Isoprenoid emissions of Quercus spp. (Q. suber and Q. ilex) in mixed stands contrasting in interspecific genetic introgression

Abstract

Summary• Among oak species, Quercus ilex is classified as a monoterpene emitter and Q. suber is mainly known as a nonisoprenoid emitter. The extent and origin of this diversification is unknown.• We examined intra-and interspecific emission variability in two mixed stands which differed in their level of hybridization and reciprocal genetic introgression based on variations in cytoplasmic (chloroplast DNA) and nuclear (allozyme) markers.• At both sites all trees identified as Q. ilex , or as recent descendants from Q. ilex × Q. suber hybrids, emitted monoterpenes. Of Q. suber trees (genetically introgressed or not by Q. ilex ), 91% were also monoterpene emitters, and the remainder nonemitters. One tree identified as a Q. canariensis × Q. ilex hybrid emitted both isoprene and monoterpenes. Compared with Q. ilex , the standard emission rate of Q. suber was higher in summer and lower in autumn. Both species emitted the same monoterpenes, proportions of which showed significant intra-and interspecific variability.• The results suggest that Q. suber populations in the French Mediterranean intrinsically emit monoterpenes, and that gene flow between oak species contributes to diversification of emission signatures.

Detection of hybrids in nature: application to oaks (Quercus suber and Q. ilex)

“…The low frequency (o2%) of contemporary gene exchange detected between Q. suber and Q. ilex is consistent with the available knowledge on nuclear variability for the species. A low number of hybrids has been reported in previous surveys of isozyme diversity (Elena-Rosselló et al, 1992;Toumi and Lumaret, 1998;Lumaret et al, 2002;Staudt et al, 2004). Nevertheless, the extensive sharing of chloroplast DNA haplotypes between Q. suber and Q. ilex in some regions has led some authors to hypothesize widespread introgressive hybridization events in the past ( , 2005).…”

“…Putative hybrids with parental morphology (Toumi and Lumaret, 1998;Belahbib et al, 2001;Staudt et al, 2004), intermediate morphology (Toumi and Lumaret, 1998;Lumaret et al, 2002;Bellarosa et al, 2005) or leaf morphology skewed toward Q. ilex (Staudt et al, 2004) have been reported. Bark cannot be used as a discriminating feature because F1s are considered to lack cork and, thus, they could be confused with pure Q. ilex (Lumaret et al, 2002;Bellarosa et al, 2005).…”

“…Furthermore, extensive surveys of chloroplast DNA diversity of both species and of other relatives (such as Q. coccifera) across the whole distribution range have demonstrated widespread cytoplasmic introgression, mainly localized along a northeast-southwest line, from French Catalonia and eastern Iberia to Morocco (reviewed in Lumaret et al, 2005). Interspecific exchanges seem to be limited to introgression of Q. ilex cpDNA and mtDNA into Q. suber, with only very few cases of Q. suber cpDNA introgressing into Q. ilex (Belahbib et al, 2001;Lumaret et al, 2002;Jiménez et al, 2004;Staudt et al, 2004). Because organelle DNA is maternally inherited in Quercus (Dumolin et al, 1995), this asymmetry implies that Q. ilex has acted predominantly as the maternal species in interspecific crosses.…”

“…In such a context, identifying F1 hybrids and backcrosses would be important, particularly when the proportion of hybrid individuals is low and when they are morphologically cryptic (as seems to be the case for Q. suber and Q. ilex; Lumaret et al, 2002;Staudt et al, 2004). We present here a broad-scale survey of molecular variation across the overlapping range of Q. suber and Q. ilex to explore the extent and pattern of nuclear introgressive hybridization, using a panel of eight highly discriminating microsatellite loci.…”

Leaf volatile isoprenoids: an important defensive armament in forest tree species

“…Genera of the same family, or species within the same genus (e.g., Quercus), may have different emission patterns, including both isoprene and monoterpene-emitting species, as well as non-or low-emitters (Loreto et al 1998). In Quercus suber (cork oak), -the only species not storing isoprenoids in which the emission of these volatile compounds has been studied at the intraspecific level (Staudt et al 2004) -, different individuals emit different blends of monoterpenes. It may be suggested that these differences are not only caused by adaptation to the environment, but might rather be associated with past genetic isolation of cork oak populations, whose gene pools have been dated to originate several million years before present (Magri et al 2007).…”