The Geography of Phytochemical Races

3.3 Europe 165
levels of 3-carene in the southern populations was taken as indication that those
populations have not been in (reproductive) connection with the northern European
ones for a very long time, possibly since Tertiary times. These data are in substantial
agreement with several other studies that pointed to the existence of southern refugia.
Further, the high concentrations of 3-carene in trees from southern Scandinavia
and from northern Europe was taken to suggest that these were at one time part of
a continuous population, that is, when land bridged the two areas. One should note
that Scotch pine was much used by early humans and that some of the variation
observed in this study may have been the result of early reforestation since it is
known that extensive, and often severe, harvesting of this species was practiced, at
least in England and Denmark (Godwin, 1975).
The range of P. sylvestris includes an area of highland Scotland, some 500 km
from the nearest populations in Europe. This disjunct population has, of course,
drawn the attention of several botanists interested in its origin, or origins as it turns
out. Multiple colonizations of the Scottish Highlands from France were suggested
by Birks (1989) on the basis of pollen data, whereas Bennett (1995) hypothesized
two routes, one northward from France and a second along a more westerly route
possibly involving the north of Ireland. Multiple colonizations would predictably
lead to genetic heterogeneity. Evidence in the literature suggests that such is the
case. Thus, Forrest (1980b) reported signifi cantly lower levels of 3-carene from
trees sampled in the Wester Ross area than from any other Scottish population. Subsequent
studies of isozyme variation by Kinloch et al. (1986) revealed that a population
at Shieldaig (57°31′N, 5°37′W), which lies within the Wester Ross group, was
the most divergent from all other Scottish populations included in their study. They
speculated that the isozyme markers were characteristic of ancestral plants, and that
the markers have been retained for some 50 generations.
More recently, Sinclair et al. (1998) applied DNA sequence techniques to needle
and dormant bud tissue from 466 trees representing 20 natural populations of
Scots pine in Scotland. They employed a mitochondrial marker known to be maternally
inherited in order to avoid genetic noise associated with extensive pollen
fl ow among populations. Using probes for the cox1 gene, and following the usual
procedures, these workers observed three restriction fragment patterns, two that
were referred to as mitotypes a and b, and a third in a single individual that did not
fi gure further in their analysis. Seventeen of the populations exhibited only mitotype
a, with mitotype b present in three populations, Shieldaig (coordinates above),
Glen Loy (56°5′N, 5°08′W), and Doire Darach (56°32′N, 4°47′W). Mitotype b
was represented in these three populations at frequencies of 0.16, 0.59, and 0.08,
respectively. It was also reported in that paper that mitotype b was not detected,
using the cox1 probes, in 85 trees from northern Europe (northern France, Germany,
Poland, southern Sweden, and Russia). That observation and the presence
of mitotype b only in western Scottish populations were taken as clear support for
a second route of colonization, as had been postulated earlier. The hypothesis that
the western route involved populations of P. sylvestris in Ireland cannot be tested
owing to the extinction of natural populations in that country at least 1000 years
ago (Birks, 1989). The trail goes cold at this point; the postglacial source of the