High nuclear genetic diversity, high levels of outcrossing and low differentiation among remnant populations of Quercus petraea at the margin of its range in Ireland.
OBJECTIVE
Quercus petraea colonized Ireland after the last glaciation from refugia on mainland Europe. Deforestation, however, beginning in Neolithic times, has resulted in small, scattered forest fragments, now covering less than 12,000 ha.


METHODS
Plastid (three fragments) and microsatellite variation (13 loci) were characterized in seven Irish populations sampled along a north-south gradient. Using Bayesian approaches and Wright's F-statistics, the effects of colonization and fragmentation on the genetic structure and mating patterns of extant oak populations were investigated.


RESULTS
All populations possessed cytotypes common to the Iberian Peninsula. Despite the distance from the refugial core and the extensive deforestation in Ireland, nuclear genetic variation was high and comparable to mainland Europe. Low population differentiation was observed within Ireland and populations showed no evidence for isolation by distance. As expected of a marker with an effective population size of one-quarter relative to the nuclear genome, plastid variation indicated higher differentiation. Individual inbreeding coefficients indicated high levels of outcrossing.


CONCLUSIONS
Consistent with a large effective population size in the historical migrant gene pool and/or with high gene flow among populations, high within-population diversity and low population differentiation was observed within Ireland. It is proposed that native Q. petraea populations in Ireland share a common phylogeographic history and that the present genetic structure does not reflect founder effects.
Muir
Graham
G
Institut für Tierzucht und Genetik, Veterinärmedizinische Universität Wien, Josef Baumann Gasse 1, 1210, Vienna, Austria. g.muir@i122server.vu-wien.ac.at
Lowe
Andrew J
AJ
Fleming
Colin C
CC
Vogl
Claus
C
D005787:Gene Frequency; D014644:Genetic Variation; D006239:Haplotypes; D007494:Ireland; D018895:Microsatellite Repeats; D018087:Plastids / Q000235:genetics*; D029963:Quercus / Q000235:genetics*