Genetic diversity and mating system analysis of Cedrela odorata L. (Meliaceae) populations under different human dominated landscapes and primary forests

Genetic variability is an important condition for species to successfully face present challenges and survive while adapting and reproducing to meet future environmental changes. Another crucial aspect of conservation genetics for Neotropical species in fragmented landscapes is their mating systems strategies such as outcrossing and inbreeding, and conservation genetics then deals with how to maintain these systems. Cedrela odorata also known as Spanish cedar is an important tropical timber tree species which distributes widely across the continent and it‘s considered one of the main species for timber production. The objectives of the present study were: i) to assess the genetic diversity of C. odorata in primary forests and human dominated landscapes in Mesoamerica; ii) to determine and compare outcrossing rates and levels of inbreeding for the species among different levels of human dominated landscapes; and iii) to evaluate the impact of fragmentation and mother tree isolation on the genetic diversity and outcrossing parameters. Microsatellite markers for the species were developed to assess the genetic diversity and mating systems. Leave samples were collected from provenance and progeny trials established at CATIE, Turrialba. High gene diversity estimates were found for C. odorata progeny arrays, although no significant differences were found between the northern and central lineages, neither the progeny arrays of isolated mother trees nor the ones in groups or clusters. Average observed heterozigosity was 0.78 and 20.56 was the average number of alleles overall the samples. High multi-locus outcrossing rates (tm) were obtained for both isolation levels, 1.00 ± 0.08 and 1.06 ± 0.06 for isolation level 1 and 3, respectively, suggesting absence of self-fertilization. Isolation level analysis revealed significant differences for correlation of paternity and single locus inbreeding coefficient of maternal parents, which was higher for isolated families. An average of 5.0 mature trees donated pollen to isolated mother trees, while 7.7 pollen donors were found for mother trees within a ratio of 100 meters. C. odorata progenies from isolated trees have higher levels of bi-parental inbreeding, fewer pollen donors, potentially leading to a reduction of mechanisms for selective abortion among different pollen donors, and leading to a decrease in vigor of progenies. This information is significant for decision makers of the management and conservation of the species, since fertility of individual trees will depend on X the degree of isolation, human dominated habitats and availability of pollinators that may flight long distances between trees. Habitat degradation caused by selective logging has reduced the species density at natural forests, leading to common scenarios with small fragmented forests with few remnant C. odorata trees. Importance of isolated trees as stepping stones connectors between fragmented forests must be taken into account for future harvesting permits, where landscape management might be a priority for the species.