Evidence for selection on a CONSTANS-like gene between two red oak species

Abstract

The location of the polymorphism in the Quercus COL gene and given the potential role of COL genes in adaptive divergence and reproductive isolation makes this a promising candidate speciation gene. Further investigation of the phenological characteristics of both species and flowering time pathway genes is suggested in order to elucidate the importance of phenology genes for the maintenance of species integrity. Next-generation sequencing in multiple population pairs in combination with high-density genetic linkage maps could reveal the genome-wide distribution of outlier genes and their potential role in reproductive isolation between these species.

Strategies to Identify Adaptive Genes in Hybridizing Trees like Oaks and Poplars

“…This microsatellite, FIR013, was nearly fixed for alternative alleles (138bp in Q. ellipsoidalis, 141bp in Q. rubra) in the two between hybridizing species, some genes that are related to interspecific trait differences may also show significant associations with trait variation within species as shown for both poplars (Frewen et al, 2000;Ingvarsson et al, 2008) and oaks (Alberto et al, 2013;Lind-Riehl et al, 2014).…”

“…Outlier screens using 36 genic EST-SSRs, that were originally developed in Q. robur and Q. petraea (Durand et al, 2010), and eight genomic SSRs (Sullivan et al, 2013) in the ecologically divergent species Q. rubra (drought averse) and Q. ellipsoidalis (drought tolerant) revealed four outlier loci, one of which was identified as under strong divergent selection in all four interspecific population pairs from three geographic regions (Lind-Riehl et al, 2014). This microsatellite, FIR013, was nearly fixed for alternative alleles (138bp in Q. ellipsoidalis, 141bp in Q. rubra) in the two between hybridizing species, some genes that are related to interspecific trait differences may also show significant associations with trait variation within species as shown for both poplars (Frewen et al, 2000;Ingvarsson et al, 2008) and oaks (Alberto et al, 2013;Lind-Riehl et al, 2014).…”

“…On the other hand they provide a model to study ecological speciation and species coherence in the face of gene flow at the genome level Lind-Riehl et al, 2014;Scotti-Saintagne et al, 2004b). Despite interspecific gene flow, oaks maintain genetic and morphological differences as well as specific ecological adaptations (Abrams, 1990;Curtu et al, 2007;Kremer et al, 2002) suggesting that strong divergent selection might contribute to species coherence (Curtu et al, 2007;ScottiSaintagne et al, 2004b).…”

“…Hybridization is frequent in contact zones between ecologically differentiated and genetically highly divergent poplar species, but gene exchange is limited by pre-and post-zygotic reproductive barriers, and distinct species boundaries are maintained (e.g. Keim et al, species (interspecific FST = 0.38 -0.79) in adult and seedling generations (Lind-Riehl et al, 2014;Collins et al, submitted). Heterozygous genotypes were rare in each region, but more frequent in the Q. ellipsoidalis populations which might indicate asymmetric gene flow between the more frequent Q. rubra and the disjunct Q. ellipsoidalis populations (Fig.…”

“…Hybridizing oaks show overall very low interspecific genetic differentiation punctuated by genomic regions of high differentiation Lind-Riehl et al, 2014;Scotti-Saintagne et al, 2004b), a pattern that is predicted by the models of early stages of ecological speciation in the face of gene flow and strong divergent selection (Via, 2009(Via, , 2012Via and West, 2008). This pattern of genomic divergence allows for screening of loci under divergent selection and linked genomic regions (outlier regions) in hybrid zones between ecologically divergent oak species (Scotti-Saintagne et al, 2004b).…”