Temporal cline in a hybrid zone population between Fraxinus excelsior L. and Fraxinus angustifolia Vahl

Abstract

The two closely related ash species Fraxinus excelsior L. (common ash) and Fraxinus angustifolia Vahl (narrow-leaved ash) have a broad contact zone in France where they hybridize. However, little is known about the local structure of hybrid zone populations and the isolation mechanisms. We assessed the potential effect of floral phenology on the structure of a riparian ash hybrid zone population in central France. The distribution of flowering times was unimodal and lay between the flowering periods of the two species. Using microsatellite markers, we detected isolation by time, which has possibly originated from assortative mating. Multivariate analyses indicated that morphological variation is not distributed at random with respect to flowering times. Spatial autocorrelation analyses showed that temporal and spatial patterns were tightly linked. Interestingly, despite the fact that the population shows isolation by time, neighbourhood size and historical dispersal variance (sigma = 63 m) are similar to those detected in pure stands of F. excelsior where individuals flower rather synchronously and hermaphrodites are not the most frequent sexual type. Trees flowering at intermediate dates, which comprised the majority of the population, produced on average more flowers and fruits. We detected no significant differences in floral parasite infections relative to reproductive timing, although there was a tendency for late flowering trees to suffer from more gall attack. We discuss the impact of temporal variation in fitness traits and their possible role in the maintenance of the hybrid zone.

Variabilité génétique et différenciation entre populations italiennes de frêne commun (Fraxinus excelsior L.)

“…We also have to bear in mind that FEMSATL12 is likely to generate null alleles, as already suggested by Heuertz et al [22] who found a very high estimate of inbreeding coefficient (F IS = 0.697) and the lack of successful amplification in a large proportion of individuals (up to 35%). The question of null alleles of FEM-SATL12 could well be answered using different primers, as recently suggested by Gérard et al [18]. Heuertz et al [25] also indicated the presence of null alleles in FEMSATL16, although no unreliable amplification reactions were observed.…”

Quel échantillonnage pour des estimations fiables de la diversité génétique chez Fraxinus excelsior L. (Oleaceae)?

“…At least for the case of the widespread common ash in Europe, genetic diversity results derived from nuclear microsatellite loci Ferrazzini et al, 2007;Gerard et al, 2006;Hebel et al, 2006;Heuertz et al, 2001;Morand et al, 2002) suggest that allelic richness and gene diversity are fairly similar. Yet, more important than the numbers of alleles is the identity of those alleles and genetic conservation should favor the preservation of private alleles (Kalinowski, 2004;2005), a result only possible if several populations are sampled.…”

Presence of natural genetic resistance in Fraxinus excelsior (Oleraceae) to Chalara fraxinea (Ascomycota): an emerging infectious disease

“…The chosen microsatellite loci were FEMSATL11, FEM-SATL12, FEMSATL16 and FEMSATL19 (Lefort et al, 1999). We used the modified primers for FEMSATL12 (Gerard et al, 2006). PCR reactions were carried out using the Qiagen Multiplex PCR kit according to the manufacturer's instructions.…”