Genetic structure and distribution of Dictyota spiralis (Dictyotales, Phaeophyta)
Gunasekara, R. (2010). Genetic structure and distribution of Dictyota spiralis (Dictyotales, Phaeophyta). MSc Thesis. Universiteit Gent. Faculteit Wetenschappen. Vakgroep Biologie: Gent. 30 pp.
Introduction & Aim Species of the genus Dictyota (Dictyotales, Phaeophyceae), are key components of marine coastal ecosystems. Along the North East Atlantic and Mediterranean coasts they play an important role in the structuring of sallow benthic communities. Dictyota spiralis Montagne is a common warm temperate species in the NE Atlantic Ocean and Mediterranean Sea, where it co-occurs with D. Dichotoma, D. fasciola and D. implexa. The thallus shows a dichotomous branching pattern, and is sparsely branched. It has an olive greenish colour in situ with pale iridescent margins. Many Dictyota species show considerable morphologically plasticity. In addition, molecular data reveal extensive amounts of cryptic species. Therefore, DNA sequence based studies provide a convenient and reliable tool for species identification and delimitation. In this study we try to examine the genetic structure, define their distribution patterns in North East Atlantic, Macaronesian Archipelago and Mediterranean Sea and algorithmic species delimitation of Dictyota spiralis using organelle encoded molecular markers of (psbA and cox1). Method DNA sequences of the chloroplast psbA sequences and the mitochondrial cox1 genes were analyzed using by means of a Neighbor-joining analysis, statistical parsimony networks and General Mixed Yule-Coalescent (GMYC) modeling to detect species boundaries. Results Neighbor-joining analysis resulted in 3 and 4 clades in the psbA and in the cox1 phylogenetic trees, respectively. The statistical parsimony network and the NJ tree of the cox1 sequences were congruent and formed 4 putative species. Fitting of the position of the speciation-to-coalescence transition using a GMYC model resulted in the identification of 6 putative species in the psbA sequences and 5 species in cox1 sequences. Clade distribution patterns of statistical parsimony and NJ trees of both cox1and psbA were congruent with GMYC trees except minor changes in clade 1 and clade 3 in cox1 GMYC tree. Although taxon sampling was low, the distribution of haplotypes supports a Southern richness - Northern purity hypothesis, which is not surprising given the warm temperate nature of D. spiralis. Conclusion The results of this study demonstrate that D.spiralis consists of several putative species and DNA-based species delimitation approach provides a reliable tool in D.spiralis in which morphological discrimination is difficult. Given a relative low taxon sampling there are potentially more putative species present in the North Atlantic, Northeastern Atlantic coast and Macaronesia archipelagos. The number of specimens should be increased to obtain more supportive data on to investigate re-colonization path way. Therefore, further sampling is highly recommended
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