MULTIPLE ORIGINS FOR SCOTS PINE (PINUS-SYLVESTRIS L) IN SCOTLAND - EVIDENCE FROM MITOCHONDRIAL-DNA VARIATION

Data from the pollen record and from two forms of nuclear genetic mark ers suggest that present-day populations of Scots pine (Pinus sylvestr is L.) in Scotland were derived from more than one refugium after glac iation. In order to clarify this issue, genetic variation for maternal ly inherited mitochondrial DNA (mtDNA) was studied in 466 trees sample d from 20 natural populations in Scotland. A homologous probe for the cox1 mitochondrial gene of P. sylvestris was constructed and used to d etect mtDNA RFLP variation. Two common (a and b) and one rare RFLP var iant (c) were distinguished. Evidence from segregation patterns of var iants within a polymorphic population was consistent with maternal inh eritance of the RFLP variation. A survey of Scottish populations indic ates that mitotype a is present at all sites, but that mitotype b is c onfined to three western populations. Genetic differentiation for mtDN A, which migrates solely by seed is much greater (F-ST(m) = 0.370) tha n for nuclear markers (F-ST(b) = 0.028) which are dispersed by both po llen and seed. The geographical distribution of mitotype b in western Scotland, and its absence from populations in northern France and Germ any, suggest that P. sylvestris has been derived not only from contine ntal Europe via England, but also by migration from a western refugium , probably in Ireland or western France.