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

Oxford

2004

S. 691-697

2 Abb., 4 Tab., 43 Lit. Ang.

Bandaufführung

136357

Consistent with a large effective population size in the historical migrant gene pooI and/or with high gene flow among populations, low population differentiation and high levels of genetic Variation were observed in Ireland. Extensive pollen flow has been documented in Q. petraea, e.g. by Streiff et al. (1999). Deforestation at the level recorded in Ireland, however, can affect the number of migrants and can result in a decline in the number of effective mating partners. Studies on the effects of deforestation among insect-pollinated trees indicate an inverse correlation between pollen flow and tree density (Dick, 2001, White et al., 2002). However, among wind-pollinated trees, such as oak, the effective number of pollen donors, as defined by Smouse et al. (2001), can vary positively with tree density (Sork et al. (2002). Hence pollen may travel further on average among fragmented forest-trees pollinated by insects. Nevertheless, Sork et al. (2002) infer a decline in the effective number of pollen donors in Quercus lobata (Californian valley oak) over a relatively short (55-year) period. Our results do not indicate historical genetic isolation of native oaks in Ireland. However, they continue to be threatened because the present tree structure is even-ages and natural regeneratoin is unprotected from browsing. Recognition of an ageing demography has resulted in the initiation of restoraton programs. As seed collected from native/autochthonous populations is unlikely to be inbred, as shon by the present study, this material may be used to expand the present resoure. Nevertheless, the transfer of genetic material for planting should attempt to match differences in adaptive genetic variation (Ennos et al., 1998).