No abstract

Natural hybridization has significant ecological, genetic and evolutionary consequences altering morphological and chemical characters of individuals. Quercus glabrescens, Q. rugosa and Q. obtusata are white oak species well separated by their morphological characters when they occur in allopatry in Mexican temperate forests. However, in sympatry, individuals with atypical morphology have been observed, suggesting hybridization events. In this study, we determined with microsatellites and secondary metabolites if interspecific gene flow occurs when these three-oak species coexist in sympatry. In total, 180 individuals belonging to seven populations [three allopatric (one for each parental species) and four sympatric sites] were analyzed. Allopatric populations represent well defined genetic groups and the sympatric populations showed genetic evidence of hybridization between Q. glabrescens × Q. rugosa and Q. glabrescens × Q. obtusata. The hybridization percentage varied between sites and combination of involved species. We registered the presence of unique flavonoid compounds for Q. glabrescens (caffeic acid and flavonol 2), Q. rugosa (flavonol 5), Q. obtusata (flavonol 1). Three compounds (quercetin rhamnoside, flavonol 3 and alkyl coumarate) were expressed in all taxa. Finally, the hybrid genotypes identified in this study (Q. glabrescens × Q. rugosa and Q. glabrescens × Q. obtusata) showed particular chemical profiles, resulting from combination of those of their parental species. These results show that hybridization events between these oak species alter chemical expression of secondary metabolites, creating a mosaic of resources and conditions that provide the substrate for different combinations of foliar-associated species as herbivores, endophytic fungi or epiphyte plants. This article is protected by copyright. All rights reserved.

Interspecific gene flow between more than two species is a common phenomenon in oaks, which can occur simultaneously among different species, promoting the transfer of genetic material across species boundaries. However, the hybridization dynamics in multispecies hybrid zones remain unknown. In this study, we provide genetic evidence of hybridization and introgression of Quercus castanea across a natural gradient of red oak species richness. We analyzed five populations recognized morphologically as ''pure'' Q. castanea, one allopatric and four sympatric populations, where the number of red oak species associated with Q. castanea ranged from one to four. Also, one allopatric population of each red oak species that occurs in sympatry with Q. castanea was chosen as reference population (Q. crassipes, Q. laurina, Q. mexicana and Q. crassifolia). In total, six nSSRs were used in 10 and 20 individuals from each allopatric and sympatric populations, respectively. Our results showed that allopatric populations formed completely distinct genetic clusters.In sympatric populations, we found evidence of hybridization and introgression among Q. castanea and three of its associated red oak species. However, the occurrence and frequency of hybrids between Q. castanea and these species varied among stands. Our analyses provide evidence and new insights into hybridization and introgression dynamics within a Mexican red oak species complex, through a focal species, Q. castanea.

Background: Recently it has been proposed that the genetic diversity of foundation species influences the structure and function of the community by creating locally stable conditions for other species and modulating ecosystem dynamics. Oak species are an ideal system to test this hypothesis because many of them have a wide geographical distribution, and they are dominant elements of the forest canopy. In this study we explored the response of canopy arthropod community structure (diversity and biomass) to the level of genetic diversity of Quercus crassipes and Q. rugosa, two important canopy species. Also, we examined the effect of oak species and locality on some community structure parameters (diversity, biomass, rare species, and richness of arthropod fauna) of canopy arthropods. In total, 160 canopies were fogged in four localities at the Mexican Valley (ten trees per species per locality per season). Results: Q. crassipes registered the highest number of rare species, diversity index, biomass, and richness in comparison with Q. rugosa. We found a positive and significant relationship between genetic diversity parameters and canopy arthropod diversity. However, canopy arthropod biomass registered an inverse pattern. Our results support the hypothesis that the genetic diversity of the host-plant species influences the assemblage of the canopy arthropod community. Conclusions: The pattern found in our study provides a powerful tool when trying to predict the effects of the genetic diversity of the host-plant species on different community structure parameters, which permits assignment of a new conservation status to foundation species based on their genetic diversity.