Mitochondrial and nuclear dna phylogeographies for two botryllid ascidian species from the north-eastern mediterranean sea

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2020-10-22
Öztürk, Esra
With approximately 3000 species, ascidians are the largest tunicate group in the world seas. Botrylloides belongs to the genera of the worldwide spread Botryllid ascidians. In the Eastern Mediterranean coasts, a total of six Botryllid ascidians have been observed up to date. However, there is no study considering the distribution and phylogeographic analysis of ascidian species along the Mediterranean Sea's Turkish coasts. Within this study’s scope, specimens were collected from the coastal area of Hatay (Konacık), Mersin (Mezitli, Kızkalesi, Tisan) and Antalya (Alanya) regions comprising approximately 550 km of coastline between 2012 and 2019. Mitochondrial (COI, CytB) and nuclear (18s, H3) gene regions were amplified for the analysis. For COI, 100% amplification success was obtained for 62 samples; however, the success rate varied from zero to 100% for the other markers according to sampling location. The intra- and inter-specific distances were calculated between the haplotypes/locations. The Median-joining network analysis of haplotypes was done, and the phylogenetic trees were constructed for the samples. Neutrality tests and mismatch distribution analyses were applied to detect any demographic change. B. anceps, Botrylloides sp. and Botrylloides israeliense were recorded on the Turkish coasts of Levantine Sea for the first time. The phylogeographic analysis was done only for B. anceps and Botrylloides sp., which could be sampled at Konacık, Mezitli, Kızkalesi, and Alanya sampling stations, in contrast to B. israeliense, for which only one specimen could be encountered in Tisan during sampling. No genetic variation was detected for the COI and CytB regions of B. anceps and the 18S gene regions of Botrylloides israeliense. H3 gene showed low variation for B. anceps, thus resulted in an insignificant neutrality test and Raggedness statistics. Therefore, B. anceps was found to have low invasive capacity due to low genetic variation related to a single introduction event that happened via anthropogenic ways and colony age. For Botrylloides sp., both mitochondrial markers have shown variations; however, not enough for a significant P-value. Thus, population size change or population expansion could not be detected for B. anceps and Botrylloides sp. species. On the other hand, Mezitli and Kızkalesi samples of Botrylloides sp. have shown strong genetic differentiation; FST=0.556COI and 0.361CytB, is an outcome of the limited dispersal capacity of the larva. A chimera formation, a single colony, consisting of at least two colonies with distinct genotypes, recorded between B. israeliense and Botrylloides sp. The blastogenesis, weekly asexual reproduction, of the species was monitored for the first time in this study. In this study, the distribution of three ascidian species on Turkey's Mediterranean coasts was revealed, and their populations were compared for phylogeographic analysis. Populations were found to be in a constant size, and the need for the use of combined markers was emphasized.
Citation Formats
E. Öztürk, “Mitochondrial and nuclear dna phylogeographies for two botryllid ascidian species from the north-eastern mediterranean sea,” M.S. - Master of Science, 2020.