Hybridization of Quercus castanea (Fagaceae) across a red oak species gradient in Mexico

Abstract

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.

Effect of host-plant genetic diversity on oak canopy arthropod community structure in central Mexico

“…For example, Valencia (1994) proposed that a group of oaks conformed by Q. affinis, Q. crassipes, Q. crassifolia, Q. laurina, Q. mexicana, and Q. rubramenta may experience genetic exchange when they occur in sympatric/mixed stands. This last scenario has been corroborated by Tovar-Sánchez and Oyama (2004) for the Q. crassipes × Q. crassifolia complex, González-Rodríguez et al (2004) for the Q. laurina × Q. affinis complex, and Valencia-Cuevas et al (2015) for Q. castanea, Q. laurina, and Q. crassifolia. The species mentioned above are distributed along the Mexican Valley, a fact that may facilitate the genetic exchange with Q. crassipes.…”

“…Oaks (Fagaceae, Quercus) are an ideal system to study the effects of host-plant species genetic diversity on their associated canopy communities because of their high levels of genetic variation (e.g., Tovar-Sánchez et al 2008;Valencia-Cuevas et al 2014, 2015; many of their species show a wide geographical distribution and canopy dominance (Valencia 2004), and constitute the habitat of different species. Therefore, some of them can be considered as foundation species.…”

Oak canopy arthropod communities: which factors shape its structure?

“…This is because many oak species can be considered foundation species due to their wide geographic distribution (Valencia 2004) and dominance in the canopy of forests (TovarSánchez et al 2013) and because they are habitat to different species. They also show a high frequency of natural hybridization (Curtu et al 2007;Peñaloza-Ramírez et al 2010;Valencia-Cuevas et al 2015), a condition that can promote an increase in genetic diversity (Tovar-Sánchez et al 2008;Valencia-Cuevas et al 2014) and the appearance of new features in host plants (Tovar-Sánchez and Oyama 2004) which can be exploited by arthropod communities. However, to date, there are few studies that have evaluated the structure of arthropod communities associated with the canopy of oaks from a genetic perspective.…”

“…Interspecific hybridization is a common phenomenon in plants (Whittemore and Schaal 1991;Avise 1994;Rieseberg 1995;López-Caamal and Tovar-Sánchez 2014), especially common among species of the genus Quercus (Curtu et al 2007;Peñaloza-Ramírez et al 2010;Valencia-Cuevas et al 2015). Particularly, for 20 years, the hybrid zones have been attractive as unique scenarios to study the effects of natural hybridization on plant-insect interactions (Fritz et al 1994(Fritz et al , 1998Whitham et al 1999;Wimp et al 2004;Yarnes et al 2008).…”

“…Considering the high frequency of hybridization between species of oaks (Spellenberg 1995;Howard et al 1997;Tovar-Sánchez and Oyama 2004;Curtu et al 2007;Peñaloza-Ramírez et al 2010;Valencia-Cuevas et al 2015) and that hybrid host plants facilitate the establishment of herbivore species (Whitham 1989;Boecklen and Spellenberg 1990;Floate and Whitham 1993;Tovar-Sánchez and Oyama 2006a), one would expect that the change of host by herbivores between species of the genus Quercus would be well documented. However, actually, this subject has been little studied.…”