The Geography of Phytochemical Races

166 3 After the Ice
“western” Scots pine must remain a matter of speculation, at least until additional
information becomes available.
Although the existence of a western pathway to account for the western Scottish
strain of Scots pine has not been resolved, additional information on its genetic diversity
in other parts of its range has been obtained (Sinclair et al., 1998). Thirty-eight
populations were analyzed: Scotland (20 from the earlier work), Russia (1), Germany
(1), France (1), Poland (1), Sweden (2), Norway (1), Finland (2), Italy (2), and
Spain (7). Application of the mitochondrial cox1-based probe revealed the existence
of three mitotypes, a, b, and d. The populations in Spain exhibited the highest level of
heterogeneity with all three major mitotypes present. Noteworthy is the fi nding that
mitotype d was observed only in the southernmost population near Baza (37°30′N,
2°45′W). In this population, 15 trees exhibited the d mitotype with mitotype a seen in
only one. Two other Spanish populations, at Gudar and Orihuela (both southeastern
Spain), exhibited mixed mitotypes, 30 a and fi ve b in the former, four a and fi ve b in
the latter. Four other populations were homogeneous, two having only mitotype a, and
two with only b. The rest of the European populations were homogeneous. The Italian,
Finnish, Norwegian, and one of the Swedish populations exhibited exclusively
mitotype b, while the other Swedish population plus those from Poland, France, Germany,
and Russia were exclusively mitotype a. The preponderance of mitotype a in
Scottish populations was discussed above. Several interpretations of these data were
made, the fi rst of which held that the southern Spanish site represents the descendants
of one of the glacial refugia, and that the unusual mitotype d has been lost as descendants
migrated northward. As attractive as this hypothesis might sound, other data
do not support it. Thus, in the case of fl avonoids (Lebreton et al., 1990), terpenoids
(Tobolski and Hanover, 1971), and isozymes (Prus-Glowacki and Stephan, 1994),
considerable differentiation has occurred between Spanish and northern European
populations of P. sylvestris. The authors suggest that a more plausible explanation
is simply that these sites represent isolated populations that survived glaciation but
did not contribute to recolonization of northern Europe. Long isolation has led to the
accumulation of suffi cient differences that taxonomists may recognize discrete taxa,
P. sylvestris subsp. nevadensis (Christ.) S. Rivas-Martinez, A. Asensi, J. Molero-
Mesa and F. Valle, in the case of Scots pine (Vidakovic, 1991).
Sinclair et al. (1998) also addressed the origin of the difference in distribution
of mitotypes a and b in northern Europe, northern France, Germany, Poland, and
southern Sweden for the former, and northern Sweden, Norway, and Finland for the
latter. They prefer to view this distribution as refl ecting dual colonizations, one from
the south through Denmark and the other from the northeast via Finland. Available
data do not allow a resolution to this problem at the moment.
3.3.4 Abies alba (Pinaceae)
Abies alba Mill., the silver fi r, is an important forest tree in Europe. Its size—it is
the tallest on the continent—and quality of wood have attracted attention since early