, nuclear-encoded small subunit SSU, large subunit LSU, and universal plastid amplicon (UPA) were amplified and sequenced. Maximum likelihood (ML) and Bayesian inference were performed for the phylogenetic analysis. Four single-locus species delimitation methods (SDMs), namely, the generalized mixed Yule-coalescent (GMYC) method, a Poisson tree processes (PTP) model, the automatic barcode gap discovery (ABGD), and the assemble species by automatic partitioning (ASAP) method, were performed to segregate the putative species from other taxa in the <i>Polysiphonia sensu lato</i> clades. Our results revealed that <i>rbc</i>L had 1.4% interspecific genetic divergence, whereas LSU, UPA, and SSU had 1.6%, 2.5%, and 5.4% genetic divergence, respectively, from the nearest neighbors. Both comparative genetic and distinct morphological data revealed that the collected Bay of Bengal specimens comprise a species new to science. In addition, the above-mentioned SDMs supported the genetic data and segregated our specimens as <i>Melanothamnus coxsbazarensis</i> sp. nov. as a distinct species.
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