Regional scale genetic structure within two Central American tree species: the influence of geography, biology and geological history.

We examine spatial genetic structure occurring at a regional scale for two widely distributed tree species from Central America, Vochysia ferruginea and Cedrela odorata, and speculate on some of the geographic, edaphic and geological factors that may be responsible in a continent that has a complex geological history and is rich in natural resources. For V. ferruginea, the central mountain ranges of Costa Rica coincide with a major genetic differentiation and are probably acting to maintain this genetic split by reducing gene flow. A major genetic differentiation within Costa Rica is also apparent for C. odorata, for both nuclear and chloroplast markers. However, this split coincides with habitat type (dry vs. moist), not with geographic features and appears to be a case of ecotypic differentiation or possibly cryptic speciation. A cpDNA phylogeographic analysis of C. odorata across Central America reveals that the strong genetic/ecotypic differentiation continues across a large portion of the region. The pattern of cpDNA variation is discussed within the context of species colonisation and extinction. However, a scenario that involves separate and repeated colonisation of Central American regions from diverse sources most closely fits the present pattern. Future work to examine cpDNA variation across the Caribbean and South America should shed more light on this issue. Finally the importance of such genetic data for prioritising the management of forest genetic resources is discussed.