Hocheol Kim1, Chung Hyun Cho1, Jihoon Jo1, Louis Graf1, Danilo E. Bustamante2, Martha S. Calderon3, Anna V. Skriptsova4, Andres Mansilla3, Gary W. Saunders5, Christine A. Maggs6, Gayle I. Hansen7, and Hwan Su Yoon1
1Department of Biological Sciences, Sungkyunkwan University, Korea
2Instituto de Investigación para el Desarrollo Sustentable de Ceja de Selva (INDES-CES), Universidad Nacional Toribio Rodríguez de Mendoza, Peru
3Laboratorio de Macroalgas Antárticas y Subantárticas, Universidad de Magallanes, Chile
4Laboratory of the Physiology of Marine Autotrophic Organisms, A.V. Zhirmunsky Institute of Marine Biology, Far-Eastern Branch of Russian Academy of Science, Russia
5Department of Biology, University of New Brunswick, Canada
6School of Biological Sciences, Queen’s University Belfast, United Kingdom
7Marine Algal Biodiversity Research, Newport, United States
Genomic divergence and genetic differentiation of many seaweeds are associated with spatial distribution in the ocean and geographic isolation. Ahnfeltia is a red algal genus forming tangled tufts with thin branches. It is known for high quality agar production with a low sulfate ratio. Three Ahnfeltia species are distributed in different areas: A. plicata is found in the North Atlantic, Chile and Tasmania, A. fastigiata is in the North Pacific, and A. borealis is only in the North American Arctic. We postulate that Ahnfeltia species have diverged along with past climate change and somewhat strict geographic isolations by warm ocean currents and the equator because Ahnfeltia growth is favorable to cold-water condition. To investigate the evolutionary history of Ahnfeltia, we de novo assembled nuclear genomes of three Ahnfeltia species and conducted whole genome re-sequencing of 78 individuals from eight populations. Principal components analysis (PCA) and population admixture indicated that Ahnfeltia populations have been isolated without any evidence of gene flow among populations after dispersal. A high fixation index (Fst) among species and population indicated high genetic divergences of Ahnfeltia populations. However, assembled pseudo-chromosomal genomes revealed that core gene inventories were conserved. Genome expansion between A. plicata and A. fastigiata occurred mainly due to transposable elements (TEs). TEs also likely involved in the genomic recombination in A. plicata Chile population. Thus, it is suggested that TEs played an important role in genomic divergence during the speciation and divergence of Ahnfeltia.