ORIGINAL ARTICLE Phylogeography of the Coccus scale insects inhabiting myrmecophytic Macaranga plants in Southeast Asia Shouhei Ueda Æ Swee-Peck Quek Æ Takao Itioka Æ Kaori Murase Æ Takao Itino Received: 25 June 2008 / Accepted: 22 January 2009 / Published online: 2 July 2009 Ó The Society of Population Ecology and Springer 2009 Abstract Comparative historical biogeography of multi- ple symbionts occurring on a common host taxa can shed light on the processes of symbiont diversification. Myr- mecophytic Macaranga plants are associated with the obligate mutualistic symbionts: Crematogaster (subgenus Decacrema) ants and Coccus scale insects. We conduct phylogeographic analyses based on mitochondrial cyto- chrome oxidase I (COI) from 253 scale insects collected from 15 locations in Borneo, Malaya and Sumatra, to investigate the historical biogeography of the scales, and then to draw comparisons with that of the symbiotic, but independently dispersing, Decacrema ants which are not specific to different Coccus lineages. Despite the different mode of ancient diversification, reconstruction of ancestral area and age estimation on the Coccus phylogeny showed that the scales repeatedly migrated between Borneo and Malaya from Pliocene to Pleistocene, which is consistent with the Decacrema ants. Just as with the ants, the highest number of lineages in the scale insects was found in northern northwest Borneo, suggesting that these regions were rainforest refugia during cool dry phases of the Pleistocene. Overall, general congruence between the Plio– Pleistocene diversification histories of the symbiotic scales and ants suggests that they experienced a common history of extinction/migration despite their independent mode of dispersal and host-colonization. Keywords Biogeography Á Cytochrome oxidase Á Decacrema Á Myrmecophyte Á Rainforest Á Scale insects Introduction Phylogeography provides a good opportunity to identify the historical evolutionary processes, the glacial refugia and postglacial migration routes of organisms (Avise 2000). Several studies have compared the phylogeny between host and symbiont organisms (reviewed in Nieberding and Olivieri 2007), but there are currently few studies that compare phylogeography of co-occurring and distantly related symbiotic and parasitic taxa (e.g., Althoff et al. 2007; Whiteman et al. 2007). Comparative historical biogeography of multiple symbionts occurring on a com- mon host taxa can shed light on the evolutionary processes of symbiont diversification (Whiteman et al. 2007). Tropical rainforests in Southeast Asia harbor some of the greatest concentrations of biodiversity on earth. In Electronic supplementary material The online version of this article (doi:10.1007/s10144-009-0162-4) contains supplementary material, which is available to authorized users. S. Ueda (&) Department of Mountain and Environmental Science, Interdisciplinary Graduate School of Science and Technology, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan e-mail: s05t404@shinshu-u.ac.jp S.-P. Quek FAS Center for Systems Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA T. Itioka Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan K. Murase Laboratory of Biodiversity Science, School of Agriculture and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan T. Itino Department of Biology, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan 123 Popul Ecol (2010) 52:137–146 DOI 10.1007/s10144-009-0162-4