Molecular Ecology 2003 12 1451 1460 doi 10 1046 j 1365 294X 2003 01810 x Chloroplast DNA phylogeography reveals colonization history of a Neotropical tree Cedrela odorata L in Mesoamerica Blackwell Publishing Ltd S C A V E R S C N A V A R R O and A J L O W E Centre for Ecology and Hydrology Edinburgh Bush Estate Penicuik Midlothian EH26 0QB UK Centro Agr nomico Tropical de Investigaci n y Ense anza Cartago Turrialba 7170 Costa Rica Abstract Spanish Cedar Cedrela odorata L is a globally important timber species which has been severely exploited in Mesoamerica for over 200 years Using polymerase chain reaction restriction fragment length polymorphisms its chloroplast cp DNA phylogeography was studied in Mesoamerica with samples from 29 populations in six countries Five haplotypes were characterized phylogenetically grouped into three lineages Northern Central and Southern Spatial analysis of ordered genetic distance confirmed deviation from a pattern of isolation by distance The geographically proximate Northern and Central cpDNA lineages were genetically the most differentiated with the Southern lineage appearing between them on a minimum spanning tree However populations possessing Southern lineage haplotypes occupy distinct moist habitats in contrast to populations possessing Northern and Central lineage haplotypes which occupy drier and more seasonal habitats Given the known colonization of the proto Mesoamerican peninsula by South American flora and fauna prior to the formation of the Isthmus of Panama it seems most likely that the observed population structure in C odorata results from repeated colonization of Mesoamerica from South American source populations Such a model would imply an ancient pre Isthmian colonization of a dry adapted type possessing the Northern lineage or a prototype thereof with a secondary colonization via the land bridge Following this a more recent possibly post Pleistocene expansion of moist adapted types possessing the Southern lineage from the south fits the known vegetation history of the region Keywords Cedrela odorata differentiation dispersal Meliaceae Spanish Cedar universal cpDNA markers Received 19 December 2002 revision received 13 January 2003 accepted 13 January 2003 Introduction Phylogeography examines the correspondence between genetic relationships and geographical distribution Avise et al 1987 Population genetic structure is as much a product of history as of present day migration patterns and isolation of populations hence a synthesis of genealogical data with independent information including geology palynology and archaeology Avise et al 1987 Bermingham Moritz 1998 may disentangle the historical component of population structure from that which is the result of contemporary gene flow processes Correspondence S Cavers Fax 0131 4453943 E mail scav ceh ac uk 2003 Blackwell Publishing Ltd In plants the recent development of universal primer sets targeting noncoding regions of the chloroplast cp genome Taberlet et al 1991 Demesure et al 1995 Dumolin Lapegue et al 1997b Hamilton 1999 has revealed substantial amounts of intraspecific variation Newton et al 1999a and cpDNA data have now been successfully used for several phylogeographic studies of plants Petit et al 1993 Petit et al 1997 Caron et al 2000 Dutech et al 2000 Raspe et al 2000 As a result of its usual maternal inheritance in angiosperms cpDNA is transmitted only through seeds and therefore has less potential for gene flow than nuclear genes which can also move by pollen dispersal Consequently genetic variation in the chloroplast genome is often more highly geographically structured than that in the nuclear genome Furthermore as the rate of cpDNA 1452 S C A V E R S C N A V A R R O and A J L O W E sequence evolution is slow Wolfe et al 1987 observed patterns reflect the outcome of processes over long timescales Ennos et al 1999 so cpDNA is ideal for studying historical patterns of gene flow in particular migration and colonization Several recent studies have taken advantage of these characteristics to investigate vegetation changes in particular those related to glacial cycles In Europe Alnus glutinosa King Ferris 1998 Quercus sp Dumolin Lapegue et al 1997a North America Dryas integrifolia Tremblay Schoen 1999 Liriodendron tulipifera Sewell et al 1996 and the tropics Vouacapoua americana Dutech et al 2000 Dicorynia guianensis Caron et al 2000 cpDNA has been successfully used to detect spatiotemporal patterns of fragmentation and dispersal resulting from climatic variations during the Pleistocene epoch The region of interest in this study is tropical Mesoamerica between southern Mexico and northern Colombia encompassing Guatemala Honduras Nicaragua Costa Rica and Panama Present day Mesoamerica is a region rich in diversity there are still more than a quarter of a million square kilometres of primary vegetation around 24 000 plant species of which some 5000 are endemic and nearly 3000 vertebrate species of which over 1000 are endemic Myers et al 2000 The distribution and composition of the Mesoamerican flora and fauna have been strongly influenced by geological and climatic events Burnham Graham 1999 Prior to the formation of the Isthmus of Panama there was considerable interchange of flora between the separate land masses of North and South America Raven Axelrod 1974 possibly via an island chain At this time populations would have been isolated in the proto Mesoamerican peninsula by the sea to the south and by the more temperate climate to the north Savage 1982 Following the formation of the Panamanian land link between 5 and 3 million years ago Ma Coney 1982 the Great American Interchange resulted in numerous invasions of Mesoamerica by South American angiosperm flora Burnham Graham 1999 Later the climatic fluctuations of the Pleistocene 1 6 0 01 Ma had a substantial influence on the Mesoamerican flora Prance 1982a b Toledo 1982 Major fragmentation of the extensive tropical forest took place Toledo 1982 Leyden 1984 Islebe Hooghiemstra 1997 Williams et al 1998 Hewitt 2000 with many species restricted to refuge populations in the region of present day Guatemala and northwest Colombia during glacial maxima In general for many plant and animal species of Mesoamerica distinct biogeographic patterns remain reflecting the significant influence of dispersal and isolation extinction and colonization on the populations of this dynamic and diverse region Savage 1982 Bermingham Martin
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