Genetic diversity and structure of the tropical seagrass Cymodocea serrulata spanning its central diversity hotspot and range edge Dan M. Arriesgado . Hiroyuki Kurokochi . Yuichi Nakajima . Yu Matsuki . Wilfredo H. Uy . Miguel D. Fortes . Wilfredo L. Campos . Kazuo Nadaoka . Chunlan Lian Received: 5 December 2014 / Accepted: 10 June 2015 / Published online: 26 June 2015 © Springer Science+Business Media Dordrecht 2015 Abstract Persistence of populations at their distribu- tional ranges relies on local population dynamics and the fitness of species with low dispersal potential. We analyzed the population genetic diversity and structure of a tropical seagrass species, Cymodocea serrulata, at 34 sites spanning Philippine (diversity hotspot) and Ryukyu Islands (northern limit of distribution) popula- tions using microsatellite (SSR) markers. Seagrass populations in the diversity hotspot are hypothesized to contain higher genetic diversity and clonal richness than those resulting from expansion or geographic range limits. We tested this hypothesis by comparing the genetic diversity, genetic structure and clonal richness of C. serrulata populations in the Philippines and Ryukyu Islands. C. serrulata populations showed decreased genetic diversity and clonal richness at their northern limit. Clonal reproduction predominated at the northern limit, while sexual reproduction prevailed in the diver- sity hotspot. Decreased genetic diversity and clonal richness at the northern limit may be the consequence of drift resulting from founder effect, reduced habitat, sea surface temperature and low gene flow and/or natural selection across life stages, wherein clonal reproduction confers greater environmental fitness. Analysis of molecular variance (AMOVA) and the fixation index, F ST , showed significant genetic differentiation within and among geographic populations. STRUCTURE analysis revealed that the Ryukyu Islands populations were mosaics of genets from the eastern Philippines, likely carried by the Kuroshio Current. Handling Editor: Michael T. Monaghan. D. M. Arriesgado · K. Nadaoka Department of Mechanical and Environmental Informatics, Graduate School of Information Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan D. M. Arriesgado · H. Kurokochi · Y. Nakajima · Y. Matsuki · C. Lian (&) Asian Natural Environmental Science Center, The University of Tokyo, 1-1-8 Midori-cho, Nishitokyo, Tokyo 188-0002, Japan e-mail: lian@anesc.u-tokyo.ac.jp D. M. Arriesgado · W. H. Uy Institute of Fisheries Research and Development, Mindanao State University at Naawan, 9023 Naawan, Misamis Oriental, Philippines M. D. Fortes Marine Science Institute CS, University of the Philippines, 1101 Diliman, Quezon City, Philippines W. L. Campos Division of Biological Sciences, College of Arts and Sciences, University of the Philippines in the Visayas, 5023 Miag-ao, Iloilo, Philippines 123 Aquat Ecol (2015) 49:357–372 DOI 10.1007/s10452-015-9529-0