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Effect of hybridization on the morphological differentiation of the red oaks Quercus acutifolia and Quercus grahamii (Fagaceae)


In this study, the effect of hybridization on the interspecific differentiation of two species of red oaks, Quercus acutifolia and Q. grahamii, was evaluated. It is thought that hybridization is possible between these two species since they can inhabit adjacently and have periods of synchronous flowering. In addition, individuals with intermediate morphological attributes have been detected within their populations. To resolve this question, samples were collected from 280 adult individuals from 28 sampling locations: 17 of Q. acutifolia and 11 of Q. grahamii. To identify the individuals belonging to the parental species and those with the presence of hybridization, the individuals were genotyped with 10 nuclear microsatellite loci. To determine the patterns of leaf variation, two sets of morphological traits were considered: the first was 22 foliar morphological measurements, and the second was a geometric morphometry analysis using 40 two-dimensional pseudolandmarks. The results of the analysis of genetic allocation revealed that a large proportion of individuals from all populations showed evidence of introgression in their genomes. The morphological comparison showed that there was a clear differentiation between individuals classified as purebred members of the species Q. acutifolia and Q. grahamii. Individuals with evidence of primary hybridization (F1) were scarce and had morphologies similar to those of the Q. grahamii species. On the other hand, introgressed individuals (F2) seemed to be very similar to their genetically closest parents. The results show that the patterns of foliar morphological variation are not very useful for detecting hybridization events between species with continuous genetic exchange.

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Genotypes will be deposited in a public database (Dryad) upon acceptance of the manuscript.

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We thank R. Aguilar-Romero, C.D. Ortega Martínez, F. Hernández Najarro, F.S. Maradiaga Ceceña and J. Llanderal Mendoza for field and laboratory support. This paper constitutes a product of the Graduate Program Posgrado en Ciencias Biológicas, UNAM of AP-P.


This study was supported by the Consejo Nacional de Ciencia y Tecnología (México) grant 422776 to AP-P, and the Dirección General de Asuntos del Personal Académico, Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica at Universidad Nacional Autónoma de México, grants IV 201016 to KO and IA208218 to AT-M.

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Correspondence to Ken Oyama.

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Online Resource 1. The null allele detection analysis.

Online Resource 2. Leaf digitized images with the position of 40 landmarks for the geometric morphometric analysis.

Online Resource 3. Shapiro–Wilk test for all morphological traits by genetic group.

Online Resource 4. Wilk's lambda analysis and ANOVA for all the morphological traits by genetic group.

Online Resource 5. Principal component analysis for the 22 morphological traits.

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Pérez-Pedraza, A., Rodríguez-Correa, H., Valencia-Ávalos, S. et al. Effect of hybridization on the morphological differentiation of the red oaks Quercus acutifolia and Quercus grahamii (Fagaceae). Plant Syst Evol 307, 37 (2021).

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  • Genetic assignment
  • Hybridization
  • Intraspecific differentiation
  • Introgression
  • Morphology
  • Quercus