PATRÓN DE CRUZAMIENTO EN POBLACIONES NATURALES DE Pseudotsuga menziesii (Mirb.) Franco EN MÉXICO MATING PATTERN IN NATURAL POPULATIONS OF Pseudotsuga menziesii (Mirb.) Franco IN MÉXICO

Las poblaciones mexicanas de Pseudotsuga menziesii (Mirb.) Fran- co tienen una distribución natural restringida y fragmentada, sobre todo en la región centro; por tanto, hay riesgo de que éstas se pierdan por efectos del cambio climático. Con el propósito de sugerir medidas adecuadas para su conservación, se evaluó el patrón de cruzamiento y su efecto sobre el nivel de endogamia en tres poblaciones naturales de P. menziesii, dos del norte y una del centro de México, con base en el porcentaje de polinización cruzada. Con la información de cinco loci polimórficos se esti- maron las frecuencias alélicas de polen y óvulos y la proporción de cruzamiento en cada población usando modelos de loci múlti- ples ( t ^ m) y de un solo locus ( t ^ s). No se encontraron diferencias en ABSTRACT The Mexican populations of Pseudostuga menziesii (Mirb.) Franco have a restricted and fragmented natural distribution, especially in the central region, therefore there is a risk that these populations will be lost due to the effects of climatic change. With the purpose of suggesting adequate measures for their conservation, an evaluation was made of the mating pattern and its effect on the inbreeding level in three natural populations of P. menziesii, two of the north and one of the central region of México, based on the percentage of cross pollination. With the information of five polymorphic loci, the allelic frequencies of pollen and ovules were estimated, along with the proportion of mating in each ^ m and t^ s), indicates that selfing is the principal form of inbreeding in the populations evaluated. Despite the high percentage of cross breeding in the northern populations, the paternity correlation coefficient in them was over 60%, indicating a reduced number of pollinating trees. The implications of these results in the conservation of the populations are discussed, especially in the central region.